PROJECT TOPICS ON VALORIZATION OF RICE HUSK FOR CITRIC ACID PRODUCTION USING ASPERGILLUS NIGER BY SOLID STATE FERMENTATION

ABSTRACT

The utilization of agro-residues as substrate to generate new products of commercial interest through a bioprocess is considered as an important strategy for the development of sustainable technologies. Citric acid production was carried out from various pretreated (acid, alkaline, hydrogen peroxide and un-pretreated) rice husk by solid state fermentation (SSF) using Aspergillus niger.

Pyridine-acetic acid anhydride method was used for quantitative analysis of the citric acid produced. Placket Burman Design (PBD) was used to screen ten media components ((NH₄)₂SO₄, MgSO₄.7H₂O, NH₄NO_3, KH₂PO₄, FeCl₃.6H₂O, CuSO_4, FeSO₄, ZnSO₄, MnSO₄, and Molasses) required by Aspergillus niger (A. niger) to enhance citric acid production.

Face Centered Central Composite Design (FCCCD) was used to select the most contributing nutrients for the production. Thin layer chromatography, Fourier Transform Infra-Red (FTIR) analysis and melting point determination of both standard and citric acid produced were also carried out. The result obtained from PBD indicated that hydrogen peroxide pretreated rice husk was the best pretreatment method with citric acid yield of 3.65 ± 0.26g/kg RH which is statistically higher (p < 0.05) than that of acid, alkaline and un-pretreated rice husk whose yields were 2.94 ± 0.83^, 1.97 ± 1.24 and 2.34 ± 0.13 g/kg RH, respectively.

Among the media components NH₄NO_3, KH₂PO₄, and molasses were found to be vital in citric acid production using rice husk as a substrate with the optimum concentrations of 2.5g/L, 3.25g/L and 0.2275g/L, respectively with citric acid yield of 4.765±0.001. The coefficient of determination”R²“was found to be 0.9790 and is in reasonable agreement with the “Adjusted R²” of 0.9601 at p < 0.05.

Both the standard and A. niger produced citric acid gave similar Rf value of 0.242 and melting point of 153 ± 0.00 ⁰C and 153 ± 0.02 ⁰C, respectively, wavenumbers corresponding to O-H and C=O of 3338.7 cm^-1and 1565.5 cm^-1 and 3324.8 cm^-1and 1625.1 cm^-1for standard and citric acid produced, respectively. The result of this study has therefore, revealed the potential of rice husk to produce citric acid with similar characteristic to that of standard citric acid. It also showed the importance of using a statistical design like Face Centred Composite Design (FCCCD) of Response surface methodology (RSM) to optimize the production of citric acid using rice husk as a substrate by A niger as it is proved to be a useful tool in establishing optimum conditions for citric acid production.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background of Study

The amount of wastes produced from agro-processing industries is continuously increasing and poses serious environmental problems. This reason leads to many research groups to be investigating the opportunities for the valorization of such residue (Tobias et. al., 2014).

Agricultural residue is any unwanted or unsalable material produced wholly from agricultural operations which is directly related to the growing of crops or raising of animals for the primary purpose of making a profit or for a livelihood (Tobias et. al., 2014). The term “agricultural residue” is used to describe all the organic materials which are produced as by-products from harvesting and processing of agricultural crops.

Agricultural residues, which are generated in the field at the time of harvest, are known as primary or field based residues whereas those that are co-produced during processing are called secondary or processing based residues (Zafar, 2013). Many agricultural residues such as apple pomace (Hang and Woodams, 1984), kiwifruit peel (Hang and Woodams, 1987), orange waste (Aravantinos-Zafiris et. al., 1994), sugar cane bagasse (Shankaranand and Lonsane, 1993), coffee husk (Shankaranand and Lonsane, 1994), carrot waste (Garg and Hang, 1995), pineapple waste (Tran et. al., 1998), cassava bagasse, (Vandenberghe et. al., 1999), pumpkin (Majumdar, et. al., 2010), date syrup (Mostafa and Alamri, 2012), rice straw (Ali et. al., 2012), and oat bran (Raja and Kruthi 2013) were tried successfully as substrates for citric acid formation and under optimum conditions are known to produce good quantities of citric acid.

Rice husk (or hull) is the outermost layer of the paddy grain that is separated from the rice grains during the milling process (Alaric 2013). Rice husk is one of the most widely available agricultural residues in many rice producing countries around the world (Ajay et al., 2012). It has potential application in different field of endeavour which includes; preparation of activated carbons, insulating board material, chopstick production, fuel in power plant, source of silica and silicon compound, etc.

(Ajay et al., 2012). The global rice production in 2015/2016 was 472.04 million tons by the United States Department of Agriculture (USDA), and estimates that the world rice production 2016/2017 will be 480.13 million metric tons. The estimated 480.13 million tons could represent an increase of 8.09 million tons or a 1.71% in rice production around the globe. Paddy, (rice before processing) on an average, consists of about 72 percent of rice, 5-8 percent of bran, and 20-22 percent of husk (Muhammad, 2015). In Nigeria the Federal Ministry of Agriculture and Rural Development (April, 2017) reported that in 2016, total paddy production estimate is put at 17.5 million tons equivalent to 5.7 million tons milled rice.

