Improving the viability and stability of starter culture and the quality of fermented milk using some food additives

The present investigation studied the effects of L-Ascorbic acid, casein hydrolysate, whey protein concentrate (WPC), or glucomacropeptide (GMP) on the viability of Streptococcus thermophilus, Lactobacillus casei, and Bifidobacteria breve (CBT) starter culture in fermented milk during manufacture and storage period. Changes in chemical and viable total bacterial count were monitored during manufacture and storage at 5°C for 21 days of fermented milk. Dated showed that the incubation time that was needed to reach pH 4.5 was considerably affected by the added ingredients. Also, the drop in pH or the increase in acidity of this fermented milk was dependent on the added ingredients. Results showed that addition of L-Ascorbic acid, casein hydrolysates, whey protein concentrate or glucomacropeptide improved the viability of bifidobacteria and Lactobacillus casei (L.casei) and Streptococcus thermophilus

(S. thermophilus) starter culture in general compared to the control one. However, the survival of bifidobacteria was greatly reduced during storage of fermented milk, except for products containing CH, WPC and GMP in which viable counts remained at >10⁶ cfu/g after 21 days of storage at 5°C.No clear difference was observed between L-Asorbic acid treatment and the control in the effect on the fermented milk characteristics compared to the other treatments.

Supplementation of the fermented milk with CH, WPC and GMP improved the viscosity and other rheological properties and reduced the curd synersis rate. Fermented milk fortified with GMP showed higher lactase utilization and had lower lactose concentrations during storage period than other treatments.

Sensory evaluation showed that fermented milk fortified with CH, WPC and GMP recorded the highest score for and overall acceptability than the other treatments. However, fermented milk fortified with GMP showed the heights organolyptic score followed by WPC treatments, CH treatments the L-Ascorbic acid and at the end the control. Data suggested that the nitrogen source in the form of peptides and amino acids improved the viability of probiotic bacteria specially bifidobacteria in fermented milk made with a CBT (L. casei, B.breve and S. thermophilus) starter culture, which showed a dramatic decline in the counts of this organism in other studies.

It is suggested that the fermented milk of acceptable quality and high total probiotic bacterial count during storage can be made from milk supplemented with 1% (wt/vol) GMP.