Effect of Different Fermentation Time on the Microbial, Mineral and Proximate Composition of Parkia biglobosa Seeds Fermented for Iru Production

Abstract

Fermented food condiments form an integral part of African diets as they supply nutrients with claimed medicinal properties. This research was designed to investigate the effect of period of fermentation on the microbial, mineral and proximate composition of fermented Parkia biglobosa seeds. The bacteriological, nutritional and sensory parameters were carried out on the raw, dehulled and fermented seeds. The result of the total bacterial counts showed that the raw seed had 3.67 log10cfu, there was a significant increase in the total bacteria count from 2.20 log10cfu/g in dehulled unfermented bean to 9.248 log10cfu/g at 96 h of fermentation. The bacteria isolated were Bacillus subtilis (32 isolates), Lactobacillus plantarum (9 isolates), and Leuconostoc spp (3 isolates). The pH increased significantly from 4.57 in the raw seeds to 8.40 at 96 h of fermentation. The titratable acidity decreased from 0.179N in the raw seeds until it got to 0.0313N at 96 h of fermentation. The proximate composition on dry mass basis showed that ‘iru’ fermented for 48 h had the highest protein content of 41.023%. The carbohydrate decreased from 42.153% in the raw seed to 20.733% at the end of fermentation. Four of the minerals; lead, cadmium, cobalt and nickel were detected in the raw seeds but were no longer available after dehulling. Phosphorus, sodium, calcium and potassium increased during the fermentation period. The sensory result showed that the intensity of growth on the surface of the fermenting bean increased. Moreover, the sensory score on the texture showed that the seed became softer as the fermentation progressed. The colour became darker and the ammonia odour became more pungent. The overall-liking showed a significant increase as the fermentation progressed where the panelist preferred the product fermented for 72 h. The result from this study revealed that the best time for fermentation of Parkia biglobosa seeds to produce good quality ‘iru’ was between 48 h and 72 h.