Temperature and pH Influence on Citric Acid Production from Orange Peels Using Aspergillus niger

Abstract

Orange peels are undoubtedly abundant in nature, given the large volume of fruit juice produced daily across the globe from oranges coupled with ripe oranges consumed seasonally. Apart from juice industries, where they are obtained in cleaned form as raw materials for several products, including pectin and citric acid (CA), the alternative source is the uncleaned, often dry orange peels dumped in the surrounding environment. Arresting the environmental challenge posed by orange peels prompts its utilization in the grinded form to ferment and produce CA at different pH and temperature using 0.5 mL conidial suspension of Aspergillus niger in this study. At 5 days incubation period, Desing Expert 70.0 estimated 73.3% CA optimum yield at pH = 3 and optimal temperature of 70  and whose degree of substitution (DS) and reaction efficiency (RE) of 1.77 and 7.2%, respectively, implied that more citrate groups have been attached to each starch molecule. For increased emulsification, stability, and solubility, the CA produced at the highest DS and RE should be chosen to manufacture other products. Orange peel ripeness, moisture, micro or macro-nutrient contents, inoculum type, extraction method, and fermentation time (in the case of kinetic study) are influential factors to study during CA synthesis critically. Design of the solid-state fermentation technique used in this study at a laboratory scale is thus recommended.