doi: 1.1111/j.1471-37.211.75.x ORIGINAL RESEARCH Effects of gur gum nd ric gum on the physicochemicl, sensory nd flow ehviour chrcteristics of frozen yoghurt RAHIL REZAEI, MORTEZA KHOMEIRI,* MAHDI KASHANINEJAD nd MEHRAN AALAMI Deprtment of Food Science & Technology, Gorgn University of Agriculturl Sciences & Nturl Resources, Beheshti Ave., Gorgn 49138-15739, Irn This study investigted the effect of gur gum nd ric gum on physicochemicl, sensory nd flow ehviour properties of frozen yoghurt. The results indicted tht gums significntly ffected the viscosity, overrun nd melting rte of frozen yoghurt. The highest overrun vlue ws oserved in smple contining.5% ric gum. Frozen yoghurt contining.3% gur gum hd the highest viscosity. The longest first dripping time ws oserved in smple contining.5% ric gum. Flow ehviour of smples showed tht ll frozen yoghurts exhiited sher thinning ehviour. Gur gum t concentrtion of.2% nd ric gum t concentrtion of.5% presented the est totl cceptility. The results of this study reveled tht the frozen yoghurt produced with ric gum hd the etter overll sensory nd physicochemicl chrcteristics. Keywords Frozen yoghurt, Gur gum, Aric gum, Physicl properties, Flow ehviour. *Author for correspondence. E-mils: khomeiri@gu.c.ir; mkhomeiri@yhoo.com Ó 211 Society of Diry Technology INTRODUCTION Frozen yoghurt is refreshing nd nutritious dessert tht comines the flvour nd texture of ice crem nd yoghurt. The ingredients used for frozen yoghurt production re like those used for ice crem, including hydrocolloids, emulsifiers, sweeteners nd solid not ft. The viscosity of n ice crem mix is considered very importnt ttriute s it ffects the ody nd texture of the finished product. The most importnt fctor in enhncing the viscosity during ice crem processing is the ddition of stilisers (Minhs et l. 22). Stilisers lso improve shpe retention nd melting ehviour (Soukoulis nd Tzi 28) nd prevent the formtion of ojectionle lrge ice crystls in frozen desserts. They re used in such smll mounts s to hve negligile influence on foods tste (Issriychikul 28). During consumption, stilisers provide uniform meltdown, mouthfeel nd texture. Stilisers cn lso contriute to smoother nd more resistnt ody. Most polyscchride-sed ice crem stilisers influence the rheologicl properties of the continuous phse. The mount of stiliser used vries with its properties, the solid content of the mix, the type of processing nd other fctors. The mount used in regulr ice crem my e in the rnge of.5% ut is usully.2.3% (Issriychikul 28). In the food industry, gur gum is used s thickening nd stilising gent in wide vriety of foods, usully in mounts less thn 1% of food weight (Slvin nd Greenerg 23). Aric gum is used for its nutritionl nd surfce properties (Snchez et l. 22). Some studies hve een conducted on the effect of some gums on the physicochemicl properties of ice crem. Soukoulis nd Tzi (28) studied the effect of some hydrocolloids on the physicl nd sensory properties of frozen yoghurt. They reported tht the ddition of hydrocolloids incresed viscosity significntly nd tht the use of xnthn gum improved ertion, leding to the highest overrun. Minhs et l. (22) studied the flow ehviour chrcteristic of ice crem mix with vrious stilisers such s geltin, ric gum, gur gum nd kry gum. They concluded tht ll of the mixes indicted pseudoplstic ehviour. The determintion of rheologicl properties is essentil for design, process nd qulity control, sensory evlution, stility nd consumer cceptnce of product (Arsln et l. 25). To perform Interntionl Journl of Diry Technology 563
