Chilling Injury Detection Of "Xiahui 5" Peach By Hyperspectral Imaging

Peach fruit is one of the main fruits of summer, it is very popular with consumers due to its tender texture, appealing flavor and abundant nutrition. It is picked in hot and rainy summer usually and will deteriorate and change its flavor quickly at ambient temperature within 3 to 5 days, tenderness make peaches vulnerable to mechanical forces in its picking, transportation and distribution process resulting in a great loss. Low temperature storage can effectively slow these process and prolong its shelf life. However, peaches are extremely sensitive to discomfort low temperature, its subsequent disorders will seriously affect the sales of fruit. The performance of chilling injury has a certain lag, that is mean, there is no obvious abnormal appearance until they reach higher temperature, so if they are directly poured into the circulation and marketing chain, the whole fruit will be seriously affected. Detection of" Xiahui 5" peach chilling injury by hyperspectral imaging during the postharvest storage period was researched in this paper, hyperspectral acquisition systems of reflectance and half-transmittance were established respectively, in order to monitor chilling injury’s development and establish non-destructive testing methods of chilling injury.1. Construction of hyperspectral detection systems for peaches’chilling injuryHyperspectral reflectance and half-transmittance acquisition units were established respectively for the detection of chilling injury, and their parameters were made sure through repeated experiments, including light intensity, speed of conveyor, height and angle of the light source and so on.2. Quality changes during cold storageChanges of sensory evaluation score, browning index, hardness, total soluble solids, titratable acid, extractable juice content and chlorophyll of peel during cold storage were measured. Classification standard of chilling injury for "Xiahui 5" was as follows:peaches without browning and very shiny were graded 0; peaches with slight browning and could soften as normal were graded 1; peaches which browning had obviously occurred and lost its ability to soften,but were still edible were graded 2; peaches that were severely browned and wrinkled were graded 3.3.Detection of peach chilling injury by hyperspectral imagingHyperspectral reflectance and half-transmittance images of peaches during storage period were captured, then, Independent Components Analysis (ICA) and weighting coefficients’ analysis were implemented to both modes of images respectively. The optimal wavelengths selected were 656nm,674nm,704nm for reflectance mode and 640nm,745nm, 811nm for half transmittance mode respectively. At the same time, black spots were found in the ICA images of half transmittance mode for peaches at early chilling injury period. Next, spectral average of each optimized band were chosen as the input of the Fisher discrimination model, an average testing accuracy of 91.0% for half-transmittance mode was achieved to distinguish different level of chilling injury, the reflectance mode was useful for correct discrimination of chilling injury at early period with a testing accuracy of 83.0%. This research demonstrated that the hyperspectral imaging is feasible for the detection of chilling injury of peaches.