| Pineapple is native to Brazil and Praguay in south central America and is the third most important tropical fruit after bananas and mangoes. Blackheart easily occurs in pineapple pulp induced by multi-factor, and that lesion is a complicated physiological process without a exact explaination until now. Pineapple blackheart could debase fruit quality, affect fruit processing and sales, eventually lead to serious economic loss. In this topic, we choosed ’Comte de Paris’ pineapple fruits as experimental materials and investigated the problem of postharvest pineapple blackheart, then we studied the changes of metabolites, enzyme activities and corresponding enzyme’s relative gene expression in the course of ethanol metabolism and the Krebs cycle(TCA) during the process of blackheart, in order to understand how matabolic regularity change when blackheart happening, and try to control pineapple blackheart using different proportion of CO2 and N2 modified atmosphere packaging and high CO2 with low O2 controlled atmosphere storage.The results showed that:1. At room temperature(25℃), the content of pyruvic acid and acetaldehyde in the two maturity(6M and 8M) pineapple pulp decreased with the incease of the disease index of black, while the ethanol content continued to increase during the whole storage period. At the same time, pyruvate decarboxylase(PDC) and alcohol dehydrogenase(ADH) activity also reached the peak when the incidence of pineapple blackheart increased. In addition, the changes of PDC and ADH activity were consistent with the trend of its relative gene expression.2. At room temperature, the content of organic acids in pineapple pulp decreased during the process of pineapple blackheart, which resulted in the decrease of TCA metabolic activity. When pineapple blackheart was exacerbated, most TCA metabolic enzymes activities were enhanced, and the content of intermediate metabolites was accelerated. It was speculated that TCA metabolism might promote the outbreak of pineapple blackheart. At the same time, the level of TCA metabolism might be related to ethanol metabolism.3. The modified atmosphere packaging of pineapple were applied by different proportions of C02 and N2 (MAP1:10%CO2, 90%N2; 20%CO2, 80%N2; 30%CO2,70%N2) . At three storage temperatures( 15℃,20℃ and 25℃),the pineapple blackheart index was counted, the physiological indexes such as fruit hardness,soluble solids and vitamin C and the browning correlation such as total phenol and polyphenol oxidase (PPO) were measured. The results showed that the modified atmosphere had inhibited the occurrence of pineapple blackheart, maintained the fruit hardness and vitamin C content and promoted the increase of ethanol content, but the soluble solids was not significantly different from the control. The results of pineapple browning physiological indexes showed that the total phenolics content of each treatment was lower than CK, and packaging had a certain inhibitory effect on PPO activity. Comparing different storage temperature, we found that 15℃ was more conductive to modified atmosphere packaging storage. And modified atmosphere storage results showed modified atmosphere could inhibit pineapple blackheart all at 15℃, 20℃ and 25℃, similar to the result of CO2 and O2 modified atmosphere packaging treatment above. At the same time, modified atmosphere storage inhibited the total phenol accumulation and phenylalnine ammonialysase (PAL) activity elevation, reduced PPO activity, and it was beneficial to maintain the content of soluble soilds in pineapple pulp and reduce the content of titratable acid, but it has no obvious effect on pulp hardness and vitamin C content. After the comprehensive analysis,the optimum temperature for the above three modified atmosphere temperatures was 15℃. |
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