Location: Plant Polymer Research2016 Annual Report
The long-term objective of this project is to develop novel products utilizing current and new co-products from the industrial processing of agricultural materials. As a result our research will reduce dependence on non-renewable materials and produce higher value products that will benefit a large segment of our economy. Objective 1: Enable, from a technological standpoint, the commercial production of marketable products from the proteins in crops such as pennycress, camelina, soybean, cottonseed or corn. Sub-objective 1A. Establish pilot-scale extraction and biorefining techniques that generate protein-rich industrial feedstocks from plant crops, such as pennycress, camelina, soybeans, or cottonseed. Sub-objective 1B. Determine ability to form solvent cast and melt processed films or articles, as well as surface and interfacial tension agents; determine if suitable chemical modifications of these proteins will provide products that can replace petroleum-based products.
Establish pilot-scale extraction and biorefining techniques that generate protein-rich industrial feedstocks from plant crops, such as pennycress, camelina, soybeans, or cottonseed. Determine ability to form solvent cast and melt processed films or articles, as well as surface and interfacial tension agents. Determine if suitable chemical modifications of these proteins will provide products that can replace petroleum-based products.
The quality and quantity of oil from pennycress seeds are, at a minimum, competitive with those obtained from soybeans. This oil may be used to produce biodiesel. In much of the U.S., pennycress can be grown over the winter and harvested in the fall. Before industry will commit to commercial production of pennycress, the entire seed must be used. Research efforts were put forth on extracting the protein from pennycress seeds. This research concentrated on developing the optimum pilot scale process for extracting the protein from pennycress seeds. The process employed was based on the standard industrial approach using base (high pH) to extract the protein and then acidification (addition of acid, low pH) to recover the protein which was then followed by membrane purification. The key outputs for the extracted material, pennycress protein isolate (PPI), were percent yield, protein purity, and protein solubility. Process changes that led to improvements in these metrics include: 1) defatting the starting press cake to less than 1% residual oil before protein extraction; 2) using a new high-capacity centrifuge for the liquid-solid separation steps instead of the centrifugal separator; and 3) extending the time for the protein re-solubilization. Using these process changes have resulted in substantial improvements in the efficiency of the separation steps and in the recovery of the fractions of interest. The PPI obtained after acidification was nearly completely soluble in pH 7 water, unlike when using the unoptimized process for isolating PPI which resulted in a material where only 30% was soluble. The process produced 440 grams of PPI with 92% protein, representing 24% protein yield. These values are significantly greater than those from the unoptimized method. The PPI produced from larger scale extractions was further characterized and converted into films. The properties of these PPI films were determined. Of the six plasticizers tested, the one with the best overall properties yielded films that were homogeneous and had good elongations (up to 170%) but low tensile strength (2-7 megapascal). The protein is resistant to changes in structure with heating. When solutions were heated from 20-70°C, only minimal changes were observed in the secondary structure of the protein based on circular dichroism measurements. It has been shown that the oils present in coriander have high value due to their unique composition, and as a source for biodiesel. Improved oil extraction techniques have been developed by another ARS unit and the impact of using these techniques on protein extractability, composition, and functional properties was assessed. Five different coriander treatments were employed to provide the starting material: ground whole seed, dehulled seed, press cake from dehulled seed, steam-distilled dehulled seed, and press cake from steam-distilled dehulled seed. After defatting the starting material, the protein was extracted using the industrial standard method of base solubilization at 50°C followed by acid precipitation. It was found that dehulling the seed moderately increased protein extraction efficiency by 20%. Employing steam-distillation in seed processing reduced protein extractability by 33%. Protein extracts from dehulled or steam-distilled seed or press cake had higher protein purity (82% protein) than that obtained from whole seed (67% protein). This would classify the protein from these materials as high value protein concentrates. Coriander protein has high solubility (80% soluble) at pH = 7, which was further enhanced (90-96% soluble) by using the steam-distillation step during seed processing. The foam stability was higher for the protein obtained from dehulled and/or steam-distilled coriander seed or press cake relative to that obtained from the whole seed. Thus, the integrated oil extraction process has beneficial effects on coriander protein extraction and purity as well as protein solubility and foaming properties. Depending on the methods utilized during seed processing, coriander protein having different properties can be obtained and could be targeted to discrete