Postharvest oxidative stress in plums : mechanism and implications for storage and fruit quality

Postharvest life and susceptibility to chilling injury (CI) in Japanese plums (Prunus salicina Lindl.) are greatly influenced by preharvest and postharvest factors. The phenomenon of postharvest oxidative stress has been implicated in affecting fruit quality, potential storability and susceptibility to development of physiological disorders during storage of fruits. Therefore, the investigations were carried out to understand the role of various factors, such as cultivar, harvest maturity, storage conditions (temperature and atmosphere composition), duration of storage and postharvest treatments, in the development of oxidative stress in Japanese plums, in relation to fruit quality and CI. The degree of lipid peroxidation and membrane integrity was measured by determining the activity of lipoxygenase enzyme, concentration of thiobarbituric acid–reactive substances, and amount of electrolyte leakage. The activities of antioxidant enzymes, superoxide dismutase, catalase, and peroxidase, were determined as a direct measure of the enzymatic antioxidant capacity. The activities of enzymes (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, and glutathione–S–transferase) involved in the oxidation and regeneration of ascorbate (AA) and glutathione (GSH) were also determined to underpin the dynamics of the AA–GSH cycle. The concentrations of AA, dehydroascorbate (DHA), GSH, and oxidized glutathione (GSSG) were determined to compute the AA:DHA and GSH:GSSG ratios as the indicators of redox potential of fruit tissue. The total phenolics concentration and total antioxidant capacity were also determined as a part of the non–enzymatic antioxidants.The experimental data suggest that postharvest oxidative stress developed during fruit ripening in Japanese plums, but the rate was dependent on the climacteric behaviour of fruit. The climacteric cultivars, ‘Blackamber’ and ‘Amber Jewel’, showed a faster decline in the ability of antioxidative system to encounter the oxidative stress during fruit ripening as compared to ‘Angeleno’, a suppressed–climacteric cultivar. The delay in harvesting of ‘Amber Jewel’ plums by one week slightly improved fruit quality and the initial status of antioxidants than the commercial harvest. However, the fruit harvested at commercial maturity had better retention of antioxidative system during cold storage at 0°C for 3–4 weeks compared to the fruit from the delayed harvest. The changes in enzymatic and non–enzymatic antioxidants as a function of storage duration appear to be more prominent in providing protection against oxidative injury expressed as CI than their at–harvest status. The response of the antioxidative system in ‘Amber Jewel’ plums at 5°C was significantly better than at 0°C. But, the storage temperature of 5°C was not sufficiently low to inhibit the process of fruit ripening, resulting in limited storage life of 2 weeks. The multiple–point time course analysis of lipid peroxidation and changes in enzymatic and non–enzymatic antioxidants of ‘Blackamber’ plums revealed that the third week of storage is the critical point beyond which the capacity of antioxidative system to cope with the increasing oxidative stress from CI and fruit ripening began to decline, resulting in increased incidence and severity of CI during the extended periods of storage. Controlled atmospheres (CA) were found beneficial to reduce the levels of oxidative stress in ‘Blackamber’ plums.CA containing 1% O[subscript]2 + 3% CO[subscript]2 were effective in mitigating the oxidative stress during the 5 weeks of cold storage at 0–1°C, plus 6 days of shelf life at 21±1°C. The efficacy of CA (1% or 2.5% O[subscript]2 + 3% CO[subscript]2) in alleviating CI in ‘Blackamber’ plums could be further enhanced by the pre–storage treatment of fruit with 1–methylcyclopropene (1–MCP, 0.6 μL L[superscript]–[superscript]1). The combination of CA and 1–MCP exhibited synergistic effects on the alleviation of oxidative stress, resulting in enhanced storage life up to 8 weeks, plus 6 days of shelf–life. The role of nitric oxide (NO) as an antioxidant was also investigated in order to retard fruit ripening, delay the onset of senescence and development of oxidative stress in the Japanese plums. Postharvest NO fumigation (10 or 20 μL L[superscript]–[superscript]1) delayed the fruit ripening and maintained quality for 9–12 days in ‘Amber Jewel’ and ‘Blackamber’ plums at 21±1°C. NO fumigation was also beneficial to reduce the symptoms of CI during cold storage of ‘Amber Jewel’ and ‘Blackamber’ plums for 5–6 weeks at 0°C, plus 5 days of shelf–life at 21±1°C. The positive effects of NO fumigation on the enzymatic and non–enzymatic antioxidants in addition to reduced rates of lipid peroxidation were associated with the enhanced chilling tolerance in Japanese plums. The response of ‘Amber Jewel’ to postharvest NO fumigation was significantly better than ‘Blackamber’.In conclusion, the development of oxidative stress in Japanese plums was influenced by cultivar, harvest maturity, cold storage (temperature, duration and atmosphere composition), and postharvest treatments with NO and 1–MCP. The mitigation of oxidative stress by manipulation of postharvest storage conditions and treatments can be achieved to maintain fruit quality and reduce the incidence and severity of CI in Japanese plums

