1Department of Food Science and Technology, College of Agriculture, Shiraz University, Shiraz, Iran
2Ph.D. Student in Biotechnology, Department of Stock-Breeding’s Production Technology, Technology Faculty, Armenian Agricultural Academy, Yerevan, Armenia, and Fars Pegah Pasteurized Milk Company, Shiraz, Iran
3MSc Student in Food Science and Technology, Department of Food Science and Technology, College of Agriculture, Shiraz University, Shiraz, Iran, and Fars Pegah Pasteurized Milk Company, Shiraz, Iran
4Department of Stock-Breeding’s Production Technology, Technology Faculty, Armenian Agricultural Academy, Yerevan, Armenia
5BSc in Microbiology, Fars Pegah Pasteurized Milk Company, Shiraz, Iran
6Department of Food Hygiene and Public Health, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
In the present study, the effects of milk supplementation on growth and viability of yogurt (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus) and probiotic bacteria (Lactobacillus acidophilus and bifidobacteria) were studied during yogurt production and 33 days of refrigerated storage. The incubation time to reach pH = 4.5 was greatly affected by the addition of milk powder (MP), tryptone (TRY) and sucrose (SUC). Also, the increase in titrable acidity depended on added supplement. Viable counts of L. delbrueckii subsp. bulgaricus were significantly (P<0.05) increased in yogurt supplemented with whey powder (WP), TRY and milk powder plus five fold starter culture (MP-SC). However, milk supplementation did not affect the counts of S. thermophilus in probiotic yogurt until the end of storage. Supplementation with TRY and MP-SC promoted the growth and viability of L. acidophilus, whereas milk supplementation with whey protein concentrate (WPC), yeast extract (YE), SUC and Cysteine, adversely affected the viability of L. acidophilus in probiotic yogurt. Finally, using a high level of inoculums (MP-SC) improved the viability of bifidobacteria during storage for 33 days. In conclusion, tryptone and milk powder plus five fold starter culture were found the most effective supplements to improve growth and viability of starter and probiotic (L. acidophilus and bifidobacteria) bacteria in probiotic yogurt during refrigerated storage for a five week period. These findings would be applicable in industrial production of probiotic yogurt.