Extraction, composition, and functional properties of dried alfalfa (Medicago sativa L.) leaf protein

Authors: Hojilla-Evangelista, Milagros - Mila; Selling, Gordon; Hatfield, Ronald; DIGMAN, MATTHEW - Kuhn North America, Inc

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2016
Publication Date: 6/17/2016
Citation: Hojilla-Evangelista, M.P., Selling, G.W., Hatfield, R., Digman, M. 2016. Extraction, composition, and functional properties of dried alfalfa (Medicago sativa L.) leaf protein. Journal of the Science of Food and Agriculture. doi: 10.1002/jsfa.7810.

Interpretive Summary: In this research, we produced a protein concentrate (59% protein content) from dried alfalfa leaves by adapting a conventional method so that we may identify and develop novel uses for the protein. Alfalfa is traditionally used for animal feed, but the crop is being developed as a dual-purpose biofuel plant, with stems as the substrate for fuel and leaves for feed and other industrial products. The viability of the process would be enhanced by co-products with value-added uses. In the present work, we determined the extractability of protein from dried alfalfa leaves and also the composition and functional properties (solubility, foaming, emulsification, heat stability). We found that dried alfalfa leaves contained 26% protein, most of which were water-soluble. We observed that the protein isolated by the conventional technique showed only moderate solubility but was a good foamer in acidic solution. We also noted that alfalfa leaf protein concentrate was an excellent emulsifier in various aqueous environments and very stable to heating. Our results showed that dried alfalfa leaf proteins have foaming and emulsifying properties that would be desirable in whipped or foam products and emulsions. However, it may not be practical to use the dried form as a starting material for production of protein concentrates because of the difficulty of achieving high yields and high-purity protein product.

Technical Abstract: Alfalfa, traditionally used for animal feed, has attracted attention as a potential feedstock for biofuels and the viability of the process would be enhanced by co-products with value-added uses. This study describes extraction of protein from dried alfalfa leaves and the functional properties of the protein. Ground, dried alfalfa leaves contained 26% db crude protein. Albumins were the major fraction (26% of total protein) while globulins were the least (1%). SDS-PAGE detected nine polypeptide bands between 7-77 kDa. The method of alkali solubilization for 2 hr at 50°C, acid precipitation, dialysis, and freeze-drying produced a protein concentrate (60% crude protein). Our alfalfa leaf protein concentrate showed only moderate solubility (maximum 50% from pH 5.5 to 10), but good foaming properties at pH 2 (117 ml foam, 90% volume retention after 15 min). The protein also showed high emulsifying activity (158-219 m2/g protein) and emulsion stability (17-49 min), with values increasing with pH. Alfalfa leaf protein was very stable to heating (1-2% loss of solubility) at pH = 7.0. Results indicate that it is technically feasible to extract protein with desirable foaming and emulsifying properties from dried alfalfa leaves; however, it may not be practical to use the dried form as starting material for production of protein concentrates, given the difficulty of achieving high yields and high-purity protein product.