Postharvest factors affect under-skin browning in 'Honey Gold' mango fruit.

BACKGROUND: Under-Skin Browning (USB) is a physiological skin disorder that significantly reduces quality of 'Honey Gold' mango (HG) fruit. Relationships between potential causative factors (vibration, holding temperature, sap) and expression factors (enzymes activities, phenolic concentration, anatomy) were investigated. RESULTS: USB incidence was 2.6-3.6-fold higher in ripe HG fruit vibrated for 3-18 h at 12 °C to simulate transport damage and held then at 12 °C for 8 days compared to control fruit held under the same conditions. USB severity of fruit lightly abraded with sand paper to simulate physical damage and artificially induce USB was higher in fruit held at 10 °C than at 6-8 °C or 12-13 °C for 6-8 days. Compared to non-affected skin, USB-affected tissue had a 7.4% increase in total phenolics concentration. However, polyphenol oxidase (PPO) and peroxidase (POD) activities decreased by 19%. Anatomical similarities were observed between USB symptoms and sapburn caused by spurt sap or terpinolene (a major sap component) to abraded skin areas. Incidence of sapburn was higher in abraded fruit held at 12 °C than at 20 °C. CONCLUSION: Holding HG mango fruit at 10 °C can intensify USB. Activities of PPO and POD appear not to be regulatory factors in USB expression in HG. Sap components may be involved in USB expression under conducive postharvest conditions. © 2021 Society of Chemical Industry.

Diurnal Harvest Cycle and Sap Composition Affect Under-Skin Browning in 'Honey Gold' Mango Fruit.

Under-skin browning (USB) is an unsightly physiological disorder that afflicts 'Honey Gold' mango fruit. Under-skin browning symptoms develop after harvest upon the interaction of physical abrasion and physiological chilling stresses. Less understood preharvest and/or harvest factors may also influence fruit susceptibility to USB. In this study, we examined the impact of harvest time during the diurnal cycle and fruit sap components on USB development. Fruits were harvested at 4- to 6-h intervals, lightly abraded with sandpaper to simulate vibration damage during refrigerated road transport, held at 12 ± 1°C for 6 days, transported to the research facilities and ripened before USB assessment. Spurt and ooze sap from the fruit were collected at each harvest time. The samples were separated and analysed by gas chromatography-mass spectrometry. Fruit harvested at 10:00, 14:00 and 18:00 h had 3- to 5-fold higher incidence of USB than did those picked at 22:00, 2:00 and 6:00 h. Sap concentrations of the key aroma volatile compounds 2-carene, 3-carene, α-terpinene, p-cymene, limonene and α-terpinolene were higher for fruit harvested at 14:00 h compared to those picked at other times. In the fruits harvested in the afternoon, abraded skin treated with spurt sap sampled at 14:00 h had 14.3- and 29.0-fold higher incidence and severity, respectively, of induced browning than did those treated with sap collected at 6:00 h. The results showed that fruit harvested in the afternoon were more susceptible to USB than those picked at night or in early morning. The diurnal variation in fruit sensitivity was evidently associated with specific compositional differences in sap phytotoxicity. Topical application to the fruit skin of pure terpinolene and limonene resulted in induced USB damage, whereas pure carene and distilled water did not. Microscopy examination showed that while skin damage caused by pure terpinolene and limonene was not identical to USB per se, similarities suggested that sap components cause USB under inductive commercial conditions. Considered collectively, these findings suggest that night and early morning harvesting will reduce USB and thus improve the postharvest quality of Honey Gold mango fruit.

Stable isotope dilution assay (SIDA) and HS-SPME-GCMS quantification of key aroma volatiles for fruit and sap of Australian mango cultivars.

Reported herein is a high throughput method to quantify in a single analysis the key volatiles that contribute to the aroma of commercially significant mango cultivars grown in Australia. The method constitutes stable isotope dilution analysis (SIDA) in conjunction with headspace (HS) solid-phase microextraction (SPME) coupled with gas-chromatography mass spectrometry (GCMS). Deuterium labelled analogues of the target analytes were either purchased commercially or synthesised for use as internal standards. Seven volatiles, hexanal, 3-carene, α-terpinene, p-cymene, limonene, α-terpinolene and ethyl octanoate, were targeted. The resulting calibration functions had determination coefficients (R2) ranging from 0.93775 to 0.99741. High recovery efficiencies for spiked mango samples were also achieved. The method was applied to identify the key aroma volatile compounds produced by 'Kensington Pride' and 'B74' mango fruit and by 'Honey Gold' mango sap. This method represents a marked improvement over current methods for detecting and measuring concentrations of mango fruit and sap volatiles.

