Quality and microbiological study of bambara groundnut fortified injera, a fermented flat bread

Abstract

Cereal fermented products are popular in developing countries, especially in Asia and Africa, because of their unique taste and fulfilment. Throughout the years, they have played a vital part in bringing up infants as part of their weaning foods and contributing to the daily diet of many households. Food fortification and supplementation of cereal grains with inexpensive readily available legumes, which have higher protein content compared to cereals may lead to a potential decrease in protein-energy malnutrition. Underutilised and indigenous crops such as Bambara groundnut can be in incorporated into the fermentation of cereal fermented foods, such as injera. In this study, injera was prepared by substituting only 9% and 12% Bambara groundnut flour and comparing them with the traditionally fermented original control, which is injera made from only tef flour. The first part of the study was to identify and characterise the lactic acid bacteria (LAB) and yeast involved in the spontaneous fermentation of traditional tef-injera and the newly developed injera fortified with Bambara groundnut (which contains 12% Bambara groundnuts) at different fermentation intervals of 0, 24, 48, and 72 hour. A total of 70 LAB isolates and 30 yeast isolates were identified from both fermentations using rep-PCR fingerprinting followed by sequencing the 16S rRNA gene and the D1/D2 region of the 26S rRNA gene. Weissella confusa, Lc. lactis and Lb. curvatus predominated in both fermentations at different intervals of the fermentation. The second part of the study investigated the effectiveness of the isolated LAB starter cultures on the production of injera and injera fortified with Bambara groundnut after which their physicochemical properties were evaluated. There was a significant increase (p<0.05) in titratable acidity and a significant decrease in pH to below four within 24 hours; recorded for samples inoculated with LAB starter cultures when compared to samples fermented without inoculation. The third and fourth parts of the study investigated the proximate composition and storage stability of the injera samples. Injera fortified with 12% Bambara groundnut + LAB culture had a significantly high (p<0.05) protein of 23.21%, the lowest protein content being Tef injera at 7.35%. The protein digestibility of Tef injera increased with the addition of Bambara groundnut and LAB starter culture. The digestibility of protein increased from 40% for Tef injera to 80% for injera fortified with 12% Bambara flour + LAB culture. There was no significant increase (p >0.05) in the amino acid content after the addition of Bambara flour + LAB cultures; the amino acid concentrations were slightly lower than the standard concentration recommended by the Food and Agricultural Organisation/World Health Organisation for adults. Injera samples fortified with Bambara groundnut flour and inoculated with lactic acid starter cultures were stable with microbial counts ranging from 4.42 log cfu/g to 4.68 log cfu/g for TPC at 4 ̊C, yeast and mould, coliforms and aerobic spore formers were not detected in all the samples from day 0 to day three upon storage. Higher counts had been perceived at room temperature ranging from 4.60 log cfu/g to 7.53 log cfu/g for moulds and 4.90 log cfu/g to 9.26 cfu/g for TPC; coliforms were detected in one tef injera only ranging from 4.48 log cfu/g to 6.16 log cfu/g and no detection of aerobic spore formers in all samples. Refrigeration temperatures effectively maintained the microbiological quality of injera for three days. The nutritional quality, distinctively the protein content increased with the addition of Bambara groundnut flour and through the use of lactic acid bacteria as a starter culture This will potentially pave the way for the commercialisation of injera in the industry with the use of LAB starter culture to ensure a fast and continuous supply of fresh injera that is in high demand.