Probiotic culture survival and implications in fermented frozen yogurt characteristics

Low-fat ice cream mix was fermented with probiotic-supplemented and traditi onal starter culture systems and evaluated for culture survival, compositio n, and sensory characteristics of frozen product. Fermentations were stoppe d when the titratable acidity reached 0.15% greater than the initial titrat able acidity (end point 1) or when the pH reached 5.6 (end point 2). Mix wa s frozen and stored for 11 wk at -20 degrees C. The traditional yogurt cult ure system contained the strains Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The probiotic-supplemented system contained the traditional cultures as well as Bifidobacterium Longum and Lactobacillus acidophilus. We compared recovery of Bifodobacterium by three methods, a repair-detection system with roll-tubes and plates on modi fied bifid glucose medium and plates with maltose + galactose reinforced cl ostridial medium. Culture bacteria in both systems did not decrease in the yogurt during froz en storage. The roll-tube method with modified bifid glucose agar and repai r detection system provided at least one-half log(10) cfu/ml higher recover y of B. longum compared with recoveries using modified bifid glucose agar o r maltose + galactose reinforced clostridial agar on petri plates. No chang e in concentrations of lactose or protein for products fermented with eithe r culture system occurred during storage. Acid flavor was more intense when product was fermented to pH 5.6, but yogurt flavor was not intensified. Th e presence of probiotic bacteria in the supplemented system seemed to cause no differences in protein and lactose concentration and sensory characteri stics.