quntittive comprison of mterils, the experimentl dt must generlly e fitted to some form of est-fit mthemticl eqution or model. The model is used to predict the viscosity of flow s function of sher stress or sher rte. Some useful flow models hve een developed; the ones used in this study for fitting the flow curve of frozen yoghurt were s follows: 1 Power lw model (Ostwld-de Wele eqution): s ¼ kðcþ n ð1þ where k is the consistency coefficient (P.s n ), c is the sher rte (per second), s is the sher stress (P) nd n is the flow ehviour index. For sher-thinning fluids, n<1, nd for sherthickening fluids, n>1. 2 Herschel Bulkley model (Bourne 1982) s ¼ s þ kðcþ n In this eqution, s is the sher stress, s the yield stress (P), c the sher rte, k consistency coefficient nd n the flow ehviour index. 3 Csson model (Csson 1959) s :5 ¼ kc :5 þ k cðc :5 Þ where s, k c nd k c re sher stress, intercept of the plot of (s.5 )c.5 ) nd slop of plot, respectively. In this eqution,kc 2 ¼ l c nd kc 2 ¼ s c tht re Csson viscosity (P.s) nd Csson yield stress (P), respectively. There is little informtion out the effect of gums on the physicl properties nd flow ehviour of frozen yoghurt. In this study, we imed to produce frozen yoghurts contining gur gum nd ric gum t different concentrtions nd to investigte their physicochemicl, sensory nd flow ehviour properties. contining different levels of gur nd ric gums. After freezing, the smples were distriuted mong plstic cups (pproximtely 5 ml) nd hrdened t )18 C. ph mesurement The ph of frozen yoghurt mix ws mesured with Methrom- 827 ph meter (Methrom, Herisu, Switzerlnd) fter geing. Viscosity nd flow ehviour The viscosity of the ged frozen yoghurt mix ws mesured using viscometer (RV-DV II Brookfield, Middleoro, MA, USA). Smples were tested t 5 C using spindle No.6. Sher rte nd sher stress vlues were clculted using the viscosity dt ccording to Mitchk s equtions (Mitschk 1982). Plots of sher stress vs sher rte were creted for ech frozen yoghurt smple t speeds of 1 2 rpm. Flow ehviour index (n) nd consistency coefficient (K) vlues were clculted for ech smple. To select the most pproprite model of the smples ehviour, the correltion coefficient (R 2 ) ws used, with coefficients closer to 1 showing etter correspondence etween the vlues predicted y the model nd numericl vlues derived from experiments. Overrun Overrun mesurement ws crried out y compring the weight of frozen yoghurt mix nd frozen yoghurt in continer of known volume. Overrun ws clculted ccording to the following eqution: weight of unit mix weight of equl volume of frozen yoghurt 1 Overrun ¼ weightof equl volume of frozen yoghurt MATERIALS AND METHODS Preprtion of yoghurt Milk contining 2.5% ft nd 8.25% Solid Not Ft (SNF) ws stndrdised to 11% SNF ccording to the Irnin stndrd for yoghurt (ISIRI, NO: 695, 4th revision) using skim milk powder. Milk ws heted t 85 C for 3 min nd cooled to 42 C. Commercil yoghurt strter culture (YC-X11; CHR-Hnsen, Horsholm, Denmrk) ws inoculted t concentrtion of.2% in milk followed y incution t 42 C. When cidity reched 8 dornic, the yoghurt ws cooled to refrigertor temperture (pproximtely 7 C). Preprtion of frozen yoghurt Sugr (16%) nd skim milk powder (to djust totl solid to 3%) were thoroughly mixed nd dissolved in skim milk nd psteurised t 85 C for 3 min. This mix ws cooled to refrigertor temperture nd then thoroughly lended with yoghurt to produce the finl frozen yoghurt mix. The mix ws refrigerted t 7 C for 15 h. The ged frozen yoghurt mix ws frozen using lortory tch home ice crem mker (Gud et l. 1993). The sme procedure ws used to produce frozen yoghurt Melting rte The melting properties of frozen yoghurt were studied through the exmintion of two prmeters: melting rte