Formylated phloroglucinols from Eucalyptus loxophleba foliage

Two new naturally occurring formylated phloroglucinol compounds (FPCs), a dimer, loxophlebal B (10) and a cyclized FPC, loxophlebene (8) together with eight other formylated phloroglucinols (1-7 and 9) were isolated from the chloroform-methanol (8:2) extract of the leaves of Eucalyptus loxophleba ssp. lissophloia. The structures of new compounds were established by comprehensive spectral analysis and by comparison of their NMR data with those of related compounds in the literature. All the isolated compounds were evaluated for anti-leishmanial activity against promastigotes of Leishmania donovani

Terpenoidal constituents of Eucalyptus loxophleba ssp. lissophloia

Context: Eucalyptus has been a source of a number of biologically active compounds. The anti-leishmanial activity of terpenoids from Eucalyptus loxophleba (Benth.) ssp. lissophloia (Myrtaceae) has not yet been investigated. Objective: Isolation of the terpenoidal constituents for evaluation of in vitro anti-leishmanial activity against the Leishmania donovani (Dd8 strain) promastigotes. Materials and methods: The chloroform-methanol (8:2) extract of dried leaves of Eucalyptus loxophleba was used to isolate terpenoidal constituents employing solvent partitioning, column chromatography and preparative high performance liquid chromatography and characterized from spectral data. The anti-leishmanial activity of the isolated compounds was tested in vitro using an Alamar blue assay against a culture of L. donovani (Dd8 strain) promastigotes. Results: Two new naturally occurring triterpenes, named loxanic acid and 3-acetyl loxanic acid together with four known ursane triterpenoids and one bis-monoterpene glycoside, cuniloside B isolated from the leaves showed anti-leishmanial activity (IC50 133 to 235 μM) against the promastigotes of the tested strain. Conclusion: The terpenes isolated from the leaves of E. loxophleba showed moderate anti-leishmanial activity

Targeted Metabolomics Approach to Study Secondary Metabolites and Antioxidant Activity in ‘Kinnow Mandarin’ during Advanced Fruit Maturity

In this study, we investigated the impact of harvest maturity stages and contrasting growing climates on secondary metabolites in Kinnow mandarin. Fruit samples were harvested at six harvest maturity stages (M1–M6) from two distinct growing locations falling under subtropical– arid (STA) and subtropical–humid (STH) climates. A high-performance liquid chromatographytandem mass spectrometry (HPLC-MS/MS) technique was employed to identify and quantify secondary metabolites in the fruit juice. A total of 31 polyphenolics and 4 limonoids, with significant differences (p < 0.05) in their concentration, were determined. With advancing maturity, phenolic acids and antioxidant activity were found to increase, whereas flavonoids and limonoids decreased in concentration. There was a transient increase in the concentration of some polyphenolics such as hesperidin, naringin, narirutin, naringenin, neoeriocitrin, rutin, nobiletin and tangeretin, and limonoid aglycones such as limonin and nomilin at mid-maturity stage (M3) which coincided with prevailing low temperature and frost events at growing locations. A higher concentration of limonin and polyphenolics was observed for fruit grown under STH climates in comparison to those grown under STA climates. The data indicate that fruit metabolism during advanced stages of maturation under distinct climatic conditions is fundamental to the flavor, nutrition and processing quality of Kinnow mandarin. This information can help in understanding the optimum maturity stage and preferable climate to source fruits with maximum functional compounds, less bitterness and high consumer acceptabilit

Comparative analysis of phenolic compound characterization and their biosynthesis genes between two diverse bread wheat (Triticum aestivum) varieties differing for chapatti (unleavened flat bread) quality

AbstractPhenolic compounds (PCs) affect the bread quality and can also affect the other types of end-use food products such as chapatti (unleavened flat bread), now globally recognised wheat-based food product. The detailed analysis of PCs and their biosynthesis genes in diverse bread wheat (Triticum aestivum) varieties differing for chapatti quality have not been studied. In this study, the identification and quantification of PCs using UPLC-QTOF-MS and/or MS/MS and functional genomics techniques such as microarrays and qRT-PCR of their biosynthesis genes have been studied in a good chapatti variety, ‘C 306’ and a poor chapatti variety, ‘Sonalika’. About 80% (69/87) of plant phenolic compounds were tentatively identified in these varieties. Nine PCs (hinokinin, coutaric acid, fertaric acid, p-coumaroylqunic acid, kaempferide, isorhamnetin, epigallocatechin gallate, methyl isoorientin-2’-O-rhamnoside, and cyanidin-3-rutinoside) were identified only in the good chapatti variety and four PCs (tricin, apigenindin, quercetin-3-O-glucuronide, and myricetin-3-glucoside) in the poor chapatti variety. Therefore, about 20% of the identified PCs are unique to each other and may be ‘variety or genotype’ specific PCs. Fourteen PCs used for quantification showed high variation between the varieties. The microarray data of forty-four phenolic compound biosynthesis genes and seventeen of them on qRT-PCR showed variation in expression level during seed development and majority of them showed low expression in the good chapatti variety. The expression pattern in the good chapatti variety was largely in agreement with that of phenolic compounds. The level of variation of twelve genes was high between the good and poor chapatti quality varieties and has potential in development of markers. The information generated in this study can be extended onto a larger germplasm set for development of molecular markers using QTL and/or association mapping approaches for their application in wheat breeding