Characterisation of betalain biosynthesis in Parakeelya flowers identifies the key biosynthetic gene DOD as belonging to an expanded LigB gene family that is conserved in betalain-producing species.

Plant betalain pigments are intriguing because they are restricted to the Caryophyllales and are mutually exclusive with the more common anthocyanins. However, betalain biosynthesis is poorly understood compared to that of anthocyanins. In this study, betalain production and betalain-related genes were characterized in Parakeelya mirabilis (Montiaceae). RT-PCR and transcriptomics identified three sequences related to the key biosynthetic enzyme Dopa 4,5-dioxgenase (DOD). In addition to a LigB gene similar to that of non-Caryophyllales species (Class I genes), two other P. mirabilis LigB genes were found (DOD and DOD-like, termed Class II). PmDOD and PmDOD-like had 70% amino acid identity. Only PmDOD was implicated in betalain synthesis based on transient assays of enzyme activity and correlation of transcript abundance to spatio-temporal betalain accumulation. The role of PmDOD-like remains unknown. The striking pigment patterning of the flowers was due to distinct zones of red betacyanin and yellow betaxanthin production. The major betacyanin was the unglycosylated betanidin rather than the commonly found glycosides, an occurrence for which there are a few previous reports. The white petal zones lacked pigment but had DOD activity suggesting alternate regulation of the pathway in this tissue. DOD and DOD-like sequences were also identified in other betalain-producing species but not in examples of anthocyanin-producing Caryophyllales or non-Caryophyllales species. A Class I LigB sequence from the anthocyanin-producing Caryophyllaceae species Dianthus superbus and two DOD-like sequences from the Amaranthaceae species Beta vulgaris and Ptilotus spp. did not show DOD activity in the transient assay. The additional sequences suggests that DOD is part of a larger LigB gene family in betalain-producing Caryophyllales taxa, and the tandem genomic arrangement of two of the three B. vulgaris LigB genes suggests the involvement of duplication in the gene family evolution.

Effect of MeJA treatment on polyamine, energy status and anthracnose rot of loquat fruit.

The effect of methyl jasmonate (MeJA) on changes in polyamines content and energy status and their relation to disease resistance was investigated. Freshly harvested loquat fruit were treated with 10 µmol l(-1) MeJA and wound inoculated with Colletotrichum acutatum spore suspension (1.0 × 10(5) spores ml(-1)) after 24h, and then stored at 20 °C for 6 days. MeJA treatment significantly reduced decay incidence. MeJA treated fruit manifested higher contents of polyamines (putrescine, spermidine and spermine) compared with the control fruit, during storage. MeJA treatment also maintained higher levels of adenosine triphosphate, and suppressed an increase in adenosine monophosphate content in loquat fruit. These results suggest that MeJA treatment may inhibit anthracnose rot by increasing polyamine content and maintaining the energy status.

Cu2+ inhibition of gel secretion in the xylem and its potential implications for water uptake of cut Acacia holosericea stems.

Maintaining a high rate of water uptake is crucial for maximum longevity of cut stems. Physiological gel/tylosis formation decreases water transport efficiency in the xylem. The primary mechanism of action for post-harvest Cu(2+) treatments in improving cut flower and foliage longevity has been elusive. The effect of Cu(2+) on wound-induced xylem vessel occlusion was investigated for Acacia holosericea A. Cunn. ex G. Don. Experiments were conducted using a Cu(2+) pulse (5 h, 2.2 mM) and a Cu(2+) vase solution (0.5 mM) vs a deionized water (DIW) control. Development of xylem blockage in the stem-end region 10 mm proximal to the wounded stem surface was examined over 21 days by light and transmission electron microscopy. Xylem vessels of stems stood into DIW were occluded with gels secreted into vessel lumens via pits from surrounding axial parenchyma cells. Gel secretion was initiated within 1-2 days post-wounding and gels were detected in the xylem from day 3. In contrast, Cu(2+) treatments disrupted the surrounding parenchyma cells, thereby inhibiting gel secretion and maintaining the vessel lumens devoid of occlusions. The Cu(2+) treatments significantly improved water uptake by the cut stems as compared to the control.

