Viability of bifidobacteria in commercial yogurt products in North Carolina during refrigerated storage

Abstract

Fifty‐eight commercial yogurt products of seven brands (which claimed to include bifidobacteria) were obtained from local stores in Greensboro, North Carolina, USA. These products were examined at 0, 1, 2, 3 and 4 weeks for the viability of bifidobacteria and yogurt starter culture during refrigerated storage at 4°C. Our results showed that bifidobacteria counts were variable, ranging from 0 to 5.5 log cfu/mL. The average yogurt starter culture counts ranged from 5.20 to 8.87 log cfu/mL and 7.51–8.94 log cfu/mL for Lactobacillus delbrueckii spp. bulgaricus and Streptococcus thermophilus, respectively. Of the 58 products tested, only 44 products (76%) contained viable cultures. Viability of bifidobacteria in yogurt samples remained within the same levels during 3 weeks of storage at 4°C; however, the bacterial count started to decline during the fourth week. These results suggest optimal beneficial consumption of yogurt foods with live bifidobacteria should occur within 3 weeks of production. Results obtained from this research could be used by the industry to develop new technologies to ensure consumers receive high‐quality products.