Abstract #T92

# T92
The physical and chemical effect of thermal processing on high- and low-heat nonfat dry milk set yogurt.
S. Brooks*1, 1Kansas State University, Manhattan, KS.

The physical and microstructural properties of yogurt are often a function of the whey protein denaturation that occurs during mix processing. Nonfat dry milk (NDM) is manufactured to have high amounts of denatured whey proteins (high-heat) or low amounts of denatured whey proteins (low-heat). When used in yogurt, these denatured whey proteins influence the texture due to increased formation of large, denatured whey aggregates that leads to decreased casein micelle saturation. Thus, this study was undertaken to determine if a subsequent thermal process step in yogurt mixes made of high-heat (HH) NDM or low-heat (LH) NDM could improve physical properties or chemical characteristics in set-style yogurts. Yogurt mixes were formulated to 3.5% protein from either HH- or LH-NDM. Half of each mix received an additional thermal process (85°C for 30 min) before cooling, inoculation incubation (until pH of 4.6), storage at 4°C overnight, and followed by yogurt assessment. Data were analyzed with SAS â statistical software as a 2-way ANOVA, followed by a Tukey’s pair-wise (99% confidence level) at p £ 0.05. Statistically, syneresis was significantly lower in low-heat processed (LHP) yogurt and low-heat non-processed (LHNP) yogurt than high-heat processed (HHP) yogurt and high-heat non-processed (HHNP) yogurt. Cohesiveness and firmness were significantly greater in LHP yogurts followed by HHNP, HHP, and then LHNP yogurts. Additional thermal processing in yogurt reveals an association between improved yogurt texture and initial denatured whey protein in yogurt mixes. The thermal processing on whey protein-casein micelle interactions during a subsequent heat treatment of LH-NDM in a yogurt mix may result in better coalescence of casein micelles leading to cross-linking in a gel rather than a possible spatial interference occurring from yogurt mixes made with HH-NDM.

Key Words: yogurt, nonfat dry milk, thermal processing