Preparation of Heat-Sensitivity Proteins from Walnut Meal by Sweep Frequency Ultrasound-Assisted Alkali Extraction

• Published in: Journal of food quality 2021, Vol.2021, p.1-12
• Main Authors: Qu, Wenjuan, Fan, Wei, Feng, Yiting, Li, Yunliang, Ma, Haile, Pan, Zhongli
• Format: Article
• Language: English
• Subjects: Cardiovascular disease; Cavitation; Decomposition; Food quality; Heat; High temperature; Nutrition; Potassium; Protein binding; Proteins; Reagents; Ultrasonic imaging
• ISSN: 0146-9428; 1745-4557
• DOI: 10.1155/2021/9478133

Sweep frequency ultrasound- (SFU-) assisted alkali extraction was conducted to increase the yield and content of heat-sensitive protein of walnut meal under a relatively mild condition. The physicochemical and structural characteristics of the proteins obtained by SFU-assisted alkali extraction and the conventional alkali extraction were compared. It was found that the optimal parameters for the SFU-assisted extraction were the solid-liquid ratio of 1 : 12, pH value of 9, initial temperature of 25°C, ultrasonic frequency of 28 kHz, sweep frequency amplitude of 1.5 kHz, sweep frequency cycle of 100 ms, duty ratio of 77%, and ultrasonic time of 90 min. Under this condition, a vast improvement in the walnut protein yield (34.9%) and the walnut protein content (9.8%) was observed. Such improvement was due to the structural changes of the sonicated protein; e.g., SFU decreased the intermolecular/intramolecular hydrogen bond force of proteins and, therefore, caused more order secondary structures and more loosen microstructures. This helped to improve the thermoplastic and solubility of the heat-sensitivity protein. Thus, SFU treatment could be an effective auxiliary technology in the alkali extraction of heat-sensitivity walnut protein. It might also be a promising technology for the extraction of heat-sensitivity protein from other agricultural by-products.