Aamir Iqbal1, Ayesha Murtaza1, Krystian Marszałek2, M Amjed Iqbal3, Muhammad F J Chughtai4, Wanfeng Hu1, Francisco J Barba5, Jinfeng Bi6, Xuan Liu6, Xiaoyun Xu1. 1. College of Food Science and Technology, Huazhong Agricultural University, Wuhan, China. 2. Department of Fruit and Vegetable Product Technology, Prof. Wacław Dąbrowski Institute of Agricultural and Food Biotechnology, Warsaw, Poland. 3. Institute of Agricultural and Resource Economics, University of Agriculture Faisalabad, Faisalabad, Pakistan. 4. Department of Food Science & Technology, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, Pakistan. 5. Nutrition and Food Science Area, Preventive Medicine and Public Health, Food Science, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de València, València, Spain. 6. Key Laboratory of Agro-Products Processing, Ministry of Agriculture and Rural Affairs, Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences (CAAS), Beijing, China.
Abstract
BACKGROUND: Polyphenol oxidase (PPO) is considered a problem in the food industry because it starts browning reactions during fruit and vegetable processing. Ultrasonic treatment is a technology used to inactivate the enzyme; however, the mechanism behind PPO inactivation is still unclear. For this reason, the inactivation, aggregation, and structural changes in PPO from quince juice subjected to ultrasonic treatments were investigated. Different intensities and times of ultrasonic treatment were used. Changes in the activity, aggregation, conformation, and structure of PPO were investigated through different structural analyses. RESULTS: Compared to untreated juice, the PPO activity in treated juice was reduced to 35% at a high ultrasonic intensity of 400 W for 20 min. The structure of PPO determined from particle size distribution (PSD) analysis showed that ultrasound treatment caused initial dissociation and subsequent aggregation leading to structural modification. The spectra of circular dichroism (CD) analysis of ultrasonic treated PPO protein showed a significant loss of α-helix, and reorganization of secondary structure. Fluorescence analysis showed a significant increase in fluorescence intensity of PPO after ultrasound treatment with evident blue shift, revealing disruption in the tertiary structure. CONCLUSION: In summary, ultrasonic treatment triggered protein aggregation, distortion of tertiary structure, and loss of α-helix conformation of secondary structure causing inactivation of the PPO enzyme. Hence, ultrasound processing at high intensity and duration could cause the inactivation of the PPO enzyme by inducing aggregation and structural modifications.
BACKGROUND:Polyphenol oxidase (PPO) is considered a problem in the food industry because it starts browning reactions during fruit and vegetable processing. Ultrasonic treatment is a technology used to inactivate the enzyme; however, the mechanism behind PPO inactivation is still unclear. For this reason, the inactivation, aggregation, and structural changes in PPO from quince juice subjected to ultrasonic treatments were investigated. Different intensities and times of ultrasonic treatment were used. Changes in the activity, aggregation, conformation, and structure of PPO were investigated through different structural analyses. RESULTS: Compared to untreated juice, the PPO activity in treated juice was reduced to 35% at a high ultrasonic intensity of 400 W for 20 min. The structure of PPO determined from particle size distribution (PSD) analysis showed that ultrasound treatment caused initial dissociation and subsequent aggregation leading to structural modification. The spectra of circular dichroism (CD) analysis of ultrasonic treated PPO protein showed a significant loss of α-helix, and reorganization of secondary structure. Fluorescence analysis showed a significant increase in fluorescence intensity of PPO after ultrasound treatment with evident blue shift, revealing disruption in the tertiary structure. CONCLUSION: In summary, ultrasonic treatment triggered protein aggregation, distortion of tertiary structure, and loss of α-helix conformation of secondary structure causing inactivation of the PPO enzyme. Hence, ultrasound processing at high intensity and duration could cause the inactivation of the PPO enzyme by inducing aggregation and structural modifications.