Benefits from Tween during enzymic
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论证酵素是否对人体有好处作文英文回答:Enzymes are indeed beneficial to the human body. Enzymes are proteins that act as catalysts in biochemical reactions, speeding up the rate at which these reactions occur. They play a crucial role in digestion, metabolism, and various other physiological processes in the body.For example, digestive enzymes help break down foodinto smaller molecules that can be easily absorbed by the body. Without these enzymes, our bodies would struggle to extract essential nutrients from the food we eat. This can lead to digestive issues such as bloating, gas, andnutrient deficiencies.In addition, enzymes also play a role in detoxification, immune function, and inflammation. For instance, the enzyme superoxide dismutase (SOD) helps neutralize harmful free radicals in the body, reducing oxidative stress andlowering the risk of chronic diseases.Furthermore, enzymes are essential for energy production. ATP synthase, for example, is an enzyme that helps produce ATP, the main source of energy for cellular processes in the body. Without ATP, our cells would not be able to function properly, leading to fatigue and other health problems.Overall, enzymes are crucial for maintaining optimal health and well-being. Including enzyme-rich foods in your diet, such as fruits, vegetables, and fermented foods, can help support your body's enzyme production and ensure proper digestion and nutrient absorption.中文回答:酵素对人体确实有好处。
高三测试题制作天然眼部精华英语作文Nowadays, the beauty industry is flooded with variousskincare products promising to enhance our skin and make us look youthful. However, many of these products contain chemicals and artificial ingredients that may have harmful effects on our skin in the long run. In this regard, making your own natural eye serum at home can be a great alternative to commercial products.To create a natural eye serum, you will need a few simple ingredients that are easily accessible. One popular ingredientis rosehip seed oil, which is rich in vitamins and antioxidants that nourish the delicate skin around the eyes. Anotherbeneficial ingredient is sweet almond oil, known for its moisturizing properties and ability to reduce dark circles and puffiness. Additionally, a few drops of lavender essential oil can be added for its soothing and antiinflammatory effects.To make the eye serum, mix one tablespoon of rosehip seed oil with one tablespoon of sweet almond oil in a small, clean bottle. Add 34 drops of lavender essential oil to the mixture and shake well to combine the ingredients. This natural eye serum can be applied gently around the eyes using clean fingertips everynight before bedtime.Using this homemade eye serum regularly can help to hydrate and rejuvenate the delicate skin around the eyes, reducing the appearance of fine lines and wrinkles. The natural ingredientsin the serum work together to nourish and protect the skin, promoting a healthy and youthful complexion.In conclusion, creating your own natural eye serum at home is a simple and effective way to take care of your skin without exposing it to harmful chemicals. By using natural ingredients like rosehip seed oil, sweet almond oil, and lavender essential oil, you can pamper your skin while ensuring its health and vitality. Give this homemade eye serum a try and enjoy the benefits of nature's goodness for your skin.。
外刊精读让马拉松变得更环保导读:似乎在世界各地,每个主要的大城小镇都会举办年度马拉松比赛。
成千上万的参赛运动员要经受艰难的体能考验,跑完42.1 公里的赛程。
和其它大型比赛一样,马拉松比赛也会产生大量的碳足迹。
数千人乘坐飞机前来参赛或观赛,观众和运动员留在赛道的食物垃圾、包装袋、礼品袋等等。
本期《外刊精读》讨论相关部门针对马拉松比赛所采取的各项环保措施。
一、语篇泛读Even if you’re a couch potato like me, you’ll know the benefits of running - pounding the pavements, working up a sweat, burning off some calories and generally keeping fit. But if you’re a real fitness junkie, the ultimate running challenge is to take part in a marathon.It seems every major city and town aro und the world hosts an annual marathon, with thousands of athletes running a gruelling 42.1 kilometers. Whilst many runners’ motivation is to beat their personal best and cross the finishing line without collapsing, they’re also doing it for a good cause– to generate funds for charity. But like other major events, the marathon also generates a massive carbon footprint. Thousands travel - some by plane - to the location, and waste from food packaging and goody bags gets left behind by spectators and runners. For example, during the London Marathon in 2018, 47,000plastic bottles were collected, although some were recycled.This is becoming a big issue for cities –how to host a worthwhile event, encouraging people to exercise and help charities, whilst protecting the environment? Several cities have developed formal plans to reduce their environmental impact and promote sustainable ideas. One event in Wales, for example, introduced recycling for old running kit and ethically sourced the race t-shirts.It’s something that this year’s London Marathon tried to tackle by reducing the number of drink stations on the running route, giving out water in paper cups and offering some drinks in edible seaweed capsules. They also trialed new bottle belts made from recycled plastic so 700 runners could carry water bottles with them during their run. London Marathon event director Hugh Brasner told the三、测试与练习阅读课文并回答问题。
The Importance of Preventing DiabetesIn recent years, diabetes has become a significanthealth concern worldwide, affecting millions of people. Itis a chronic disease that occurs when the body cannot produce enough insulin or cannot effectively use theinsulin it produces. The consequences of diabetes can be severe, including heart disease, stroke, blindness, kidney failure, and amputations. Therefore, it is crucial to understand the importance of preventing diabetes and take necessary measures to protect oneself.Maintaining a healthy weight is one of the mosteffective ways to prevent diabetes. Obesity is a major risk factor for type 2 diabetes, as extra body weight can leadto insulin resistance. Regular physical activity and a balanced diet are essential for maintaining a healthy weight. Engaging in at least 150 minutes of moderate-intensity aerobic activity per week, such as walking, cycling, or swimming, can help reduce the risk of diabetes. Eating a balanced diet is also crucial for diabetes prevention. A diet rich in fruits, vegetables, whole grains, and lean protein can help maintain a healthy weight andprovide the body with essential nutrients. Avoiding sugary drinks and foods high in saturated and trans fats can help reduce the risk of diabetes. Additionally, limiting salt intake can help prevent high blood pressure, which is a common complication of diabetes.Moreover, regular health screenings can help detect diabetes early and prevent its progression. People at risk of diabetes should have their blood sugar levels checked regularly. If diabetes is detected, prompt treatment can help manage the condition and prevent complications.In addition to lifestyle changes, some people may benefit from taking medication to prevent diabetes. Medications such as metformin or GLP-1 agonists can help lower blood sugar levels and reduce the risk of diabetes in people with prediabetes. However, it is important to consult a healthcare provider before taking any medication. In conclusion, preventing diabetes is crucial for maintaining good health. By maintaining a healthy weight, eating a balanced diet, engaging in regular physical activity, limiting salt intake, and undergoing regular health screenings, people can reduce their risk ofdeveloping diabetes. Additionally, taking medication as prescribed by a healthcare provider can help prevent diabetes in those with prediabetes. Remember, prevention is always better than cure, and taking proactive steps to prevent diabetes can help enjoy a healthy and fulfilling life.**糖尿病预防的重要性**近年来,糖尿病已成为全球范围内的重要健康问题,影响着数百万人。
Artificial sweeteners not recommended for weight loss, says WHO 世卫组织:人工甜味剂无助于减肥,长期摄入或增加健康风险英文新闻:Artificial sweeteners not recommended for weight loss, says WHOOn Monday, the World Health Organization released new guidelines warning the public not to use non-sugar sweeteners for weight loss, revealing that it may actually do more harm to the body than good.New findings showed that artificial sweeteners — like aspartame, a sugar substitute found in Diet Coke — don't do much to reduce your waistline. In fact, long-term use of these fake sugars could even potentially increase the risk for Type 2 diabetes, cardiovascular disease and mortality in adults, the WHO said.The WHO advised that the new recommendations encompassed "all synthetic and naturally occurring or modified non-nutritive sweeteners that are not classified as sugars found in manufactured foods and beverages, or sold on their own to be added to foods and beverages by consumers." However, it does not apply to artificial sweeteners that are found in hygiene products, like toothpastes, skin creams or medications.重点词汇1. mortality英 [mɔːˈtæləti] 美 [mɔːrˈtæləti]n. 死亡率2. synthetic英 [sɪnˈθetɪk] 美 [sɪnˈθetɪk]adj. 合成的,人造的中文新闻:世卫组织:人工甜味剂无助于减肥,长期摄入或增加健康风险5月15日,世界卫生组织最新发布的一份指南提醒公众,不要借助非糖甜味剂减肥,这一表态意味着非糖甜味剂对身体健康或弊大于利。
