Isolation, characterization and identification of potential probiotic lactic acid bacteria from Malaysian fermented foods / Siti Nasiroh Ismail

Faculty of Industrial Sciences and Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2019

Includes bibliographical references

Probiotics, generally bacteria or yeast are defined as living microorganism with beneficial effects on the host if consumed in sufficient amount. Probiotic products such as food supplement, cultured milk and yogurt commonly found in Malaysian market are manufactured using imported strains. Fewer researches done on potential probiotic isolated from Malaysian fermented foods leads to this study. Therefore, this research aims to identify potential probiotics from Malaysian fermented foods by screening and isolating lactic acid bacteria (LAB), to determine probiotic properties of the LAB, and to evaluate the viability of freeze-dried LAB. The LAB isolated from Tapai, Tempoyak, Pekasam and Jeruk Maman were characterized, following by in-vitro studies to assess the probiotics properties such as acid and bile tolerance, antibiotic susceptibility, hemolytic activity, aggregation activity, coaggregation activity, and antimicrobial assay. The most potential probiotics were identified, freeze-dried, and the effect of freeze drying on survival rate, salt sensitivity, thermal tolerance and storage stability were determined. This study has found that 20 of 250 isolates were confirmed as LAB based on the morphological and physiological properties. All 20 LAB strains showed high tolerance to acid (pH 3) and bile salt (0.6% w/v). Moreover, all LAB were resistant to Vancomycin, a common antibiotic used to treat bacterial infection. Three LAB strains obtained from pekasam (P-8, P-1) and jeruk maman (M-3) were resistant to all eight antibiotics used namely Chloramphenicol, Vancomycin, Tetracycline, Streptomycin, Ampicillin, Kanamycin, Rifampicin and Penicillin. Further analysis showed that all 20 LAB strains did not exhibit hemolytic activity and able to adhere to epithelial cell by showing high percentage of aggregation activity. However, 9 selected LAB showed various degree of coaggregation with Escherichia coli, Salmonella typhi, Vibrio parahaemolyticus, Bacillus cereus and Staphylococcus aureus. Furthermore, the result of antimicrobial activity against the same pathogens also showed various degree of inhibition. In addition, all 9 LAB showed the ability to produce antibacterial agents. P-8 and Ta-1 showed the best inhibitory effects toward five pathogens used. Considering all these properties, P-8 and Ta-2 were chosen as the promising probiotic candidates and were identified as L. plantarum CIP103151 dan JCM1149. It was found that both strains survived >80 % after freeze drying with the addition of skim milk as cryoprotectant. Furthermore, the sensitivity towards salt increased after freeze drying indicated that the cells were damaged during freeze drying. The results also showed that L. plantarum CIP103151 was tolerant to 55 and 65°C, while JCM1149 has shown tolerance to 55°C, 65°C and 75°C after exposure for 0, 30, 60, 90 up to 120s. The freeze-dried LAB was notably stable during storage at 4°C and 30°C for 360 days. Therefore, P-8 and Ta-2 have showed the most promising potential probiotics with excellent stabilities during storage.