Influence of fruit dietary fibre addition on physical and sensorial properties of strawberry jams

In¯uence of fruit dietary ®bre addition on physical and sensorialproperties of strawberry jamsN.Grigelmo-Miguel,O.Mart õn-Belloso *Department of Food Technology,UTPV-CeRTA,University of Lleida,Rovira Roure 177,25198Lleida,SpainReceived 11December 1998;accepted 25March 1999AbstractThe physical and sensorial properties of strawberry jams using fruit dietary ®bre (DF)as a stabiliser were evaluated andcompared with those made with a commercial thickener.Strawberry jams of up to 55°Brix were obtained from the total or partial substitution of commercial amidade pectin by peach DF in a standard formulation.The strawberry jams showed a pseudoplastic behaviour well described by the power-law model and the higher the DF content,the higher the viscosity observed in the jams.The pH value was kept within the ranges 3.08±3.29with no in¯uence of the DF addition.Sensory evaluation indicated that high fruit DF jams were as acceptable as conventional jams,but high DF strawberry jams were darker than the control ones.Ó1999Elsevier Science Ltd.All rights reserved.1.IntroductionThe traditional market of jams has been stable during the last few years as a consequence of changes in con-sumption habits and the appearance of alternative products,such as breakfast cereals,on the market.Therefore,the jam industry needs to improve its competitivity and developing high dietary ®bre (DF)jams may be a way of achieving this objective.There are medical studies about the bene®ts of DF consumption such as falling serum cholesterol concen-tration,lowering the risk of coronary heart disease,re-ducing blood pressure,aiding weight control,improving glycemic control,reducing the risk of certain types of cancer and improving gastrointestinal functions (An-derson,Smith &Gustafson,1994).As a result,®bres from di erent sources and compositions are being ob-tained and DF forti®cation of foods is increasing.DF from fruits are adequate to ®bre enrichment due to the well-balanced soluble/insoluble DF fractions re-lationship and also showed interesting functionality and physico±chemical characteristics (Chevalier,1993;L o pez et al.,1996;Grigelmo-Miguel &Mart õn-Belloso,1999;Grigelmo-Miguel,Gorinstein &Mart õn-Belloso,1999a).The use of a DF,which combines the physio-logical properties of the ®bre with other properties such as a high water holding capacity (WHC),provides an interesting area of application.Peach DF,like other fruit DF,contains pectins and shows a high WHC (Grigelmo-Miguel et al.,1999a),which aids the gel formation and texture stability of the product by avoiding syneresis.Syneresis or ``weeping''occurs in many food products with a gel structure,in-cluding jams and yoghurt,when water is no longer physically bound to the food system.Because oftheJournal of Food Engineering 41(1999)13±21/locate/jfoodengNotation D a *Increment of a *D b *Increment of b *D C *Chrome di erence D E *Colour di erence D L *Increment of L * c Shear rate,s À1g app Apparent viscosity,Pa s s Shear stress,Pa s 0Yield stress,Pa a *Redness b *Yellowness DF Dietary ®bre H *HueK Consistency coe cient,Pa s n K 0Casson Õs yield stress,Pa L *Luminositym Plastic viscosity of Casson (Pa s)1a 2n Flow behaviour index,dimensionless p Signi®cance levelr 2Determination coe cient*Corresponding author.Tel.:+34-973-702593/702521;fax:+34-973-702596/238264;e-mail:Omartin@tecal.udl.es0260-8774/99/$-see