nd first dripping time. A piece of frozen yoghurt (3 ± 1 g) ws plced on sieve (mesh:.5 mm) on top of eker t 25 C nd llowed to melt. The percentge of melted frozen yoghurt fter 6 min ws determined. The time required for first dripping of frozen yoghurt ws recorded (Aklin nd Erisir 28). Sensory nlysis Sensory nlysis of the smples ws conducted y seven expert pnel memers who evluted flvour, colour, texture nd totl cceptility on 5-point scle (1 = unplesnt, 5 = plesnt). Flvour ws evluted y the smple s closeness to n cceptle stndrd nd intensity of refreshing yoghurt flvour nd its reltive freedom from ny cooked or whey rom. The colour of the frozen yoghurt ws evluted s either white or cler. Some ttriutes of texture (uniform nd without gummy, sndy nd icy defect) were evluted. Overll cceptility ws lso evluted, sed on chrcteristics including colour, texture nd flvour. 564 Ó 211 Society of Diry Technology
Sttisticl nlysis Sttisticl nlysis of the dt ws performed using SAS softwre (version 9.1, SAS Institute Inc., Cry, NC, USA). Ech experiment ws replicted three times. Anlysis of vrince ws conducted s completely rndomised design, nd Duncn s multiple rnge test t P =.5 ws used to compre mens when the effect ws significnt. RESULTS AND DISCUSSION ph Neither gur nor ric gum hd ny significnt effect on the ph of the frozen yoghurt smples (Tle 1), which rnged from 5.5 to 5.17. Viscosity Tle 1 presents the effect of different gums on the viscosity of frozen yoghurt. The viscosity of smples contining gur nd ric gums ws significntly higher thn tht of the control smple (P <.5). It ws lso found tht incresing the levels of oth gums incresed the viscosity. The lowest vlue for viscosity elonged to the control smple (1522 cp) nd the highest to the smple contining.3% gur gum (335 cp). There ws no significnt difference etween gur gum t concentrtions of.1% nd.2%, ut concentrtion of.3% incresed viscosity significntly. The viscosity of smples contining different levels of ric gum differed significntly from ech other (P <.5). Viscosity is n importnt chrcteristic in tht specific viscosity mount is required for chieving desirle whipping ility nd retining of ir ules (Trkshvnd 25). Stilisers hve high wter-holding cpcity nd cn influence the rheologicl properties of ice crem mix; in other words, n increse in concentrtion of stilisers in ice crem cuses n increse in viscosity (Moeenfrd nd Mzheri Tehrni 28). Higher viscosity in smple contining gums cn e explined y the interction of gums nd liquid prt of ice crem mix (Aklin nd Erisir 28). Similrly, Soukoulis nd Tzi (28) showed tht hydrocolloids such s croxymethylcellulose, xnthn nd gur could increse the viscosity of ice crem mixes. Flow ehviour Figures 1 nd 2 show curves for sher stress sher rte nd viscosity sher rte, respectively, in frozen yoghurts contining gur gum. It could e seen tht the sher rte sher stress reltion in ll of gur-contining smples ws not liner. Results showed tht the viscosity decresed when the sher rte incresed (Figure 2). The decrese in viscosity ws initilly shrpened nd slowed grdully. An initil reduction in viscosity in the control smple ws slower thn tht in the gur-contining smples, showing stronger sher-thinning ehviour in smples tht contined gur gum. The flow ehviour index of these smples lso ws elow 1, indicting non-newtonin ehviour. Increse in the concentrtion of gur gum resulted in decrese in the flow ehviour index nd increse in the consistency coefficient (Tle 2). The reltionship etween sher rte nd sher stress in frozen yoghurt contining ric gum ws similr to tht of frozen yoghurt contining gur gum (Figure 3). The increse in sher rte ws not liner with respect