VOA慢速英语[健康报道]抗炎药帮助对抗抑郁症What is an autoimmune disease?An autoimmune disease is a disease where the body attacks itself. Examples include the skin condition psoriasis, rheumatoid arthritis, type 1 diabetes and Crohn's disease.White blood cells are part of the body’s natural defense against disease. They help to protect us against infection. In autoimmune diseases, the white blood cells are over-activated. Instead of simply attack ing bacteria and viruses, the body’s natural defense system also attacks healthy tissue.To treat an autoimmune disease, patients often are told to take anti-inflammatory drugs. Now, a study suggests that the drugs also appear to treat signs of depression. The study also suggests that anti-inflammatory medicines may soon take their place with traditional treatments to help people with this disorder.Researchers looked at a number of drug studies that involved patients with autoimmune diseases. They noted an improvement in patients with signs of depression after the research ended.Anti-inflammatory drugs quiet the body’s natural defenses by disarming proteins known as cytokines. These proteins are important in the body's reaction to inflammation. A small amount of inflammation is necessary to activate the immune system to fight an infection. But too much pain or swelling is harmful.Golam Khandaker is a professor of psychiatry at the University of Cambridge.'Slow burning inflammation that's circulating in our body can cause a number of physical and psychiatric conditions. For example, in the brain, it could lead to increased risks of depression. Similarly in the body, it could lead to increased risk of heart disease, particularly coronary heart disease such as stroke … or also type 1 diabetes or type 2 diabetes.'People with autoimmune diseases often suffer from depression. Some earlier studies suggested these people are depressed because of their condition. But the new study suggests that inflammation changes the chemistry of the brain, causing depression.Antidepressant drugs work to help to re-establish the operation of brain chemicals, called neurotransmitters. However, the drugs are not always successful in treating patients with depression.Anti-inflammatory drugs, which work differently in the brain, give doctors another choice.For the study, Khandaker and his team looked at the results of 20 studies of people treated with anti-inflammatory drugs. These patients had arthritis, psoriasis or Crohn's disease.The researchers found that individuals who reported signs ofhard-to-treat depression before the study had a mild to moderate reduction in those symptoms after the study. In fact, the results were similar to the effectiveness of antidepressants.'And what they showed is that patients who were inflamed at the beginning of the trial showed benefits from the anti-cytokine drug. And the higher the level of inflammation, the greater the improvement in the severity of depressive symptoms.'The researchers published their findings in the journal Molecular Psychiatry.Researchers say anti-inflammatory drugs could someday be used in patients with depression for whom other drugs have failed.Depression will be the second highest cause of disease burden in middle-income countries by the year 2030. This prediction comes from the World Health Organization.For the Health & Lifestyle report, I’m Anna Matteo.VOA science reporter Jessica Berman wrote this story for . Anna Matteo adapted it for Learning English. George Grow was the editor.。
中药的好处英语辩论作文Title: The Benefits of Traditional Chinese Medicine: A Debate。
Traditional Chinese Medicine (TCM) has long been a subject of debate regarding its efficacy and relevance in modern healthcare. While some argue its merits, others remain skeptical. In this discourse, we explore the advantages of TCM, shedding light on its valuable contributions to human health.Firstly, one cannot overlook the rich history and cultural significance embedded within TCM. With a legacy spanning thousands of years, TCM encompasses a holistic approach to health, focusing on the balance of Qi, or vital energy, within the body. This ancient wisdom has been passed down through generations, embodying centuries of accumulated knowledge and experience in treating various ailments.Moreover, TCM offers a wide array of therapeutic modalities, ranging from herbal medicine and acupuncture to tai chi and qigong. These modalities address not only physical symptoms but also aim to restore harmony within the body, mind, and spirit. For instance, acupuncture, a cornerstone of TCM, involves the insertion of thin needles at specific points along the body's meridians to regulate Qi flow and alleviate pain. Numerous studies have demonstrated its effectiveness in treating conditions such as chronic pain, migraines, and even depression.Furthermore, the personalized approach of TCM tailors treatments to individual needs, taking into account one's unique constitution and underlying imbalances. Unlike Western medicine, which often adopts a one-size-fits-all approach, TCM practitioners emphasize the importance of thorough diagnosis and individualized treatment plans. By addressing the root cause of illness rather than merely suppressing symptoms, TCM aims to promote long-term health and well-being.Additionally, TCM places a strong emphasis onprevention, advocating lifestyle modifications and dietary changes to maintain health and prevent disease. Herbal remedies, comprising a vast repertoire of medicinal plants and natural substances, are prescribed not only to treat existing conditions but also to strengthen the body's defenses and enhance resilience against illness. This proactive approach aligns with the principles of holistic health, fostering a deeper connection between individuals and their environment.Furthermore, TCM's integration with modern medicine presents opportunities for synergistic collaboration and enhanced patient care. Increasingly, healthcare systems around the world are recognizing the value of integrative medicine, combining the best of both Eastern and Western traditions to optimize health outcomes. By bridging the gap between ancient wisdom and modern science, TCM offers a comprehensive approach to healthcare that addresses the complex needs of today's society.In conclusion, the benefits of Traditional Chinese Medicine are manifold, encompassing not only therapeuticefficacy but also cultural heritage, personalized care, prevention, and integration with modern medicine. As we navigate the complexities of healthcare in the 21st century, TCM stands as a beacon of wisdom, offering valuableinsights into the holistic nature of human health and healing. Embracing the principles of balance, harmony, and vitality, TCM continues to enrich lives and inspire generations to come.。
中医的好处英语作文The Benefits of Traditional Chinese Medicine。
Traditional Chinese Medicine (TCM) has been practiced for thousands of years and has gained popularity in recent years due to its many benefits. TCM includes a range of practices such as acupuncture, herbal medicine, and massage therapy. Here are some of the benefits of TCM:1. Holistic Approach。
TCM takes a holistic approach to health, treating the body as a whole rather than just treating individual symptoms. This means that TCM practitioners look at a person's physical, emotional, and spiritual health to determine the root cause of their illness.2. Personalized Treatment。
TCM treatments are personalized to each individual'sneeds. Practitioners take into account the patient's age, gender, and overall health when developing a treatment plan.3. Natural Remedies。
糖醇的好处英文作文下载温馨提示:该文档是我店铺精心编制而成,希望大家下载以后,能够帮助大家解决实际的问题。
