Development of a method for profiling of volatile organic compounds to monitor heat stress in hot water dipped apples

Storage rot is a major contributor to losses of organic apples due to restrictions in spraying in orchards. Postharvest pre-treatments such as hot water dipping (HWD) have been proven successful to reduce storage rot. However, excessive heat during dipping easily induces heat stress and physiological disorders, which only show up after several weeks of cold storage. To develop further the HWD technology, a method for early detection of physiological disorders is desirable. As apples emit volatile organic compounds (VOCs) in response to stress and ripening, VOC profiling can be a useful tool for detecting the immediate heat stress and latent physiological disorders. In this study, a selected ion-monitoring program was developed for analyzing VOCs from apples (Malus domestica 'Ingrid Marie' and 'Pinova') dipped in water at 20 and 56 degrees C for 3 min. VOCs were sampled by solid-phase microextraction and analyzed by GC-MS in total ion current mode. From these results, a selected ion-monitoring program was developed which enabled detection of trace VOCs collected by static headspace sampling. The results showed that all apples dipped in 56 degrees C for 3 min developed visual signs of physiological disorders in cold storage. At the same time, the VOC profile of these apples differed from that of the 20 degrees C treated apples. This work provides a solid basis for a future development of the VOC method to forecast physiological disorders and to improve the HWD technology for better control of storage rot.