Assessment of Probiotic Potential of Nepalese Nak Cheese and Development of Probiotic Yoghurt
Katawal I., Poudel B.H. Kharel G.P.
Central Department of Biotechnology, Tribhuvan University, Kirtipur, Kathmandu, Nepal.
Abstract: Dairy products such as cheese, yoghurt, butter are the most prominent source of probiotic microorganisms. Nepal was the first country in Asia to make any Western-style cheeses, and until the 1980s certainly the only Asian country making Nak Cheese (McGee, 2008). Though being an essential component of regular diet for people of higher altitudes, nak cheese has not been assayed for its probiotic potential. The objective of this study was to isolate different probiotic LAB from nak cheese produced in Nepal and develop probiotic yoghurt using the isolates. Three nak and a cow cheeses were collected randomly from regional factories of Dairy Development Corporation (DDC) in Nepal, located at altitude of 2900 m, 2600 m, 2400 m and 1900 m, respectively. Total probiotic Lactic acid bacteria (LAB) present in these cheeses enumerated on MRS media with 0.25 % bile salts were lower than 106 cfu/g. The total LAB population were negatively affected by the ripening duration of cheese. Total of 32 colonies on MRS media with 0.25 % bile salts were assayed for their ability to tolerate pH 3.0 for 3 h, 0.25% bile salts for 4 h and show antibacterial activity against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa respectively. Only 12 isolates were able to meet all the 3 selection criteria. These potential probiotic isolates were presumptively identified as Streptococcus thermophilus based on morphological observation and biochemical tests. Under identical laboratory conditions 3 yoghurt types were prepared from 3 Streptococcus thermophilus obtained from nak cheeses, 2 from cow cheese and a commercial probiotic LAB i.e., Bifidobacterium animalis (BB-21) respectively. The stability of yoghurts prepared from S. thermophilus was higher than yoghurt prepared from the BB-21 whereas viability of S. thermophilus was higher than BB-21 in the yoghurts during 7 days of refrigeration. All the 3 yoghurts received similar preferences by the untrained panelist during sensory evaluation. Thus, nak cheese doesn’t meet the recommended minimal population of 106 -107 cfu/g for any probiotic strain of LAB in a product at the end of shelf-life (Miller, 2004) to have their functional aspects but it was found to have predominant presence of Streptococcus thermophilus species at its latter stage of maturation. Therefore nak cheese may not be considered a potential source of different probiotic bacteria other than Gal+ strains of Streptococcus thermophilus. The health benefits conferred by the probiotic bacteria isolated from cheese can be delivered through short shelf-life products such as yoghurt.
Keywords: Functional food, Nak cheese, LAB, Probiotics.
Pages: 71 – 79 | Full PDF Paper