文档下载后可定制随意修改,请根据实际需要进行相应的调整和使用,谢谢!并且,本店铺为大家提供各种各样类型的实用资料,如教育随笔、日记赏析、句子摘抄、古诗大全、经典美文、话题作文、工作总结、词语解析、文案摘录、其他资料等等,如想了解不同资料格式和写法,敬请关注!Download tips: This document is carefully compiled by theeditor. I hope that after you download them,they can help yousolve practical problems. The document can be customized andmodified after downloading,please adjust and use it according toactual needs, thank you!In addition, our shop provides you with various types ofpractical materials,such as educational essays, diaryappreciation,sentence excerpts,ancient poems,classic articles,topic composition,work summary,word parsing,copyexcerpts,other materials and so on,want to know different data formats andwriting methods,please pay attention!Sugar alcohols, also known as polyols, are a type of low-calorie sweetener that are commonly used in food and beverage products. They offer several benefits over traditional sugar, making them a popular choice for people who want to reduce their sugar intake. In this article, we will explore the advantages of sugar alcohols.Firstly, sugar alcohols have fewer calories than traditional sugar. While regular sugar contains 4 calories per gram, sugar alcohols contain only 1.5 to 3 calories per gram. This means that they can help to reduce overall calorie intake, making them a great choice for people who are trying to lose weight or maintain a healthy weight.Secondly, sugar alcohols do not cause a rapid spike in blood sugar levels. Unlike traditional sugar, which can cause a sudden surge in blood sugar levels, sugar alcohols are absorbed more slowly by the body. This means that they can help to prevent blood sugar crashes and reduce the riskof developing type 2 diabetes.Thirdly, sugar alcohols do not promote tooth decay. Traditional sugar can cause cavities and other dental problems, but sugar alcohols do not have the same effect. In fact, some sugar alcohols, such as xylitol, have been shown to have a protective effect on teeth and gums.Fourthly, sugar alcohols are safe for people with diabetes. Because sugar alcohols do not cause a rapid increase in blood sugar levels, they are a good alternative to traditional sugar for people with diabetes. However, it is important to note that sugar alcohols still contain carbohydrates and can affect blood sugar levels if consumed in large amounts.Finally, sugar alcohols have a lower glycemic index than traditional sugar. The glycemic index is a measure of how quickly a food raises blood sugar levels. Foods with a high glycemic index can cause a rapid increase in blood sugar levels, while foods with a low glycemic index are absorbed more slowly. Sugar alcohols have a lower glycemicindex than traditional sugar, which means that they can help to regulate blood sugar levels and reduce the risk of developing insulin resistance.In conclusion, sugar alcohols offer several benefits over traditional sugar, including fewer calories, a slower absorption rate, a reduced risk of tooth decay, and a lower glycemic index. While sugar alcohols are generally safe for most people, it is important to consume them in moderation and to be aware of their potential side effects, such as bloating and diarrhea.。
为什么要吃的健康英语作文英文回答:Eating healthy is essential for overall well-being and quality of life. Maintaining a balanced diet provides the body with the necessary nutrients to function optimally, reducing the risk of chronic diseases, and improving physical and mental health.1. Reduced Risk of Chronic Diseases:Consuming a healthy diet significantly reduces the likelihood of developing chronic illnesses such as heart disease, stroke, type 2 diabetes, and certain types of cancer. Healthy foods are rich in antioxidants, vitamins, and minerals, which help protect cells from damage and reduce inflammation. For example, fruits and vegetables contain fiber, which aids in digestion and lowers cholesterol levels.2. Improved Physical Health:Eating healthy promotes a healthy weight, increased energy levels, and improved physical performance. A balanced diet provides the body with the fuel it needs to function optimally. Whole grains, fruits, and lean proteins provide sustained energy throughout the day. Healthy eating habits also reduce the risk of obesity, which is a major contributing factor to various health problems.3. Enhanced Mental Health:Research has shown a strong correlation between a healthy diet and improved mental health. Foods rich in omega-3 fatty acids, such as fish and nuts, have beenlinked to reduced symptoms of depression and anxiety. Vitamins and minerals, like magnesium and B vitamins, also contribute to cognitive function, mood regulation, and sleep quality.4. Increased Life Expectancy:Eating healthy habits can help extend life expectancyby reducing the risk of premature death. A study publishedin the Journal of the American Medical Association foundthat individuals who followed a healthy diet had a significantly lower mortality rate than those who did not. Healthy eating promotes longevity by protecting the body from chronic diseases and maintaining overall well-being.5. Improved Immune Function:A healthy diet supports a strong immune system.Vitamins C and D, found in citrus fruits and dairy products, respectively, are essential for immune function. Zinc, present in nuts and legumes, also plays a crucial role in immunity. By consuming a balanced diet, the body is better equipped to fight off infections and diseases.中文回答:为什么健康的饮食十分重要?保持健康的饮食对于整体健康和生活质量至关重要。
缓解用眼疲劳英语作文标题,Alleviating Eye Fatigue。
In today's digital age, where screens dominate ourdaily lives, eye fatigue has become a common issueaffecting people of all ages. The excessive use of smartphones, computers, and other electronic devices hasled to a significant increase in eye strain and discomfort. However, there are various effective ways to alleviate eye fatigue and protect our vision.First and foremost, it's essential to take regular breaks when using electronic devices for an extended period. The American Optometric Association recommends followingthe 20-20-20 rule: every 20 minutes, take a 20-second break and look at something 20 feet away. This simple practice helps relax the eye muscles and reduce strain.Additionally, adjusting the brightness and contrast settings on screens can make a significant difference inreducing eye fatigue. Dimming the brightness and increasing the contrast can minimize glare and make it easier for the eyes to focus, especially in low-light environments.Furthermore, proper lighting in the workspace iscrucial for eye health. Natural light is the best option, so if possible, position your desk near a window. Avoiding harsh overhead lighting and using task lighting instead can also help reduce glare and eye strain.Moreover, practicing good ergonomic habits while using electronic devices can prevent eye fatigue and other related issues. Ensure that your screen is at eye level and approximately an arm's length away from your face. Adjust the font size and screen resolution to make text easier to read without straining your eyes.Another effective way to alleviate eye fatigue is to stay hydrated. Drinking an adequate amount of water throughout the day helps maintain moisture in the eyes and prevents dryness, which can exacerbate eye strain.Furthermore, incorporating eye exercises into yourdaily routine can help strengthen eye muscles and improve focus. Simple exercises like blinking rapidly for a few seconds or rolling your eyes in circles can help reduce tension and alleviate fatigue.Moreover, wearing blue light-blocking glasses can be beneficial, especially for those who spend long hours in front of screens. These glasses filter out harmful blue light emitted by electronic devices, which can cause eye strain and disrupt sleep patterns.In addition to these preventive measures, it'sessential to prioritize overall eye health by scheduling regular eye exams with an optometrist. Detecting and addressing any underlying vision problems early can prevent them from worsening and causing additional strain on the eyes.In conclusion, while the prevalence of electronic devices in our daily lives may contribute to eye fatigue, there are various effective strategies to alleviate andprevent it. By incorporating regular breaks, adjusting screen settings, maintaining proper lighting and ergonomics, staying hydrated, practicing eye exercises, wearing blue light-blocking glasses, and prioritizing regular eye exams, we can protect our vision and reduce the impact of eye fatigue on our daily lives. Remember, taking care of our eyes is essential for maintaining overall well-being in today's digital world.。