front matter Ó1999Elsevier Science Ltd.All rights reserved.PII:S 0260-8774(99)00067-9water a nity of fruit DF,it can prevent syneresis bybinding the released water (Kuntz,1994).The objective of this study was to evaluate the physico±chemical (pH,soluble solids,colour and rheo-logical behaviour)and sensorial qualities of strawberry jams where peach DF totally or partially replaced a commercial thickener.2.Experimental 2.1.Raw materialsStrawberry (mixture of vars.Oso grande and Chal-lenger)pur e e and peach DF were supplied by In-dul e rida,S.A.,Alguaire,Lleida,Spain.The pH value of strawberry pur e e was 3.65 0.01and its soluble solids content was 6.1 0.1.Peach DF was character-ised in a previous study (Grigelmo-Miguel et al.,1999a).Fig.1shows the colour parameters of straw-berry pur e e and peach DF.Saccharose as sweetener,amidade pectin or peach DF as thickener,citric acid as acidulant and ascorbic acid as antioxidant were used in the formulations.No colorant was added when evalu-ating the in¯uence of ®bre incorporation on the colour of jams.2.2.Formulation and processingFormulations of strawberry jams were made up to 40,45,50or 55°Brix in the ®nal product (Table 1).The uronic acids content in the formulations was 0,25,50,75or 100%from peach DF concentrate and the rest from commercial pectin.The procedure was the fol-lowing:Commercial amidade pectin was dispersed in 45g saccharose.The mixture was dissolved in 100ml water with the aid of a mixer (type 4187,Braun AG,Kron-berg,Germany)and then heated up to 60°C to get the complete dissolution.Peach DF was dispersed into the rest of the sugar,mixed with the strawberry pur e e and,afterwards,heat-ed.At the beginning of boiling,the pectin solution was poured into this mixture and citric and ascorbic acid were also added.The ®nal mixture was boiled for 2min and,after that,370ml glass containers were ®lled up with the obtained jam at 85 1°C and closed.Then,they were cooled in a water bath till 35°C and stored at room temperature at least 24h to be sure that gelli®cation was achieved.2.3.pH and soluble solidsThe pH and soluble solids of jams were analysed according to AOAC (1997)procedures.2.4.ColourThe cieLab co-ordinates (L *,a *,b *)were directly read in a glass cuvette with a spectrophotocolorimeter MiniScan MS/Y-2500(HunterLab,In.,Reston,VA,USA),calibrated with a white tile (L * 94.0,a * À1.1,b * 0.6),at 60°with a D-65illuminant source.Hue (H *),colour di erence (D E *)and chrome di erence (D C *)were calculated as follows:r Ãarctan ÃÃY1D i ÃD v à 2 D à 2 D à 2q Y2D g ÃD à 2 D à 2q X32.5.Rheological behaviourAll the jams were tested using a concentric cylinder viscometer Haake Rotovisco RV 12(Haake Mess-Tecjnik Gmbh u.,Karlsruhe,Germany)with an M 500-type measurement attachment which can transmit a maximum torque of 4.90N cm using an SVII-typepairFig.1.Position of peach DF concentrate and strawberry pur e e in cieLab diagram.