Preparation and properties of solution cast films from pilot scale cottonseed protein isolate

Authors: Selling, Gordon; Hojilla-Evangelista, Milagros - Mila; Hay, William; Utt, Kelly; Grose, Gary

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2022
Publication Date: 2/3/2022
Citation: Selling, G.W., Hojilla-Evangelista, M.P., Hay, W.T., Utt, K.D., Grose, G.D. 2022. Preparation and properties of solution cast films from pilot scale cottonseed protein isolate. Industrial Crops and Products. 178. Article 114615. https://doi.org/10.1016/j.indcrop.2022.114615.
DOI: https://doi.org/10.1016/j.indcrop.2022.114615

Interpretive Summary: Around 25 billion pounds of cotton are produced annually in the United States. Of this, approximately 50% gets incorporated into cotton bales destined for fabric production and the remainder is the cottonseed. The seed is crushed to remove oil and the defatted solids (cottonseed meal) can be used for animal feed. In order to support cotton prices, increasing the value of cottonseed meal would be useful. Cottonseed meal will have around 55% protein. An improved technique is needed to provide a high purity protein from the cottonseed meal. In addition, a good solvent is needed to dissolve this protein, which can then be used to produce defect-free films. These films may be of use in packaging applications. ARS researchers at Peoria, Illinois, have developed an improved method for producing a high purity protein from the cottonseed meal and discovered a solvent that provides clear solutions while still containing high concentrations of cottonseed protein. Light-amber colored, clear and defect-free films were made from this solution. The film’s strength was comparable to polyethylene but had less elongation. Film properties were affected by moisture, with strength dropping and elongation increasing as humidity climbed. By developing an improved method to isolate cottonseed protein and an improved solvent system, other researchers will be able to develop higher value uses of this material. These results will be useful to industrial, government and academic researchers interested in increasing the value of cotton, which will benefit all participants in the cotton value-chain.

Technical Abstract: This research defines the value of films made from cottonseed protein isolate (CPI). A high-quality (95% protein content) protein isolate was recovered from glandless cottonseed meal using room temperature water (pH=11), after centrifugation, acid-precipitation, washing, and freeze-drying. Formic acid (FA) was found to be a good solvent for CPI and solutions of 23% solids were made to prepare poured films. FA had not been used as a solvent for CPI previously, and it was found to be capable of forming solutions with solids concentration four times greater than previously reported solvent systems. Dissolution into FA and film production did not affect molecular weight, indicating that hydrolysis did not occur. Six reagents were evaluated as plasticizers for CPI. Of these reagents, glycerol and levulinic acid were selected for additional research. Films having between 5% and 40% plasticizer were made, and the clear, defect-free, hygroscopic films with preferred formulations had good tensile strength (TS), ~ 30 MPa with low elongation (Elo), ~13% at 30% relative humidity (Rh). The TS and Elo of these films were better, and had similar Young’s modulus, when compared to CPI films reported earlier by other researchers. As the Rh increased, the film’s Elo increased while TS decreased. The films had glass transition temperatures of ~110 °C and began to experience a high rate of degradation above 200 °C. The results show a significant improvement in the isolation method and formulation of CPI films with superior tensile properties compared with previous literature methodologies. These improvements are due to the quality of the protein and the use of a superior solvent. These films may ultimately be of value for food packaging applications when the Rh sensitivity is resolved.