The quality of ice cream is in great extent determined by its sensoric properties. Therefore, it is important to know and to predict the effect of the hydrocolloid and emulsifier addition on the consistency of the ice cream mixtures. In this work, the influence of several carboxymetylcellulose hydrocolloids (DIKO, YO-EH, HVEP) and emulsifier E-420 (mixture of sorbitol, monoglicerids and diglicerids) on the rheological properties of the model ice cream mixture as well as their ability to prevent crystallization and recrystallization were examined. The rheological properties as well as electroconductivity before and after pasteurization were measured at 20 °C. The results of these investigations have shown that the viscosity of all ice cream mixtures significantly increased after pasteurization. All investigated systems exhibited non-Newtonian characteristics. Hydrocolloid YO-EH showed the greatest influence on the rheological properties of the model systems. After pasteurization conductivity increased for all investigated samples. Sensory evaluation have shown that the most acceptable product was that prepared with emulsifier E-420.Kakvoću sladoleda u velikoj mjeri određuju njegova senzorska svojstva, te je važno znati kakav će utjecaj na njih, posebno na konzistenciju, imati dodatak hidrokoloida odnosno emulgatora. U ovom radu ispitan je utjecaj hidrokoloida na bazi karboksimetilceluloze (DIKO, YO-EH, HVEP) i emulgatora (smjesa sorbitola, monoglicerida i diglicerida, E-420) na reološka svojstva modelnih sladolednih smjesa kao i njihova sposobnost da spriječe kristalizaciju i rekristalizaciju vode te u vodi otopljenih tvari. Reološka svojstva određena su u rotacionom reometru Brookßeld DV-IIl kod temperature od 20 °C prije i poslije pasterizacije. Nakon provedene pasterizacije i smrzavanja izmjerena je provodljivost na konduktometru "Iskra " Kranj pri temperaturi od 20 °C. Rezultati ispitivanja su pokazali da je nakon provedene pasterizacije došlo do značajnog povećanja viskoznosti svih modelnih smjesa. Svi sastavi su pokazali nenewtonski karakter. Najveći utjecaj na reološka svojstva modelnih sustava imao je hidrokoloid YO-EH. Mjerenje elektroprovodljivosti pokazalo je da tijekom pasterizacije te smrzavanja dolazi do kontinuiranog rasta provodljivosti. Ocjena senzorskih svojstava pokazala je da se upotrebom emulgatora E-420 dobiva senzorski najprihvatljiviji proizvod

Mirjana Škreblin

Suzana Rimac

Vesna Hegedušić

Zoran Herceg

English

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V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. Influence of stabilizers addition on the rheological proper­ties of the model ice cream mixtures* Vesna Hegedušić, Suzana Rimac, Zoran Herceg, Mirjana Škreblin Original scientific paper UDC: 663.674 Summary The quality of ice cream is in great extent determined by its sensoric proper­ties. Therefore, it is important to know and to predict the effect of the hydrocolloid and emulsifier addition on the consistency of the ice cream mixtures. In this work, the influence of several carboxymetylcellulose hydrocolloids (DIKO, YO-EH, HVEP) and emulsifier E-420 (mixture of sorbitol, monoglicerids and diglicerids) on the rheological properties of the model ice cream mixture as well as their ability to prevent crystallization and recrystallization were examined. The rheological properties as well as electroconductivity before and after pas­teurization were measured at 20 °C. The results of these investigations have shown that the viscosity of all ice cream mixtures significantly increased afierpasteurization. All investigated systems exhib­ited non-Newtonian characteristics. Hydrocolloid YO-EH showed the greatest in­fluence on the rheological properties of the model systems. Afier pasteurization conductivity increased for all investigated samples. Sensory evaluation have shown that the most acceptable product was that prepared with emulsifier E-420. Key words: ice cream mixtures, rheological properties, hydrocolloids, emulsi­fier, pasteurization Introduction The