Effects of mutant and non-mutant strains of Bacillus subtilis to produce ogiri from Citrullus vulgaris seeds on their microbial diversity and physicochemical properties

Abstract

The desire for safe and natural seasoning is increasing as a result of side effects associated with artificial seasonings. Ogiri, one of such natural seasonings is a fermented product with different substrates in Africa, especially West Africa. Isolated Bacillus subtilis strains from fermented Citrullus vulgaris were exposed to different Ultraviolet (UV) irradiations and Sodium Dodecyl Sulphate (SDS) at varying intervals of time to obtain mutant strains. Eight (8) mutant strains of B. subtilis that produced high D-ribose metabolites were used for controlled starter-fermentation of C. vulgaris for 5 days to produce ogiri. The non-mutant (NMS00) and the market (RTE00) served as control samples. Microbial ecology (load and occurrence) and colour characteristics of the samples were determined. The pH increased with the fermentation period from 4.08 {+/-} 0.01 to 9.86 {+/-} 0.01, while the total titratable acidity fluctuated with the fermentation days. The microbial count increased from 1.0 x 103 cfu/g to 5.2 x 104 cfu/g. B. subtilis was mainly isolated from ogiri samples fermented with mutant strains, while other microorganisms were isolated from samples NMS00 and RTE00. Sample fermented with a mutant strain of B. subtilis exposed to inoculating chamber UV light for 90 sec (MIC67) was closer to sample RTE00 in colour measurements. Some of the ogiri produced from mutant strains of B. subtilis had improved colour characteristics and were not characterized by spoilage or pathogenic microorganisms associated with the market sample. Therefore, could be incorporated into food systems. ImportanceGenetic modification of Bacillus subtilis strains for the fermentation of Citrullus vulgaris seeds to produce a food condiment (ogiri), which modified and controlled the kind of microbial load, occurrence and isolations during the fermentation. This prevented pathogenic microorganisms proliferation that usually characterized traditional way of its production. The behavioural coordination of pH and the total titratable acidity during fermentation reflected on the availability of the microbial metabolism to improve the fermentation rate. Furthermore, it was revealed that the colour measurements of some samples fermented with mutant strains of Bacillus subtilis, which is usually used to determine food acceptance were improved and better than the control samples. Introducing a natural seasoning to serve as functional food in combating the side effects of consumption of artificial seasoning linked to harmful effects that has become a global cause of health issues, which necessitated this research, aside serving as a low-cost protein substitute.