Extraction, Modification, and Chemical Characterization of Protein and Dietary Fiber from Camelina Sativa

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Extraction, Modification, and Chemical Characterization of Protein and Dietary Fiber from Camelina Sativa

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2018-07

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Abstract

Camelina sativa, a sustainable short-season cover crop, is an oilseed (35% oil) gaining interest due to the increasing global demand for sustainably sourced ingredients. Camelina provides numerous agricultural benefits—low production cost, low nitrogen requirements, drought resistance, cold weather tolerance, and short growing season—in addition to being high in protein (20%) and dietary fiber (30%), which are two of the fastest growing segments of the food ingredient market. In order to create functional, market-viable ingredients from camelina, the following need to be explored: efficient means of protein extraction, evaluation of protein functional properties, and chemical characterization of the dietary fiber constituents. The objectives of this study were as follows: (1) determine the impact of oil pressing conditions and protein extraction protocol on protein yield and content; (2) characterize structural differences in proteins extracted following salt precipitation and pH solubilization; (3) determine the impact of structure and enzymatic modification on the functionality of the different protein extracts; (4) isolate, quantify, and characterize the insoluble and soluble dietary fiber fractions of defatted camelina meal (DCM) prepared by two different oil pressing conditions. Protein extraction by pH solubilization and salt precipitation was tested and optimized. Camelina meal obtained from hot and cold press was further defatted by hexane and analyzed for protein content. Protein from DCM was extracted following degumming and pH solubilization at pH 12, separating non-protein material by centrifugation, acidifying the supernatant to pH 5 to precipitate out the protein, neutralizing and desalting. Protein from DCM was also extracted following salt precipitation, first by solubilizing the protein using 0.05 M phosphate buffer (pH 8, 1 M NaCl), followed by precipitation using 85% saturated ammonium sulfate solution, and desalting. To produce protein hydrolysates, extracted proteins were subjected to hydrolysis with Aspergillus oryzae protease by pH-stat methodology to a degree of hydrolysis less than 8%. Protein purity of the extracts was analyzed, and mass balances were tracked in order to evaluate extraction yields. The denaturation state, protein profile, and surface hydrophobicity of the protein extracts were determined using DSC, SDS-PAGE, and a fluorometric assay, respectively. Functionality was evaluated by determining protein solubility as well as emulsification, foaming, and gelation properties. Total dietary fiber (TDF) from DCM was determined following the AOAC method 2011.25, and three fractions —insoluble dietary fiber (IDF), soluble dietary fiber that precipitates in 78% ethanol (SDFP), and soluble dietary fiber that is soluble in 78% ethanol (SDFS) — were isolated preparatively. IDF and SDFP were analyzed spectrophotometrically for pectin content. The monomers of IDF and SDFP fractions were determined by alditol acetate formation and measured by GC-FID. Degree of pectin methylation (DM) of SDFP was determined by 1H NMR. The degree of polymerization (DP) of saccharides in the SDFS fraction (DP 2 – DP 7) was determined by liquid chromatography-ESI-mass spectrometry (LC-MS) using a ligand-exchange stationary phase and quantified by high performance anion exchange chromatography coupled with a pulsed amperometric detector (HPAEC-PAD). Disaccharides in DCM were differentiated and quantified spectrophotometrically following standard enzymatic assays. Compared to camelina protein concentrates (CPC) produced by alkaline pH extraction, CPC produced by salt extraction were less denatured and more functional. The functionality of the salt extracted CPC was comparable and sometimes better than that of soy protein isolate (SPI). Specifically, the solubility of the salt extracted CPC at pH 3.4 was significantly (P < 0.05) higher than that of SPI. Additionally, salt extracted CPC had significantly higher emulsification capacity and foaming capacity than SPI. On the other hand, the gelation property of CPC was inferior to that SPI, an observation attributed to the molecular size of camelina protein compared to SPI. Upon hydrolysis of CPC with Aspergillus oryzae protease, a limited benefit to solubility was noted at pH 7 post thermal treatment. TDF of DCM averaged 51.2% (45.3 – 49.1% IDF, 2.00 – 5.98% SDFP, 1.1 – 1.2% SDFS). The SDFS fraction was comprised mainly of stachyose and raffinose, which is in line with other Brassicaceae crops. The chief disaccharide present in DCM was verified to be sucrose (2.43 – 3.36%). Free glucose and fructose were also present in the SDFS fraction. Of the pectic polysaccharides measured in SDFP, low methoxyl pectin represented the major constituent, with a DM of 12.5 – 14.5%. Based on alditol acetate analysis, glucose was the main monomer in the IDF fraction. Other monosaccharides detected in the IDF fraction were xylose, arabinose, mannose, and galactose. The monosaccharide composition indicated the presence of cellulose, xyloglucans, galactomannans, and arabinoxylans in the IDF fraction. In SDFP, the monosaccharides rhamnose, arabinose, galactose, and mannose were evenly distributed. Monomer composition of the SDFP fraction indicated the presence of pectin and galactomannans. Results show that camelina meal contains a significant amount of protein and dietary fiber that can be isolated into functional ingredients. This is the first study to provide a comprehensive evaluation of protein and dietary fiber from camelina as potential alternatives to traditional ingredients. Further work is needed to understand how isolated camelina ingredients interact in various food matrices.

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University of Minnesota M.S. thesis.July 2018. Major: Food Science. Advisor: Baraem Ismail. 1 computer file (PDF); xiii, 117 pages.

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Boyle, Claire. (2018). Extraction, Modification, and Chemical Characterization of Protein and Dietary Fiber from Camelina Sativa. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/200151.

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