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ThesisItem Open Access Quality characteristics of soy milk blended yoghurt(College of Veterinary Science, Assam Agricultural University, Khanapara Campus, 2022) Khatun, Arifa; Borpuzari, TA study was carried out to evaluate the quality characteristics of soy milk blended cow’s milk yoghurt. The study was carried out in the laboratories of the Department of Livestock Products Technology, the All India Coordinated Research Project on Post-Harvest Engineering and Technology, the Department of Veterinary Biochemistry, College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati- 781022 and in the Central Analytical Instrumentation Facility, Guwahati Biotech Park Incubation Centre, Amingaon, Kamrup, Guwahati-781031 during the period from December, 2021 to September, 2022. Organic whole soybeans procured from the local super markets were used for preparing sprouted and unsprouted soy milk. The NCDC 144 obtained from the National Dairy Research Institute, Karnal was used @ 3% (v/v) as yoghurt starter culture in the study. The effects of addition of soy milk on the pH, per cent lactic acid content, free fatty acids, flavour and colour profile, proximate composition, microbiological quality, sensory scores and the best before end of the cow’s milk yoghurt were studied. A gradual decrease in the pH values of the Control samples as well as in all the samples of the Treatment groups was noted. Fatty acids and flavour compounds were identified with the help GC-MS. The colour profiling revealed that L, a and b values were the highest in control samples followed by T2 group while the samples of T1 group showed the least values for these colour components. The samples of T2 group contained the maximum mean values of 4.23±0.02, 19.65±0.10 and 1.26±0.00% for protein, total solids and ash, respectively, while the Control samples showed the maximum mean value of 4.37±0.03 and 82.96±0.12% for fat and moisture, respectively. The protein content of the cow’s milk yoghurt incorporated with 25% of soy milk had higher protein content than the cow’s milk yoghurt. Addition of sprouted soymilk increased the per cent protein content of the cow’s milk yoghurt than those incorporated with unsprouted soymilk. The highest mean TVC of 9.13±0.01 log10cfu/ml was recorded in the samples of the T2 group which might be due to rapid growth of the added starter organisms accelerated by the synergistic effect of the germination metabolites of soybeans. Coliforms, E. coli, Salmonella, Shigella, Staph. aureus and yeast and moulds were not detected in any of the samples. The cow’s milk yoghurt prepared with 25% unsprouted soymilk had higher contents of caproic, caprylic, and lauric acids over the control samples. The yoghurt prepared with 25% sprouted soymilk had higher concentrations of margaric, palmitoleic, proprionic, tricosylic, tridecylic and vaccenic acids as compared to the control as well as the unsprouted samples. These free fatty acids might have contributed to the typical flavour of soy blended cow’s milk yoghurt. The cow’s milk yoghurt blended with 25% of unsprouted and sprouted soy milk enjoyed identical panel acceptance for the appearance, colour, body and texture, and flavour characteristics indicating that soy milk could be successfully blended with cow’s milk up to 25% in yoghurt without affecting its sensory properties. However, the cow’s milk yoghurt was more preferred for its taste as compared to the soy milk blended yoghurts. Cow’s milk yoghurt blended with 25% soy milk had the ‘Best Before End’ of 5d at refrigeration temperature.