knowledge of the rheological properties of foodstuffs and the influ­ence of various ingredients and additives (hydrocolloids and emulsifiers) on those properties is important in defining the product's and process quahty control, predicting product stability during storage as well as creating the food texture (Kokini, 1987; Hegedušić, 1991; Hegedušić, 1994; Goff, 1994; Davidson 1996; Demetriades, 1997). Hydrocolloids, macromolecular carbohydrates are usually added in many foodstuffs in order to achieve the appropriate rheological properties, to prevent * The paper was presented at the 3''' Croatian Congress of Food Technologists. Biotechnologists and Nutritionists, held in Zagreb (June 10-12) 1998. 87 V. Hegedušić et al.: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. a sinerasis, to control crystallization process or to inhibit recrystallization of ice (Carr, 1993). In emulsion-based food products, like ice cream, very important ingredi­ents are stabilizers because of theirs emulsifying properties and ability to pre­vent recrystallization during storage at low temperatures (Dickinson, 1992; Damodaran, 1996). The physicochemical properties of emulsions depend first of all on the nature, strength and range of attractive and repulsive forces among droplets (Phillips etal.,1994;DickinsonandMcClements,1995;Dalgleish, 1996). Van der Waals and electrostatic forces as well as hydrophobic reactions can cause the overall interaction potential between a pair of droplets. Mathematical equation defining these forces has been published by Walstra, 1996. Hydrophobic interactions have been suggested to be important in deter­mining the stability of heated emulsions (Hunt and Dalgleis, 1994; Monahan et al, 1996). The strength of hydrophobic interactions depends on the distribution, and the amount of hydrophobic groups on the surface of colloidal particles (Israelachivili, 1992). Sutton et al. (1994,1996a, 1996b) have developed a model which deter­mines recrystallization rate in aqueous solutions of carbohydrates and ice creams. Many investigations are related to the effectiveness of hydrocoUoids on the re­crystallization in frozen desserts and ice cream mixtures (Hegedušić 1995; Miller-Livney, 1995; Vafiadis, 1997). Goff et al. (1993) found that the ice crystal sizes before and after frozen storage are smaller in ice cream mixtures with stabilizer addition compared to those without stabilizers. However, Muhr andBlanshard (1986)andMinn (1994) showed that the stabilizer addition did not prevent but did delay recrystallization of ice crys­tals in aqueous solutions of carbohydrates and ice cream mixtures. In this work, the influence of three carbo?Q^metylcellulose hydrocoUoids and emulsifier E-420 (mixture of sorbitol, monoglicerids and diglicerids) on the rheological properties of model ice cream mixtures as well as their ability to prevent crystallization and recrystallization were examined. Materials and methods Investigations were carried out with the model ice cream mixtures pre­pared according to recipes shown in Table 1. The following ingredients were used: V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. 1. milk - pasteurized, 3,2% milk fat "Dukat" 2. sugar - N crystal - sugar refinery "Županja" 3. egg yolk - S class of eggs from "Agrokoka" 4. sorbitol p.a. "Merck" 5. hydrocolloids - DIKO, YO-EH, HVEP - "Guliver-Chemie", Wiener Neudorf 6. emulsifier E-420 (mixture of sorbitol, mono and diglicerids) Table 1: Recipes for the model Ice cream mixture preparation Tablica 1: Recepti za pripravu modelniti sladolednih smjesa Recipe Milk (g) Water (g) Sugar (g) Sorbi­tol (g) Egg yolk (g) Solid matter (%) Stabi­lizer (g) Before pasteuriza­tion After pasteuriza­tion 1 78 - 14,4 0,4 7,0 29,5 31,4 0.2 2 78 - 14,2 0.4 7,0 26,3 29,3 0,4 3 39 39 14,2 0,4 7,0 23,4 25,9 0.4 4 39 39 14,4 0,4 7,0 24,2 26,3 0,2 Model ice cream mixtures (marked asrecipes 1 and 2) were prepared by mixing egg yolk and sugar in a blender. Hydrocolloid was mixed with sorbitol, dissolved in a part of warm milk and then added to the prepared