Project Abstract

Abstract
Rice husk is a major byproduct of rice milling and its disposal poses environmental challenges. However, rice husk is rich in cellulose and hemicellulose, making it a potential substrate for citric acid production through solid-state fermentation. Aspergillus niger is a well-known citric acid producing microorganism that can thrive in solid-state fermentation conditions. This study aims to valorize rice husk for citric acid production using Aspergillus niger through solid-state fermentation. The research involves optimization of various process parameters such as moisture content, pH, temperature, and inoculum size to enhance citric acid production. Additionally, the impact of different pretreatment methods on rice husk to improve its enzymatic digestibility and subsequent citric acid yield will be investigated. The study will also explore the kinetics of citric acid production, substrate utilization, and fungal growth during the solid-state fermentation process. Analytical techniques such as high-performance liquid chromatography (HPLC) will be used to quantify citric acid production and identify any potential byproducts. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) will be employed to analyze the structural changes in rice husk before and after fermentation, providing insights into the degradation of lignocellulosic components. The economic feasibility of citric acid production from rice husk will be assessed to determine the overall viability of the process. This will involve cost analysis, energy consumption estimation, and comparison with traditional citric acid production methods. The environmental impact of utilizing rice husk as a substrate for citric acid production will also be evaluated to understand the sustainability aspects of the proposed approach. Overall, this research aims to provide a comprehensive understanding of valorizing rice husk for citric acid production using Aspergillus niger through solid-state fermentation. The findings of this study could contribute to the development of sustainable bioprocesses for citric acid production, utilizing agro-industrial waste streams. This research could have implications for the bio-based economy by converting a waste product into a valuable biochemical with potential industrial applications.

Project Overview

CHAPTER TWO

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