THE INFLUENCE OF INGREDIENT SUPPLEMENTATION ON THE TEXTURAL CHARACTERISTICS OF YOGURT

This investigation studied the effects of cysteine, whey powder (WP), whey protein concentrates (WPC1 and WPC2), acid casein hydrolysate (AC H) and tryptone on the textural properties of yogurts. Yogurt suppleme nted with 2% WPC1 was the firmest among all yogurt samples and its fir mness was significantly higher (p<0.001) than other yogurts. The firmn ess of the control yogurt was similar to that supplemented with AGH, t ryptone or cysteine at 50 and 250 mg/L level, but the firmness was sig nificantly higher (p<0.001) with WPC1 and significantly lower (p<0.001 ) in yogurt made with WP and a high level of cysteine (500 mg/L). The viscosity of yogurt made with various ingredients showed significant d ifferences (p<0.001) and an average increase in viscosity of similar t o 1.2 to 1.6 times was observed during refrigerated storage of 30 days , except for that supplemented with WPC2. The microscopic texture anal yses of yogurt showed that the protein network of yogurt varied with v arious ingredients. Increased concentration of cysteine resulted in an irregular network of protein in the finished product and also affecte d the firmness and viscosity of the yogurt. The flocs and pores were l arge in the product supplemented with WPC. By contrast, an even and mo re regular protein network with very small flocs and pores was observe d in the control yogurt and that supplemented with ACH or tryptone.