The antimicrobial effect of Corn Steep Liquor (CSL) was investigated over a five day period. The pH and titrable acidity of the liquor were determined, while the antimicrobial effect on some diarrhoea causing organisms such as Escherichia coli, Salmonella enteriditis, Staphylococcus aureus and Vibrio parahaemolyticus was also determined. Using well diffusion method, 0.1 ml (100 l) of the liquor effectively inhibited the growth of the test organisms with zones of inhibition ranging from 4.00 ± 0.28 to 20.20 ± 0.14 mm. The zones of inhibition increased with increasing number of days of fermentation of the filtrate on which is the CSL. However, there was no significant difference (P>0.05) in the antimicrobial properties of the liquor on day 3 and 4 for S. enteriditis, S. aureus and V. parahaemolyticus. The zone of inhibition on day 5 was significantly different (P<0.05) from all other days except in S. enteriditis whose zone of inhibition was not significantly different from day 4 and 5. The degree of inhibition was highest in E. coli (20.20 ± 0.14 mm), followed by V. paraheamolyticus (18.50 ± 2.12mm); while S. enteriditis showed the minimum degree of inhibition to the CSL (13.20 ± 0.28 mm. The total microbial count and the titrable acidity of the liquor increased with increasing number of days and reached a peak on day 4 (355.60 ± 21.07 cfu/ml and 23.25 ± 2.05%, respectively). The pH however decreased with number of days. The result suggests that corn steep liquor which is considered a waste inhibits the growth of some diarrhoeic microbes especially by day four of fermentation.
Volatile compounds (VOCs) and associated microbes of ogi at varying soaking and fermentation periods were detected with the aid of Gas Chromatography-Mass Spectrometry (GC-MS) and cultural methods, respectively. Thirty-five (35) VOCs were identified and classified into Carbonyl, Alcohol, Aldehydes, Esters and Organic acid. The average amount of volatile compounds of Ogi produced at varying period (16 and 24 h) varies significantly. Twelve (12) of the detected VOCs had higher concentration and the principal components analysis (PCA) revealed that few of the identified VOCs contributed significantly to the characteristic attributes of Ogi. The first principal components (PC1) had Eigen values of 15.33 (43.80%) and 17.84 (51%) while the second principal components (PC2) had Eigen values of 12.57 (35.90%) and 9.67 (27.60%), respectively. Presence of different species of Candida and Lactic Acid Bacteria (LAB) isolates at different fermentation levels (0 to 48 h) of Ogi was established. The population of LAB and yeast increased with rate of fermentation from 0 to 24 h but remained constant at 36 and 48 th h of fermentation. The isolated LAB include Pedicoccus spp, Leuconostoc spp, Lactobacillus acidophilus, Lactococcus spp and other Lactobacillus spp. while the Candida spp present in the Ogi samples include; Candida krusei, Candida glabrata, Candida parasilosis, Candida albicans, Candida tropicalis and Candida kefyr. Candida spps exhibited a varying temperature for growth while growth of LAB ceased at temperature above 45 o C but not below 15 o C. Molecular identification further revealed the following LAB; Lactobacillus pentosus strains, Lactobacillus fermentum strains, Pediococcus pentosaceus strains and Weissella confusa strains, while dominant yeast were Candida tropicalis strains, Candida auris isolate, Candida glabrata strain, Pichia kudriavzevii culture, Candida albicans strain and Issatchenkia orientalis strain. This study revealed that LAB and Yeast are actively involved in the fermentation of ogi. The fermentation condition and the identified microorganism evidently contributed to the amount and types of VOCs detected. Practical application The consumers" acceptance of Ogi slurry is predominantly hinged on the aroma, flavour and taste. Sensory acceptability is indirectly or directly connected to the concentration of volatile compounds of the product. The processing conditions (fermentation periods) stand the chance of playing very important role in the types and concentration of these volatile compounds. The knowledge of the volatile compounds will be useful in monitoring Ogi"s freshness and quality and subsequently may be of commercial interest, most especially with the identified Lactic Acid Bacteria and yeast and the detected volatile compounds. This information may be of commercial interest if the predominant volatile compounds detected in Ogi are to be synthesized artificially.
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