Seasonal Variations in Protein Fractions, Yields and Quality of Leaf Protein Concentrates Extracted From Pasture Herbage

Abstract

Permanent pasture stands were used for protein extraction in laboratory‐scale operation during the spring, summer and autumn seasons. Mixed herbage was in its 3rd, 4th, 5th and 6th weeks of regrowth. Efficiency of the protein extraction process at different stages of herbage maturity was measured within each season as well as the nutritional and biochemical characteristics of the recovered protein. Significant interaction between the seasons and herbage regrowth stage was observed in relation to a number of measurements of efficiency of protein extraction. In general however, protein recovery declined with herbage maturity. Significantly less leaf protein concentrate (LPC) with lower nitrogen content was produced from yields of herbage in the summer season as compared to that harvested and processed in either the spring or autumn. To achieve a PER value similar to casein protein, LPC produced in spring and autumn had to be supplemented with DL‐methionine and Llysine while to obtain similar PER with summer produced LPC it was necessary to supplement LPC with L‐tryptophan in addition to L‐lysine and DL‐methionine. Juice from spring and autumn‐grown herbage showed high proportion of low molecular weight protein fractions as compared to summer where there was a substantial increase in high molecular weight proteins with simultaneous decrease in low molecular weight fractions.