(a)Co-ordinates L *and a *;(b)co-ordinates b *and a *.PDF:peach DF concentrate;SP:strawberry pur e e.14N.Grigelmo-Miguel,O.Mart õn-Belloso /Journal of Food Engineering 41(1999)13±21of coaxial cylinders(radii ratio R e/R i 1.14).Newton-ian shear rates were calculated from the angular velocity and the radii of the measuring-system cylinders.For non-Newtonian samples,the Newtonian shear rates were corrected by the procedure of Brodkey(1967).A thermostatic bath controlled the working temperature at 25°C 1°C.The rotor speeds were within the range1±512rpm which enabled rheograms(shear stress versus shear rate diagrams)to be constructed.Readings were taken at increasing rotor speeds until maximum speed was reached,and then when it was gradually reduced.In order to eliminate the possible e ects of thixotropy,the jams were previously sheared at maximum speed for3 min.To determine the rheological behaviour of jams three models were tried(Kokini,1992):1.Power-law models u c n X 42.Herschel and Buckley model,s s0 u c n X 53.Casson's models1a2 u1a20 m c1a2X 62.6.Sensory evaluationAn untrained panel of45members evaluated colour, consistency and acceptability of the jams on a9-point hedonic scale(9 like extremely;1 dislike extremely).Table1Formulation of strawberry jams aDF(%)UA from peachDF(%)Ingredients(g)40°Brix45°Brix50°Brix55°Brix00Pur e e750750750750Saccharose475.25554.25704.25884.25Pectin 5.45 6.14 6.827.5Water100100100100Citric acid27272727Ascorbic acid0.30.30.30.3125Pur e e750750750750Saccharose475.25554.25704.25884.25Pectin 4.09 4.605 5.115 5.625Water100100100100Citric acid27272727Ascorbic acid0.30.30.30.3DF12.514.0815.6417.2250Pur e e750750750750Saccharose475.25554.25704.25884.25Pectin 2.725 3.07 3.41 3.75Water100100100100Citric acid27272727Ascorbic acid0.30.30.30.3DF2528.1631.2834.4375Pur e e750750750750Saccharose475.25554.25704.25884.25Pectin 1.36 1.535 1.705 1.875Water100100100100Citric acid27272727Ascorbic acid0.30.30.30.3DF37.542.2546.2351.64100Pur e e750750750750Saccharose475.25554.25704.25884.25Water100100100100Citric acid27272727Ascorbic acid0.30.30.30.3DF5056.3362.5768.81a UA±uronic acids;DF±dietary®bre.N.Grigelmo-Miguel,O.Mart õn-Belloso/Journal of Food Engineering41(1999)13±2115Five jams(0%,1%,2%,3%and4%added®bre)with constant nominal soluble solids content(40,45,50or55°Brix)were evaluated in each session.A randomised complete block was the statistic design followed.During test sessions,panellists worked in individual booths.A 3-digit random number placed on a transparent plastic glass identi®ed the samples.Panellists were given room-temperature water to cleanse the palate before presen-tation of samples.Consumer evaluations of jams tried in di erent ses-sions were separately analysed to avoid the in¯uence of atmospheric and consumer conditions(physiological, sociological and psychological).An acceptable mean was arbitrarily set at!5.0as the panellists were in-structed that any rating at midpoint or above would be considered acceptable.2.7.Statistical analysisThree replicates were taken for each instrumental analysis,and the results were expressed as the mean of those values standard deviation.An analysis of vari-ance procedure(Statgraphics7.0,Statgraphics STSC Inc.,Rockville,MD,USA,1993)was used to determine signi®cant di erences(p 0.05)among jams with dif-ferent levels of DF or soluble solids content,and a Least Signi®cant Di erence(LSD)test was employed to de-termine di erences among formulations.A correlation procedure was used to evaluate any relationship between composition and colour parameters,composition and sensorial parameters,and instrumental and sensory re-sults.3.Results and discussion3.1.pHThe addition of peach DF,which had a pH 3.91 (Grigelmo-Miguel et al.,1999a),to strawberry jams did not in¯uence the pH of the®nal products (3.19 0.04).Costell and Dur a n(1983)and Costell, Izquierdo