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Submitted to: Food and Bioprocess Technology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/1/2008 Publication Date: 8/30/2008 Citation: Onwulata, C.I., Tomasula, P.M. 2008. Gelling properties of tyrosinase-treated dairy proteins. Food and Bioprocess Technology. DOI 10.107/S11947-008-012-4. Interpretive Summary: Cheese whey, the watery by-product of the cheese making process, is concentrated and then dried to powder form to make ingredients such as whey protein concentrate and whey protein isolate. These products are highly nutritious and are added as ingredients to many food products to improve their nutritional profile, to improve their functionality and to add flavor as well. However, the powdered whey products can not be added to some food products because they do not readily bind to the other ingredients. In this study, the conversion of whey protein isolate to a gel form so that it may be included as an ingredient in food products such as ice cream, caramel candies, yogurt and certain baked goods was examined. The whey protein isolate was blended with another dairy protein, brewed with the tyrosinase enzyme from mushrooms, and then cooked under vacuum to form gels. All gels maintained their strength and thickness for 10 days. The gelled whey protein isolate ingredient may be added to foods to replace carbohydrate-based gel ingredients to create reduced calorie or low –fat foods products. Technical Abstract: The crosslinking of milk protein and food gums increases their viscosity and forms the base for various foods such as ice cream, milk based beverages and caramel candies. Protein-based viscous gels are needed to replace carbohydrate-based ones for reduced calorie or low-fat food applications. In this study, slurries of whey protein isolates and calcium caseinate mixed with alginic acid (20% T.S.) were subjected to high shear homogenization (microparticulation) at 27,000 rpm for 2, 3, 4, and 6 min. The resulting slurries were incubated with mushroom tyrosinase (E.C. 1.14.18.1) enzyme at levels of 3, 6, 9 mg/100 g to facilitate gel formation by crosslinking alginic acids to the dairy proteins. After microparticulation and incubation with tyrosinase for 15, 30, and 60 min, the slurries were evaporated at 45 deg C for 60 min under a partial vacuum (20 to 45 mm Hg) to form composite gels at 0 min (66 cP) and 6 min (279 cP), respectively. The viscosities and viscoelastic properties of the gels were studied using both static and dynamic rheometry. The results indicate that the time of high shear homogenization had significant (P<0.05) effect on the viscosities of the gels. Highest gel viscosity was obtained with 6 mg tyrosinase at 60 min, but increases in gel viscosity depended on time of shear with 2 and 4 min shear resulting in higher viscosity (484 and 6143 cP) and stronger viscoelasticity (49 and 38 Pa.s), respectively, compared to the control viscosity (69 cP) and viscoelasticity (12 Pa.s). Gels were stable in refrigerated storage up to 240 hr, strengthening with time of refrigeration storage, and became significantly more viscoelastic. Optimal viscous properties were obtained at 4 min microparticulation, 60 min incubation, 6 mg tyrosinase treatment. There was significant evidence of protein and alginic acid crosslinking indicated by the increased viscoelasticity of the tyrosinase treated samples. |
