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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.

The mango cultivar 'Honey Gold' (HG) was developed in Queensland, Australia. Ripe defect-free HG fruit are characterized by bright yellow skin with red blush on their sun-exposed shoulders. HG mangoes are mostly grown from the Northern Territory down though Queensland into northern New South Wales (nNSW). As with many mango cultivars, HG suffers from a range of skin disorders. However, HG mango fruit grown in nNSW almost uniquely express a blotchy 'skin reddening' disorder that detracts from their visual appeal. The non-uniform reddening, which can encompass 'red lenticels', appears to be a host defense response. Causal agents of the reddening disorder are currently elusive. There may be a range of pre- and postharvest abiotic and/or biotic stresses, and they could be additive. A number of physical and chemical treatments were applied pre- or postharvest with a view to either suppress (i.e., prevent) or enhance (i.e., mask) uneven skin reddening. The physical treatments included preharvest fruit bagging and post-harvest exposure to different wavelengths of light. These physical treatments are considered in this paper. The chemical treatments included known modulators of host defense and ethylene responses. Those treatments are not reported in this short paper. However, among the full suite of treatments tested, one only notably influenced skin reddening. In this case, postharvest exposure to blue light increased reddening. Future research with HG will build on this initially promising finding.

Lenticel discoloration (LD), under-skin browning (USB) and resin canal disorder (RCD) are three important fruit skin disorders of concern to the Australian mango industry. They result in downgrading of fruit quality and loss of market confidence. LD is confined to the discoloration of lenticels on the fruit skin. USB is a sub-surface spreading grey-brown lesion that may only become evident in the marketplace. RCD is a dark brown discoloration of the finely branched pattern of ramifying sub-surface resin canals. These three browning disorders were compared and contrasted at the cellular level by light microscopy after free-hand sectioning. Discoloured lenticels on the surface of 'Honey Gold' mango fruit typically appeared as small round spots comprised of a dark brown centre surrounded by a white corona. Non-coloured lenticels were visible as small round spots surrounded by a white corona. In cross-section, there was browning of cells surrounding the cavity of discoloured lenticels. Nonetheless, there was no such browning in non-coloured lenticels. USB symptoms in 'Honey Gold' fruit were evident as dark-brown cells in the tissue surrounding the resin ducts. In contrast, RCD, which was evident in 'Kensington Pride' mango fruit, was characterised by browning of the lumen of resin ducts. Accordingly, LD, USB and RCD involve different browning biology processes at the cell and tissue levels. A greater understanding of symptom development and expression could aid in informed management of these physiological disorders.

Refrigerated containers are used to transport mangoes over long distances. In Australia, mangoes grown in northern tropical production areas for the domestic market are transported by road and/or rail for up to 4000 km to southern ripening centres. There is no other viable option for growers to ripen their fruit. A current project is investigating sustained ethylene release systems for ripening mango fruit in road transport containers over an in-transit period of up to 4 days. This approach could potentially provide an alternative cost-effective ripening strategy for the mango industry. Studies have been and will be performed using shipments of 'B74' and 'Honey Gold' mango fruit, respectively, in refrigerated road containers. In-container environment monitoring, fruit shelf life and quality evaluation at outturn are carried out. Corresponding laboratory experiments that simulate transit are also to be conducted with a view to modelling mango fruit responses to in-transit conditions.

Resin canal discoloration (RCD) is a quality defect that reduces the visual appeal and marketability of mango fruit. Market reports of RCD have increased recently, particularly for 'Kensington Pride' fruit produced in the Northern Territory, Australia. Anecdotal observations by mango growers suggest that early fruit harvest maturity, rain before harvest and handling conditions may be associated with RCD. In the current study, we completed a series of preliminary experiments with 'Kensington Pride' fruit to characterise RCD symptom development and to identify potential contributing factors. RCD was seldom present in hard green-mature fruit at harvest. The defect was first visualised as lightly discoloured resin canals in partially ripe fruit. The severity of RCD symptoms steadily increased as fruit developed from firm-ripe to eating-ripe. The incidence of RCD was 42-52% higher for fruit picked early in the season at KLEINERDAN13% dry matter content (DMC) than for those harvested 2-4 weeks later at 15-17% DMC. Harvesting fruit within 12 h of a 14-mm rainfall event resulted in 45% higher RCD incidence than in fruit picked after 60 h of sustained dry weather. The incidence of RCD varied from 0 to 45% for fruit from nine orchards in the Northern Territory when harvested and ripened directly off the tree. RCD incidence was threefold higher in the same fruit that were exposed to commercial handling and interstate transport. Overall, these observations suggest that RCD is a complex disorder that occurs when field conditions result in sensitised fruit that may express the defect when exposed to postharvest handling practices.

A novel ethylene-α-cyclodextrin (α-CD) inclusion complex (IC) powder was investigated to ripen Calypso mango fruit. Modulated release of ethylene gas from the IC powder was achieved by admixture with deliquescent salt CaCl2 at RHs of 75.5% and 93.6%. The IC powder was tested in the laboratory and for in-transit ripening of mango fruit over two seasons. In the laboratory experiment, ethylene gas started to release from the IC powder in 2 h and complete release was achieved in 24 h. Assessments of fruit colour and firmness showed that encapsulated ethylene and commercial grade ethylene from pressurised cylinder similarly shortened the ripening time to 9–10 days (after harvest) for treated fruit as compared with 15 days for untreated mango. Mango fruit treated in both ways with ethylene showed more uniform ripening than the control. For the in-transit ripening using the IC powder, ethylene was found to be between 4.9 and 10.5 μL L−1 in the headspace of the truck containers over 48 h. Mango fruit from the treated containers shortened the ripening time by 3–6 days as compared to the untreated control fruit. Thus, the safe and convenient IC powder has demonstrated promise for in-transit fruit ripening.