to sher stress. Aric gum t concentrtions of.1% nd.3% ws not noticely different from the control, ut ric gum t concentrtion of.5% resulted in different sher rte nd sher stress from the other smples. Figure 4 shows the effect of sher rte on viscosity in frozen yoghurt contining ric gum. The flow ehviour index in these smples ws elow 1, nd it ws enhnced with increses in gum concentrtion. Viscosity reduction in these Sher stress (p) 9 8 7 6 5 4 3 2 1 Gur.1% Gur.2% Gur.3% 1 2 3 4 5 Figure 1 Flow curve of frozen yoghurts contining gur gum. Tle 1 Effect of gur nd ric gum on physicochemicl properties of frozen yoghurt Frozen yoghurt Concentrtion of gum (%) ph Overrun (%) Viscosity (cp) First dripping time (s) Melting rte (%) 5.17 ±.4 22.37 ±.9 c 1522 ± 13 e 132 ± 161 d 96.4 ± 1.1 5.15 ±.5 32.39 ± 1 2729 ± 58 1744 ± 4 84.51 ± 6 Gur.2 5.7 ±.1 35.34 ± 1 2828 ± 33 1788 ± 152 75.66 ± 4.3 5.7 ±.3 38.22 ±.5 335 ± 295 1945 ± 112 74.72 ± 3 Aric.1 5.14 ±.2 3.19 ±.8 1828 ± 148 d 142 ± 22 c 77.62 ± 1.3 5.5 ±.4 3.56 ± 2 2257 ± 33 c 1893 ± 163 75.94 ± 4.5 5.7 ±.1 39.38 ±.2 3278 ± 53 2363 ± 12 72.3 ± 4 Mens in the sme column followed y different letters were significntly different (P <.5). Ó 211 Society of Diry Technology 565
Viscosity (cp) 12 1 8 6 4 2 Gur.1% Gur.25 Gur.3% 1 2 3 4 5 Figure 2 Effect of sher rte on pprent viscosity of frozen yoghurts contining gur gum. smples is ttriutle to the disruption of moleculr entnglements of the polyscchride y the pplied sher (Sntipnichwong nd Suphnthrik 29). At concentrtion of.5% ric gum, viscosity reduction t initil sher rte ws greter thn for concentrtions of.1% nd.3%. Although the slope of curve in control smple ws less thn tht of frozen yoghurt contining ric gum, sher thinning ehviour could e seen. Tle 2 shows the results of fitting of dt with rheologicl models. Our results showed Power lw model stisfctorily fitted the experimentl dt for ech smple with good correltion coefficient when compred to other models. Minhs et l. (22) studied the flow ehviour of ice crem mixes contining vrious stilisers nd reported tht ice crem mixes hving ric gum exhiited sher-thinning ehviour. Overrun The overrun vlue of frozen yoghurt in this study rnged from 22.37% to 39.38%. The low overrun my e due to using tchtype household ice crem mker. Aklin et l. (28) nd Issriychikul (28) lso reported low overrun vlues when using tch freezers. In the current study, the ddition of gums hd significnt effect on the overrun of frozen yoghurt smples (P <.5) (Tle 1). Moreover, incresing concentrtions of Sher stress (p) 9 8 7 6 5 4 3 2 1 Aric.1% Aric.3% Aric.5% 1 2 3 4 5 Figure 3 Flow curve of frozen yoghurts contining ric gum. Viscosity (cp) 14 12 1 8 6 4 2 Aric.1% Aric.3% Aric.5% 1 2 3 4 5 Figure 4 Effect of sher rte on pprent viscosity of frozen yoghurts contining ric gum. different gums improved the overrun of smples. Frozen yoghurts contining.5% ric gum nd.3% gur gum hd higher overrun vlues thn other smples. The lowest vlue for overrun elonged to the control frozen yoghurt. The difference etween overrun for gur gum t concentrtions of.1% nd.2% ws not significnt. Protein, ft nd hydrocolloids re importnt for ir incorportion (Mrshll et l. 23). Frozen yoghurt with high concentrtion of hydrocolloids nd therefore Tle 2 Vlues of power lw, Herschel Bulkley nd Csson model prmeter for frozen yoghurt contining gur nd ric gum Tretment Concentrtion of gum (%) Models Power lw Herschel Bulkley Csson n k R 2 n k s R 2 Kc 2 s c R 2.51 6.51.998.83 1.49 12.4.992.36 7.77.995 Gur.1.4 15.45.996.76 3.18 19.56.98.48 16.5.993.2.31 2.997.74 3.4 21.5.956.34 19.72.988.3.36 2.92.992.79 3.53 22.38.96.58 19.4.995 Aric.1.44 9.14.997.72 2.53 12.51.997.36 1.25.997.3.43 11.75.997.88 1.58 14.6.994.43 12.67.997.5.35 22.36.995.79 3.82 24.14.968.61 2.53.992 n, flow ehviour index (dimensionless); k, consistency coefficient (P.s n ); R 2, correltion coefficient; s, yield stress (P); s c, Csson yield stress (P); Kc 2, Csson viscosity (P.s). 566 Ó 211 Society of Diry Technology
