Improvement of postharvest quality, regulation of antioxidants capacity and softening enzymes activity of cold-stored carambola in response to polyamines application

The efficacy of putrescine (PUT) and spermidine (SPD) application in preserving postharvest quality, regulating bioactive compounds and cell wall softening enzymes was examined during cold storage of carambola fruit (Averrhoa carambola cv. B10). Three different concentrations (0.0, 0.1, 1.0 and 2.0 mM) of PUT and SPD were applied to fruit by immersion for 5 min and further stored at 3 °C, 85–90 % RH for 28 d. The highest concentration (2.0 mM) of PUT effectively reduced weight loss, maintained peel colour (L*, C*, h°), retained higher firmness, lowered respiration rate and ethylene emission, and suppressed the degradation of soluble solids content (SSC) and titrable acidity (TA) throughout storage. Moreover, 2.0 mM PUT treatment delayed the advancement of β-galactosidase (β-gal), polygalacturonase (PG) and pectin methylesterase (PME) enzymes activity concomitant with less apparent changes in fruit firmness. Ascorbic acid (AA), total antioxidant content (TAC) and phenolic content (TPC) were enhanced to higher levels in treated fruit, while control fruit experienced significant loss of these bioactive compounds. The highest concentration (2.0 mM) of PUT and SPD exhibited the best result of increasing TAC activity through an increment of TPC. In contrast, higher AA content was stimulated by lower concentration of SPD (1.0 and 0.1 mM). This present finding throws light on the potential of polyamines (PAs) as an effective mean for maintaining postharvest quality, enhancing antioxidants capacity and provokes reduction on softening enzymes activity, with the prolong shelf-life of B10 carambola.