Submitted to: Biological Engineering (ASABE)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2013
Publication Date: 2/28/2013
Publication URL: http://handle.nal.usda.gov/10113/57318
Citation: Digman, M.F., Runge, T.M., Shinners, K.J., Hatfield, R.D. 2013. Wet fractionation for improved utilization of alfalfa leaves. Biological Engineering (ASABE). 6(1):29-42. Interpretive Summary: When working with grains such as soybeans, corn, or cereal crops, the farmer separates the value streams (e.g., grain and straw) for different uses. If alfalfa leaves could be efficiently separated from the plant’s stem in a similar way, it could result in flexible uses of the crop, from augmenting traditional uses such as customized leaf and stem blends in livestock feed rations, to the opening of new markets for alfalfa’s use in bioproducts and biofuels. This work envisions a new harvest scheme combining mechanical leaf separation, dewatering, and fermentation. In this study, we quantified the effectiveness of different methods of leaf dewatering: maceration and four levels of screw press back pressures. We found that maceration did not affect the amount of water extracted, but did increase the protein concentration of the press filtrate. All moisture levels of press cake were successfully ensiled. This information will guide us as we continue our research to better define this process.
Technical Abstract: Utilization of alfalfa could be greatly improved if protein-rich leaves were efficiently separated and preserved from fibrous stems. This work envisions a new harvest scheme combining three processes: mechanical leaf separation, dewatering, and fermentation. Gross plant fractionation is accomplished by in-field mechanical separation of leaves from stems. This operation foregoes field wilting of the leaf fraction, thereby minimizing losses associated with plant and microbial respiration and weather. However, leaves are moist and not biologically stable, even when ensiled conventionally. To overcome this limitation, the next step in the proposed system is to dewater the leaves. To quantify the effectiveness of leaf dewatering, experiments were conducted in which leaves were dewatered in a replicated factorial experiment including maceration and four levels of backpressures in a single-screw press. The amount of juice extracted varied proportionally with press backpressure from 38 to 121 L per Mg of fresh leaves and was composed of about 90% water. The resulting dewatered leaf press-cakes were successfully ensiled and were found to be compositionally similar to high-quality, whole-plant alfalfa silages. Additionally, we demonstrated that the nutritionally valuable components in the juice could be conserved by anaerobic storage, or the press-filtrate could be simply returned to the field with low losses of leaf dry matter and protein of 2.0 and 2.5%, respectively.