Short communicationApplication of in vitro methods for selection of Lactobacillus casei strains as potential probiotics
Introduction
The science of probiotics, live microbial cultures which, when ingested in sufficient numbers, provide beneficial effects to the consumer beyond basic nutrition (Schaffsma, 1996), may be traced to Metchinikoff in 1907. The characteristics of a successful probiotic are acid and bile tolerance, antimicrobial activity against intestinal pathogens, and ability to adhere and colonize the intestinal tract. Probiotic organisms include Lactobacillus, lactococci, bifidobacteria and Saccharomyces with several species of the first listed genus the most studied. Beneficial effects include control of diarrhea (Reddy et al., 1998), alleviation of lactose intolerance (Fonden et al., 2000), inhibition of intestinal pathogens (Bhatia et al., 1989). Other effects studied include reduction in cholesterol level (Agarbaek et al., 1995), enhanced immune response (Kimura, 1997) and antimutagenic and anticarcinogenic activity (Fuller and Gibson, 1997). Lactobacillus casei has been used successfully as a probiotic in traditional milk products, as well as cheeses and a number of commercial fermented food products. The present study aimed to apply in vitro methods for selection of suitable strains of L. casei for use as probiotics and incorporation in Dahi, a popular traditional lactococcal fermented milk product of India.
Section snippets
Lactobacillus cultures
L. casei ssp. casei 17, 19 and 63 were procured from National Collection of Dairy Cultures (NCDC), NDRI, Karnal. L. casei ssp. casei VT was a gift from Dr. Hans Heilig, Wagnenigen University and Research Centre, The Netherlands. Other L. casei strains viz. C1, C2 and Y were isolated from milk and milk products in Quality Assurance Laboratory of Dairy Microbiology Division, NDRI, Karnal. The strains were characterized by cell morphology, colony appearance, biochemical methods and substrate
Tolerance to simulated human stomach pH
The survival of L. casei strains at pH 1, 2 and 3 was observed for 0, 1, 2 and 3 h (Table 1). While none of the strains survived at pH 1 for any time period (data not shown), only strains NCDC 17, isolate C1 and Y could survive pH 2 for 1 h. All seven strains except for NCDC 17 showed consistency in terms of tolerance to pH 3. The residual counts were more than 107 cfu/ml even after 3 h of incubation. Survival at pH 3 was promising for all strains but not at pH 2. Survival at pH 3 is
Conclusion
The present investigation was undertaken to identify suitable probiotic L. casei strains for incorporation in Dahi, a lactococcal fermented milk product of India. The strains varied in ability to tolerate acid and bile, adherence properties and cholesterol assimilation which indicate that selection of probiotics has to be carefully undertaken. In the present study L. casei C1 and Y, both isolates from milk products, showed promising results for both acid tolerance and adherence properties.
Acknowledgements
The authors acknowledge Dr. Hans Helig, Wageningen University and Research Centre for providing L. casei VTT E/85225 strain and suggestions made by Dr. William Charteris during the course of study.
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