high viscosity could trp ir cells etter thn low-viscosity mixes tht could not trp enough ir. Soukoulis et l. (28) nd Soukoulis nd Tzi (28) lso reported tht incresing levels of gur gum incresed the overrun of vnill ice crem nd frozen yoghurt. Melting properties Meltdown of ice crem involves oth het nd mss trnsfer. Het grdully penetrtes from the exterior to the interior of ice crem owing to the melting of ice crystls. The wter of melted ice crystls diffuses into concentrted serum phse (Soukoulis et l. 28). In this study, smples with high consistency coefficients hd more resistnce to flow nd thus melted more slowly (Muse nd Hrtel 24). The first dripping time of frozen yoghurt incresed with the ddition of oth gums (Tle 1). However, there ws no significnt difference etween the dripping times of smples contining different levels of gur gum. While gur gum t concentrtion of.1% showed no significnt difference from the control smple, concentrtions of.2% nd.3% could slow the melting rte significntly (P <.5). Levels of ric gum hd significnt effect on first dripping time. The longest time ws otined for the smple contining.5% ric gum (P <.5). Aric gum lso decresed the rte of melting compred with the control smple, ut there ws no considerle difference etween the three concentrtions of this gum. Stilisers cn form sticky network in yog-ice crem tht results in more resistnce to melting (El-Ngr et l. 22). Furthermore, it hs een previously showed tht ice crems with higher overrun melt more slowly (Sofjn nd Hrtel 24). Our results confirmed the sme for frozen yoghurt. Increse in the time of melting might e ttriuted to the lower het trnsfer rte of ir trpped in the mixture (Moeenfrd nd Mzheri Tehrni 28). Sofjn nd Hrtel (24) lso found tht ir cted s good insultor, slowing the rte of het trnsfer in ice crem nd thus decresing melting rte. Sensory properties Figures 5 nd 6 show the men scores for the smples colour, texture nd flvour. Result showed tht the ddition of ric gum nd gur gum hd no significnt effect on the colour of frozen yoghurt smples. Gur gum nd ric gum hd significnt effect on flvour, texture nd totl cceptility. Addition of gums decresed the formtion of ice crystls, improving texture. Similr results hve een reported y Moeenfrd nd Mzheri Tehrni (28) who found tht increses in concentrtion of stilisers result in increse in score of texture. El-Syed et l. (22) reported tht the ddition of xnthn gum hd no dverse effect on flvour of yoghurt, wheres it did ffect texture nd ody. CONCLUSION This study investigted the effects of gur gum nd ric gum on physicl nd flow ehviour chrcteristics of frozen yoghurt. Score 5 4 3 2 1 c Color Texture Flvor Totl.1.2.3 Gur gum concentrtion (%) Figure 5 Effect of gur gum on sensory properties of frozen yoghurt. Score 5 4.5 4 3.5 3 2.5 2 1.5 1.5 Color Texture Flvor Totl cceptnce.1.3.5 Aric gum concentrtion (%) The results showed tht oth gums hd significnt effects on the properties of frozen yoghurt. Incresing the concentrtion of gums led to greter overrun, viscosity nd melting resistnce. The gretest improvements in these physicochemicl properties were otined in frozen yoghurt contining.3% gur gum nd.5% ric gum. Results for flow ehviour showed tht the flow ehviour index of ll smples ws elow one, in other words, tht they were non-newtonin. We oserved sher-thinning