Optimization of Ultrasonic Extraction Combined with Ultrafiltration for Purification of Mulberry Leaf Protein and Its Nutritional Evaluation

This paper discussed the preparation of protein nutrients from mulberry leaves by ultrasonic extraction combined with ultrafiltration technology. In order to obtain the optimal conditions for ultrasonic assisted extraction of mulberry leaf protein, we used response surface methodology to optimize the preparation of crude extract of mulberry leaf protein. In addition, we used ultrafiltration technology to purify and concentrate the protein components in the crude protein extract of mulberry leaves, and optimized the ultrafiltration membrane flux by orthogonal test. The amino acid components of solid crude protein prepared by ultrasonic extraction coupled with ultrafiltration technology were determined by referring to the method in GB 5009.124-2016 National Standard for Food Safety and further analyzed its nutritional value. The results showed that the optimal extraction conditions were as follows: The ratio of liquid-material ratio was 29:1 mL/g, ultrasonic extraction at 360 W for 15 min, and heating in water bath at 42 ℃ for 34 min, and the protein yield was up to 5.56%. Using the ultrafiltration technology to purify and concentrate the protein components in the crude protein extract, the optimal purification conditions were as follows: Operating pressure 0.6 MPa, diluting the crude extract by 1 time, and concentration ratio: 4:1. Under these conditions, the membrane flux was 21.40 L/m²·h, and the purity of solid protein was over 35%. The total amino acid content of solid mulberry leaf protein prepared by ultrasonic extraction coupled with ultrafiltration technology was 22.22 g/100 g, and the ratio of essential amino acids to total amino acids and the ratio of essential amino acids to non-essential amino acids were higher than the FAO/WHO adult model values. It could effectively extract and purify protein components from mulberry leaves by ultrasonic extraction combined with ultrafiltration technology. The prepared mulberry leaf proteins have good nutritional value and might meet the nutritional requirements of adults.