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Studies were conducted to describe flavor and aroma in ripe tomatoes stored at 5, 10, 12.5 and 20°C. Fruit stored for 2 d below 20°C were rated by trained sensory panelists as significantly lower (P < 0.05) in ripe aroma, tomato flavor, compared to those stored at 20°C. Fruit stored at 5°C for 4 d were rated significantly lower in ripe aroma, sweetness, tomato flavor, and significantly higher in sourness, compared to those stored at 20°C. Following 8 and 12 d storage, fruit at 5°C were rated lowest in ripe aroma and sweetness. Significant reductions in important GC aroma volatiles and chemical composition and electronic nose analyses concurred with sensory descriptor ratings.

Melatonin acts as a crucial signaling and antioxidant molecule with multiple physiological functions in organisms. To explore effects of exogenous melatonin on postharvest browning and its possible mechanisms in litchi fruit, 'Ziniangxi' litchi fruits were treated with an aqueous solution of melatonin at 0.4 mM and then stored at 25 °C for 8 days. The results revealed that melatonin strongly suppressed pericarp browning and delayed discoloration during storage. Melatonin treatment reduced relative membrane-leakage rate and inhibited the generation of superoxide radicals (O), hydrogen peroxide (HO), and malondialdehyde (MDA). Melatonin treatment markedly promoted the accumulation of endogenous melatonin; delayed loss of total phenolics, flavonoids, and anthocyanins; and enhanced the activities of antioxidant enzymes, including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2). By contrast, the activities of browning-related enzymes including polyphenoloxidase (PPO, EC 1.10.3.1) and peroxidase (POD, EC 1.11.1.7) were reduced. In addition, melatonin treatment up-regulated the expression of four genes encoding enzymes for repair of oxidized proteins, including LcMsrA1, LcMsrA2, LcMsrB1, and LcMsB2. These findings indicate that the delay of pericarp browning and senescence by melatonin in harvested litchi fruit could be attributed to the maintenance of redox homeostasis by the improvement of the antioxidant capacity and modulation of the repair of oxidatively damaged proteins.

Polyuronides and hemicelluloses derived from ethanol powders or cell walls of strawberry (Fragaria x ananassa, Duch. Dover) receptacle tissue were examined to determine if these wall polymers might be involved in the softening of this fruit. Throughout maturation and ripening, total polyuronides increased on a per fruit basis although as a percentage of ethanol powder they remained constant. Gel-filtration chromatography confirmed that polyuronide solubility was not correlated with extensive enzymic hydrolysis, an observation consistent with the fact that D-galacturonanase (polygalacturonase) activity was not detected in strawberry fruit. The sugar composition of alkali-soluble wall polymers showed little change throughout development. However, changes occurred in the molecular weights of these polymers during ripening.

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from 13 to 37 mM. The levels of Na + and divalent cations did Apoplastic pH and ionic conditions exert strong influence on not change, whereas the anions P and Cl − increased in ripe cell wall metabolism of many plant tissues; however, the nature of the apoplastic environment of ripening fruit has been fruit. Ca 2 + levels remained relatively constant during ripening the subject of relatively few studies. In this report, a pressure-at 4 -5 mM, concentrations that effectively limit pectin solubilization. The electrical conductivity of the apoplastic liquid bomb technique was used to extract apoplastic fluid from increased 3-fold during ripening, whereas osmotically active tomato fruit (Lycopersicon esculentum Mill.) pericarp at several developmental stages. pH and the levels of K + , Na + , solutes increased 2-fold. Pressure-treated fruit retained the capacity to ripen. The decline in apoplastic pH and increase in Ca 2 + , Mg 2 + , Cl − and P were determined and compared ionic strength during tomato fruit ripening may regulate the with the values for the bulk pericarp and locule tissues. The activity of cell wall hydrolases. The potential role of apoplas-pH of the apoplastic fluid from pericarp tissue decreased from tic changes in fruit ripening and softening is discussed. 6.7 in immature and mature-green fruits to 4.4 in fully-ripe fruit. During the same period, the K + concentration increased

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Avocado (Persea americana) fruit experience a rapid and extensive loss of firmness during ripening. In this study, we examined whether the chelator solubility and molecular weight of avocado polyuronides paralleled the accumulation of polygalacturonase (PC) activity and loss in fruit firmness. Polyuronides were derived from ethanolic precipitates of avocado mesocarp prepared using a procedure to rapidly inactivate endogenous enzymes. During ripening, chelator (cyclohexane-trans-l,2-diamine tetraacetic acid [CDlA])-soluble polyuronides increased from approximately 30 to 40 pg of galacturonic acid equivalents (mg alcohol-insoluble solids)-' in preripe fruit to 150 to 170 pg mg-' in postclimacteric fruit. In preripe fruit, chelator-extractable polyuronides were of high molecular weight and were partially excluded from Sepharose CL-26-300 gel filtration media. Avocado polyuronides exhibited marked downshifts in molecular weight during ripening. At the postclimacteric stage, nearly all chelator-extractable polyuronides, which constituted from 75 to 90% of total cell wall uronic acid content, eluted near the total volume of the filtration media. Rechromatography of low molecular weight polyuronides on BioCel P-4 disclosed that oligomeric uronic acids are produced in vivo during avocado ripening. l h e gel filtration behavior and pattern of depolymerization of avocado polyuronides were not influenced by the polyuronide extraction protocol (imidazole versus CDTA) or by chromatographic conditions designed to minimize interpolymeric aggregation. Polyuronides from ripening tomato (fycopersicon esculentum) fruit extracted and chromatographed under conditions identical with those used for avocado polyuronides exhibited markedly less rapid and less extensive downshifts in molecular weight during the transition from mature-green to fully ripe. Even during a 9-d period beyond the fully ripe stage, tomato fruit polyuronides exhibited limited additional depolymerization and did not include oligomeric species. A comparison of the data for the avocado and tomato fruit indicates that downshifts in polyuronide molecular weight are a prominent feature of avocado ripening and may also explain why molecular down-regulation of PC (EC 3.2.1.15) in tomato fruit has resulted in minimal effects on fruit performance until the terminal stages of ripening.Avocado fruit soften extensively during ripening, with mesocarp firmness, measured in terms of resistance to penetration, exceeding 450 N at the preripe stage and decreasing severa1 orders of magnitude during ripening (Pesis et al., 1978; Awad and Young, 1979; O'Donoghue and Huber,