Effect mechanism of freeze–thaw cycles on browning of “Nanguo” pears peel

Abstract Freezing is an effective way to prolong the storage period of “Nanguo” pears, but the pear peel would browning during thawing. The browning mechanism of “Nanguo” pears peel under different freeze–thaw cycles was studied in this paper. The membrane lipid peroxidation products, fatty acid content and related enzyme activities of peel browning during freeze – thaw cycles were determined. The results showed that the browning of ‘Nanguo’ pears peel induced by freeze – thaw cycles might be caused by the increased of lipoxygenase (LOX) activity, the decreased of superoxide dismutase (SOD) activity and the degradation of unsaturated fatty acids. Then destroyed the integrity of cell membrane structure and resulted in the loss of cell partition, thus leading to the browning of “Nanguo” pears peel. This caused polyphenol oxidase (PPO) and peroxide (POD) to came into contact with the phenolic substrate and subsequently oxidized the phenolic to formed a brown polymer, leading to browning. Practical Applications During the storage and transportation of frozen fruits and vegetables, freezing – thawing phenomenon occurs frequently due to temperature fluctuation, which affects their frozen quality. Freezing and thawing experiments were used to simulate the storage and transportation process to study the effect mechanism of repeated freezing and thawing on ‘Nanguo’ pears peel browning. The results provided a theoretical basis for maintaining the quality of ‘Nanguo’ pears during storage. And it is beneficial to the industrialized production of frozen pear in northeast China.