用咖啡因的影响写一篇英文作文范文模板The Effects of Caffeine: Exploring its Role in Our Daily LivesCaffeine is a substance that many of us consume on a daily basis. Whether it's as a morning pick-me-up or an afternoon boost, the effects of caffeine can be felt throughout our day. But what exactly are these effects and how do they impact us?Firstly, one of the most well-known effects of caffeine is its ability to increase alertness and improve concentration. This is due to caffeine's ability to block adenosine receptors in the brain, which can lead to feelings of drowsiness and decreased mental acuity. With caffeineacting as an antagonist to adenosine, we are able to maintain focus and stay awake for longer periods of time.In addition to this, caffeine has also been shown to enhance physical performance. This is because caffeine stimulates the production of adrenaline, which can lead toincreased heart rate and blood flow. As a result, athletes often use caffeine as a natural way to improve their endurance and stamina during training sessions.However, while there are certainly benefits associated with consuming caffeine, it's important to note that excessive consumption can also have negative consequences. Too much caffeine can lead to jitters, anxiety, and even insomnia in some cases. There's also evidence to suggest that long-term use of caffeine may contribute to increases in blood pressure and other cardiovascular issues.So what does all this mean for us? Ultimately, it meansthat our consumption of caffeine should be done in moderation. While it can certainly help us feel more alert and perform better physically, we should be mindful not to overdo it. We should also consider our individualsensitivity levels when consuming caffeinated beverages or products.In conclusion, the effects of caffeine are complex and multifaceted. From improved focus and physical performanceto potential negative consequences from excessive use, understanding how this substance impacts our bodies is an important part of making informed decisions about our daily habits and routines. By being mindful about how much we consume and paying attention to our own reactions, we can enjoy the benefits that caffeine has to offer without letting its downsides impact our overall health and well-being.。
给我艾灸的好处英文作文英文:As someone who has experienced the benefits of moxibustion first-hand, I am a firm believer in the power of this traditional Chinese medicine practice. Moxibustion, also known as ai jiu in Chinese, involves burning a herb called mugwort on or near specific acupuncture points on the body. The heat generated by the burning herb stimulates the flow of qi (energy) in the body and promotes healing.One of the main benefits of moxibustion is its ability to relieve pain. It can be particularly effective in treating chronic pain conditions such as arthritis, back pain, and migraines. The heat from the burning mugwort helps to increase blood flow to the affected area, which in turn promotes healing and reduces inflammation.Moxibustion can also be used to boost the immune system and improve overall health. By stimulating the flow of qiin the body, moxibustion can help to strengthen the body's natural defenses against illness and disease. It can also help to improve digestion, relieve stress and anxiety, and promote better sleep.In addition to its physical benefits, moxibustion can also have a positive impact on mental and emotional well-being. The practice is known to promote feelings of relaxation and calmness, and can be a helpful tool for managing stress and anxiety. It can also be used to treat depression and other mood disorders.Overall, moxibustion is a safe and effective alternative or complementary therapy for a wide range of health conditions. While it may not be suitable for everyone, it is definitely worth considering if you are looking for a natural and holistic approach to healing.中文:作为一个亲身体验过艾灸好处的人,我坚信这种传统中医疗法的力量。
关于治愈系食物的英语发言稿Here is the English essay on the topic "A Speech on Comfort Foods":Comfort foods are a type of food that provide a sense of emotional well-being and nostalgia. They are often associated with childhood memories, home-cooked meals, and a feeling of being cared for. These foods have the power to soothe the soul and lift our spirits, making them an essential part of our culinary experiences.One of the primary reasons why comfort foods are so popular is their ability to evoke a sense of familiarity and security. When we consume these familiar dishes, we are transported back to a time when we felt safe, loved, and nurtured. This can be especially comforting during times of stress, anxiety, or loneliness, as it provides a sense of emotional connection and stability.Moreover, comfort foods often have a strong connection to our cultural and personal identities. They can be a reflection of our upbringing, the traditions of our families, and the flavors that have been passed down through generations. These foods can serve as a link to our heritage and provide a sense of belonging, allowing us to feel grounded and connected to our roots.Another important aspect of comfort foods is their ability to provide a sense of physical comfort. Many of these dishes are known for their rich, creamy, or hearty textures, which can be soothing and satisfying. The act of consuming these foods can trigger the release of feel-good neurotransmitters, such as serotonin and dopamine, which can improve our mood and reduce stress levels.It is worth noting that the concept of comfort food is not limited to a specific cuisine or cultural background. Around the world, people have their own unique comfort foods that hold a special place in their hearts and memories. From the warm, gooey mac and cheeseof the United States to the steaming bowls of pho in Vietnam, these dishes serve as a source of comfort and connection, transcending cultural boundaries.However, it is essential to approach comfort foods with moderation and balance. While they can provide a temporary emotional lift,over-reliance on these foods can lead to unhealthy eating habits and potential weight gain. It is important to find a healthy balance between indulging in comfort foods and maintaining a nutritious diet.In conclusion, comfort foods are a powerful and meaningful part of our culinary and emotional experiences. They have the ability tosoothe our souls, evoke nostalgic memories, and provide a sense of physical and emotional comfort. By embracing and celebrating these special dishes, we can cultivate a deeper connection to our personal and cultural identities, while also finding ways to incorporate them into a balanced and healthy lifestyle.。
如何预防加深近视英语作文To prevent worsening myopia, it is important to take regular breaks from screens and books to rest your eyes.Make sure to maintain a proper distance from screens and books when using them, as holding them too close can strain your eyes.Try to spend more time outdoors and engage inactivities that require distance vision, such as sports or hiking.Consider using blue light blocking glasses when using electronic devices for extended periods of time.Get regular eye check-ups and follow the advice of your optometrist to monitor and manage your myopia.Avoid rubbing your eyes, as this can exacerbate myopia and cause further damage to your eyes.Eat a balanced diet rich in vitamins and minerals that are beneficial for eye health, such as vitamin A, C, and E.Make sure to get enough sleep, as lack of sleep can contribute to the progression of myopia.Limit the amount of time spent on electronic devices, especially before bedtime, to reduce eye strain and promote better sleep quality.Practice good posture and ergonomics when using electronic devices or reading, as poor posture can contribute to eye strain and worsen myopia.。
消暑作用英语作文Ah, summer heat, the relentless oppressor of comfort, suffocating us in its fiery embrace. But fear not, for there are myriad ways to combat its tyrannical rule. One such method is the glorious invention known as air conditioning. Picture this: a blast of cool air enveloping you like a refreshing waterfall on a scorching day. Ah, sweet relief!Another champion in the battle against summer's fury is the almighty ice cream. Oh, the joy of indulging in a scoop of creamy, cold deliciousness as it melts on your tongue, sending shivers of delight down your spine. It's not just a dessert; it's a lifeline in the sweltering heat.Let's not forget about the age-old tradition of seeking refuge in the cool shade of a leafy tree. There's something magical about the way sunlight filters through the green canopy, casting dappled shadows on the ground below. It's nature's own air conditioning, providing solace to wearysouls seeking respite from the relentless heat.And what about those refreshing dips in a crystal-clear pool? The feeling of weightlessness as you glide through the water, the gentle caress of coolness against your skin—it's like being transported to a blissful oasis where the heat dares not tread.Of course, there's always the tried and true method of sipping on a chilled beverage. Whether it's a frosty glass of lemonade, a tangy iced tea, or a crisp mojito, there's something undeniably satisfying about quenching your thirst with a cold drink on a hot summer's day.So there you have it, a smorgasbord of strategies to beat the heat and reclaim your summer sanity. From the icy embrace of air conditioning to the simple pleasures of an ice-cold treat, there's no shortage of ways to stay cool when the temperature soars.。