end-uses. In order to more fully utilize corn protein (zein), additional information regarding how melt processing effects the protein on a molecular level and on the final physical properties of the article is required. A series of extrusion processed zein was produced where the amount of plasticizer was changed (10-15%) and the injection molding conditions were altered (130-140°C). It was determined that the tensile strength, elongation, molecular weight, and protein solubility did not change for each formulation across these molding conditions. As expected, the injection molded bars, having lower amounts of plasticizer, had higher modulus than those formulations having higher amounts of plasticizer. Altering the injection molding conditions did not alter the physical properties, demonstrating that uncrosslinked zein has a similar processing window as that of petroleum-based products. It has been demonstrated that zein can be crosslinked with glyoxal using melt processing techniques, including injection molding, to give articles with improved tensile strength and solvent resistance. Varying injection molding conditions from 130-150°C did not result in large changes in the physical properties of the articles. It was observed that altering the injection molding conditions for the cross-linked zein formulations, that is the amount of time the zein remained in the hot screw, did result in changes in the molecular weight of the protein. The molecular weight could increase or decrease depending on the length of time. If the molecular weight of the protein was reduced, the solubility of the protein increased. Therefore, selection of injection molding conditions is more important in zein formulations which employ cross-linking reagents. The rate of biodegradation of zein films when buried in the ground was determined. In this first real world degradation study, it was found that zein films degraded very quickly, with little sample remaining after three weeks. Surprisingly, for the residual films that were collectible, there was no evidence of molecular weight loss. Using electrophoresis techniques, it was found that the molecular weight shifted slightly to higher values for the collected samples. This suggests that when enzymatic soil degradation took place at a given location on the zein film, the process happened quickly, resulting in mass loss with no detectable loss in molecular weight of the zein in the remaining film which could be collected. In addition, there are enzymes present in the soil which are capable of creating cross-links between the proteins. Evaluation of the impact of cross-linking the zein on the rate of soil degradation is in progress.
1. Pilot scale isolation of pennycress protein isolate. To extract the most value from the pennycress seed, a winter annual plant which is a good potential source for biodiesel, the entire seed must be utilized. ARS scientists in Peoria, Illinois, have established the parameters for pilot-scale (10 lb) extraction and recovery of protein from pennycress press cake to produce one pound of high purity protein. The yield (ca. 24%) and purity (> 90%) are notable improvements over the earlier pilot-scale trials. Pilot-scale pennycress protein has good properties such as foam production and stability desired by both industrial and food companies. Developing larger volumes of high purity pennycress protein for conversion into higher value products will enhance the value of the pennycress crop and support the overall pennycress effort, which will result in an additional revenue stream for farmers and downstream processers, as well as reduce dependence on petroleum.
2. Isolation of new proteinaceous coproducts from processed coriander. New processing techniques have been developed to extract high value essential oils from coriander seeds, however the impact this technique has on coriander protein, its isolation and value, is not known. ARS scientists in Peoria, Illinois, have developed a bench-scale method to extract protein from coriander meals produced by using the improved oil extraction process. While the improved oil extraction delivered higher quantities of essential oils, the new process reduces the yield of coriander protein. However, the coriander protein isolated had high purity, high nutritional value, good solubility, and excellent foaming properties. All of these attributes are industrially valued and coriander protein isolates would be a valuable coproduct for coriander seed oil processing. Developing more coproducts with novel uses will broaden the markets for coriander and increase the value of the crop, thus providing an additional cash crop.
3. Improved understanding of the impact of injection molding on zein. In order for corn protein, zein, to be utilized in the traditional plastic industry, it must be processable using the standard techniques of the trade. ARS scientists in Peoria, Illinois, have produced zein-based formulations using techniques employed by industry where the zein was processed as-is or after chemical modification (the modification provided improved solvent resistance). While both formulations could be processed, the zein formulation that was not modified had a larger processing window; similar to that of petroleum-based products. Developing new processing techniques for the production of renewable materials on existing equipment being used to manufacture petroleum-based materials will reduce the cost of utilizing this renewable material and provide a higher value revenue stream to corn producers and processors.
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