Peel Degreening Research Articles

CsERF003 enhanced peel coloration by promoting both chlorophyll degradation and carotenoid accumulation in citrus

Uneven coloration is a common phenomenon in citrus fruit during the ripening stage, as affects the appearance and economic value of the fruit. The elevated expression of CsERF003 during the degreening process of both lemon and satsuma mandarin peels was reported. In this research, a similar performance of CsERF003 in the pericarp coloration process was also identified by transcriptome analysis of 'Fengjie 72–1' navel orange and Lane Late navel orange. However, the regulatory mechanism of CsERF003 is not clear yet. Overexpression of CsERF003 could deepen the color of citrus callus and promote peel degreening of Newhall navel orange, which was attributed to the upregulation of genes involved in chlorophyll degradation and carotenoid synthesis. Furthermore, CsERF003 acted as an activator to promote the expression of CsLCYE, but couldn’t activate the expression of CsLCYB1 and CsLCYB2; CsERF003 could also bind to the promoter of CsSGR to activate its expression. Together, our findings shed light on the regulatory mechanism of CsERF003 in chlorophyll degradation and carotenoid accumulation, particularly in the α-branch of carotenoid metabolism. These insights offer valuable perspectives for the genetic enhancement of peel coloration in citrus.

Jasmonate Promotes Ester Aroma Biosynthesis during Nanguo Pears Storage

Volatile organic compounds (VOCs) have been known to confer the flavor of fruits, characterizing the quality of fruits. Nanguo pear (Pyrus ussuriensis Maxim.) is widely popular among consumers due to its excellent ‘fruity’ aroma derived from ester aroma substances. Jasmonate (JAs) plays an indispensable role in the formation of many qualities in fruit. Therefore, the present study aimed to explore the effect of jasmonate on the VOCs in the Nanguo pear fruit during storage. During storage, the fruits were treated with various concentrations of methyl jasmonate (MeJA) and sodium diethyldithiocarbamate (DIECA, a JAs inhibitor), the inhibitors of JAs biosynthesis. Subsequently, the composition and levels of VOCs in the fruits were determined using GC-MS. The results showed that 100 uM MeJA treatment could promote the accumulation of ester aroma compounds in Nanguo pear fruits, while 100 mM DIECA had the opposite effect. Meantime, MeJA treatment significantly promoted peel degreening, soluble solids content (SSC), fruit softening, and ethylene formation. The RT-qPCR results showed that JAs stimulated the expression of PuAAT1 and repressed the expression of PuCXEs, leading to an increased accumulation of ester aroma compounds. Overall, these results provide a reference for further research on the effect of JAs on fruit aroma.

Synthesis of 1-(2,2-Dimethylpropyl)-Cyclopropene (1-DCP) as an Ethylene Antagonist.

Ethylene is a gaseous hydrocarbon molecule known as a plant hormone that promotes fruit ripening and senescence. Efficiently controlling ethylene is a central key to maintaining the quality of agricultural products. The current study uncovered a synthetic method for 1-(2,2-dimethylpropyl)-cyclopropene (1-DCP) as a cyclopropene derivative to inhibit ethylene action in fruit ripening and senescence. We synthesized 1-DCP using α-diisobutylene through a two-step process, including allylic chlorination by hypochlorite and HCl, followed by α-elimination of the allylic chloride using a strong base, lithium diethylamide. GC-MS and NMR analyses demonstrated that 1-DCP was synthesized efficiently with 35% yield and 95% purity. When treated as an aqueous emulsion on plants, including persimmon and banana fruits, 1 mM 1-DCP showed effective inhibition of ethylene action by delaying the flesh softening and peel degreening, which are representative phenomena of fruit ripening and senescence induced by ethylene. Our data demonstrated that 1-DCP could be synthesized and used as a sprayable ethylene antagonist for pre- or post-harvest growth regulation in plants and fruits.

Cold pretreatment promotes chlorophyll degradation of green ripening banana peel by activating MaCBF1 to MaCBR and MaSGR1

Inhibition of peel de-greening in postharvest bananas under high temperature storage, resulting in green ripening, causes significant deterioration in fruit quality. Herein, we reported that cold treatment accelerated chlorophyll degradation of postharvest banana fruit at 30 °C, which was associated with the upregulated expression of MaCBR (Chlorophyll b reductase) and MaSGR1 (Stay-green 1). Moreover, cold treatment increased the expression of C-repeat binding factor MaCBF1. MaCBF1 bound directly to the promoters of MaCBR and MaSGR1 and activated their expressions. More importantly, transient expression of MaCBF1 in bananas enhanced chlorophyll degradation and weakened the repression of de-greening caused by high temperature. In summary, the cold treatment promotes chlorophyll catabolism by activating MaCBF1-induced transcriptional activation of MaCBR and MaSGR1, and attenuates high temperature-caused green ripening in bananas. These results study expand the understanding of the molecular events of high temperature-inhibited chlorophyll degradation and provide a feasible strategy to alleviate green ripening of banana fruit.

Environmentally driven transcriptomic and metabolic changes leading to color differences in "Golden Reinders" apples.

