Effect of Controlled Fermentation of Ogiri, on the Nutritional Composition, Mineral Profile, and Sensory Acceptability Using Bacillus subtilis as Starter

Abstract

Ogiri is a traditional African fermented condiment made from oil-rich seeds such as melon (Citrullus vulgaris) or castor oil seeds (Ricinus communis), used as a flavouring in sauces and soups. This study investigated the fermentation characteristics, nutritional composition, mineral profile, and sensory properties of laboratory-fermented ogiri using Bacillus subtilis as a starter culture. Mature melon seeds were purchased from a local seller at Rail-way market in Makurdi, Nigeria. The seeds were cleaned, boiled for 4 h, dehulled, mashed, and aseptically distributed into sterile containers. The samples were autoclaved at 121 °C for 15 min and inoculated with 1 mL of standardized Bacillus subtilis suspension (0.5 McFarland standard). Fermentation was carried out at 28 ± 2 °C for 96 h, with samples collected at 0, 24, 48, 72, and 96 h. Changes in pH and temperature were monitored throughout the fermentation period. Proximate composition and mineral content were determined using standard analytical methods, while sensory evaluation was conducted using a nine-point hedonic scale with ten semi-trained panelists. The pH increased from 6.01 to 7.60, indicating typical alkaline fermentation, while temperature increased from 31 °C to 38 °C before declining slightly to 34 °C at 96 h. Proximate analysis showed that fermented ogiri contained 22.62 ± 0.02 % crude protein, 22.97 ± 0.04 % fat, and 40.72 ± 0.06 % moisture, while carbohydrate content decreased to 8.89 ± 0.04 %. Mineral analysis revealed that zinc (5.12 mg/100 g) was the most abundant mineral, followed by copper (3.33 mg/100 g), sodium (1.23 mg/100 g), iron (1.00 mg/100 g), and potassium (0.44 mg/100 g). Sensory evaluation showed good consumer acceptance with appearance scoring 7.7, aroma 7.5, and overall acceptability 7.1 on the hedonic scale. The results demonstrate that controlled fermentation using Bacillus subtilis enhances the nutritional value and sensory quality of ogiri, confirming its potential as a nutritionally valuable traditional condiment.