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^C) 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 noncoated

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 0.150.25%

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.

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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.