The effects of host defence elicitors on betacyanin accumulation in Amaranthus mangostanus seedlings.

The effect of elicitors associated with host defence on betacyanin accumulation in Amaranthus mangostanus seedlings was investigated. Under the conditions of the experiments, betacyanin accumulation was generally enhanced by light. Methyl jasmonate (MeJA) treatment increased betacyanin synthesis in a concentration-dependent response. Seedlings treated with ethylene as 5mM Ethephon also had elevated levels of betacyanin. In contrast, salicylic acid (SA) and H(2)O(2) treatments had no influence on betacyanin contents in light or dark. Combined MeJA with Ethephon or H(2)O(2) had an additive effect on betacyanin accumulation in dark-grown seedlings. However, a decline was recorded in light-grown seedlings. Moreover, an antagonistic effect on betacyanin synthesis was found when MeJA and SA were added simultaneously. Our results indicate that betacyanin content in A. mangostanus seedlings can be upregulated by MeJA and ethylene. Both additive and antagonistic effects in regulating betacyanin synthesis in A. mangostanus seedlings were observed between MeJA and other elicitors.

The role of 1-methylcyclopropene in lignification and expansin gene expression in peeled water bamboo shoot (Zizania caduciflora L.).

BACKGROUND: Water bamboo shoot (WBS) (Zizania caduciflora L.) is a fleshy aquatic vegetable susceptible to lignification. In this study, effects of 1-methylcyclopropene (1-MCP) anti-ethylene treatment on lignification of harvested peeled WBS were investigated. RESULTS: Peeled shoots were treated with 0.5 µL L(-1) 1-MCP for 20 h at 20 °C and then stored at 20 °C for up to 9 days. Sensory quality, lignin content and activities of the lignification-associated enzymes peroxidase (POD) and phenylalanine ammonia lyase (PAL) were evaluated. Expression of expansin (ZcExp) was also assessed. 1-MCP application maintained better sensory quality and inhibited the increase in lignin content. Lessened lignification was associated with reduced activities of POD and PAL. Moreover, 1-MCP-treated shoots showed lower expression of the ZcExp gene. CONCLUSION: 1-MCP pretreatment suppressed the synthesis of lignin and thereby delayed lignification in peeled WBS.

Encapsulation of ethylene gas into α-cyclodextrin and characterisation of the inclusion complexes.

Molecular encapsulation of various apolar compounds with α-cyclodextrin (α-CD) is becoming a widely applied technique to produce food, pharmaceutical and agricultural materials. Encapsulated ethylene in the form of inclusion complexes (ICs) with cyclodextrin, which is in powder form, could be used in fruit ripening and other aspect of plant growth regulation. In this research, ethylene was complexed with an α-CD under 0.2-1.5MPa for 12-120h. Ethylene concentration in the inclusion complexes (ICs) varied from 0.98 to 1.03mol ethylene/mole CD. Pressure and time did not increase ethylene concentrations in the complexes, but did yield significantly higher amounts of the crystal complex. The physico-chemical properties of the ethylene-α-CD complexes at various concentration of ethylene were characterised using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP-MAS (13)C NMR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Complex formation was confirmed by sharp peaks in the XRD diffractograms, crystal images by SEM, double bond of ethylene gas and chemical shifts at C(4), C(3) and C(5) in NMR spectra, intensity changes of C-H bending and CC stretching in the FTIR spectra, and water loss and physico-chemical property modifications in the DSC and TGA scans.

Release kinetics of ethylene gas from ethylene-α-cyclodextrin inclusion complexes.

