Protein Secondary Structure Changes of Watermelon Juice Treated with High Hydrostatic Pressure by FTIR Spectroscopy

Abstract

AbstractWatermelon (Citrullus lanatus) is rich in nutrients, such as lycopene, ascorbic acid and amino acids. It also has effect on thirst quenching, diuretic action and lowering the blood pressure. Traditional thermal sterilization will destroy the active ingredient of watermelon juice and lead to an odd smell, which seriously affects the sensory juice quality and the acceptability of consumers. High hydrostatic pressure (HHP), a nonthermal processing technology, can realize food sterilization process at room temperature or lower temperature. This study aims to study the HHP effect on protein secondary structure of watermelon juice. Crude protein of the treatment group was extracted after the HPP device treatment. Different degree, time, temperature and interval frequency of HHP were imposed on the watermelon juice protein, followed by characterization of the protein secondary structure of watermelon juice by the Fourier transform infrared spectroscopy. The absorption of protein in watermelon juice decreased with the pressure of higher degree, longer time, higher temperature and more interval frequency. The α‐helix content became lower after treatment; and β‐sheet level was decreased while random coil increased after 400 MPa treatments for 20, 40 and 60 min compared with control. The trends of β‐turn values changed variously in different treatment groups. HHP treatment can change the secondary structures of proteins and affect the content of α‐helix with higher degree of HHP, longer time, higher temperature and more interval frequency.Practical ApplicationsThis study pays attention on the proper sterilization for watermelon juice products. HHP treatment on watermelon juice at a condition of 400 MPa, 30C for twice interval of 10 min may be the best choice. Under this condition, HHP treatment performs better inactivation effects on endogenous enzymes and lead to relatively less adverse effects on flavor of products.