Evaluation of the prebiotic effect of oat, rice, and barley bran on growth and activity of ‎‎probiotic bacteria

Introduction: Synbiotic foods refers to food ingredients or dietary supplements includes ‎probiotics and prebiotics in a form of synergism; therefore, synbiotics are mixtures of probiotics ‎and prebiotics that beneficially affect the host by improving the survival and implantation of ‎live microbial dietary supplements in the gastrointestinal tract, by selectively stimulating the ‎growth and/or by activating the metabolism of one or a limited number of health-promoting ‎bacteria, thus improving host welfare (Kelly et al., 2008). Prebiotic compounds are substrates ‎that are not metabolized by host enzymes, but by its microbiota, which provide many health ‎benefits related to the gastrointestinal tract, cardiac metabolism, mental and bone health. Among ‎these are the xilooligosaccharides (XOS), which are emerging prebiotics derived from ‎arabinoxylans, polysaccharides present in cereals such as wheat bran, oats bran, buckwheat ‎bran, rice bran, barley bran (Suman and‏ ‏Sreeja, 2019). These compounds are promising bioactive ‎ingredients for the development of new functional ingredients/ products for food and feed ‎industries. As described by previous studies, prebiotics are non-digestible food compounds ‎stimulate the growth and metabolic activity of probiotic bacteria, in food and in the body and ‎exert positive effects on the survival and activity of probiotic bacteria as well as the health of ‎the consumer (Wilson & Whelan, 2017). The use of cereal bran as agroindustrial waste ‎represents a great sustainable way to minimize the impact caused by its accumulation in the ‎environment, as well as explore its beneficial health properties.Considering the important role of ‎prebiotics in the functionality of the probiotic bacteria and the availability of valuable prebiotic ‎sources in agricultural waste such as cereal bran, the purpose of this study was to investigate the ‎effect of oat, rice, and barley bran on the proliferation and activity of probiotic bacteria, ‎Lactobacillus casei and Bifidobacterium bifidum in milk. Material and methods: In this study, ‎barley (Hordeum vulgare L.) Iranian Nusrat variety, oat (Avena sativa) and rice (Oryza sativa) ‎Iranian Khazar variety (under genetic modification) were prepared from the institute of plant ‎breeding research. Barley, oats, and rice seeds were cleaned, brushed, and then milled using a ‎laboratory mill to obtain white flour, fine bran particles, and coarse bran particles. Then, these ‎three components were separated into coarse bran particles, fine bran particles and white flour ‎using a set of sieves with different meshes. Fine bran particles were used for the experiments. ‎To carry out the fermentation process, the inoculation volume of 10 ml (cell population 1012 ‎cfu/ml) of each bacterial culture was mixed with 90 ml of high-fat milk at room temperature. ‎Then, different percentages of oat, rice, and barley bran powder (2.5, 5 and 7% w/w) were ‎added to the milk medium. Control samples were prepared according to a similar method ‎without using bran. All the prepared samples were placed in an incubator at a temperature of 37 ‎degrees Celsius and the pH was measured at one-hour intervals and fermentation was stopped ‎when the pH reached 4.6. After primary fermentation, all the samples were kept at 4 ºC and the ‎cell survival rate, pH, acidity, amount of vitamins B1, B2, B5, B6, B12 and inulin were ‎determined after 1, 7, 14, 21, and 28 days of storage. All tests were performed in three ‎repetitions and the data obtained in the study were presented as mean ± standard deviation. Data ‎analysis was performed using two-way analysis of variance (ANOVA) and Tukey HSD ‎supplementary test (for pairwise comparisons). Results and discussion: The highest survival rate ‎of Lactobacillus casei and Bifidobacterium bifidum was observed in the samples containing ‎‎7.5% oat bran, rice and barley during the entire storage period in the refrigerator, and ‎Lactobacillus casei had a higher potential for survival than Bifidobacterium bifidum. Barley bran ‎showed more prebiotic activity in stimulating the growth and survival of studied probiotic ‎bacteria, followed by barley bran and rice bran. The highest value titratable acidity was obtained ‎in the samples treated with 5 and 7.5% of the brans, which contained higher bacterial ‎populations than the control and other samples. The content of group B vitamins was ‎significantly higher in the samples containing rice bran, followed by the samples containing ‎barley and oat bran. The amount of inulin showed the highest amount in the treatments ‎containing barley bran and barley bran during the entire storage period. According to the results ‎of this study, the synbiotic milk medium containing Lactobacillus casei and Bifidobacterium ‎bifidum and rice, barley, and oat bran has a positive prebiotic effect on the metabolic activity ‎and survival of the examined probiotic bacteria during the 28-day storage period in the ‎refrigerator compared to the control samples and has caused an increase in the rate of bacteria ‎reproduction, a rapid decrease in pH‏ ‏and an increase in acidity. The content of vitamins B1 and ‎B2 increased more than 2 times, and the amount of vitamin B5 increased by about 1.5 times, ‎and a slight increase in the amount of vitamins B6 and B12 was observed. Conclusion: ‎According to the results of this study, rice, barley, and oats bran have prebiotic activity and ‎stimulate the growth of probiotic bacteria.‎