Benefits from exerciseWhen I was a child, I liked all kinds of games. Everyday I played to my heart’s content, often forgetting my meals. When a little older, I turned to be lazy, and didn’t go in for sports any more. But things changed again recently.Last term, our college organized a badminton match, in which I was chosen to be a contestant. In the play, my partner Luo Lijuan and I tried our best to win the women’s double. In the end we lost the game. We felt a little sad, but we were convinced that who wins last wins the best. Now my badminton skills have greatly improved and I feel fit and energetic everyday.Playing badminton can provide us with a lot of physical activities and real mental relaxation. A ballgame can build up muscles, keep joints flexible, speed up blood circulation and enhance bodily organs. We may feel physically exhausted after vigorous exercise, but we can sleep soundly and be absorbed in study more whole-heartedly. So playing badminton is not only good for our health but also good for our study.Everyone can gain a lot from doing exercise.Everyone can derive invaluable benefits from regular exercise.根据Everyone can derive invaluable benefits both physically and mentally from regular exercise. 展开的文章:Everyone can derive invaluable benefits both physically and mentally from regular exercise.First of all, Exercises can make people physically strong, fit and healthy. When doing exercise, all the systems of our bodies can be enhanced. For example, as our body temperature rises, the toxic substances can be burned up. Exercise can help the secretion of wastes and stimulate the blood circulation and intestinal movement. We all know that “Life lies in exercise”. We become agile and flexible and adaptable if we do regular exercise. If we stay indoors all day long, we get stiff knees and joints and it is easier to fall ill, for the defensive mechanism against diseases is getting weak. That’s why a lot of people work out regularly in order to stay far away from illness and remain energetic.Secondly, exercises, at the same time, do good to our mental health. It is well-known to students that after a whole day’s studying and reading, it is always refreshing and relaxing to play basketball or badminton on the court, to run several quarter-miles on the playground, or to swim for an hour in the pool. Only a sound body can house a sound mind. That’s whywe always find that exercises can improve our efficiency in our study.Sports or exercises provide us a good means to communicate with people. As human beings are social animals, we need to associate with people. We learn not only how to compete but also how to cooperate with people in a game.In one word, to live healthily and work efficiently, we need to do exercise regularly.。
Bananas and salmon help counter effect of salt inwomen’s diet, study finds研究发现:女性多吃香蕉、三文鱼,有助降低高盐饮食负面影响Eating foods such as bananas, avocados and salmon could help reduce the negative effects of salt in women’s diet, research suggests. The study found that potassium-rich diets were associated with lower blood pressure, particularly in women with high salt intake. Researchers say their findings indicate the mineral helps preserve heart health, and that women benefit more than men. Study author Professor Liffert V ogt of Amsterdam University Medical Centers, in the Netherlands, said: “It is well known that high salt consumption is associated with elevated blood pressure and a raised risk of heart attacks and strokes. “Health advice has focused on limiting salt intake, but this is difficult to achieve when our diets include processed foods. In our study, dietary potassium was linked with the greatest health gains in women.” The study included 11,267 men and 13,696 women, which recruited adults aged 40 to 79 from general practices in Norfolk, UK, between 1993 and 1997. Foods high in potassium include vegetables, fruit, nuts, beans, dairy products and fish.研究表明,摄入香蕉、牛油果和三文鱼等食物有助于降低女性摄入盐的负面影响。
喝咖啡能拯救视力A daily cup of coffe e can save your eyesight, scientists claim.科学家称,每日一杯咖啡能够拯救你的视力。
A chemical found in the drink prevents deteriorating eyesight and possible blindness f rom retinal degener ation due to glaucoma(青光眼), ageing and diabetes.Researchers at Cornell U nivesity in New York were looking at coffee's ant ioxidant effects when they made the discove ry.Coffee contains 1 percent caffeine but between 7 and 9 percent chlorogenic acid(绿原酸)which is a strong antioxidant.The study, published in the Journal of Agricultural and Food Chemistry, found that in mice this acid prevented retinal degeneration.Chang Y. Lee, a professor of food science and the study's senior author said: 'Th e re tina is a thin tissue layer on the inside, back wall of the eye with millions of light-sensitive cells and other nerve cells that receive and organise visual information.'It is also one of the most metabolically active tissues, demanding high levels of oxygen and making it prone to oxidative stress.'The lack of oxygen and pr oduction of free radicals leads to tissue damage and loss of sight.'He added: 'The study is important in understanding functional foods, that is, natural foods that provide beneficial health effects.'Coffee is the most popular drink in the world, and we a re understanding what benefit w e can get fro m that.'Previous studies ha ve shown that coffee also cuts the risk of such chronic diseases as Parkinson's, prostate cancer, di abete s, Alz heimer's a nd age-related cognitive declines.。
Benefits from Tween During Enzymic Hydrolysis of Corn StoverWilliam E.Kaar,*Mark T.HoltzappleDepartment of Chemical Engineering,Texas A&M University,College Station,Texas77843-3122;telephone:409-845-9708;fax:409-845-6446; e-mail:mth4500@Received7February1997;accepted27December1997Abstract:Corn stover is a potential substrate for fermen-tation processes.Previous work with corn stover demon-strated that lime pretreatment rendered it digestible by cellulase;however,high sugar yields required very high enzyme loadings.Because cellulase is a significant cost in biomass conversion processes,the present study fo-cused on improving the enzyme efficiency using Tween 20and Tween80;Tween20is slightly more effective than Tween80.The recommended pretreatment condi-tions for the biomass remained unchanged regardless of whether Tween was added during the hydrolysis.The recommended Tween loading was0.15g Tween/g dry biomass.(The critical relationship was the Tween load-ing on the biomass,not the Tween concentration in so-lution.)The72-h enzymic conversion of pretreated corn stover using5FPU cellulase/g dry biomass at50°C with Tween20as part of the medium was0.85g/g for cellu-lose,0.66g/g for xylan,and0.75for total polysaccharide; addition of Tween improved the cellulose,xylan,and total polysaccharide conversions by42,40,and42%, respectively.Kinetic analyses showed that Tween im-proved the enzymic absorption constants,which in-creased the effective hydrolysis rate compared to hy-drolysis without Tween.Furthermore,Tween prevented thermal deactivation of the enzymes,which allows for the kinetic advantage of higher temperature hydrolysis. Ultimate digestion studies showed higher conversions for samples containing Tween,indicating a substrate ef-fect.It appears that Tween improves corn stover hydro-lysis through three effects:enzyme stabilizer,lignocellu-lose disrupter,and enzyme effector.©1998John Wiley& Sons,Inc.Biotechnol Bioeng59:419–427,1998.Keywords:corn stover;Tween;hydrolysis;enzyme;sac-charificationINTRODUCTIONA previous article(Kaar and Holtzapple,in press),showed that lime is an effective pretreatment for the enzymic sac-charification of corn stover;however,high enzyme loadings were required for high conversions.For example,the7-d glucan conversion at50°C using5FPU cellulase/g dry bio-mass was about60%compared to88%when25FPU/g dry biomass was used(Kaar and Holtzapple,in press).An im-portant and expensive input into any potential biomass con-version system is the enzyme loading,which can amount to as much as60%of the process cost(Helle et al.,1993; Nguyen and Saddler,1991;Wilke et al.,1981);hence,en-zyme use should be as low as possible.Clearly,a method to increase enzyme effectiveness would be beneficial.Toward this aim,it has been reported that addition of non-ionic surfactants,particularly Tween species,effectively im-proves the cellulase activity as well as preserves them for recycle(Castanon and Wilke,1981;Helle et al.,1993;Kaya et al.,1995;Park et al.,1992).This article focuses on the benefits derived from adding Tween20and Tween80to the corn stover saccharification hydrolytic medium.Tween20(polyoxyethylene sorbitan monolaurate,CAS #9005-64-5)and Tween80(polyoxyethylene sorbitan mo-nooleate,CAS#9005-65-6)are surfactant polysorbates. Previous reports using Tween additives for enhancing en-zymic saccharification have focused on non-native cellulose and cellulose analogs such as newsprint,microcrystalline cellulose,and carboxymethylcellulose(CMC).Castanon and Wilke(1981)reported a14%increase in glucose yield and more than twice as much recovered enzyme from news-paper saccharification(5%suspension,13FPU/g newsprint, 45°C,48h)when0.02g Tween80/g newsprint was added. These researchers postulated that Tween80assists the de-sorption of enzyme from substrate.Park et al.