and Dur a n(1985)found similar results in apricot jams with di erent percentages of pectin.pH ranged between3.08and3.29in the strawberry jams with no signi®cant di erences between them because the concentration of added acids was kept constant in all the formulations.3.2.ColourIn strawberry jams with a constant soluble solids content,the higher the DF content,the yellower and lighter the product was(Figs.2and3)because the peach DF showed L*and b*values higher than strawberry pur e e(Fig.1)and no colourant was added.However, the a*parameter gave a negative correlation with DF content(Table2)indicating that redness decreased when DF content increased.Nevertheless,the parameter a* changes less markedly with the incorporation ofpeachFig.2.Position of strawberry jams in cieLab diagram(co-ordinates a*and b*).(a)40°Brix;(b)45°Brix;(c)50°Brix;(d)55°Brix;AF:added®bre. r Control,j1%AF,m2%AF,Â3%AF,*4%AF.16N.Grigelmo-Miguel,O.Mart õn-Belloso/Journal of Food Engineering41(1999)13±21DF than parameter b *.On the other hand,H *,D E *and D C *also increased with DF content (Figs.3b,c and d and Table 2).Thus,the addition of DF turned the strawberry jams more yellow,green and lighter.Nev-ertheless,it must be taken into account that no colorant was added.Colorants are used in the food industry to mask the colour problems that always showed in strawberry jams,because heat transforms the red com-ponents of strawberries (anthocyanins)into brown components.3.3.Rheological behaviourThe ¯ow behaviour of jams was ®tted to the power-law Eq.(4),Herschel and Buckley Eq.(5)and Casson's Eq.(6)models.The power-law and Herschel and Buckley models were those which best described the ¯ow behaviour of the analysed jams.But,in the Herschel and Buckley model yields stress values (s 0)under 1Pa were obtained (data not shown).According to Vitali and Rao (1984),when the yield stress values,obtained experi-mentally with concentric cylinder viscometers,are under 1Pa it can be considered that the analysed products have,in practice,a pseudoplastic behaviour since these s 0values include the friction inherent in the measuring head-drive system of the viscometer as well as the inertia of the entire system.Therefore,the 2parameter power-law model was the one that best described the rheolog-ical behaviour of the high fruit DF jams,and the ¯ow behaviour index (n )and the consistency coe cient (K )values are shown in Table 3.This behaviour is similar to those previously observed in peach jams (Costell,Bai-don &Dur a n,1988),strawberry,plum,peach and apricot jams (Carbonell,Costell &Dur a n,1991),andFig.3.Colour parameters of strawberry jams.(a)luminosity,L *;(b)hue,H *;(c)colour di erence,D E *;(d)chrome di erence,D C *;AF:added®bre.r 40°Brix,j 45°Brix,m 50°Brix,Â55°Brix.Table 2Correlation between DF content and instrumental colour parameters of strawberry jams for each soluble solids content Nominal soluble solids (°Brix)Colour parameters L *a *b *H *D E *D C *400.9982ÃÃÀ0.9767ÃÃ0.8959ÃÃ0.9376ÃÃ0.9848ÃÃ0.9209ÃÃ450.9789ÃÃÀ0.8854ÃÃ0.9365ÃÃ0.9617ÃÃ0.9705ÃÃ0.9367ÃÃ500.9951ÃÃÀ0.7634ÃÃ0.9453ÃÃ0.9546ÃÃ0.9883ÃÃ0.9626ÃÃ550.8174ÃÃÀ0.5133ÃÃÃ0.8325ÃÃ0.9262ÃÃ0.8658ÃÃ0.8839ÃÃ**p 0.01.