Suitability of Common Bean ‘Milk’ as a Nutritious Vehicle for Probiotic Bacteria Calvince

Abstract

In a bid to address the challenges of hard-to-cook phenomenon, oligosaccharides and antinutrients in common beans (Phaseolus vulgaris L.), the goal of the study was to evaluate the ability of selected pro-biotic bacteria in fermenting oligosaccharides and reducing antinutrients in fermented bean milk. The study aimed at determining nutritional and antinutritional composition of pinto, yellow kidney and red haricot dry beans and their corresponding fermented and non-fermented bean milk. The specific objectives of the study were (i) to determine nutritional properties of the selected dry beans and their corresponding milk extracts, (ii) to evaluate growth of probiotic bacteria during fermentation and their survival during storage of fermented common bean milk (iii) to determine the effect of fermentation on the nutritional properties of common bean milk and (iv) to evaluate sensory acceptability of fermented milk extracted from pinto beans, yellow kidney beans and red haricot beans Common bean milk was extracted from local dry grains of three varieties of common beans at the Food Biochemistry Laboratory of Jomo Kenyatta University of Agriculture and Technology. The samples were analyzed for their proximate composition, minerals (iron, zinc, calcium, phosphorus and magnesium), phenolic compounds (tannins, total phenols and flavonoids) and phytates, vitamin B complex (thiamine, riboflavin, niacin, pyridoxine and folic acid) and oligosaccharides. Each of the bean milk samples was inoculated with three starter cultures at 1g/l of sample and incubated at 45°C until a pH ≤4.3 was attained. The enumeration of probiotic bacteria contained in Yoba Fiti® culture was performed on MRS agar, MRS with 0.5% L-cysteine was used to enumerate bacteria contained in ABT® culture while M17 was used to enumerate probiotic bacteria present in YF L-903® culture. The effect of fermentation on chemical composition was determined. Carbohydrates concentration significantly increased in milk extracted from red haricot beans (66.3±0.5 – 77.0±0.2) and pinto beans (62.7±1.3 – 71.2±2.8), but was retained in milk extracted from yellow kidney beans (67.3±1.4 - 68.2±1.4), while crude ash decreased (4.6±0.1 – 1.9±0.1) and crude fiber was not detected. Protein significantly (p<0.05) increased in milk extracted from yellow kidney beans (20.8±1.3 – 26.0±1.7) but was retained in milk extracted from pinto beans while crude fat significantly (p<0.05) increased in all bean milk samples. However, protein reduced in milk extracted from red haricot beans (22.0±0.3 – 17.7±0.2). At the end of fermentation, bean milk fermented with ABT and YF L-903 cultures had colony forming units (CFU) greater than Log10 6, but only milk extracted from pinto beans fermented with Yoba Fiti culture reached the recommended CFUs of Log10 6. Stable survival of probiotic bacteria was found in bean milk samples fermented with Yoba Fiti culture while loss in survival of probiotic bacteria during storage was found in bean milk fermented with ABT and YF L-903 cultures (p<0.05). Bacterial survival in bean milk fermented with YF L-903 was greater than Log10 6 during the 28 days storage in milk extracted from yellow kidney and red haricot beans. Fermentation with any of the three cultures caused significant reduction in raffinose, verbascose and stachyose sugars (p<0.05) in all bean milk samples. It was observed that regardless of the culture used, fermentation caused significant increase in niacin, pyridoxine and folic acid which is an xxi indication that probiotic bacteria could be used for vitamin biosynthesis in bean milk. Overall acceptability was statistically similar (p>0.05) for bean milk fermented with YF L-903 and ABT cultures (3.5±0.3 and 3.7±0.2 in milk extracted from yellow kidney beans, 4.1±0.1 and 4.0±0.1 in milk extracted from red haricot beans and 3.5±0.3 and 3.3±0.3 in milk extracted from pinto beans), while significantly lower sensory scores for overall acceptability, aftertaste and aroma were found in pinto beans fermented with Yoba Fiti culture. The findings from this study provide evidence that the three cultures used for fermentation improved the nutritional characteristics of common bean milk. However, in terms of probiotics, fermentation of bean milk with YF L-903 culture has great potential for commercial utilization since it led to better growth of CFUs and survival of the bacteria during storage to levels that could confer health benefit. Therefore, from the findings of the study it is recommended that (i) fermentation with probiotic LAB should be exploited in development of a nutritious probiotic common bean milk, (ii) specific health benefits of the fermented bean milk should be exploited and (iii) strategies to improve sensory acceptability should be exploited to enable consumer acceptability