(1991),also working with newspaper,examined several surfactants and found Tweens to be among the best performers.The rec-ommended Tween80loading(4%suspension,0.75FPU/g newsprint,50°C,22h)was0.0125g Tween80/g newsprint, with little enhancement with loadings greater than0.025g Tween80/g newsprint and no enhancement when loadings exceeded0.25g Tween80/g newsprint.After adding0.16g Tween80/g cellulose,Helle et al.(1993)reported a seven-fold increase in the saccharification of Sigmacell100cel-lulose(2.5%suspension,40FPU/g cellulose,50°C,100h); they concluded that the Tween80disrupted the cellulose structure as well as facilitated enzyme desorption from the substrate.Finally,Kaya et al.(1995)conducted an extensive evaluation of surfactants used during the saccharification of CMC and xylan.Tween80at a loading of0.015g Tween 80/g substrate increased the conversion of CMC(0.5%so-*Present address:The Foxboro Company,10707Haddington Drive,Houston,Texas77043Correspondence to:Mark HoltzappleContract grant sponsors:National Renewable Energy LaboratoryContract grant numbers:DE-AC02-83CH10093;XAW-3-11181-03©1998John Wiley&Sons,C0006-3592/98/040419-09lution,0.77FPU/g CMC,50°C,1h)by50%and improved the xylan(1%suspension,0.59IU/g xylan,50°C,1h)hy-drolysis by about9%.Concerning the mechanism,Kaya et al.(1995)referred to the work of Kim et al.(1991)who concluded that surfactants help prevent cellulase denatur-ation at the air interface by competing with the cellulase for the free surface area.Thus,while the experimental sub-strates and Tween loadings have differed,the unanimous conclusion in the literature has been that,by whatever mechanism,Tween assists the enzymic saccharification of cellulose and cellulose analogs.Based on these previous results,it was suspected that Tween might improve the enzymic saccharification of a native lignocellulose like corn stover.Experiments were conducted to identify the recommended Tween loading and to verify the recommended pretreatment conditions when using Tween as an additive for the enzymic saccharification. Additional tests were performed to show that Tween acts as enzyme stabilizer,lignocellulose disrupter,and enzyme ef-fector.MATERIALS AND METHODSGeneralHydrolyses were performed in parallel with and without Tween.Except for the lime loading study,pretreatment of corn stover samples(−20+80mesh;39.0%glucan,20.1% xylan,2.0%arabinan,21.5%lignin,6.8%ash,and3.9% protein,by weight)was conducted according to previously reported methods(Kaar and Holtzapple,in press)using standard conditions(0.1g Ca(OH)2/g dry biomass,10g H2O/g dry biomass,120°C,5h).Unless otherwise speci-fied,the enzymic saccharification was performed at a solids content of50g biomass/L in500-mL culture flasks at a pH of4.8using procedures described previously(Kaar and Holtzapple,in press).Tween20and Tween80were obtained from Fisher Sci-entific(Pittsburg,PA).The cellulase mixture(Spezyme-CP, from Trichoderma reesei with reported activity91.9FPU/ mL)was provided by the National Renewable Energy Labo-ratory(NREL)and had an assumed specific activity of700 FPU/g enzyme(Holtzapple et al.,1991).The-glucosidase (Novozym188)was obtained from Novo Nordisk(Fran-klinton,NC),had a vendor-reported activity of250IU/mL, and was used at a loading of28.4IU/g dry biomass.The typical procedure for conducting the hydrolysis was:trans-fer of pretreated solids to culture flask;addition of citrate buffer and sodium azide solutions;neutralization to pH4.8 with glacial acetic acid;preheating sample for10min in the incubator shaker;and,addition of Tween or an equal vol-ume of water,followed by immediate addition of the en-zymes.(Note:For this enzyme system,there was no inhi-bition by the calcium acetate resulting from the lime neu-tralization.)Post-hydrolysis samples were heated in a boiling water bath for10min to denature the enzymes,centrifuged,and the clear supernatants analyzed by DNS assay(Miller,1959)or by High Performance Liquid Chro-matography(HPLC)(Kaar et al.,1991).(Note:Tween does not affect,nor contribute to,the absorbance measurement in the DNS assay.)Tween Loading StudiesThis experiment was conducted using Tween80.The hy-drolysis was conducted at50°C.Aliquots(4mL)were re-moved after hydrolysis times of0.5,1,1.5,2,3,4,5,6,7, and8d;the supernatants were analyzed by HPLC. Pretreatment StudiesExperiments were repeated to verify that the previously de-termined recommended pretreatment conditions(Kaar and Holtzapple,in press)were also best for samples saccharified in the presence of Tween80.For all cases the samples were pretreated at120°C.In the pretreatment time experiment, the zero-time samples were mixed with the standard loading of0.1g Ca(OH)2/g dry biomass at room temperature and immediately neutralized to pH4.8with acetic acid.For the calcium hydroxide loading evaluation,pretreatments were conducted for5h using lime loadings of0.0,0.025,0.05 0.075,0.1,and0.125g Ca(OH)2/g dry biomass;the inter-mediate loadings of0.055,0.060,0.065,and0.070g Ca(OH)2/g dry biomass were also evaluated with Tween only.The enzymic hydrolysis time was100h at50°C.At the conclusion of the hydrolysis,the samples were analyzed by DNS assay.Enzyme Loading DependenceThe hydrolysis was conducted at50°C with Tween80and 40°C with Tween80or Tween20as additives.For both experiments,4-mL samples were removed at time intervals of1,3,6,10,16,24,36,48,72,and100h and analyzed by DNS assay.Hydrolysis Temperature DependenceThe hydrolyses were conducted for72h at temperatures of 30,40,50,and60°C.Before adding the enzymes,the samples were placed in the shaker for5min to ensure thor-ough mixing and to warm the samples partially to the hy-drolysis temperature.The samples were not allowed to com-pletely reach the designated temperature to avoid heat shocking the enzymes upon their addition.After the5-min warm-up,Tween20,Tween80,or water was added to a pair of samples.The samples were hydro-lyzed in sets of six and the hydrolyzates were analyzed by HPLC.Tween Dependence:Loading or Concentration? Corn stover samples were pretreated in triplicate using3.75, 7.5,11.25,and15.0g of dry biomass per reactor.The420BIOTECHNOLOGY AND BIOENGINEERING,VOL.59,NO.4,AUGUST20,1998samples were prepared for hydrolysis by the previously de-scribed standard methods;the resulting solids concentra-tions in the hydrolytic solutions were25,50,75,and100g dry biomass/L.The pretreated samples were separated into three sets such that each set contained one of each of the four different substrate concentrations.To one set of samples,Tween80 (0.15g Tween/g dry biomass)was added;another set re-ceived aliquots of water equal in volume to the Tween80 added to the first set;and the third set of samples received a combination of water and Tween80such that the25g/L sample received a double loading(0.3g Tween/g biomass) of Tween80;the75g/L sample received a two-thirds load-ing(0.1g Tween/g biomass);and the100g/L sample re-ceived a one-half loading(0.075g Tween/g biomass).The samples were hydrolyzed in the shaker at50°C for100h. Ultimate DigestionThe experiment was conducted in duplicate according to NREL Chemical Analysis and Testing Standard Procedure No.009(Torget,1993)with Tween20and Tween80as additives and distilled water as the control.The following loadings were used(all per gram dry biomass):Tween20or Tween80,0.15g/g;-glucosidase,28.4IU/g;and cellulase, 25FPU/g.The samples were hydrolyzed for7d at50°C.At the conclusion of the hydrolytic period,the supernatants were analyzed by HPLC.Initial Reaction Rate MeasurementInitial reaction rates were measured for two sets of samples; for one set the enzyme concentration was constant(variable substrate concentration)and for the other the substrate con-centration was constant(variable enzyme concentration). For the sample set with variable substrate concentration, pretreated stover was weighed into500-mL screw-cap cul-ture flasks and distilled water was added as appropriate, such that the volume for enzymic hydrolysis after the ad-dition of all reagents would be150mL and the resulting biomass concentrations would be25.0,33.3,41.7,and50.0 g/L.Six50g/L samples and three samples for each of the other concentrations were prepared.After neutralization,the samples were placed in the incubator/shaker to preheat to the desired hydrolytic temperature(40and50°C).Once the samples had reached the incubator temperature,Tween20 (0.15g/g dry biomass),Tween80(0.15g/g dry biomass),or water,was