***p 0.05.N.Grigelmo-Miguel,O.Mart õn-Belloso /Journal of Food Engineering 41(1999)13±2117high concentrated peach DF suspensions(Grigelmo-Miguel et al.,1999b).The rheological analysis of the high fruit DF jams indicated that,for a DF content within0±4%,the con-sistency coe cient ranged between1.4and10.6Pa s n and the¯ow behaviour index ranged between0.582and 0.443(Table3).In high DF jams,the higher the DF added,the greater the consistency and pseudoplasticity became(Table3).The comparison between the¯ow characteristics of the high DF jams(pseudoplastic)and those of pectin gels after destroying their``gelli®ed''structure(Bing-ham's plastic)(Fiszman,Costell&Dur a n,1984),led us to assume that the pseudoplasticity of jams was related to the presence of fruit and®bre particles.The evolution of apparent viscosity(g app s/ c)values of the analysed jams as a function of shear rate( c)illustrated this fact: the higher the DF content,the higher the viscosity variation observed in the jams(Fig.4).For non-Newtonian foods,it may be use of g app at a speci®c c instead of the viscosity to analyse the in¯uence of concentration;for¯uids obeying the power law,it may be use of K.To study the variation of K with the DF content two models were tried:u u0e a g Y 7 u u1exp b g d g2 Y 8 where K0,a,K1,b and d are constants and C is the concentration of DF(%).Eq.(8)was the one that best®tted to the data(Table 4).The K1parameter increased when DF increased, whereas b and d parameters did not follow any ten-dency(Table4).The K1constant represents the value of K when the DF concentration is0%,so K1values should be and were similar to those of K obtained in control jams within each soluble solids concentration (Table3).The¯ow behaviour index(n)decreased linearly with the DF content of jams(Fig.5).3.4.Sensorial analysis and correlation9sStrawberry jams were considered acceptable with the exception of the40°Brix jams with4%peach DF(Table 5).The hedonic scores of colour,consistency and ac-ceptability decreased as the DF content of jams in-creased(r À0.8692,À0.8408,À0.8560,respectively). When the sensory results were compared,all the pa-rameters turned out to be signi®cantly correlated (p P0.01)(Table6).The high correlation between b*and H*,H*andD E*,and D E*and D C*parameters stood out(Table6).For this purpose,the D E*parameter(which related L*,a*and b*values)may be used to de®ne the colour of high DF jams.At the same time,all instrumental measures of viscosity related well to each other(Table6);so on increasing viscosity(g),the consistency co-e cient(K)and pseudoplasticity increased(n de-creased).Table3Parameters of power-law model(s K c n)in¯ow behaviour of strawberry jams aNominal soluble solids Fibre added K n r2(°Brix)(%)(Pa s n)(dimensionless)400(control) 1.4 0.10.582 0.0130.9981 2.7 0.10.515 0.0060.9982 3.7 0.10.506 0.0060.9983 6.5 0.20.460 0.0050.99848.5 0.20.443 0.0040.998450(control) 2.65 0.180.515 0.0120.9981 2.74 0.090.530 0.0060.9982 3.71 0.110.513 0.0050.9983 6.40 0.190.465 0.0060.99848.48 0.220.458 0.0050.998500(control) 3.50 0.390.497 0.0200.991 4.15 0.250.507 0.0110.9982 5.30 0.140.497 0.0050.99837.10 0.070.476 0.0020.99849.09 0.300.458 0.0060.998550(control) 3.5 0.40.543 0.0190.9921 5.2 0.30.512 0.0120.99627.5 0.30.479 0.0070.99839.2 0.20.475 0.0040.998410.6 0.30.474 0.0060.998a Mean values con®dence interval,s:shear stress(Pa);K:consistency coe cient;c:shear rate(sÀ1);n:¯ow behaviour index;r2:determination coe cient.18N.Grigelmo-Miguel,O.Mart õn-Belloso/Journal of Food Engineering41(1999)13±21According to these results,the D E *parameter may be used as a reference of the high DF jams colour to fa-cilitate normalisation,replacing