Quantities and quality of protein extracted from pasture herbage using heat precipitation or ultrafiltration procedures

Abstract

Permanent pasture stands in northern Victoria (Australia) were used for protein extraction in both laboratory-scale and plant-scale operations during the spring, surnmerandautumnseasons. Mixedherbagewasinits third,fourth,fifthandsixthweeks of regrowth. Efficiency of the protein extraction process at different stages of herbage maturity was measured, as well as the proximate analysis, amino acid composition, availability of lysine, methionine, tryptophan and protein efficiency ratio (PER) of the protein, recovered by both steam coagulation (85OC) and ultrafiltration procedures. Recovery of protein nitrogen from pasture herbage determined by the steam precipitation (85°C) procedure was on average, slightly higher in spring and autumn, as cornpared with summer. Significant interactions between the seasons and herbage regrowth stages were observed in both herbage dry matter (DM) and crude protein (N x 6.25) content, protein recovery and yield of protein from the unit of herbage DM. In general however, protein recovery declined with herbage maturity. Significantly less leal' protein concentrate (LPC) with lower nitrogen content was produced from yields of herbage in the summer season as compared with that harvested and processed in the spring and autumn seasons. LPC produced using an ultrafiltration procedure was superior to LPC obtained by the steam coagulation process in terms of LPC yield and protein nitrogen recovery, crude protein and total essential amino acids, lysine, threonine and tryptophan content and tryptophan availability. After synthetic m-methionine and L-lysine supplementations, freeze-dried ultrafiltered LPC gave (in tests with rats) a similar PER to casein which was used as a standard control protein.To achieve a PER value similar to casein, LPC produced by heat coagulation had to be !supplemented with L-tryptophan in addition to L-lysine and Dr-methionine.

Plant leaf proteins for food applications: Opportunities and challenges

“…Nevertheless, red and white clover LPC showed no increase in protein digestibility due to LPC processing (Stødkilde et al., 2019). Pasture LPC prepared by ultrafiltration showed a protein digestibility of 78%, whereas LPC prepared by thermo‐coagulation has a protein digestibility of 73% (Ostrowski‐Meissner, 1980). Therefore, choosing the right processing method is necessary to obtain the highest protein digestibility and eliminate the maximum quantity of anti‐nutritional factors in the plant leaf matrix.…”

“…In the case of ryegrass, 59% of crude protein was obtained through the ultrafiltration technique which is much higher than the heat coagulation technique with a yield of 45% (Koschuh et al., 2004). Protein concentrates of pasture leaves obtained using a DIAFLO membrane having an MWCO of 20 kDa were reported to have a better yield of the native protein, total essential amino acids, threonine, lysine, tryptophan content, and tryptophan availability when compared with LPC produced by steam coagulation at 85°C (Ostrowski‐Meissner, 1980). Ultrafiltration is also capable of removing anti‐nutritional and toxic compounds found in leaf extracts.…”

Biorefinery of Green Biomass─How to Extract and Evaluate High Quality Leaf Protein for Food?

“…Ultrafiltration can be used to concentrate protein from leaf juice, producing the same protein yields as heat precipitation. − Ultrafiltration has been performed on Alamo switch-grass in combination with alkaline extraction and diafiltration has been used to concentrate protein and lower the salt content in the leaf juice from Atriplex lampa . , Different microfiltration and ultrafiltration systems were tested by Zhang, Grimi et al (2015) for concentration of protein in alfalfa juice, and microfiltration was suggested to be the most efficient method to concentrate the protein. These results correlate with our own preliminary data, which suggests that fouling of the microfiltration membrane results in protein concentration.…”