Physical, Chemical and Physiological Responses of Pineapple to Glazing after Harvest.

Abstract

The post-harvest management of pineapple quality is a problem that many Ghanaian pineapple exporters are grappling with. Importers pay premium only on top quality fruits that satisfy market and consumer expectation. An effective Quality Management Approach (QMA) which takes into consideration market demands and consumer expectation would be the key to making Ghanaian exports competitive on the world pineapple trade. In this study, glazing or surface coating of pineapple was employed as a QMA tool, and the physical, chemical and physiological responses of the fruit were monitored under ambient and refrigerated storage. The results of a comparative study of four levels of coating viz: 0, 5, 7.5 and 10% concentration showed that the physical and chemical quality attributes of pineapple could be enhanced by surface coating with the wettable emulsion "stay fresh 7055" and refrigerated storage at 8°C. 7.5% polymeric coated fruit gave the overall best quality attributes evaluated. However, 5% coating was preferred for further study because of economy and also because it was frequently observed that there was no significant difference in the treatment means of the 5% and 7.5% coated fruit. Refrigeration (8°C) minimised physical and chemical quality deterioration. However, fruit quality deteriorated when redrawn into physiological temperature (18°C and above). Physical and chemical quality deteriorated with increasing storage interval. Incorporating fungicide (thiobendazole) in the polymeric coating mixture had no significant effect on the quality indices studied. Mass Shrinkage Characteristics (SHC), Shell Colour Break (SCB) and Crown Withering Index (CWI) could be predicted using mathematical models. Mean SHC, SCB and CWI were significantly higher for fruits harvested at 160 days after floral induction (FI) than fruits harvested at 140 days FI. SHC and SCB were significantly higher for fruits evaluated at night (6pm - 6am) than for fruits evaluated during the day (6am - 6pm). 5% polymeric coating significantly arrested SHC, SCB and CWI under both low temperature (8°C) and ambient (28°) storage. Application of fungicide at 0.01% was significant in reducing shrinkage under ambient storage. Shrinkage Characteristic, Shell Colour Break and Crown Withering Index increased with increasing storage interval, but the effect was twice as much for ambient than for low temperature storage. The pineapple fruit exhibited a non-climacteric respiration. CO2 production and O2 utilisation increased with increasing holding time. The effect was more pronounced in non-coated than for coated fruit. Respiration Quotient (RQ) was 1.25 for coated and 1.92 for non-coated fruits. Nitrogen content in the storage atmosphere decreased with increasing holding time. Post Low Temperature Storage (LTS) behaviour of pineapple significantly affected the vitamin C content of whole fruit. 5% coating was effective in enhancing mean vitamin C retention by 27% over non-coated fruit 5 days after LTS. Sugar content, pH and pulp temperature increased while firmness retention deteriorated from the apical to the basal section of the fruit. Coated fruits were firmer, had higher pulp temperature and lower pH value. Internal browning was over 150% times more intense for non-coated fruits than for coated fruits. Internal browning and firmness retention could be predicted by linear mathematical models. Peroxidase activity determination in pineapple was optimised using the Central Composite Rotatable Design. Activity was highest at the basal section and showed a decreasing effect through the mid to the apical section. Maximum response to peroxidase activity was observed at pH range 5.5 - 6.0, using 0.5% 3.3’-dimethoxybenzidine and 0.15- 0.25% hydrogen peroxide. 5% polymeric coating was effective in delaying the onset of internal browning 5 days after LTS (8°C) and showed low peroxidase activity at 23°C. Non-coated fruit showed severe internal browning two days post LTS at 23°C ambient and had a higher peroxidase activity. Elevating conditioning temperature from 23°C to 30°C and 45°C respectively resulted in isozyme formation, an increase in peroxidase activity of polymeric coated fruit and a decreased activity in non-coated fruit. Finally, it can be concluded from the results of this study that glazing or surface coating holds great promise for the Ghanaian pineapple exporter in minimising the many physical, chemical and physiological disorders associated with the export trade.