实验一、脱水香蕉片一、实验目的掌握蔬菜干制品的加工方法和设备。
二、实验原理本实验的目的是研究香蕉热风干燥过程中水分的传递现象,并观测加工过程中褐变引起的颜色变化, 以探索生产高质量脱水香蕉制品所适宜的干燥技术。
在干燥过程的初始阶段,水分在潮湿的物料内自由移动在最后阶段,残留的水分在近乎干燥的物体内扩散。
人们一般将干燥过程视为两个阶段, 即恒速干燥阶段和减速干燥阶段。
从恒速干燥阶段向减速干燥阶段转变时的水分含量水分临界含量,是每一物料在给定干燥条件的干燥特性。
微波产热是由于食品中有水的存在,当含水量一定时,微波功率越高,产热量越大,食品升温越快,膨化时气泡产生也越快,食品内气体压力也越大,同时,干燥越快。
过高的微波密度使生热太快太高,不利于控制,食品宜焦化;过低的微波密度使食品内气压太小,不利于膨化。
三、材料与设备香蕉，柠檬酸，亚硫酸钠，食盐，玉米淀粉、ＣＭＣ、蜂蜜、电热恒温烘箱、微波炉、砧板、不锈钢刀、小托盘四、工艺流程原料验收→浸泡→切片→漂白→干燥→分选→包装→入库五、操作要点（1）原料验收香蕉，新鲜、无病虫害或机械损伤，市售。
（2）干燥处理A 常压热风干燥a 将香蕉去皮，然后将其切成厚度约2-3 mm和3-5mm的薄片。
b 称取香蕉片(液固比= 3 :1) 放入护色液冷浸10min,将其放置在恒温热风干燥箱中，以60℃-70℃温度进行干燥，直至安全水分（香蕉片含水量在30%—35%）。
为了研究热风温度对香蕉片质量的影响，对香蕉片进行热风干燥实验，设定热风干燥过程的0、1、2、3、4、5小时测定含水率。
c 绘制干燥速率曲线。
评定其外观质量品质。
并对其营养物质进行分析。
B 微波干燥a 香蕉去皮，切成2-3mm和3-5mm。
b 将适量香蕉片至于护色液冷浸10min。
c 每次投料量为120 g ，分别测得不同厚度的苹果片在中火下微波0、2、4、6、8、分钟香蕉片的质量，以确定香蕉片的微波密度。
(3)评定产品外观质量品质。
并对其营养物质进行分析。
(4)平衡水分。
烘干后的香蕉片稍冷却后，立即装人套有塑料袋的箱内，保持1-2天，使干品内水分相互转移，达到均衡。
(5)包装经过分选后进行包装，每箱净重为20kg。
内为尼龙袋包装，外包装为纸箱，采用水胶纸袋密封箱口。
六、质量标准1 感官指标脱水香蕉片为白色略淡黄，无深色。
香蕉片浓郁。
口感酥脆。
香蕉片薄厚、大小应基本均匀，碎屑另行包装销售。
2 理化指标含水量小于6%。
七、注意事项1、整个加工过程中，切忌使用铁器、铜容器，可用不锈钢器具。
2、脱水香蕉片成品为白色略淡黄，无深色。
香蕉片成品的水分不得超过6%。
3、贮藏成品香蕉蒜片必须在干燥、凉爽的库房内。
贮运过程中不得与有毒有害物质接触。
八、思考题1 香蕉片护色的原理？2 不同干制条件对香蕉片质量的影响。
Experiment 1 Dehydrated banana sliceExperimental purpose:Master the processing method and equipment of dried vegetables.Experimental principleDuring drying, fruit slices can undergo enzymatic and nonenzymatic darkening, and visible color change is considered .However, diffusion is generally accepted as the principal mechanism of moisture transport in drying processes the moisture transfer phenomenon during banana drying and observe the color change caused by browning in processing, to explore the production of high quality dehydrated banana products that were suitable to the drying technology. In drying，water molecules must make their way through the food product to the surface (internal resistance to drying ) in contact with drying air. Once at the surface, water molecules are transfered into the air (external resistance to drying) based on the difference in vapor pressure between same value as the vapor pressure of water at the surface of the food, drying ceases. The rate of drying may be limited by either the rate of internal migration of water molecules to the surfaces or the rate of evaporation of water molecules from the surface into the air, depending on the conditions of drying. The initial period of constant rate drying is called the “constant rate period,” or CRP, once the critical moisture content is reached at later stages of drying, the rate at which moisture migrates to the surface limits drying. The rate of drying decreases, this is called the “falling rate period,” FRP. Here drying rate depends on the moisture content remaining in the product.Microwave energy offers several advantages compared to conventional heating methods, including speed of operation, energy savings, precise process control and faster start-up and shut down times However, as microwaves penetrate within a food and generate heat internally, their greater processing interest is the capacity to deliver energy within the product. In thermal processing this means accelerated and more uniform internal heating and thus substantially decreased processing times, which leads to higher product quality as the detrimental effects of high temperatures are minimised. Other benefits include that microwave processing can also help control energy costs, since heating takes place only in the food material being processed and not in the surrounding medium.Materials and equipmentBananas, citric acid, sodium sulfite, salt, corn starch, CMC, honey, electrothermal constant temperature oven, microwave oven, chopping boards, stainless steel knife, the small trayProcess flowThe check and acceptance of raw materials→soaking→slicing→bleaching →drying →sorting→packaging →storageOperation points( 1)The check and acceptance of raw materialsBanana, fresh, no pests or mechanical damage, commercially available.