Naturally fermented milk from Indonesia: a study of microbial diversity and probiotic potency for the potential treatment of intestinal mucositis

Abstract

Naturally fermented milk (NFM) is prepared from fresh milk which is fermented spontaneously, without any inoculation of starter cultures. With increasing interest in novel dairy products, naturally fermented milks have become of interest to food microbiologists as a result of their potential as technologically important microorganisms. Dadih is a well-known naturally fermented milk product developed by local people in West Sumatra, Indonesia. This product is manufactured using unpasteurized buffalo milk which is then fermented spontaneously at ambient temperature. Dangke is prepared from heat-treated buffalo milk, and then processed enzymatically utilizing papain from papaya latex. Identification and characterization of the indigenous microbiota is essential for understanding how the microbial ecology impacts on the organoleptic, safety and potential health benefits of dadih and dangke. In addition, the presence of probiotic microorganisms in these products was also evaluated by investigating their potential to reduce the severity of chemotherapy-induced intestinal mucositis in rats. Probiotics have been defined as ‘live microorganisms that, when administered in adequate amounts, confer a health benefit on the host’ (Hill et al. 2014). Lactic acid bacterial (LAB) groups detected using culture-dependent techniques in dadih were Lactobacillus plantarum, Lactococcus lactis subsp. lactis, and Enterococcus faecium (Chapter 2). Only one species of acetic acid bacteria was found, namely Acetobacter orientalis, while yeasts isolates were identified as Saccharomyces cerevisiae, Candida metapsilosis and Kluyveromyces marxianus, with C. metapsilosis as the principal yeast (Chapter 3). Other bacteria detected included Klebsiella oxytoca, Klebsiella sp. and Bacillus pumilus. Among these bacteria, L. plantarum was the most frequently isolated LAB from dadih, followed by L. lactis subsp. lactis. Indigenous microbiota detected in dangke were relatively similar to dadih (Chapter 2). However, E. faecium and B. pumilus were not found in dangke. Lactococcus lactis subsp. lactis was the most predominant LAB, while S. cerevisiae was the most frequently isolated yeast (Chapter 3). Moreover, based on a culture-independent method (pyrosequencing), genus Lactococcus had the greatest relative abundance in dadih. Based on pyrosequencing results, a more diverse population of mesophilic LAB was found in dangke sourced from cow’s milk; while family Enterobacteriaceae dominated dangke samples from buffalo milk. Lactobacillus plantarum S1.30 isolated from dadih demonstrated probiotic properties which included tolerance to low pH and bile salts, antimicrobial activity and the presence of a bacteriocin regulating gene (plantaricin A) and msa and bsh genes, susceptibility to antibiotics and ability to adhere to Caco-2 cells (Chapter 4). From these probiotic features, only antimicrobial activity and the presence of msa and bsh genes were not demonstrated by L. lactis subsp. lactis SL3.34. However, from the pyrosequencing results, this strain was selected as the representative of the dominant genus/species in dadih. The efficacy of probiotics evaluated in the present study was variable at treating 5-fluorouracil (5-FU)-induced intestinal damage in vivo (Chapter 5). The results suggested that L. plantarum S1.30 and L. lactis subsp. lactis SL3.34 could have beneficial effects through partially improving metabolic parameters such as water intake, urine output, food intake, and fecal output in 5-FU challenged rats. The severity of damage in the jejunum and ileum was also reduced following probiotic culture treatment. In conclusion, this insight into the microbial composition of dadih and dangke will assist in the development of sustainable and technologically feasible starter cultures with probiotic properties. This information has the potential to enhance human health, food safety and food security from locally produced traditional fermented milk products.