Chemical Composition of Defatted Cottonseed and Soy Meal Products

RESEARCH ARTICLE Chemical Composition of Defatted Cottonseed and Soy Meal Products Zhongqi He1*, Hailin Zhang2, Dan C. Olk3 1 USDA-ARS, Southern Regional Research Center, New Orleans, Louisiana, United States of America, 2 Dept. of Plant and Soil Sciences, Oklahoma State University, Stillwater, Oklahoma, United States of America, 3 USDA-ARS, National Laboratory for Agriculture and the Environment, Ames, Iowa, United States of America * Abstract OPEN ACCESS Citation: He Z, Zhang H, Olk DC (2015) Chemical Composition of Defatted Cottonseed and Soy Meal Products. PLoS ONE 10(6): e0129933. doi:10.1371/ journal.pone.0129933 Chemical composition is critical information for product quality and exploration of new use. Hence defatted cottonseed meals from both glanded (with gossypol) and glandless (without gossypol) cotton seeds were separated into water soluble and insoluble fractions, or water soluble, alkali soluble as well as total protein isolates. The contents of gossypol, total protein and amino acids, fiber and carbohydrates, and selected macro and trace elements in these products were determined and compared with each other and with those of soy meal products. Data reported in this work improved our understanding on the chemical composition of different cottonseed meal products that is helpful for more economical utilization of these products. These data would also provide a basic reference for product standards and quality control when the production of the cottonseed meal products comes to pilot and industrial scales. Academic Editor: Randall P. Niedz, United States Department of Agriculture, UNITED STATES Received: March 24, 2015 Introduction Accepted: May 14, 2015 Cotton (Gossypium hirsutum L.) is produced in more than 30 countries [1] and provides a major fiber source for the textile industry. Much of the cotton land in the US is located in the southern and southeastern region which includes Georgia, Alabama, Arkansas, North Carolina, Mississippi, and Texas [2, 3]. Harvesting and ginning a cotton crop generates two marketable products: lint and seed. Although accounting for about 60% of biomass of cotton bolls, cottonseed products provide only a secondary revenue stream of the cotton crop (15–25% of the value of the crop), and mainly from the oil fraction [4, 5]. The residual fraction after oil crushing, called defatted cottonseed meal, is mainly used as fertilizers or animal feed [2, 5–9]. Thus, enhanced utilization of meal products as industrial and biobased raw materials would increase the profitability of cotton growers and processors. The potential value-added products include but are not limited to wood adhesives [10], bioplastics and films [11], superabsorbent hydrogel [12] antioxidant meal hydrolysates [13], as well as bio-oil and biochar [14]. These functional products differentially utilize the chemical components (e.g., proteins, peptides, and carbohydrates) in meal although expensive purified fractions are not always necessary. Published: June 16, 2015 Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Data Availability Statement: All relevant data are within the paper. Funding: The authors received no specific funding for this work. Competing Interests: The authors have declared that no competing interests exist. PLOS ONE | DOI:10.1371/journal.pone.0129933 June 16, 2015 1 / 13 Composition of Cottonseed and Soy Meal Products For better and economic utilization of the different functional fractions in cottonseed meal, we have separated meal into a water soluble fraction (WSF) and a water insoluble fraction (WIF) [15]. Further work demonstrated that WIF could serve as bio-based wood adhesives [16, 17]. The protein fraction in meal can be extracted by weak base as a whole cottonseed protein isolate (PI), or sequentially extracted into a water soluble protein fraction (PIw) and an alkali soluble protein fraction (PIa) [18, 19]. Fluorescence study has shown that PIw is more hydrophilic than PIa [20]. This observation suggests PIw and PIa may not always behave the same when they are used to prepare a functional product. For example, Nordqvist et al. [21] reported that the wood adhesive per aqueous ethanol (60–70%) soluble gliadin fraction of wheat gluten penetrates to a larger extent and more deeply into the wood material than the adhesive per aqueous ethanol insoluble glutenin fraction of wheat gluten. As chemical composition is critical information for product quality and for exploration of new uses, in this work, we determined the contents of gossypol, amino acids, fiber and carbohydrates, and selected macro and trace elements in these cottonseed meal fractions. For comparison, these parameters in defatted soy meal and its protein isolate were also determined, as soy meal is widely studied as a bio-based raw material [22–24]. Information derived from this work will be helpful in promoting enhanced utilization of these defatted oilseed meal fractions as renewable and environment-friendly industrial resources. Materials and Methods Raw materials Meals from both glanded (with gossypol, Gd)) and glandless (without gossypol, Gl) cottonseeds were used. Gossypol [1,1,6,6,7,7-hexahydroxy-5,5-diisopropyl-3,3-dimethyl(2,2-binaphthalene)-8,8-dicarbaldehyde, or 2,20 -bis-(formyl-1,6,7-trihydroxy-5-isopropyl3-methylnaphthalene)] is a yellow polyphenolic binaphthyl dialdehyde stored in the pigment glands of cotton and a few related species [5, 25]. Three glanded samples came from three expander-solvent processers. Two glandless meal samples were donated by Cotton, Inc. (Cary, NC, USA) and received as partially defatted products. It was re-extracted with hexane at 50°C for 2 h in a rotary evaporator, which was sufficient to reduce the oil content to less than 1%. Soy meal was obtained from Kentwood Co-op (Kentwood, LA, USA). The working soy meal was obtained by grinding the meal in a cyclone sample mill (Model 3010–014, UDY Corporation, Fort Collins, CO, USA) to pass a 0.5-mm steel screen [26]. Preparation of water washed meals and protein fractions The sequential fractionation procedure reported in He et al. [15] was used to separate the whole meal into water soluble and insoluble fractions of both cottonseed and soybean meals. Total protein isolates (PI) of cottonseed and soy meals were prepared by one-step alkali extraction and acid precipitation. PIw and PIa fractions of Gd cottonseed protein were sequentially extracted by water and 0.015 M NaOH, and then precipitated at pH 4.0 and 7.0, respectively [18]. Both fractions were freeze dried and kept in a dessicator at room temperature (22°C) until use. Gossypol in cottonseed samples The gossypol enantiomers in Gd meal and products were detected by a slightly modified procedur (...truncated)