( 2) Drying processAt ambient pressure drying①The fruit was peeled manually and cut into slices of 2-3 mm and 3-5mm thick. Slices wereplaced into glass jars filled with six times their weight of a sucrose solution. solution, and left for up to four hours of drying. The syrup was mixed gently with a magnetic stirrer. Sugarcane was of the first class commercial grade, and pH was controlled by citric acid or calciumhydroxide solutions.②Three slices were removed from the batch every 30 min, gently washed with distilled water toeliminate syrup from the surface, and residual water was removed with tissue paper.③For the purpose of estimating the initial and final moisture contents, banana samples fromeach experiment were dried in an oven at 60℃for 3-4 h. Banana samples were prepared from the fresh bananas and the dried bananas that had been dried in the kiln.④The empty containers were weighed before they were used. The masses of the containers withthe samples in them were measured before and after drying.⑤Drying curves: Analysis of banana drying behavior using the concept of a characteristicdrying curve. The average moisture content of the dried bananas is plotted as a function of time.Microwave drying①The fruit was peeled manually and cut into slices of 2-3 mm and 3-5mm thick. Slices were placed into glass jars filled with six times their weight of a sucrose solution. solution, and left for up to four hours of drying. The syrup was mixed gently with a magnetic stirrer. Sugarcane was of the first class commercial grade, and pH was controlled by citric acid or calcium hydroxide solutions.( 3) Sensory evaluation.( 4) Balance moisture. Dried banana chips after cooling slightly, immediately loaded with plastic box, keeping 1-2 days, so that the moisture of dried food will be transferred to achieve equilibrium.( 5) PackagingAfter sorting then packaging it, the weight of each box should be 20kg. Inner space pack with nylon bag, outer would package carton. Use the glue water bag to seal the mouth.Quality standard1.Sensory index:In the scores obtained for color, texture, taste, crispness, and overall impression.Dehydrated banana slices are white and slightly yellowish, no dark color. Banana is full of flavor. And taste crisp. The thickness and size of Ba nana slice should be the basic uniform, what’s more, the fragement should be packaged separately and then sale out.2.Physicochemical indexes: moisture content should be less than 6%.Attention:1. Slicing foods allows the dry air to circulate and dry the surface area of the food first. Cut foodsinto 1/8-inch to 1/2-inch slices. The higher the water content, the larger you should make the slice size. Small slices of high-moisture foods, such as watermelon, would disappear when all the moisture has evaporated.2. Drying banana is a very imprecise process and exact drying times cannot be predicted. Complete drying is important since foods that are not completely dry are susceptible to mold and may still harbor harmful pathogens that could cause foodborne illness.Thinking problem1. What’s the principle of banana slice’s color protection?2. The effect of various operating conditions on the quality of banana slices。
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