mention mix­ture. Afterwords the rest of the milk was added and the whole suspension was homogenized in a blender. Model ice cream mixtures (marked as recipes 3 and 4) were prepared in the same way, except that 50% of milk was replaced with water. The mixture was pasteurized in a hot water bath for 30 minutes at Tl^C. Pasteurized model ice cream mixtures were frozen in "Philips" ice cream maker. Frozen samples were placed in the polyethylene containers (volume of 150 ml) and stored for 5 days at -18°C. After storage sensory properties were determined by 5 assessors using 20 points scale. Rheological properties of investigated model ice cream mixtures, before and after pasteurization, were determined at 20 "C using a Brookfield DV-III rotational viscometer. 8 ml of sample was poured in to a fixed coaxial cylinder and shear stress vs. shear rate was measured. The measurements were performed at shear rates increasing from the lowest (3s'̂ ) to the highest (158s"̂ ) value, and 89 V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. then backwards to the lowest shear rate (3s'̂ ). Ostwald - Reiner's power-law model was applied for calculating the rheological parameters. T=kY" where: k = consistency coefficient (Pa s") n = flow index Electroconductivity was measured at 20 °C using a conductometer ("Iskra", Kranj) with Ni-electrode. Mass fraction of solid matter in model systems was determined by drying at 105 °C to the constant weight. Discussion The quality of ice creams is, primary determined by theirs taste and con­sistency. Therefore, the sensory evaluation is one of the most important param­eters in the quality control of these products. Table 2: Sensory evaluation of the model ice cream mixture Tablica 2: Senzorska analiza modelnih sladolednih smjesa Quality parameter RECIPE 1 RECIPE 2 RECIPE 3 RECIPE 4 DIKO YO-EH HVEP E-420 DIKO YO-EH HVEP E-420 DIKO YO-EH HVEP E-420 DIKO YO-EH HVEP E-42C Taste 5.8 4,8 5,0 5,8 6,6 6,4 6,2 6,2 4,8 4,2 4,2 4.2 4,6 3,8 4,6 4,4 Odour 2,4 2,0 2,2 2,2 2,4 2,4 2,4 2,4 2,2 2,2 2,0 2,2 2,2 2,0 2,0 2,0 Consistency 4,8 4,6 4,2 4,6 5,6 4,8 4,8 5,4 4,0 2,8 3,2 4,2 4,6 4,2 3,8 4,2 Colour 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 Total 15,0 13,4 13,4 14,6 16,6 15,4 15,6 16,0 13,0 11,2 11,4 12,6 13,412,012,412,6 In Table 2 the average results of sensory properties evaluation of investi­gated model ice cream mixtures are shown. The highest scores are obtained for the ice cream mixtures containing the highest amount of milk and stabilizers (recipe 2). Significant differences exist in the sensory properties of samples pre­pared using a variety of stabilizers or emulsifier. The best ice cream mixture is proved to be the one containing E-420 emulsifier indicating that special atten­tion must be paid in order to create stabilized emulsions, (with positive effect on the sensory properties) rather than to use hydrocolloids to prevent ice crys­tals formation or the recrystallization of water. The ideal solution is to use hydrocolloid which main functional characteristics could prevent ice crystals growth, create a smooth texture and, at the same time, achieve the emulsifying affects. DIKO hydrocolloid, because of its functional characteristics (emulsifying properties) is used only in the ice cream preparation. This is also confirmed by 90 V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96,1998. sensory evaluation, as the ice cream prepared with DIKO hydrocolloid, rather than with YO-EH and HVEP hydrocoUoids which do not possess these emulsi­fying properties, is significantly better evaluated. The electroconductivity of ice cream mixtures depends on the mass frac­tion of solid matter and stabilizer presence. Ice-cream mixtures prepared in accordance with recipes 1 and 2 (higher solid mater content) showed lower con­ductivity than mixtures 3 and 4 (lover solid mater content). However, the con­ductivity of all mixtures depends on the type of hydrocoUoids or emulsifiers added. In the ice-cream mixtures containing emulsifier E-420 the highest con­ductivity is determined. This is closely related to the ability of water binding capacity of hydrocolloid, thus causing a decrease in electroconductivity. Fig. 1: Shear stress vs. shear rate of the model ice cream mixtures prepared according to the recipe 2 Slika 1: Odnos između napona smicanja i brzine smicanja kod modelnih sladolednih smjesa pripremljenih prema receptu 2. 