Polyamine biosynthesis in flavedo of ‘Fortune’ mandarins as influenced by temperature of postharvest hot water dips

'Fortune' mandarins were submitted to postharvest hot water dips to verify the influence of this treatment on polyamine content in fruit flavedo. Dip time was 3 minutes and temperatures tested were 44, 47, 50, 53, 56, and 59°C. Putrescine content in flavedo of untreated fruit was 2.66 μM-g-1 FW. This concentration increased proportionally to bath temperatures up to 6.43 μM-g-1 FW in fruit dipped at 59°C. Not so linear was the increase in spermidine from 0.064 μM-g-1 FW in control fruit to the maximum of 0.183 μM-g-1 FW in fruit treated at 53°C, with decreasing concentrations in fruit dipped at 56 and 59°C. Spermine content also increased from 0.007 μM-g-1 FW to 0.022 μM-g-1 FW in fruit treated at 47°C and ranged around this value at higher temperatures. Treatment at 47°C was the most effective in reducing chilling injury index in fruit after 4 week storage at 2°C and 90-95% RH. Scald damage was observed with temperatures over 53°C. No correlation was found between polyamine content and chilling injury control, with slight differences for spermine. Consequently, increases in polyamine levels appeared to be a response to heat stress, without having a specific role in inducing chilling resistance.