Project Abstract

Abstract
Rice husk, a byproduct of rice milling, is a rich source of lignocellulosic materials that can be utilized for various biotechnological processes. This study focuses on the valorization of rice husk for citric acid production using Aspergillus niger through solid-state fermentation. Citric acid is a versatile organic acid with a wide range of industrial applications, including food and beverage production, pharmaceuticals, and cosmetics. Aspergillus niger is a well-known citric acid-producing fungus that has been extensively studied for its ability to convert various carbon sources into citric acid. Solid-state fermentation (SSF) is a promising technology for citric acid production as it offers several advantages over submerged fermentation, including higher product yields, lower water requirements, and reduced energy consumption. In this study, rice husk was utilized as the substrate for SSF to produce citric acid using Aspergillus niger. The process parameters such as moisture content, pH, temperature, and incubation time were optimized to enhance citric acid production. The lignocellulosic composition of rice husk provides a complex carbon source for microbial growth and citric acid production. Aspergillus niger secretes enzymes such as cellulases, hemicellulases, and pectinases that can degrade the lignocellulosic components of rice husk into fermentable sugars, which are then metabolized to produce citric acid. The optimization of process parameters is crucial to maximize citric acid production while minimizing unwanted byproducts. Various analytical techniques were employed to monitor the progress of citric acid production during SSF, including high-performance liquid chromatography (HPLC) for quantification of citric acid, as well as scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) for characterizing the structural changes in rice husk during fermentation. The results demonstrated the efficient conversion of rice husk into citric acid by Aspergillus niger under optimized SSF conditions. Overall, this study highlights the potential of utilizing rice husk as a renewable and cost-effective substrate for citric acid production using Aspergillus niger through solid-state fermentation. The findings contribute to the development of sustainable bioprocesses for value-added chemical production from agricultural residues, ultimately promoting a more circular and eco-friendly economy.

Project Overview

2.0 LITERATURE REVIEW

2.1 Chemistry and Occurrence of Citric Acid

Citric acid or 2-hydroxypropane 1, 2, 3-tricarboxylic acid is an alpha-hydroxyl acid with a three carbon skeleton, which has three carboxylic acid groups (COOH), and one hydroxyl group (Max, et al., 2010), with molecular formula of C6H8O7 and molar mass of 192.12 g/mol., it’s also known as p-hydroxyl tricarboxylic acid is a weak organic acid occurring in high concentrations in citrus fruits (Anastassiadis and Rehm, 2006). It is ubiquitous in nature as it serves as an intermediate in citric acid cycle, where by carbohydrates are oxidized to CO2. The widespread presence of citric acid in animal and plant kingdom is an assurance of its non- toxic nature and it has been used as an acidulant in manufacture of soft drinks, jams and confectioneries (Anastassiadis and Rehm, 2006). Citric acid is found as colorless translucent crystals, odorless, with strongly acid taste. The solid has density of 1.66 g/mL, melting point of 153°C and boiling point of 175°C. It is highly soluble in water to give an acidic, sour tasting solution (Pratiti, 2013). Citric acid is found in large quantities in citrus fruits with lime having the highest concentration of the acid (Pratiti, 2013). In addition to fruits, citric acid is found in all animal species. The citric acid cycle is vital in the oxidation of sugars and acetate to CO2 and water, releasing energy for physiological functions (Pratiti, 2013). The chemical structure of citric acid is presented in Figure 2.1