Abstract

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The high demand for citric acid by many industries cannot be over emphasized. Presently, 70 % of the total citric acid produced globally is consumed by food industries, 12 % by pharmaceutical industries and the remaining 18 % by other industries. Moreover, rapid increase in food/beverage industries in Nigeria with no known company producing citric acid in Nigeria makes its scarcity severe. Cassava peels from cassava processing industries and lemon peels are abundant. Surface fermentation method was employed in production of citric acid at varying pH from 3.0 to 4.5. Physico-chemical properties and Fourier Transform Infra Red spectroscopic analysis were conducted using standard methods. The kinetics of the production process was also determined. The yields and physico-chemical properties of the citric acid obtained from both substrates were comparable to that of commercial citric acid. The yields obtained from cassava peels are lower when compared to those from lemon peels when the same quantities were used. The optimum yield obtained from lemon and cassava peels after 192 h of fermentation at optimum pH 4 were found to be 34.4 g/kg and 32.7 g/kg respectively. The infra red spectra of citric acid produced from cassava and lemon peels showed bands at 3497, 3290 and 3288 cm-1 depicting hydroxyl group bonded to carboxyl. The 1750 cm-1 carbonyl band was observed for both peels. There was increase in percentage yields of citric acid over 48 – 192 h fermentation periods for pH range of 3.0 – 4.5. The kinetics of the production process was observed to follow a pseudo-second order as it gave best fit compared to other models used. The range of pseudo – second rate constant fell within 1.045 x 10-3 – 2.411 x 10-3 kg/g.hr for pH range of pH 3.0 – 4.5 for lemon peels while that of cassava peel ranged from 1.071 x 10-3 to 98.91 x 10-3 kg/g.hr for pH 3.0 – 4.5 range. The possibility of production of citric acid in Nigeria from lemon and cassava waste peels could reduce importation of this product by industries and thus save enough revenue for the country.

Keywords: Citric acid, fermentation, kinetics, yield, physico-chemical properties