Application of Hot Water Dip in Reducing Chilling Injury of Banana Cv. Berangan During Low Temperature Storage

‘Berangan’ banana (Musa sapientum cv. Berangan), being an extremely perishable commodity, requires low temperature storage before sale or consumption. However, chilling injury (CI) symptoms were exhibited when exposed to very low temperatures. Hot water dip (HWD) has been recognized able to alleviate CI symptoms. The reduction of sensitivity to CI by HWD could be due to the induction of heat shock proteins (HSP) and polyamines (PA) which protected the lipid peroxidation in membrane lipids. In the present study, the CI symptoms developed in Berangan banana were characterized. The banana was then treated with HWD in order to reduce the CI development. The HSP and PA contents were identified to determine the causal factor contributing to CI reduction in HWD-treated banana. The peroxidation of membrane lipids in relation to reduction of CI in HWD-treated banana was also assessed. The results obtained in this study showed that peel colour (L*, C* and ho) decreased significantly (P≤0.01), while peel firmness (PF), weight loss (WL), degree of browning (DOB), peel electrolyte leakage (PEL) and soluble solids concentration (SSC) increased significantly (P≤0.01) when Berangan banana fruits were exposed to 5 oC. However, there was only a significant (P≤0.01) decrease in peel colour (L*, C* and ho), and a significant (P≤0.01) increase in DOB and SSC when banana fruits were exposed to 10 oC. Banana treated with HWD at 48 oC for 8 min showed significantly (P≤0.05) lower peel colour (L*, C* and ho) and DOB values when exposed to 10 oC as compared to the control. However, HWD has no significant effect on the SSC of these fruits. The results of this study indicated that HWD at 48 oC for 8 min could be considered as an optimum treatment combination in reducing CI development in Berangan banana. Nevertheless, the treatment did not sufficiently prevent CI development in Berangan banana stored for 16 days at 10 oC. Since there was no new synthesis of protein in banana exposed to HWD treatment, HSP was probably not involved in the reduction of CI. However, the reduction of CI was followed by a significant (P≤0.05) increase in PA, especially putrescine (PUT) and spermidine (SPD) after 8 days storage at 10 oC. This indicated that PUT and SPD could be involved in the reduction of CI development in Berangan banana. The increase in PUT and SPD could be associated with the reduction of peroxidation in the membrane lipids. As indicated by the HWD treatment results, there was no significant decrease in fatty acids composition, especially linolenic and arachidonic acid, as compared to the control fruit which showed a significant (P≤0.05) decrease. There was also no significant increase of lipoxygenase (LOX) activity which was reported to be responsible for the fatty acids degradation. These results might then contribute to the retaining of unsaturated to saturated (U/S) ratio of fatty acids in HWD-treated banana. There was a significant (P≤0.05) increase observed in the malonaldehyde (MDA) content of both the HWD-treated and control banana. However, the increase was found to be significantly (P≤0.05) higher in the control banana.The significant (P≤0.05) decrease of fatty acids (linolenic and arachidonic) and the significant (P≤0.05) increase of both LOX activity and MDA content in control fruits suggested significant (P≤0.05) higher lipid peroxidation as compared to that of HWD-treated banana. Therefore, the reduction of CI development in HWD-treated banana could be related to the increase of PUT and SPD in the fruits, which then contributed to the reduction of lipid peroxidation. It can be concluded that HWD could reduce CI development in Berangan banana due to retardation of lipid peroxidation which was in turn due to the increase in PUT and SPD contents