Production and optimisation of citric acid by yeasts isolated from Kola nut pod husk.

Abstract

Citric acid is an organic acid commonly used in food, pharmaceutical, chemical industries.Citric acid is a weak acid found in nearly all tissues; both in plants and animal and it is generally regarded as safe. The work aimed to obtain yeast isolates capable of citric acid production from kola nut pod waste and to know optimum conditions that favour higher citric acid production. One hundred twenty seven (127) isolates were obtained out of which 46 were selected following primary screening for production of citric acid on compounded solid media. Nine (9) of these yeasts that had the highest potential for citric acid production having the largest acid production zones after primary and secondary screening were selected. KI8 identified as Candida rugosa, KI8 identified as Pichia kudriavzevii and KF16 identified as Rhodotorula rubra using molecular methods. Three (3) isolates with the highest citric acid were used for citric acid production and optimization. Box-Benkhen design was the statistical technique used for optimization of the experimental factors. Four factors:pH, carbon source (g/L), nitrogen source (g/L) and temperature were tested as the variables affecting citric acid production using Box-Benkhen design. The results showed that pH (5.0), glucose concentration (7.5 g/L), ammonium sulphate concentration of (1.5 g/L) and temperature (30 °C) were the best conditions for the highest yield of citric acid. The yield of citric acid yield was high at 17.8 g/L under the optimized conditions. Crude citric acid (4.00 g) was crystallized from the production medium. The citric acid recovered after recrystallization was 3.10%. The recovery was 78%. Hence, citric acid production through fermentation by yeasts can greatly increase acid availability for its various industrial applications.