分析‘台農17號’鳳梨果實不同部位之多酚氧化酵素(polyphenol oxidase; PPO)活性，結果顯示貯藏前後果心PPO比活性均顯著高於其他部位。而果實各部位抗氧化力(FRAP)由內而外遞增。當果實經過8℃貯藏2週再移至室溫貯藏4天，除果心外，其他部位果肉之FRAP均明顯上升。
本研究之不同鳳梨品種中，除‘台農20號’鳳梨之外，其他品種果實經過低溫貯藏後，皆有黑心劣變發生。採收時果實FRAP與貯藏後黑心劣變指數呈正相關，但貯藏後果實FRAP則與黑心劣變指數呈負相關。不同品種鳳梨之FRAP有很大差異，但黑心劣變嚴重之品種，雖然採收時FRAP可能較高，但貯藏後FRAP明顯下降，例如黑心劣變嚴重之‘台農16號’鳳梨採收時FRAP值為230.8 (Fe+2 μmole/g Fw)，貯藏後降至115.5(Fe+2 μmole/g Fw)，降低50%。而耐黑心劣變品種，雖然採收時FRAP較低，但貯藏後FRAP顯著提升，例如‘台農20號’鳳梨冷藏後並無黑心劣變發生，其採收時FRAP為148.4(Fe+2 μmole/g Fw)，而貯藏後增加至209.0 (Fe+2μmole/g Fw)，增加40%。顯示貯藏前後FRAP提升較多之鳳梨品種，其耐黑心劣變之能力較強。
Fruit flesh translucency and blackheart are two major physiological disorders of pineapple. When the disorders are severe, fruit quality decreases, which could result in serious financial loss. The main objective of this study was to analyze the correlation between physical-chemical characteristics of pineapple fruit and the occurrence of blackheart disorder, and to investigate the key factors in blackheart occurrence.
The physical-chemical characteristics in different parts of ‘TN17’ pineapple fruit flesh were examined. The results indicated that the total soluble solid and total titratable acid increased progressively from the core to outer pulp, and there were no significant changes after storage. Citric acid、malic acid and total acid contents in the inner pulp decreased after storage, but ascorbic acid content increased. Ascorbic acid content in the outer pulp was significant higher than that in the core before and after storage.
Polyphenol oxidase activity in different parts of ‘TN17’ pineapple fruit flesh was analyzed. The results showed that PPO specific activity in the core of pineapple fruit was the highest. Ferric reducing activity power (FRAP) increased progressively from the core to outer pulp of fruit. After fruits were stored at 8℃ for 2 weeks, followed by at room temperature for 4 days, the FRAP in pulps increased, but not in the core.
‘TN17’pineapple fruit, harvested from different producing areas, were stored at 8℃ for 2 weeks, followed by at room temperature for 1 week. Fruit harvested from all producing areas had severe blackheart disorder. There was no significant change in the average of ascorbic acid content after storage but FRAP increased significantly. However, there was no significant correlation between FRAP and blackheart index. The correlation between sugar content and total sugar content before storage and blackheart index after storage was significantly negative. It indicated that fruits with lower sugar contents had more severe blackheart disorder.
Fertilizer management is one of the factors affecting the occurrence of pineapple fruit disorders. The relative factors regarding blackheart disorder in pineapple fruits harvested from different producing areas were analyzed. The results indicated that there was a positive correlation between nitrogen content in fruit flesh at harvest and blackheart index after storage. The correlation between copper content and blackheart index was also significantly positive. In addition, same correlation was found in the analysis of different pineapple cultivars, which suggested that copper might an important factor. Therefore, copper content could be used as an index to predict blackheart occurrence. In contract, there were no significant correlations between calcium content and blackheart index in fruits harvested from different producing areas and in fruits of different cultivars. It suggested that calcium may not be a major factor affecting of blackheart occurrence.
In this study, pineapple fruits of different cultivars developed blackheart disorder after cold storage except ‘TN20’ pineapple. The correlation between FRAP at harvest and blackheart index after storage was negative but the correlation between FRAP after storage and blackheart index was positive. There was a significant variation in FRAP in fruits of different pineapple cultivars. Fruits of cultivars which developed severe blackheart disorder had higher FRAP at harvest, but decreased significantly after storage. For example, the FRAP of ‘TN16’ pineapple, a cultivar that is highly susceptible to disorder, was 230.8 (Fe+2 μmole/g Fw) at harvest, which decreased to 115.5(Fe+2 μmole/g Fw) after storage, a 50% decrease. For blackheart resistant cultivars, although it was low at harvest, FRAP significantly increased after storage. For example, ‘TN20’ pineapple had no blackheart development after storage, and its FRAP value was 148.4(Fe+2 μmole/g Fw) at harvest, which went up to 209.0(Fe+2 μmole/g Fw) after storage, a 40% increase. The result suggested that pineapple cultivars whose fruits had more increase in FRAP after storage, had higher potential to tolerate blackheart development.
Compared to other fruits, pineapple has low ascorbic acid content. The contribution of ascorbic acid to total antioxidant potential in pineapple fruit is low. FRAP and blackheart index was negatively correlated after cold storage, indicating that, besides ascorbic acid, more important antioxidants should exist in pineapple fruit.