40 50 Shear rate (1/s) The results of the investigation of rheological properties showed that all the investigated ice-cream mixtures possess non-Newtonian characteristics. The regression coefficient for all investigated systems is extremely high (between 0.96 and 0.99), which means that the rheological properties of ice creams can be described by Ostwald - Reiner's power-law model. The flow behavior index of all the ice cream mixtures, before and after pasteurization, ranged from 0.50 and 0.85 indicating pseudoplastic characteristics of the mixtures. The consis­tency of ice cream mixtures expressed as consistency coefficient value (Tables 4, 5, 6, 7) depends on the mass fractions of solid matter, hydrocolloid and stabi­lizer, type of stabihzer used, as well as phase of investigation (before or after 91 V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. Table 3: Rheological characteristics of the ice cream mixtures prepared accordirig to the recipe 1 Tablica 3: Reološke l<aral<teristii<e sladolednih smjesa pripremljenih prema receptu 1 Apparent Consistency viscosity Flow coefficient Regression Sample (mPas) index (Pas") coefficient Flow 1 DIKO 29,1 0,59 0,087 0,984 pseudoplastic 1 DIKO* 87,0 0,84 0,134 0,997 pseudoplastic 1 YO-EH 29,1 0,70 0,062 0,999 pseudoplastic 1 YO-EH* 96,9 0,77 0,173 0,999 pseudoplastic 1 HVEP 30,3 0,68 0,075 0,996 pseudoplastic 1 HVEP* 41,1 0,77 0,083 0,999 pseudoplastic 1 E-420 10,7 0,64 0,016 0,999 pseudoplastic 1 E-420* 33,6 0,80 0,083 0,998 pseudoplastic *after pasteurization *nakon pasterizacije Table 4: Rheological characteristics of the ice cream mixtures prepared according to the recipe 2 Tablica 4: Reološke karakteristike sladolednih smjesa pripremljenih prema receptu 2 Sample Apparent viscosity (mPas) Flow index Consistency coefficient (Pas") Regression coefficient Flow 2 DIKO 2 DIKO* 2 YO-EH 2 YO-EH* 2 HVEP 2 HVEP* 2 E-420 2 E-420* 70,5 126,0 214,0 288,0 63,9 77,7 6,0 17,4 0,80 0,58 0,72 0,83 0,82 0,71 0,82 0,71 0,119 0,506 0,457 0,465 0,103 0,170 0,010 0,037 0,999 0,960 0,998 0,999 0,999 0,998 0,996 0,998 pseudoplastic pseudoplastic pseudoplastic pseudoplastic pseudoplastic pseudoplastic pseudoplastic pseudoplastic *after pasteurization *nakon pasterizacije pasteurization) (Hegedušić, 1994). The type of stabilizer had a significant ef­fect on the consistency of the investigated systems. The lowest value of consis­tency coefficient is obtained in the ice cream mixtures containing E-420 emulsi­fier, which is understandable due to its functional characteristics. By increasing amount of the emulsifier no significant influence on the rheological parameters is observed. However by increasing the mass fraction of all hydrocolloids (from 0.2 to 0.4%) a significant effect on the coefficient consistency value is observed. 92 V. Hegedušić et al.: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. Table 5: Rheologlcal characteristics of the Ice cream mixtures prepared according to the recipe 3 Tablica 5: Reološke karakteristike sladolednih smjesa pripremljenih prema receptu 3 Apparent Consistency viscosity Flow coefficient Regression Sample (mPas) index (Pas") coefficient Flow 3 DIKO 39,6 0,76 0,069 0,998 pseudoplastic 3 DIKO* 55.2 0,56 0,187 0,961 pseudoplastic 3 YO-EH 75,3 0,85 0,106 0,998 pseudoplastic 3 YO-EH* 93,6 0,81 0,152 0,999 pseudoplastic 3HVEP 42,0 0,81 0,068 0,998 pseudoplastic 3 HVEP* 57,3 0,83 0,090 0,999 pseudoplastic 3 E-420 5,4 0,83 0,007 0,999 pseudoplastic 3 E-420* 12,0 0,76 0,024 0,999 pseudoplastic *after pasteurization *nakon pasterizacije Table 6:Rheologlcal characteristics of the Ice cream mixtures prepared according to the recipe 4 Tablica 6: Reološke karakteristike sladolednih smjesa pripremljenih