Citric acid (2- hydroxypropane-1, 2, 3-tricarboxylic acid), is an essential multifunctional weak organic acid, which has wide range of household and industrial applications (Selvankumar, 2014). It is a common metabolite of plants and animals. It exists widely in nature and is one of the organic acids found in juice of lemon, orange, pineapple, plum, peas, and peach. It is also found in animal bones, muscles and blood (Pratiti, 2013). Microbial citric acid is globally used in most of the food and pharmaceutical industries because of its ecofriendliness, biodegradability, and cost-effectiveness (Angumeenal and Venkappayya, 2013).

It has many applications in food, pharmaceutical and cosmetic industries as an acidulant, flavour enhancer, preservative, antioxidant, emulsifier and chelating agent (Soccol et al., 2006). Citric acid is mainly used in food industry because of its pleasant acid taste and its high solubility in water. It is worldwide accepted as “GRAS” (generally recognized as safe), based on approval by the Joint FAO/WHO Expert Committee on Food Additives (Pandey et. al., 2001).Global citric acid production at industrial-scale processes was reported to be 1.7×10⁶ tons annually (Dhillon et al., 2011), and its demand is continuously increasing.

Several microorganisms belonging to the genia Aspergillus sp., Bacillus sp., Penicillium sp., Candida sp., Arthrobacter sp., Corynebacterium sp., have been reported as efficient citric acid producers (Grewal and Kalra, 1995; Schuster et. al., 2002 and Betiku et. al., 2013). Fungus Aspergillus niger has received much attention recently as a potential candidate for large-scale production of citric acid. The rapid growth rate, ability to utilize wide substrates as carbon and nitrogen source, high yield and secretion of different metabolites enhanced the application of Aspergillus niger in fermentation studies (Selvankumar et al., 2014).

The primary uses of Aspergillus niger are for the production of enzymes and organic acids such as citric acid and gluconic acid by fermentation. Perhaps the largest application of Aspergillus niger is described as the major source of citric acid as this organism accounts for over 99% of global citric acid production (Mohsen and Alireza, 2013)Studies by Micheal et. al., (2013), revealed that all the Aspergillus niger strains studied have the potential for citric acid production. Citric acid productivity further increased after strain improvement studies.

Solid state fermentation (SSF) is a fermentation process which is carried out in solid matrix with limited volume of water. Microorganisms especially fungi, can favourably grow in the solid substrate as a carbon source and growth carrier. Solid state fermentation is economical, low water consuming and eco-friendly. It plays an important role and has a great perspective for bioconversion of different agro-industrial residues (Selvankumar et al., 2014)

Recommended : QUALITY AND NUTRIENT ADEQUACY OF CASSAVA-BASED DISHES AMONG HOUSEHOLD IN AGBOBU COMMUNITY OF OKIGWE LOCAL GOVERNMENT AREA OF IMO STATE

1.2 Statement of Research Problem of the Study

Most of the citric acid that is being used in this country today is imported (Betiku et al., 2013), and therefore there is a need for indigenously produced citric acid for domestic and industrial use.

The global demand for citric acid is growing faster than its production, which implies that more economical process is required (Adeoye et. al., 2015). Many residues of agriculture and agro industries can be used for production of citric acid (Pandey et. al., 2000). Therefore, reduction in production cost can be achieved by using less expensive substrates. In addition, the use of agro industrial residues as support materials in fermentation processes is not only economically important, but will also minimize environmental problems arising from improper disposal and handling of agro wastes (Adeoye et. al., 2015).

The current method of producing citric acid via fermentation requires the use of glucose and other soluble sugars which are costly, hence there is need to explore relatively low cost raw material for citric acid production.

PROJECT TOPICS ON VALORIZATION OF RICE HUSK FOR CITRIC ACID PRODUCTION USING ASPERGILLUS NIGER BY SOLID STATE FERMENTATION

1.3 Justification of the Study

Both the continuous growing demand for citric acid and the economics of fermentation encourage the exploration of different technical approaches to use cheap raw materials for citric acid production (Parekh et. al., 2000; Haq et. al., 2003; Husseiny et. al., 2010).

Non-conventional raw materials like rice husk could be used for production of several value added products including citric acid.

This research could serve as source of effective utilization of low cost raw materials (rice husk) as well as using non-conventional substrate for citric acid production.

1.4 Aim of the Study

The aim of this work is to produce citric acid from rice husk as a carbon source using Aspergillus niger by solid state fermentation under optimized media conditions.

1.5 Objectives of the study

1. To determine the best pretreatment method(s) for rice husk to be used as carbon source for the production of citric acid.
2. To optimize the medium components required for citric acid production by Aspergillus niger using rice husk as a carbon source.

• To characterize the citric acid produced from rice husk.

See Also : EFFECT OF AN EXOGENOUS LIPASE ON BACTERIAL UTILIZATION OF PETROLEUM HYDROCARBON