Conversion of Corn Waste into Value Added Products

Abstract

Corn waste is an abundant lignocellulosic agricultural waste. The chemical composition of corn waste such as stalks, husks, cobs and leaves was analyzed to get cellulose, hemicelluloses, lignin, fatty and waxy matters, pectic matters and aqueous extract. Corn husk contained higher amount of cellulose (45%), was furnished as the raw material for the production of food-grade carboxymethyl cellulose (CMC). Cellulose was carboxymethylated using sodium hydroxide (NaOH) and monochloroacetic acid (MCA), in aqueous ethanolic medium, under heterogeneous conditions. The carboxymethylation reaction was optimized in terms of DS with respect to the cellulose particle size, NaOH concentration, MCA concentration, reaction temperature and reaction time. By-products of the etherification reaction such as sodium glycolate and sodium chloride were removed in a series of alcohol washes and separations, and sodium salts content in the purified CMC was determined. The degree of substitution (DS) was determined using chemical method. The CMC product had an optimized DS of 2.41 and the optimal conditions for carboxymethylation were NaOH concentration, 7.5 molL-1; MCA concentration, 12 molL-1; reaction temperature, 55°C; reaction time, 3.5 h and cellulose particle size, 74 µm. These optimization factors allowed to prepare highly substituted CMC with higher purity, providing plenty of opportunities for its manifold applications. Qualitative and quantitative analyses of CMC were carried out to determine molecular weight, purity, yield, solubility; water and oil holding capacities, moisture, ash and gel contents. Characterizations of cellulose and CMC were carried out by analyzing the spectra of FTIR, XRD patterns, SEM photomicrographs and TGA thermogram. The molecular structure of the CMC was determined by the analysis of 13C NMR spectra. Microbiological testing of the prepared CMC was done by the pour plate method. Concentrations of heavy metals in the purified CMC were measured by AAS technique and found to be within the WHO/FAO recommended value. Solubility, yield, molecular weight and DS of CMC increased with decreased cellulose particle sizes. A comparative study with CMC available in the international market was conducted. The purity of the prepared CMC was higher, at 99.99% well above the purity of 99.5% for standard CMC. High purity CMC showed yield 2.4 g/g , water holding capacity 5.11 g/g, oil holding capacity 1.59 g/g, ash content 18.05%, moisture content 2.21% & gel content 99.96%. Extensive analysis for potential external contaminants of CMC such as heavy metals (arsenic, lead, cadmium, mercury) and microbial contaminants, such as Total plate count, Yeast and Mold, Colliform, Salmonella and E. coli that are generally associated with food products, suggest either the absence of these contaminants or their presence at very low levels that are considered as safe. Similarly, the presence of processing aids and by-products from the manufacturing are minimized in the final product to levels that are safe for human consumption. The product meets or exceeds the specification or purity requirements of the FCC, USP and JECFA. A study was conducted to assess the toxicity of prepared CMC when administered orally, via dietary admixture, to Swiss albino mice (5/sex/group) at dose levels of 0 (control), 5, 10, and 20 mg/g body weight/day for a period of at least 3 months. Studies were conducted in compliance with OECD principles of Good Laboratory Practice and according to OECD Guidelines 408. Animals were observed for mortality, morbidity, body weight changes, feed and water intake. Urinary, biochemical and haematological assessments as well as body and organ weights of the mice were carried out at every one month. After 3 months of treatment, all mice scheduled for terminal sacrifice were killed and selected organs were weighed. Complete macroscopic examinations and histopathological evaluation of selected tissues were conducted on all animals. No major abnormalities in the histopathology of liver, kidney, heart and lung were detected compared to control group under microscope. This indicated that the compound has no toxic effect on cellular structure. No mortality occurred during the study. Water intake, urine production and urinary sodium, calcium and citrate excretion increased with increasing doses of CMC due to their increasing sodium intake. Body weight, water and food consumption, haematology, clinical biochemistry, behavioural observational assessments and organ weights did not reveal any significant, consistent, dose-dependent test article-related adverse effects. A no observed adverse effect level (NOAEL) from the present study was determined to be 20 mg/g body weight/day for mice under the conditions of this study, the highest dose tested. These findings support the safety of CMC for use as an excipient or as food additives and for pharmaceuticals.