Effect of Lactic Acid Bacteria Fermentation on the Nutritional and Anti-nutritional Content of Soaked and Boiled Whole Red Haricot Bean (Phaseolus vulgaris L.).

Abstract

Common beans are a leguminous plant of the genus Phaseolus. They are grown worldwide making them easily available and affordable. In addition to providing high protein, energy and minerals, their consumption confers health benefits ranging from lowering blood cholesterol, maintaining blood glucose balance, alleviating constipation and contributing to the improvement of the gastrointestinal microbiome. Utilization of common bean has however been poor due to high anti-nutrient content that results in reduced carbohydrate and protein digestibility and mineral bioavailability. Flatulence after consumption is also a huge deterrent to bean consumption. Fermentation is a food processing technique that uses microorganisms and their enzymes to break down complex food structures resulting in desirable nutrient and compositional changes as well as detoxification of foods. Lactic acid fermentation is the most common form of food fermentation with the Lactobacilli spp dominating most spontaneous food fermentations. The objective of this study was to determine the effect of Lactic acid bacteria (LAB) on the nutritional, anti-nutritional and flatulence causing oligosaccharides composition of red haricot bean. A factorial research design was used in the study. Red haricot beans were sorted, soaked overnight and boiled for 60 minutes. The soaked and boiled beans were fermented in salt-only and salt-sugar solutions at 2% solute concentration for 120 h. Experimental batch was inoculated with Lb. plantarum BFE 5092 and the control batch spontaneously fermented. Microbial growth and pH were monitored during the fermentation. After fermentation, the beans were dried and milled and the flour subjected to proximate and anti-nutrient composition analysis. Analysis of variance was done using SPSS statistics 23. Salt-sugar solutions lowered pH significantly (P<0.05) after 72 h of fermentation whereas salt-only solutions recorded a slow decline with fermentation time. The total aerobic bacteria and LAB counts significantly increased (P<0.05) with fermentation time. Coliform counts decreased significantly (P<0.05). Yeast and mold were not detected in all the batches. Fermentation of the boiled beans increased ash and protein content and lowered the crude fiber, and carbohydrate content. Soaking and boiling lowered the tannin content to 306.82 mg/100 g and 274.78 mg/100 g respectively. Fermentation further lowered them to 109.50-54.04 mg/100 g and 97.07-68.47 mg/100 g respectively. Phytic acid content decreased significantly after soaking and boiling to387.25 mg/100 g and 350.11 mg/100 g respectively. Fermentation further lowered the phytate content to 242.52-163.43 mg/100 g and 160-109.07 mg/100 g in the soaked and boiled beans respectively. Spontaneous fermentation resulted in more phytate and tannin reduction. Soaking and boiling lowered stachyose and raffinose content. Fermentation of soaked beans resulted in up to 35.82% and 42.63% loss of stachyose and raffinose respectively. Fermentation of boiled beans resulted in up to 76.53% and 78.56% decrease in stachyose and raffinose respectively. Salt-sugar solution provided the best condition for growth of LAB which dominated the fermentation, lowered pH and suppressed growth of coliforms. Spontaneous fermentation resulted in more anti-nutrient and oligosaccharide loss compared to inoculation with Lb. plantarum BFE 5092. Fermented boiled beans recorded higher anti-nutrient losses.