CHARACTERISATION AND PROBIOTIC POTENTIAL OF LACTIC ACID BACTERIA AND YEAST ISOLATE FROM WHOLEGRAIN MILLET SOURDOUGHS

Abstract

The need to provide scientific data to back up the claims on the health functionality of sourdoughs produced from wholegrain millet; a neglected and under-utilized species by evaluating its probiotic potentials necessitated this research. Four species of millet were used for this study. Finger millet, brown fonio and white fonio were obtained from a local market in Zaria, Kaduna State, while pearl millet was purchased from Owena market, Osun State, Nigeria. The sourdoughs were analysed for physicochemical properties, isolation of dominant strains of lactic acid bacteria (LAB) and yeast, the isolates were tested for bile salt tolerance, acid tolerance, antimicrobial and antibiotic abilities. The breads produced were subjected to sensory evaluation. The moisture content of the flours ranged between 7.48% and 11.20%, crude protein was from 9.53% to 12.4%, total ash between 2.13% and 2.78%, crude fibre (0.82% and 2.87%) and crude fat between 2.10% and 4.67%. The total titratable acidity (TTA) between 1.00 ml and 2.13 ml, diacetyl production between 234.4 mg and 437.6 mg and hydrogen peroxide production between 0.50 mM and 1.62 mM. The LAB counts ranged between 2.0 × 107 cfu/g and 4.9 × 107 cfu/g and the yeast counts between 3.0 × 106 cfu/g and 9.4 × 106 cfu/g. A total of 127 isolates were identified on the de Man Rogosa Sharpe (MRS) agar plates according to morphological characteristics and a total of 16 isolates were characterized using API 50 CHL kits with respect to dominance in the fermentation process. The following organisms were identified; Lactobacillus plantarum, Pediococcus pentosaceous, Lactobacillus pentosus and Lactobacillus brevis. On the Malt Extract Agar (MEA) plates, a total of 74 isolates were identified and from phenotypic identification using API 20 C AUX kits 8 of the isolates were characterized as Saccharomyces cerevisiae, Candida utilis, Candida famata, Candida parapsilosis, Candida zeylanoides, Cryptococcus humicola and Rhodoturola minuta. The 16 isolates of LAB and some of the yeast showed reasonable tolerance to bile salts and acid under conditions simulating the gastrointestinal tract (GIT). Since pH 3.0 is the recommended pH and the residence time for food in the stomach is 3 h, 7 strains (LAB) revealed best tolerances to this acidic condition and only Lp3B showed weak tolerance to bile salt at 0.3% concentration. All the yeast except YFCP showed reasonable tolerance to this environment, while isolates YPCU and YBCF revealed weak tolerance to bile concentration of 0.3%. It was also observed that all the isolates of LAB were resistant to antibiotics (gentamycin, ampicillin, rifampicin and norfloxacin). Antimicrobial activities of the sourdoughs and LAB exhibited clear zones of inhibitions against all the tested pathogenic organisms, and S. cerevisiae had the highest zone of inhibition against Klebsiella spp, while Rhodotorula minuta inhibited Pseudomonas spp and Staphylococcus spp with inhibition zones of 16 and 22 respectively. From the results obtained all the isolates of LAB, together with yeast isolates of S. cerevisiae, R. minuta and C. humicola can be considered as potential probiotics