VIABILITY OF LACTOBACILLUS acidophilus AND SYNERESIS OF PROBIOTIC YOGHURT PRODUCED FROM RECONSTITUTED SKIM AND WHOLE MILK POWDER DURING 35 DAYS REFRIGERATED STORAGE AT 4±2 oC

Abstract

Currently, the food industry wants to expand the range of probiotic yogurts but each probiotic bacteria offers different and specific health benefits. This study examined the viable counts of Lactobacillus acidophilus and percentage syneresis of probiotic yoghurt produced from reconstituted skim and whole milk powder stored for 35 days at 4±2 oC. Skim milk probiotic yoghurt (SMPY) and Whole milk probiotic yoghurt (WMPY) were produced by reconstituting dry milk powder (130 g/900 ml w/v), which was pasteurized at 85 oC for 15 mins, cooled to 43 oC and inoculated with freeze dried probiotic yoghurt mixed starter culture containing Streptococcus thermophilus (ST), Lactobacillus bulgaricus (LB) and Lactobacillus acidophilus (LA). The yoghurt samples were analyzed for viability of ST, LB, LA and also syneresis. During storage, the viable counts of ST in SMPY decreased from 5.43x108 to 5.18x106 cfu/ml, LB (2.47x108 to 8.10x105 cfu/ml) and LA (1.83x108 to 5.78x105 cfu/ml). Similarly, the viable counts of ST in WMPY decreased significantly from 5.40x108 to 5.15x106 cfu/ml, LB (2.43x108 to 7.82x105 cfu/ml) and LA (1.80x108 to 5.84x105 cfu/ml). Although the mean viable counts of the LA decreased during storage, both SMPY and WMPY still contained an average of 1.48x106 cfu/ml of probiotic cells up to 28 days of storage, which is above the “therapeutic minimum” of 106 cfu/ml. The percentage syneresis of SMPY and WMPY increased significantly during the 35 days of storage, from 24.4-32.0 % and 24.8-32.7 % respectively. There was a positive correlation between storage time and syneresis thus affecting the texture. In conclusion, yoghurt made from either skim or whole milk powder can be used as an adequate carrier of LA (probiotic bacteria) up to a period of 28 days at 4±2 oC and a stabilizer should be used to reduce the separation of whey and thus maintain the texture.