Assessing the probiotic activity in conventional yoghurt produced at a dairy processing company in Sri Lanka

Abstract

Yoghurt is a potential source of probiotic 𝘭𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘪, because the bacterium is highly adapted to milk environment and is also able to resist low pH values. Regular yogurt consumption can be a contributing factor to the establishment and survival of 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 in upper and lower gastrointestinal tract. The objective of the present study was to assess the probiotic activity in conventional yoghurt produced by a leading dairy processing company in Sri Lanka and to determine whether it has accomplished to reach the minimum level of 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘪, specified by regulation in conventional starter culture, as probiotic bacteria. Further, survival of 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘪 under simulated gastric pH range was tested. The conventional yoghurt samples were enumerated for 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 and assessment was conducted to examine whether the final product reaches the minimum level of 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘪, 1.0x10⁷ cfu/g specified by International Dairy Federation, in order to exert the suggested health benefits to the consumer. The mean count of 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 was greater than the minimum level at the 0.05 level of significance. Yoghurt samples were stored at 4 OC and duplicated plates were enumerated throughout the specified storage period, at 3, 7, 14, 21 and 28 day intervals using Lactobacillus MRS Agar, under incubation at 45⁰C for 72 h to assess the survival throughout the shelf life. The mean counts of 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 were greater than the minimum level at the 0.05 level of significance throughout the storage period and a negative relationship was observed in the 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 counts with time showing a gradual decrease in colony counts. Throughout the storage period, pH of the samples gradually decreased with time maintaining a pH value below 4.5, which fulfils the requirements of The Australian and New Zealand Food Standards Code. This also indicates that production of organic acids with antimicrobial properties have increased without affecting the sensory properties of the product. The enumerations carried out simulating gastric pH clearly showed that the probiotic bacteria, 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 present in the conventional yoghurt has a significant survival in gastric pH range. 𝘓𝘢𝘤𝘵𝘰𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘣𝘶𝘭𝘨𝘢𝘳𝘪𝘤𝘶𝘴 did show good survival abilities in lower acidic (pH 3) range of gastric pH, while a significant growth was observed in pH 4. This study concludes that the conventional yoghurt produced by a leading dairy processing company fulfills its probiotic function in terms of growth and survival under tested conditions specified by the regulations.