Microbial succession during the fermentation of blends of watermelon and tigernut

Abstract

Tigernut tubers (Citrullus lanatus) and watermelon fruits (Cyperus esculentus) are popularly consumed in Nigeria. This study investigated microbial succession occurring during the fermentation of tigernut and watermelon blends. The substrates were washed and ground into a homogenous pulp. The pulp was evenly divided into three sterile fermenters containing three litres of the blended substrates. The mixtures were allowed to ferment spontaneously (chance inoculation) for 5-days (primary fermentation). The mixtures were then sieved with a muslin cloth and transferred into a secondary fermenter, and fermented for 4 weeks. The fermented samples had an initial pH of 6.51 ± 0.00, 6.43 ± 0.00, 6.67 ± 0.00 which reduced towards the end of the fermentation to 3.15 ± 0.00, 3.16 ± 0.00, 3.22 ± 0.00 in the samples. The bacterial count ranged from 1.2 x 105 to 5.0 x 105, 3 x 104 x 4.0 x 105 3 x 104 to 6.8 x 105 CFU/mL for the samples. There was a significant reduction in sugar content after fermentation of the blends. At the early stages of fermentation, organisms from the genus Clostridium, Bacillus, Lactobacillus, Corynebacterium, Gluconobacter, Pseudomonas, Streptococcus, Candida and Saccharomyces were present within the first twenty-four hours of fermentation although Lactobacillus plantarum, Bacillus species, Pseudomonas aeruginosa and Saccharomyces cerevisiae were identified as completing the fermentation process. There was a variation in the total sugar content of the mix after fermentation. This study highlighted the microbial succession pattern in watermelon and tigernut fermentation.