Ethylene was included into α-cyclodextrin (α-CD) by molecular encapsulation. Characterisation of the ethylene-α-CD inclusion complexes (ICs) using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) confirmed their crystalline structures. Release kinetics of ethylene gas from the ICs was investigated. Release characteristics experiments were carried out at various relative humidities (RH) (52.9%, 75.5%, and 93.6%) and temperatures (45, 65, 85, and 105°C). The Power Law and Avrami's equations were used to analyse release kinetics. The latter showed better fit for ethylene release. Kinetics analysis based on Avrami's equation showed that the release of ethylene was accelerated by increases in RH and temperature. For humidity treatments, the release parameter n represented a diffusive mechanism at 52.9% and 75.5% RH and a first-order mode at 93.6% RH. However, a diffusive mechanism was found in all temperature experiments. Release rate constants increased as a function of increasing temperature. Temperature coefficient (Q10), activation energy (Ea) and half-life release of ethylene gas were also analysed.

Characterisation of xylem conduits and their possible role in limiting the vase life of cut Acacia holosericea (Mimosaceae) foliage stems.

Early desiccation limits the vase life of Acacia cut flowers and foliage and may be attributable to poor hydraulic conductivity (Kh) of the cut stems. Acacia holosericea A.Cunn. ex G.Don has been adopted as the test species to investigate the postharvest water relations of the genus Acacia. To understand potential constraints on Kh, xylem conduits in cut A. holosericea stems were anatomically characterised by light and scanning and transmission electron microscopy. Vessels with simple perforation plates and tracheids were the principal water conducting cells. Bordered vestured intervessel pits were present in xylem vessel elements. The majority of conduits (89%) were short at 1-5cm long. Only 2% were 15-16cm in length. Mean xylem conduit diameter was 77±0.9µm and the diameter profile showed a normal distribution, with 29% of diameters in the range of 70-80µm. Simple perforation plates can offer relatively low resistance to water flow. On the other hand, bordered vestured pits and short xylem conduits can confer comparatively high resistance to water flow. Overall, the presence of bordered vestured pits, together with a high proportion of short xylem conduits and high stomatal densities (232±2mm-2) on unifacial phyllodes, could contribute to early dehydration of A. holosericea cut foliage stems standing in vase water. Further research will relate these anatomical features with changes in Kh and transpiration of cut foliage stems.

Role of phenylalanine ammonia-lyase in heat pretreatment-induced chilling tolerance in banana fruit.

Increasing evidence suggests that phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) is associated with low temperature stress in plant tissues. Banana fruit are highly susceptible to chilling injury. However, little is known about the role of PAL (i.e. gene expression, protein level and activity) in fruit chilling. In this work, the involvement of PAL induced by heat treatment (38 degrees C for 3 days) prior to storage (8 degrees C) in chilling tolerance was investigated. The PAL inhibitor 2-aminoindan-2-phosphonic acid (AIP) was also used to further study the role of PAL in the chilling tolerance. The results showed that mRNA transcripts (MaPAL1 and MaPAL2) and PAL protein levels increased during storage at chilling temperature. Heat treatment prior to storage alleviated chilling injury and enhanced PAL activity, protein amount and MaPAL1 and MaPAL2 transcript levels. The increases in parameters of PAL upon heat pretreatment were all inhibited by AIP treatment, which resulted in aggravation of chilling injury. Thus, these findings indicate that the induction of PAL by heat pretreatment was regulated at both the transcriptional and the translational levels and that PAL may play a role in heat pretreatment-induced chilling tolerance of banana fruit.

1H-Nuclear magnetic resonance imaging of ripening 'Kensington Pride' mango fruit.

Physicochemical gradients occur in mango mesocarp tissue during ripening. These gradients are reflected in water activity, which is non-uniform throughout the mesocarp. Signal intensity in proton magnetic resonance images (first echo, proton density and T2) for green-mature `Kensington Pride' mesocarp tissue was highest near the endocarp and lowest near the exocarp. Relative signal intensity increased in the middle mesocarp as ripening proceeded, but remained relatively low in the outer mesocarp. T2 relaxation times for inner and middle mesocarp regions fell during ripening. The data suggest that water activity in the mesocarp tissue increased in an outward-moving flux as ripening progressed. This change in water activity was associated with starch hydrolysis and other ripening-related processes that commence near the endocarp.