The fruit of certain mango cultivars (e.g., 'Honey Gold') can develop blush on their skin. Skin blush due to red pigmentation is from the accumulation of anthocyanins. Anthocyanin biosynthesis is related to environmental determinants, including light received by the fruit. It has been observed that mango skin blush varies with position in the tree canopy. However, little investigation into this spatial relationship has been conducted. The objective of this preliminary study was to describe a 'Honey Gold' mango tree by capturing its three-dimensional (3D) architecture. A light path tracing model QuasiMC was then used to predict light received by fruit. The use of this 3D model was to better understand the relationship between mango fruit skin blush and fruit position in the canopy. The digitised mango tree mimicked the real tree at a high level of detail. Observations on mango skin blush distribution supported the proposition that sunlight exposure is an absolute requirement for anthocyanin development. No blush development occurred on shaded skin. It was affirmed that 3D mapping could allow for virtual experiments. For example, for virtual canopy thinning (e.g., 'window pruning') to admit more sunlight with a view to improve fruit blush. Improvements to 3D modelling of mango skin blush could focus on increasing accuracy, e.g., measurement of leaf light reflectance and transmission and the inclusion of the effect shading by branches.

'Honey Gold' is an Australian mango cultivar with attractive skin colour and good flavour when ripe. Under-skin browning (USB) is a disorder that develops on 'Honey Gold' fruit after harvest. The disorder is usually not evident until fruit reach the wholesale market. Thus, fruit often need re-packing at the markets, causing considerable wastage and financial loss. Previous research suggested that USB results from an interaction between physical pressure (i.e., mechanical stress) and low temperature (i.e., physiological stress) during transport and distribution. To address this issue, fruit from three farms in the Northern Territory were either cooled to 13°C within 10 h of harvest, or held at 18-20°C for 1-2 days before cooling to 13°C. The fruit were packed within commercial fibreboard trays in either standard plastic liners, a 'softer' liner to potentially minimise fruit damage, or were individually wrapped in plastic or bubble wrap to prevent any damage. The fruit were then palletised and transported for three days to southern Australia in a refrigerated truck. Delaying cooling after harvest for two days reduced the incidence of USB by 52-85%. As compared to using standard liners and cooling immediately after harvest, the proportion of fruit with USB decreased from 25 to 3% when fruit packed with soft liners were held at 18-20°C for two days before cooling at 13°C and transporting. These findings show that reducing the risk of vibration damage by using soft liners in combination with a delay in temperature reduction after harvest can significantly reduce USB in commercial practice.

Skin colour is an important quality parameter that influences mango fruit marketability. The mango industry is interested in controlled induction of skin blush in mangoes. It is desirable to understand the control of anthocyanin accumulation in mango skin. Among environmental factors known to induce anthocyanin accumulation in plants, light is the most studied. Light exposure induces pigmentation in various fruits, including apple, strawberry and grape. The effect of different light qualities on skin blush in mango fruit has received relatively little attention. The objective of this study was to assess anthocyanin accumulation and blush in response to blue, red and far red light from light-emitting diodes (LEDs) as applied to harvested mango fruit skin during storage at 12°C. Except for red light, the other wavelengths induced anthocyanin accumulation and skin blush as compared to the dark control treatment. Anthocyanin concentration and a∗ values were highest in blue light exposed fruit skin. This wavelength enhanced phenylalanine ammonia lyase activity in the mango skin, which may be associated with increased pigmentation. LED light treatment did not affect other fruit quality parameters at 21 days of storage, including firmness, total soluble solids and titratable acidity. Overall, the findings suggest that postharvest treatment with blue light can induce skin blush in mango fruit, which potentially may enhance their commercial value.

γ-Irradiation doses of 0.5 (target) and 1.0 (high) kGy were applied as insect disinfestation treatments to 'Kensington Pride' mango fruit. The effects of these treatments on fruit physicochemical properties and aroma volatile production were investigated and compared to non-irradiated controls. There were no significant effects of the irradiation treatments on flesh total soluble solids content. However, the loss of green skin colour usually associated with fruit ripening was inhibited by irradiation at both 0.5 and 1.0 kGy by approximately 32 and 52%, respectively, relative to non-irradiated fruit. Fruit exposed to 0.5 and 1.0 kGy exhibited a 58 and 80% reduction in emission of a-terpinolene volatiles, respectively. Thus, γ-irradiation at 0.5 and 1.0 kGy can have an adverse effect on 'Kensington Pride' mango fruit aroma volatile production and skin colouration.

A novel ethylene-α-cyclodextrin inclusion complex powder was produced and tested for ripening 'Calypso' mango fruit. Ethylene was released from the powder under controlled humidity and temperature. Admixture with deliquescent calcium chloride (CaCl2) salt gave fast release of ethylene gas over 24 h. Ethylene gas released from the powder triggered mango ripening ascertained as fruit firmness and colour changes in a temporal manner similar to as for conventional ethylene gassing as compared to non-ethylene treated control fruit. The novel powder formulation has demonstrated promise for commercial application to ripen mango fruit.

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.