Effect of Casein Hydrolysates on Yogurt Fermentation - Food ...

432 Q.Z. ZHAO et al.: <strong>Effect</strong> <strong>of</strong> <strong>Casein</strong> <strong>Hydrolysates</strong> on Yogurt Fermentation, Food Technol. Biotechnol. 44 (3) 429–434 (2006)Coagulation time/h4.54.03.53.02.52.01.51.00.50CH1 CH2 CH3<strong>Casein</strong> hydrolysatesFig. 2. Coagulation time <strong>of</strong> yogurt with added casein hydrolysates.CH1, CH2, CH3 and the columns represent the same as inFig. 1Probiotic counts/(log CFU/mL)9.08.58.07.57.06.56.0pH4.454.404.354.304.254.204.154.104.054.003.95CH1CH2<strong>Hydrolysates</strong>CH3Fig. 3. Change in pH <strong>of</strong> yogurts with added hydrolysates afterstorage for 30 days. CH1, CH2, CH3 and the columns representthe same as in Fig. 1riod <strong>of</strong> 30 days at low temperature. Post-fermentationacidification had a negative effect on the quality, andshortened the shelf life. It is closely associated with thepersistent metabolic activity <strong>of</strong> lactobacilli during coolingat4°C(24).Decrease in post-fermentation acidificationwas favourable for sensory improvement and consumers’preference.5.50 1 2 3 4 5Fermentation time/hFig. 4. <strong>Effect</strong> <strong>of</strong> the supplement <strong>of</strong> hydrolysates on growth <strong>of</strong> probioticbacteria in yogurt. CK, CH1 (0.5 %), CH1 (1.5 %), CH2 (0.5 %), ´ CH2 (1.5 %), + CH3 (0.5 %), CH3 (1.5 %). CH1,CH2 and CH3 are the same as in Fig. 1Change in growth and viability <strong>of</strong> probiotic bacteriaduring fermentation and storageThe growth <strong>of</strong> probiotic organisms during fermentationis presented in Fig. 4. The hydrolysates increasedthe probiotic counts at initial stage compared to the control.It indicated that the hydrolysates enhanced thegrowth <strong>of</strong> probiotic organisms. However, the growth <strong>of</strong>the probiotic organisms decreased at the final stage whenthe hydrolysates were added. The growth <strong>of</strong> these bacteriadecreased with the increase in the addition <strong>of</strong> hydrolysates.This was related to the decrease in fermentationtime.L. acidophilus and B. bifidum have to retain viabilityand activity in the food system to meet the requirementsfor consumption (25). Viability <strong>of</strong> probiotic bacteria inproducts during long shelf life at refrigeration temperatureis generally unsatisfactory (8,26) because the lowsurvival <strong>of</strong> probiotic organisms in the fermented dairyproducts is the greatest obstacle encountered in processing,and especially during storage (27).The counts <strong>of</strong> probiotic bacteria in yogurts decreasethroughout storage. However, decline in the counts <strong>of</strong>probiotic organisms during storage can be retarded byhydrolysates (Fig. 5). After 30 days <strong>of</strong> storage, the yogurtswith the hydrolysates have more probiotic bacteriathan the control. The yogurt with 1.5 % <strong>of</strong> CH3 hasabout 3-fold more probiotic bacteria than the control.The hydrolysates significantly (p