Biochemical and Visual Changes in Cactus Stems (Opuntia ficus-indica Mill.) Stored at 4, 12 and 26C

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Abstract
The purpose of this study was to identify visible and microscopic symptoms as well as certain biochemical changes associated with chilling injury (CI) in “Atlixco” cactus stems. Cladodes were harvested, disinfected, minimally processed and stored at 4, 12 and 26C for 14–21 days. Results indicated that cactus stems were sensitive to CI at 4 and 12C and exhibited pitting and bronzing as visible symptoms of this disorder. Confocal microscopy showed that mitochondrial integrity was maintained at 4C whereas a deterioration of these organelles occurred at 12 and 26C. Electrolyte leakage, together with an increase in the levels of Adenosine triphosphate (ATP), glutathione and the reduced form of ascorbic acid were associated with CI. In spite of the presence of CI at 4C, cactus stems were still able to preserve their taste quality and no adverse effects were observed on either firmness or color for 21 days. Practical Applications Minimally processed products should be refrigerated at ≤4C in order to maintain their quality and prevent the growth of harmful microorganisms. However, the refrigeration of cactus stems at suboptimal temperatures causes the appearance of chilling injury (CI). Previous studies have mentioned the general symptoms of this physiological disorder in cactus stems, but no one has described the symptomatology in detail and there is yet to be reported histological and biochemical characterization that might serve to confirm or diagnose its presence. This study describes the symptoms of CI and provides histological and biochemical indicators for its early identification during storage. It also constitutes the preliminary stage to the future application of postharvest technologies that induce tolerance to CI, preventing browning and preserving the quality of minimally processed cactus stems in order to expand their domestic and international markets.

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