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Bioactive peptides are small molecular peptides with some physiologically active functions. These peptides have been shown to possess antibacterial, antioxidant, and blood pressure lowering activities. Although walnuts are rich in high-quality plant proteins, the extracted walnut dregs have low utilization by the walnut industry chain. Therefore, the aim of the study was to investigate the nutritional value and antioxidant activity of walnut dregs in order to increase the added value of walnut by-products. Using the response surface methodology, the optimum process parameters of purification and stability for walnut polypeptide liquid were determined as follows: pH 4.5, 8 column/hours (h) column speed and 3:2 ratio of anion to cation. The scavenging reaction rates for hydroxyl radicals and superoxide anion by 3, 5, 10 u ultrafiltration membrane fractionation screening were found to be 73.3% and 64.4%, 66.1% and 58.9%, 59.2%, and 51.6%, respectively. After comparison, walnut polypeptide liquid showed some degree of antioxidant capacity. The stability of walnut polypeptide liquid was optimized by the response surface. Under the homogeneous pressure of 35 Mpa, the use of a certain amount of stabilizers improved the stability of walnut polypeptide liquid. In conclusion, with the addition of additives, the optimum values of parameters for walnut polypeptide liquid obtained using response surface methodology were determined as follows: the ratio of solid to liquid was 15%; the amount of protein sugar was 0.2%; the amount of citric acid was 0.25%; and the addition of walnut powder flavor was 0.15%. Also, the study has provided a theoretical basis for the waste utilization of walnut by-products, and partial support for the intensive processing of the walnut industry chain. [ABSTRACT FROM AUTHOR]

Currently, edible walnuts are either eaten fresh or being processed as walnut oil. However, the walnut dregs produced after the oil is pressed from the walnuts cannot be used for comprehensive utilization. Instead, they are often used as animal feed after simple treatment or directly used as waste landfill. The walnut dregs contain >20% of high-quality plant protein. Walnut protein consists of gluten, prolamin, albumin, and globulin. Poor function of walnut protein has been reported. Therefore, the gluten in walnut cake protein was modified by enzymatic method and the microstructure of walnut protein was changed, thereby improving the functional properties of walnut protein. It is generally believed that walnut protein modified by enzymatic method might be more suitable for industrial production. Our study showed that the modified walnut glutelin (WG) increased the solubility by ~1.33 times, the water holding capacity by ~0.23 times, the emulsifiability by ~0.32 times, and the emulsion stability by ~0.75 times. The oiliness was slightly lowered and the foaming characteristics were not greatly changed. Therefore, our study concluded that the microscopic structure of the protein had undergone certain changes based on the spectrum and electron microscopy. The modification of the microstructure also provides a theoretical basis for the comprehensive utilization of walnut protein, which could broaden the application of walnut protein in the industrial food production. [ABSTRACT FROM AUTHOR]