Calcium lactate fortification of reduced fat yogurt and fortification of 'simulated yogurt gel' with partially hydrolyzed whey protein

There has been great demand of calcium fortified dairy products as they can serve as ideal vehicle for carrying extra calcium to fulfill the nutritional needs but there is need to generate information on the effect of fortification of calcium on the physical properties of these products. In the present study the calcium enriched fruit yogurt was prepared after fortification of pasteurized yogurt mix with 50 mg Ca/100 ml of calcium lactate, this level was selected from a preliminary study of sensory evaluation. Fortification of yogurt with calcium lactate at this level significantly (P<0.005) increased the water holding capacity (WHC) by 7.76 % on 1st day of storage. WHC of calcium fortified fruit yogurt was higher than control fruit yogurt on 7th and 14th day of storage. Measurements performed on slowly stirred samples (flow curves, apparent viscosity, and viscoelastic properties) showed that calcium enriched fruit yogurt had stronger structures. Calcium fortified fruit yogurt showed less shear thinning behavior as compared to control. Also, apparent viscosity measurements at constant shear rate showed a significantly (P<0.05) less decrease in initial apparent viscosity in calcium fortified fruit yogurt. However, no statistically significant (P>0.05) difference was observed in tan delta values of control and calcium fortified fruit yogurt indicating similar nature of bonds involved in the gel structure formation of both the yogurt samples. The firmer structure of the calcium fortified fruit yogurt is thus attributed to the higher extent of bonding due to presence of dissolved calcium. Also flavor, color, and body and texture scores of control and calcium fortified fruit yogurt did not show any significant difference (P>0.05).; The physical properties such as WHC, apparent viscosity, TPA analysis etc. along with sensory characteristics of yogurt containing whey protein hydrolysates (WPH) and whey protein isolate (WPI) were studied. WPH and WPI were added at a concentration of 1%, 3%, 5%, 7%, and 9% w/v. Two stages of addition were studied i.e. addition before pasteurization and after pasteurization treatment. The resulting yogurts were compared among each other and with control without supplementation. At 7% and 9% level of addition yogurt mix destabilized during incubation due to protein destabilization. For further investigation 1%, 3%, and 5% level of addition was selected. Yogurt with WPH added at concentrations of 3% and 5% w/v received lowest flavor score among all the WPI and WPH added yogurt samples in addition to control due to the bitterness perceived during the sensory analysis (P<0.05). Addition of WPI and WPH to yogurt caused an improvement in almost all the physical characteristics such as color, water holding capacity, firmness, and apparent viscosity. In case of WPI added yogurt this increase was statistically much higher (P<0.05) when WPI were added before pasteurization than after pasteurization. For WPH added yogurt, WHC, apparent viscosity, and firmness, were not statistically different (P>0.05) between WPH addition before pasteurization and after pasteurization. Further, yogurt with WPI addition before pasteurization had similar rheological characteristics to yogurt with WPH addition before and after pasteurization. Also, the storage of WPI and WPH added yogurt did not cause any significant change in the physical characteristics of the yogurt samples, which confirms the stability of WPH fortified yogurt. Thus, present investigation reveals that the maximum attainable level of WPH fortification in yogurt is 5% w/v. Unlike WPI fortified yogurt, heating does not exhibit any additional impact on physical properties (WHC, apparent viscosity, firmness etc.) of yogurt fortified with WPH.