Physicochemical properties of probiotic frozen yogurt with different levels of glycerol and overrun

The study was design to investigate the effects of overrun and glycerol supplementation on physicochemical properties of probiotic frozen yogurt. Frozen yogurt was prepared containing different types of probiotics (Lactobacillus acidophilus and Bifidobacterium lactis) along with yogurt starter culture (Streptococcus thermophilus and Lactobacillus bulgaricus). In frozen yogurt mixture glycerol in 1.5, 3 and 4.5% concentrations were supplemented and frozen with 60, 80 and 100 % overrun. Frozen yogurt was stored at -20ºC after production and hardening. Physicochemical analysis was carried out in the mixture before freezing while melting rate, microstructure and textural analysis were carried out after one week of frozen storage.  Melting rate and stickiness significantly decreased with increased overrun levels (P<0.05) while glycerol supplementation has shown non-significant effect on melting rate and stickiness (P<0.05). Hardness of the frozen yogurt was highest (43.57 Newton) with 60% overrun and 0% glycerol (P<0.05). Air cell size and ice crystal subsequently decreased with increased overrun and glycerol levels (P<0.05). The 100% overrun and 4.5% glycerol supplementation have shown the better effects on the improvement of physicochemical properties of the probiotic frozen yogurt.