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

Watermelon (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 theHHPeffect on protein secondary structure of watermelon juice. Crude protein of the treatment group was extracted after theHPPdevice treatment. Different degree, time, temperature and interval frequency ofHHPwere imposed on the watermelon juice protein, followed by characterization of the protein secondary structure of watermelon juice by theFourier 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. Theα‐helix content became lower after treatment; andβ‐sheet level was decreased while random coil increased after 400 MPatreatments for 20, 40 and 60 min compared with control. The trends ofβ‐turn values changed variously in different treatment groups.HHPtreatment can change the secondary structures of proteins and affect the content ofα‐helix with higher degree ofHHP, longer time, higher temperature and more interval frequency. Practical Applications This study pays attention on the proper sterilization for watermelon juice products.HHPtreatment on watermelon juice at a condition of 400 MPa, 30C for twice interval of 10 min may be the best choice. Under this condition,HHPtreatment performs better inactivation effects on endogenous enzymes and lead to relatively less adverse effects on flavor of products.