added.Then213IU-glucosidase was pipetted into each flask,the shaker was started,and37.5FPU cel-lulase was added to each at30-s intervals.As each flask received its aliquot of cellulase,the cap was secured on the flask.The first sample to receive cellulase was removed from the shaker after exactly1h and a4-mL aliquot was immediately removed and heated in a water bath for15min to denature the enzymes.At30-s intervals,the remaining samples were similarly removed from the shaker.When the last sample had been removed from the water bath,the tubes were centrifuged and the hydrolyzates were analyzed by DNS assay.The50g/L samples from each temperature were also analyzed by HPLC to determine the relative amounts of glucose and xylose.The variable-enzyme samples were prepared by the pro-cedure described above using a substrate concentration of 50g/L and enzyme concentrations of0.36,0.50,0.71,and 1.07g/L.The samples were hydrolyzed at40and50°C and were analyzed by DNS assay.RESULTS AND DISCUSSIONTween Loading StudiesA portion of the data from the Tween loading experiment is plotted in Figure1.The Tween80clearly aided the enzymic hydrolysis of the pretreated corn stover;the average rate and extent of conversion in the Tween80samples was higher than for Tween-free samples.At the apparent optimum loading level of0.15g Tween/g dry fiber,a30%increase in the total sugar yield in the192-h saccharification was ob-tained.Interestingly,for unknown reasons,the Tween80 appeared to be slightly inhibitory at loadings of around 0.005g Tween/g dry fiber.For comparison,the individual glucan and xylan conver-sions for the0.15g Tween/g dry fiber loading are plotted in Figure2.In the Tween-free samples,the192-h conversion for glucan and xylan were approximately the same,about 0.60g anhydromonomer/g polysaccharide.In the samples which were loaded with0.15g Tween80/g dry fiber,the xylan conversion was about0.71g anhydromonomer/g xylan,an improvement of about18%,whereas the glucan conversion increased by36%to0.83g anhydromonomer/g glucan.This would indicate that Tween80is more benefi-cial for the cellulose hydrolysis,as was also reported by Kaya et al.(1995).Pretreatment StudiesFigure3shows that,whereas the yields obtained in the Tween samples were universally higher than the Tween-free counterparts,the recommended pretreatment conditions were identical.Therefore,using Tween during the hydroly-sis does not eliminate,or even reduce,the requirements for effective pretreatment,but does lead to much higher yields. Comparisons should also be made between the pretreated and untreated samples.The lime pretreatment,when con-ducted at the recommended conditions(0.1g Ca(OH)2/g dry biomass,10g H2O/g dry biomass,120°C,5h),increased the saccharification of the stover from about50mg equiv glucose/g dry stover to450mg equiv glucose/g dry fiber. Adding Tween80during the hydrolysis further improved the sugar yield to665mg equiv glucose/g dry stover.Only marginal hydrolysis improvement,from50to80mg equiv glucose/g dry stover,was achieved by adding Tween to the untreated biomass samples.Enzyme LoadingThe results from the50°C experiment are plotted in Figure 4as a function of hydrolysis time;this figure contains sev-eral interesting and important features.First and foremost,the enzymes performed better in the samples containing Tween80;a loading of1FPU/g dry biomass with Tween80achieved the same yield after100h of hydrolysis as a7FPU/g dry biomass loading without Tween80.Furthermore,the slopes of the yield lines for the 1and3FPU/g dry biomass samples that contained Tween 80are positive after100h at50°C indicating that the en-zymes were still active.These slopes can be compared to the flat yield lines for all of the Tween-free samples;without Tween80the enzymes were completely deactivated after about72h.Finally,a loading of3FPU/g dry biomass with Tween80resulted in a yield that was higher than that ob-tained with15FPU/g dry biomass without Tween80.In fact,when the data are plotted as a function of enzyme loading(Fig.5),the recommended enzyme loading,identi-fied as the shoulder of the yield curve,with Tween80is about3FPU/g dry biomass,vs.10FPU/g dry biomass without Tween80.When the hydrolysis was conducted at40°C(Fig.6), samples containing Tween20performed better than Tween 80samples,which in turn outperformed the Tween-free samples.However,the advantage of the Tween samples over the Tween-free samples was less at40°C than at50°C, especially with the higher enzyme loadings.For example,at 50°C an enzyme loading of15FPU/g resulted in a sugar yield(100h reaction)of697mg equiv glucose/g dry bio-mass in the Tween80sample,vs.only534mg equiv glu-cose/g dry biomass in the Tween-free sample,an improve-ment from the Tween80addition of30.5%.At40°C the corresponding samples had656mg equiv glucose/g dryFigure2.Conversion of glucan(a)and xylan(b)from saccharification ofpretreated corn stover.Pretreatment conditions:0.1g Ca(OH)2/g dry bio-mass and10g H2O/g dry biomass for5h at120°C.Hydrolysis conditions: 5FPU cellulase/g dry biomass at50°C.Legend:ࡗ0.15g Tween80/g dry biomass;᭡no Tween.Figure3.Sugar yields from pretreatment variations:(a)time at120°C,and(b)lime loading.Pretreatment conditions:(a)0.1g Ca(OH)2/g drybiomass and10g H2O/g dry biomass;(b)10g H2O/g dry biomass for5hat120°C.Hydrolysis conditions:5FPU cellulase/g dry biomass at50°C. Legend:ࡗ0.15g Tween80/g dry biomass;᭡no Tween;ииииии0.15g Tween80/g dry biomass,no pretreatment;------no Tween,no pretreat-ment.biomass and599mg equiv glucose/g dry biomass,respec-tively,an increase of only9.5%.A key to the increased yield in the Tween-free samples can be seen in the slopes of the yield lines for the lower enzyme loadings.Unlike the curves at50°C(Fig.4),the slopes for the Tween-free samples at40°C(Fig.6)remained positive,indicating that the enzymes continued to be active throughout the reaction period.However,plotting the data as a function of enzyme loading(Fig.7)reveals that,despite the increased perfor-mance in the Tween-free samples at40°C,the recom-mended enzyme loadings for hydrolysis at40°C are com-parable with those identified for hydrolysis at50°C;when using Tween the loading should be3FPU/g dry biomass, whereas if Tween is not used,the loading should be about 10FPU/g dry biomass.Hydrolysis Temperature Dependence:Tween as an Enzyme StabilizerThe results from the experiment are plotted in Figure8;the conversions are plotted as g equiv anhydromonomer/gram of original polysaccharide as a function of hydrolysis tem-perature.As expected,the samples containing Tween had higher conversions,with Tween20performing slightly bet-ter than Tween80.Furthermore,the Tween samples had higher conversions at50°C than at40°C,whereas the con-versions for the Tween-free samples were higher at40°C.In all cases,the extent of hydrolysis was much lower at30°C and60°C than at the middle temperatures.Considering that the optimum temperature in the Tween samples was10°C higher than that for the Tween-free samples,it was con-cluded that adding Tween protects the enzymes from ther-mal deactivation.Substrate Dependence of Tween:Tween as a Lignocellulose DisrupterThe results from both the Tween Dependence and Ultimate Digestion experiments indicate that Tween acts as a ligno-cellulose disrupter.The sugar yields from the Tween Dependence experiment are plotted in Figure9.It was expected that the sugar yieldFigure5.Sugar yields for100h of hydrolysis(50°C)as a function ofenzyme loading.Pretreatment conditions:0.1g Ca(OH)2/g dry biomassand10g H2O/g dry biomass for5h at120°C.Legend:ࡗ0.15g Tween80/g dry biomass;᭡no Tween.KAAR AND HOLTZAPPLE:BENEFITS FROM TWEEN DURING ENZYMIC HYDROLYSIS OF CORN STOVER423would increase with increasing substrate concentration be-cause of the correspondingly higher enzyme concentration. Sugar yield increased with increasing concentration for the Tween-free samples,although the increase beyond the50 g/L sample was slight.In the samples for which the Tween loading was constant,a large increase in yield was observed up to the75g/L sample,after which the yield decreased slightly for the100g/L sample;the decrease was probably due to product inhibition.However,in samples for which the Tween concentration was constant,the sugar yield de-pended on the Tween loading.Doubling the Tween80load-ing in the25g/L samples did not improve the yield.This is consistent with the previous finding(Fig.1)in which adding Tween80beyond a loading of0.15g Tween/g original dry fiber did not provide additional benefit.On the other hand, the75g/L and100g/L samples both had lower yields than when the Tween80loading was maintained constant.Thus, it was concluded that the benefit of Tween is loading de-pendent,not concentration dependent,which implies a re-lationship between Tween and the substrate.This result was corroborated by the Ultimate Digestion experiment.The average HPLC analysis results and corresponding conversions for each pair of samples from the ultimate di-gestion are listed in Table I.As can be seen from Table I, while the conversions were high for all samples,the con-versions for total sugars averaged about10%higher(0.97g/g)for Tween20samples,and6%higher(0.93g/g)for Tween80samples,compared to the Tween-free samples (0.88g/g).The ultimate digestion utilizes high enzyme loadings and long hydrolysis times which obfuscate the sta-bilizer and effector roles of Tween.Therefore,the higher ultimate conversions in the Tween samples must be due to more substrate being available to the enzymes;this requires that Tween disrupt the lignocellulose matrix.Furthermore, the results from this experiment indicate that Tween20is better at disrupting the matrix than Tween80,which was also the conclusion derived by Kurakake et al.