ehviour in ll frozen yoghurt, nd the ddition of gums enhnced this property. The power lw ws the est model to predict the flow ehviour of frozen yoghurt smples contining gums. Gur gum t concentrtion of.2% nd ric gum t concentrtion of.5% resulted in the most fvourle sensory evlutions. In conclusion, frozen yoghurt with ric gum could e recommended for etter physicochemicl nd sensory properties s well s its lower cost. REFERENCES Aklin A S nd Erisir D (28) Effect of inulin nd oligofructose on the rheologicl chrcteristics nd proiotic culture survivl in low ft proiotic ice crem. Journl of food science 73 184 188. Aklin A S, Krgozlu C nd Unl G (28) Rheologicl properties of reduced-ft nd low-ft ice crem contining whey protein isolte nd inulin. Europen Food Reserch Technology 227 889 895. Arsln E, Yener M E nd Esin A (25) Rheologicl chrcteriztion of thin pekmez (sesme pste concentrted grpe juice) lends. Journl of Food Engineering 69 167 172. Figure 6 Effect of ric gum on sensory properties of frozen yoghurt. Ó 211 Society of Diry Technology 567
Bourne M C (1982) Food Texture nd Viscosity. New York: Acdemic Press. Csson N (1959) A flow eqution for pigment-oil suspensions of the printing oil type. In Rheology of Dispersed Systems, pp 82 14. Mill C C, ed. New York: Pergmon Press. El-Ngr G, Clowes G, Tudoric C M, Kuri V nd Brennn C S (22) Rheologicl qulity nd stility of yog-ice crem with dded inulin. Interntionl Journl of Diry Technology 55 89 93. El-Syed E M, Ad El-Gwd I A, Murd H A nd Slh S H (22) Utiliztion of lortory-produced xnthn gum in the mnufcture of yoghurt nd soy yoghurt. Europen Food Reserch nd Technology 215 298 34. Gud E, Atti I A, Slem S A nd Kmr M S (1993) Studies on frozen yoghurt: mnufcturing method. Egyptin Journl of Food Science 21 57 66. Issriychikul K (28) Development of modified ft ice crem products using inulin s ft replcer. Mhidol, p. 87. Mrshll R T, Goff H D nd Hrtel R W (23) Ice Crem. New York: Aspen Pulishers. Minhs K S, Sidhu J S, Mudhr G S nd Singh A K (22) Flow ehvior chrcteristics of ice crem mix mde with ufflo milk nd vrious stilizers. Plnt Foods for Humn Nutrition 57 25 4. Mitschk P (1982) Simple conversion of Brookfield R.V.T. redings into viscosity functions. Rheologic Act 21 27 29. Moeenfrd M nd Mzheri Tehrni M (28) Effect of some stilizers on the physicochemicl nd sensory properties of ice crem type frozen yoghurt. Americn-Eursin Journl of Agriculture & Environment Science 4 584 589. Muse M R nd Hrtel R W (24) Ice crem structurl elements tht ffect melting rte nd hrdness. Journl of Diry Science 87 1 1. Snchez C, Renrd D, Roert P, Schmiitt C nd Lefevre J (22) Structure nd rheologicl properties of cci gum dispersions. Food Hydrocolloids 16 257 267. Sntipnichwong R nd Suphnthrik M (29) Influence of different -glucns on the physicl nd rheologicl properties of egg yolk stilized oil-in-wter emulsions. Food Hydrocolloids 23 1279 1287. Slvin J L nd Greenerg N A (23) Prtilly hydrolyzed gur gum: clinicl nutrition uses. Nutrition 19 549 552. Sofjn R P nd Hrtel R W (24) Effects of overrun on structurl nd physicl chrcteristics of ice crem. Interntionl Diry Journl 14 255 262. Soukoulis C nd Tzi C (28) Impct of the cidifiction process, hydrocolloids nd protein fortifiers on the physicl nd sensory properties of frozen yoghurt. Interntionl Journl of Diry Technology 61 17 177. Soukoulis C, Chndrinos I nd Tzi C (28) Study of the functionlity of selected hydrocolloids nd their lends with [kpp]-crrgeenn on storge qulity of vnill ice crem. LWT-Food Science nd Technology 41 1816 1827. TrkshvndY(25) Ice Crem. Firstprint. Tehrn: At pulisher(inpersin). 568 Ó 211 Society of Diry Technology