prema receptu 4 Apparent Consistency viscosity Flow coefficient Regression Sample (mPas) index (Pas") coefficient Flow 4 DIKO 13,5 0,79 0,021 0,997 pseudoplastic 4 DIKO* 32,1 0,78 0,053 0,997 pseudoplastic 4Y0-EH 26,1 0,76 0,044 0,999 pseudoplastic 4 YO-EH* 35,7 0,77 0,061 0,998 pseudoplastic 4 HVEP 26,7 0,69 0,057 0,994 pseudoplastic 4 HVEP* 30,9 0,76 0,054 0,996 pseudoplastic 4 E-420 5,9 0,56 0,033 0,989 pseudoplastic 4 E-420* 15,9 0,61 0,047 0,994 pseudoplastic *after pasteurization *nakon pasterizacije Remarkable increase in viscosity occurred in all ice-cream mixtures after pas­teurization. The highest increase in viscosity (2,5 to 3 times) is determined for the ice cream mixtures containing E-420 emulsifier. Conclusion Investigated model ice cream mixtures exhibited non-Newtonian cha­racteristics before and after pasteurization. The most significant influence of 93 V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. Table 7: Electroconductivity of the model ice cream mixtures Tablica 7: Elektroprovodnost modelnih sladolednih smjesa Stabilizers ELEKTROCONDUCTIVITY (|aS cm-̂ ) RECIPE 1 RECIPE 2 RECIPE 3 RECIPE 4 DIKO 286 440 594 448 DIKO* 350 502 598 591 YO-EH 518 560 628 590 YO-EH* 535 625 670 600 HVEP 439 540 690 547 HVEP* 514 653 730 591 E-420 583 711 571 593 E-420* 629 718 589 600 *after pasteurization *nakon pasterizacije pasteurization is observed on the ice cream mixtures containing E-420 emulsi-fier. All hydrocolloids had a significant effect on the consistency coefficient value, with YO-EH hydrocoUoid having the most significant influence. E-420 emulsifier showed the lowest influence on the rheological proper­ties of the investigated systems. However, ice cream mixtures prepared with this emulsifier are better sensory evaluated, which means that during the produc­tion of ice cream special attention should be paid in order to create a stable emulsion. UTJECAJ DODATAKA STABILIZATOR NA REOLOŠKA SVOJSTVA MODELNIH SLADOLEDNIH SMJESA Sažetak Kakvoću sladoleda u velikoj mjeri određuju njegova senzorska svojstva, te je važno znati kakav će utjecaj na njih, posebno na konzistenciju, imati dodatak hidrokoloida odnosno emulgatora. U ovom radu ispitan je utjecaj hidrokoloida na bazi karboksimetilceluloze (DIKO, YO-EH, HVEP) i emulgatora (smjesa sorbitola, monoglicerida i diglicerida, E-420) na reološka svojstva modelnih sladolednih smjesa kao i njihova sposobnost da spriječe kristalizaciju i rekristalizaciju vode te u vodi otopljenih tvari. Reološka svojstva određena su u rotacionom reometru Brookßeld DV-IIl kod temperature od 20 °C prije i poslije pasterizacije. Nakon provedene pasterizacije i smrzavanja izmjerena je provodljivost na konduktometru "Iskra " Kranj pri temperaturi od 20 °C. 94 V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. Rezultati ispitivanja su pokazali da je nakon provedene pasterizacije došlo do značajnog povećanja viskoznosti svih modelnih smjesa. Svi sastavi su pokazali nenewtonski karakter. Najveći utjecaj na reološka svojstva modelnih sustava imao je hidrokoloid YO-EH. 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(1994): Structure - Functional Properties of Food Proteins, Academic Press, San Diego, CA. Sutton R. L., Evans L D., Crilly I. (1994): / Food Sci. 59,1227-1233. 95 V. Hegedušić et al: Influence of stabilizers addition... Mljekarstvo 48 (2) 87-96, 1998. Sutton R. L., Lips A., Piccirillo G. (1996): /. Food Sci. 61, 746-748. Sutton R. L., Lips A., Piccirillo G., SztehloA. (1996): /. Food Sci. 61, 741-745. Vafiadis D. K (1997): Dairy Field 180, 37-38. Walstra P. (1996): Dispersed systems: basic considerations. In Food Chemistry, 95-155, Marcel Dekker, New York. Author's addresses: Received: June 15,1998 Prof. dr. sc. Vesna Hegedušić Accepted: July 20,1998 Mr. sc. Zoran Herceg Suzana Rimac, dip!, inž. Faculty of Food Technology and Biotechnology, University of Zagreb Dr. sc. Mirjana Škreblin "Pliva" d.d. Zagreb 96 

Utjecaj dodataka stabilizatora na reološka svojstva modelnih sladolednih smjesa

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