(1994). The Effector Role of TweenAn effector in enzymic processes aids the interaction of the substrate and the enzyme by either making the substrate or enzyme conformation better for enzyme attachment to the substrate or facilitating the release of the enzyme from the substrate once reaction has occurred.In either case,the benefits appear in the kinetic constants associated with the reaction.Before kinetic parameters can be evaluated,an adequate model is needed.Holtzapple et al.(1984a)have developed a model for cellulose hydrolysis shown to correlate experimental data better than models derived from the traditional Michaelis-Menten approach.The HCH-1model of Holtzapple et al. accounts for enzymic limitations encountered with the in-soluble cellulose substrate.In its complete form,HCH-1 predicts the hydrolysis velocity,v,to be:v=d͓G s͔dt=͓G x͔͓E͔ͩ11+͚i͓G i͔ͪ␣+͓G x͔+͓E͔(1) where[G s]is the product concentration(cellobiose and glu-cose),is the reaction rate constant,[G x]is the total cel-lulose concentration,[E]is the total enzyme concentration,i is the enzyme binding constant for inhibitor G i(either glucose,G1,or cellobiose,G2),␣is the affinity constant,is the fraction of free cellulose sites,andis the number of cellulose sites covered by an adsorbed cellulase. Although the HCH-1model was developed for a specific enzyme(cellulase)reacting with a homogeneous substrate (cellulose),it can legitimately be used to model the enzyme mixture and heterogeneous substrate that characterize the present experiment.For example,it is likely that the mecha-nism of the reaction between the enzyme(s)and the hemi-cellulose is analogous to the cellulase-cellulose interaction because both cellulose and xylan are constructed of similar,-O-4linked,monomers.Furthermore,the HPLC analyses of the50g/L samples revealed that the major monosaccha-ride present in the1-h hydrolyzates was glucose(Table II); this is important for two reasons.First,the1-h hydrolyses, and therefore,the experimental data represented by the DNS analyses,are essentially indicative of the action of cellulase on cellulose.And second,the1-h xylan conversions implied in Table II are low relative to the corresponding1-h cellu-Figure9.Saccharification results with constant Tween80loading(0.15 g Tween/g biomass)or concentration(10g Tween/L solution).Pretreat-ment conditions:0.1g Ca(OH)2/g dry biomass and6g H2O/g dry biomassfor5h at120°C.Hydrolysis conditions:5FPU cellulase/g dry biomass for 100h at50°C.Legend:᭹constant Tween loading;constant Tween concentration;᭡no Tween.Table I.Conversions from ultimate digestion of pretreated corn stover.Sample type Glucan(g/g)aXylan(g/g)aArabinan(g/g)aTotal(g/g)aNo Tween0.880.880.920.88Tween20 1.000.920.970.97Tween800.950.900.960.93a g anhydromonomer/g polysaccharide.424BIOTECHNOLOGY AND BIOENGINEERING,VOL.59,NO.4,AUGUST20,1998lose conversions,despite the fact that xylan conversions achieved after extended time under similar experimental conditions are approximately the same as the cellulose con-versions(Figure2).This behavior suggests the action of a single enzyme that reacts with,but has different affinities for,two substrates;as the preferred substrate(cellulose)is consumed,the enzyme is increasingly available for reaction with the second substrate(hemicellulose).Thus,it is prob-able that cellulase,rather than a different enzyme,performs the hydrolysis of the hemicellulose.If a different enzyme were responsible for the hemicellulose hydrolysis,the xy-lose concentration in the1-h samples would be close to that of glucose.Therefore,the hydrolytic system of the present experiment can best be described as a single enzyme(cel-lulase)acting on two,structurally similar,substrates(cellu-lose and hemicellulose),with the initial hydrolysis of one of the substrates(cellulose)proceeding at an approximately 10-fold faster rate than the hydrolysis of the other substrate (hemicellulose).Because of the mechanistic similarity between the present experiment and the cellulose hydrolysis model proposed by Holtzapple et al.(1984a),the HCH-1model was selected to evaluate the kinetic data.However,to provide a clearer nomenclature and differentiate the model equation,as ap-plied to heterogeneous substrates,from the original HCH-1 model equation[eq.(1)],the following changes are made: The variable representing the cellulose concentration in eq.(1),G x,is replaced with S to designate total substrate con-centration;the variable representing the concentrations of inhibitors(products),G i,is replaced with S i to indicate all possible soluble inhibitors;and the concentration of soluble products,G s,is replaced with S s to account for hydrolysis products derived from all polysaccharides.Hence,the model equation for heterogeneous substrates becomes:v=d͓S s͔dt=͓S͔͓E͔ͩ11+͚i͓S i͔ͪ␣+͓S͔+͓E͔(2)where S is the total substrate concentration(for convenience assumed to be g dry biomass/L)and the other parameters are as described for eq.(1).The variablein eq.(2)represents a complicated ex-pression involving[S],[E],␣,and.However,for the pur-poses of data correlation,Holtzapple et al.(1984b)have determined thatcan be set equal to1.The conditions of the experiments used in this study allow eq.(2)to be sim-plified even further.For T.reesei cellulase Holtzapple et al. (1990)reported the glucose enzyme-binding constant,1,to be equal to0.0031L/g,whereas the enzyme-binding con-stant for cellobiose,2,was reported as0.0184L/g.In the present experiment,the maximum glucose concentration at-tained was about13g/L,and the high level of cellobiase added to the system eliminated cellobiose entirely(as ob-served in HPLC chromatograms).If the enzyme binding constants for the other hydrolysis products,such as xylose, are assumed to be of the same order of magnitude(or smaller)as the binding constant for glucose,the product inhibition term,⌺i[S i],is small and can be ignored.Thus, eq.(2)reduces to:v=d͓S s͔dt=͓S͔͓E͔␣+͓S͔+͓E͔(3) Equation(3)is similar in form to expressions derived from the Michaelis-Menten model.In the absence of product in-hibition,Michaelis-Menten kinetics would predict the hy-drolysis velocity to be:v=k͓S͔͓E o͔K m+͓S͔(4)where k is a constant,E o is the total enzyme concentration, and K m is the Michaelis-Menten constant.The product of the constant,k,and the total enzyme concentration,[E o],is also referred to as the maximum reaction velocity,max. Hence,the only difference between the simplified HCH-1 and Michaelis-Menten models is the appearance of the en-zyme coverage parameter,[E],in the denominator of eq.(3);the HCH-1model completely reduces to the Michaelis-Menten model forס0.Consequently,the HCH-1expres-sion,eq.(3)can be manipulated and the constants obtained using techniques typically used with Michaelis-Menten ki-netics.For example,both sides of eq.(3)can be inverted and linearized at either constant enzyme or constant sub-strate concentration.This allows the preparation of Line-weaver-Burk-type plots for parameter evaluation.At con-stant-enzyme concentration,1v=␣+͓E͔1+1(5) and at constant-substrate concentration,1v=␣+͓S͔͓S͔1͓E͔+͓S͔(6) Double-reciprocal plots were prepared for the initial reac-tion rates obtained with variable enzyme concentration and variable substrate concentration;the slopes and intercepts of the fitted lines are listed in Table III.The HCH-1constants were calculated from eqs.(5)and(6)for the various reac-tion systems using the respective slopes and intercepts listed in Table III;the resulting values for,␣,andare also reported in Table III.Table II.Sugar concentrations in50g biomass/L samples,1-h hydroly-sis.Sample type Temperature(°C)Glucose(g/L)Xylose(g/L)Arabinose(g/L)No Tween40 2.980.320.40Tween2040 3.310.390.54Tween8040 2.960.340.43No Tween50 4.260.680.53Tween2050 4.540.590.64Tween8050 4.680.590.44KAAR AND HOLTZAPPLE:BENEFITS FROM TWEEN DURING ENZYMIC HYDROLYSIS OF CORN STOVER425。