descriptive terms for numerical values.At the same time,the consistency coe cient (K )and the ¯ow behaviour index (n )may be used to classify the consistency.4.ConclusionsThe pH of strawberry jams was not a ected by the incorporation of DF because peach DF had a similar pH to traditional jams.On the other hand,the colour of strawberry jams turned more luminous,yellow and green when DF content increased.The rheological behaviour of strawberry jams fol-lowed the power law model and the consistencycoe -Fig.4.Variation of apparent viscosity with shear rate in strawberry jams.(a)40°Brix;(b)45°Brix;(c)50°Brix;(d)55°Brix;AF:added ®bre.r Control,j 1%AF,m 2%AF,Â3%AF,*4%AF.Table 4E ect of peach DF content on the consistency coe cient (K )of strawberry jams (Model:K K 1exp(b C +d C 2))aNominal soluble solids K 1bdr 2(°Brix)(Pa s)40 1.43 0.360.048 0.009À2.10À4 2.10À40.99145 2.46 0.270.01 0.01 3.10À4 2.10À40.97150 3.46 0.080.012 0.002 5.10À4 3.10À40.996553.49 0.060.027 0.001À16.10À5 2.10À50.999aK 1,b ,d :constants;r 2:determinationcoe cient.Fig.5.Variation of ¯ow behaviour index (n )with DF content of strawberry jams.N.Grigelmo-Miguel,O.Mart õn-Belloso /Journal of Food Engineering 41(1999)13±2119cient and the pseudoplasticity increased with the DF content.Sensory evaluation of high DF jams showed that these jams were considered acceptable,based on he-donic-scale ratings given by consumer panellists,al-though the hedonic scores decreased when the DF concentration increased.AcknowledgementsThe authors would like to thank the factory In-dul e rida,S.A.(Alguaire,Lleida,Spain)for providing the peach DF and strawberry pur e e,and Mr.Jos e Lorente-Fern a ndez for his assistance.The General Direction of Scienti®c and Technical Research of theTable5Results of sensory evaluation of strawberry jams aNominal soluble solids Fibre added Colour Consistency Acceptability(°Brix)(%)400(control)7.3 1.1hi7.6 1.4gh7.5 1.3fg1 6.7 1.3fgh 6.7 1.3ef7.1 1.4efg2 5.6 1.7bcd 5.6 1.6abcd 6.4 1.5cde3 5.1 1.7abc 5.2 1.5ab 5.7 1.6bc4 4.4 1.7a 5.3 1.6ab 4.8 1.9a450(control)7.0 1.4ghi8.0 1.2h7.6 1.4fg17.2 1.3hi7.9 0.8gh7.8 1.0g2 6.0 1.4def 5.9 1.3bcd 6.8 1.3def3 5.0 1.2ab 5.0 1.4a 5.7 1.8bc4 4.6 1.3a 5.1 1.4a 5.0 2.0ab500(control)7.5 1.2i7.5 1.7gh7.7 1.2g1 6.9 0.9ghi7.2 1.0fg7.0 1.2efg2 6.0 1.5def 6.3 1.6de 6.4 1.4cde3 5.7 1.4cde 5.9 1.4bcde 5.7 1.7abc4 5.4 1.6bcd 5.4 1.8ab 5.9 1.6c550(control)7.4 1.2hi7.2 1.3fg7.2 1.4efg17.4 0.7i7.2 1.1fg7.4 1.1fg2 6.4 1.3efg 6.2 1.2cde 6.4 1.6cde3 5.8 1.2cde 5.5 1.3abc 5.9 1.5c4 5.1 1.4abc 5.9 1.4bcde 6.1 1.5cda Means within a column with di erent letters are signi®cantly di erent at p 0.05.Table6Correlation coe cients between sensory and instrumental analysis of strawberry jams a123456789101112 1120.91Ã130.94Ã0.89Ã14À0.78ÃÀ0.69ÃÀ0.69Ã150.260.250.390.1716À0.86ÃÀ0.75ÃÀ0.78Ã0.84Ã0.1217À0.93ÃÀ0.82ÃÀ0.91Ã0.73ÃÀ0.310.91Ã18À0.82ÃÀ0.78ÃÀ0.88Ã0.50ÃÃÀ0.68Ã0.62ÃÃ0.88Ã19À0.76ÃÀ0.72ÃÀ0.84Ã0.37À0.71Ã0.57ÃÃ0.85Ã0.98Ã110À0.53ÃÃÀ0.50ÃÃÀ0.60ÃÃÀ0.02À0.85Ã0.260.62ÃÃ0.83Ã0.89Ã111À0.65ÃÀ0.61ÃÃÀ0.73Ã0.17À0.80Ã0.420.75Ã0.92Ã0.96Ã0.98Ã1120.86Ã0.83Ã0.94ÃÀ0.59ÃÃ0.53ÃÃÀ0.71ÃÀ0.89ÃÀ0.95ÃÀ0.93ÃÀ0.72ÃÀ0.84Ã1a1:Sensorial colour;2:Consistency;3:Acceptability;4:L*;5:a*;6:b*;7:H*;8:D E*,9:D C*;10:viscosity;11:consistency coe cient;12:¯ow behaviour index.*p 0.01.**p 0.05.20N.Grigelmo-Miguel,O.Mart õn-Belloso/Journal of Food Engineering41(1999)13±21Ministry 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