Apple is characterized by its high adaptation to diverse growing environments. However, little is still known about how different environments can regulate at the metabolic or molecular level specific apple quality traits such as the yellow fruit peel color. In this study, changes in carotenoids and chlorophylls, antioxidants as well as differences in the transcriptome were investigated by comparing the peel of “Golden Reinders” apples grown at different valley and mountain orchards. Mountain environment favored the development of yellow color, which was not caused by an enhanced accumulation of carotenoids but rather by a decrease in the chlorophyll content. The yellow phenotype was also associated to higher expression of genes related to chloroplast functions and oxidative stress. Time-course analysis over the last stages of apple development and ripening, in fruit from both locations, further revealed that the environment differentially modulated isoprenoids and phenylpropanoid metabolism and pointed out a key role for H2O2 in triggering apple peel degreening. Overall, the results presented herein provide new insights into how different environmental conditions regulate pigment and antioxidant metabolism in apple leading to noticeable differences in the apple peel color.

Examining the Role of Low Temperature in Satsuma Mandarin Fruit Peel Degreening via Comparative Physiological and Transcriptomic Analysis.

Peel degreening is the most conspicuous aspect of fruit ripening in many citrus fruits because of its importance for marketability. In this study, peel degreening in response to propylene (an ethylene analog) and at varying storage temperatures was characterized in Satsuma mandarin (Citrus unshiu Marc.) fruit. Propylene treatment triggered rapid peel degreening (within 4–6 days), indicated by an increase in the citrus color index (CCI) and chlorophyll loss. Peel degreening was also observed in fruit at 10°C and 15°C after 28–42 days, with gradual CCI increase and chlorophyll reduction. However, fruit at 5°C, 20°C, and 25°C remained green, and no substantial changes in peel CCI and chlorophyll content were recorded during the 42-day storage duration. The transcriptomes of peels of fruit treated with propylene for 4 days and those stored at varying temperatures for 28 days were then analyzed by RNA-Seq. We identified three categories of differentially expressed genes that were regulated by (i) propylene (and by analogy, ethylene) alone, (ii) low temperature (5°C, 10°C, or 15°C vs. 25°C) alone, and (iii) either propylene or low temperature. Gene-encoding proteins associated with chlorophyll degradation (such as CuSGR1, CuNOL, CuACD2, CuCAB2, and CuLHCB2) and a transcription factor (CuERF114) were differentially expressed by propylene or low temperature. To further examine temperature-induced pathways, we also monitored gene expression during on-tree fruit maturation vs. postharvest. The onset of on-tree peel degreening coincided with autumnal drops in field temperatures, and it was accompanied by differential expression of low temperature-regulated genes. On the contrary, genes that were exclusively regulated by propylene (such as CuCOPT1 and CuPOX-A2) displayed insignificant expression changes during on-tree peel degreening. These findings indicate that low temperatures could be involved in the fruit ripening-related peel degreening independently of ethylene.

Phosphorylation of MdERF17 by MdMPK4 promotes apple fruit peel degreening during light/dark transitions.

As apple fruits (Malus domestica) mature, they accumulate anthocyanins concomitantly with losing chlorophyll (Chl); however, the molecular pathways and events that coordinate Chl degradation and fruit coloration have not been elucidated. We showed previously that the transcription factor ETHYLENE RESPONSE FACTOR17 (MdERF17) modulates Chl degradation in apple fruit peels and that variation in the pattern of MdERF17 serine (Ser) residues is responsible for differences in its transcriptional regulatory activity. Here, we report that MdERF17 interacts with and is phosphorylated by MAP KINASE4 (MdMPK4-14G). Phosphorylation of MdERF17 at residue Thr67 by MdMPK4-14G is necessary for its transcriptional regulatory activity and its regulation of Chl degradation. We also show that MdERF17 mutants with different numbers of Ser repeat insertions exhibit altered phosphorylation profiles, with more repeats increasing its interaction with MdMPK4. MdMPK4-14G can be activated by exposure to darkness and is involved in the dark-induced degreening of fruit peels. We also demonstrate that greater phosphorylation of MdERF17 by MdMPK4-14G is responsible for the regulation of Chl degradation during light/dark transitions. Overall, our findings reveal the mechanism by which MdMPK4 controls fruit peel coloration.

Exploring the differential stages of the pigment metabolism by pre-harvest bagging and post-harvest ethylene de-greening of Eureka lemon peel.

Pre-harvest bagging or post-harvest ethylene treatments on lemons are commonly applied to change the surface color from green to favorable yellow. In this study, the differential mechanisms of the pigment metabolism by the two treatments were investigated by pigments contents and related genetic expression. The results showed that both treatments reduced the number of chloroplasts and the content of chlorophyll. The differential expression of PSY1 and PSY2 were observed, causing the different accumulation of the main carotenoid phytoene content. The differential expression of NYC resulted in altered contents of chlorophyll a and chlorophyll b, and further led to the difference in a* value. More interestingly, the degradation of chlorophyll uncovered the color of carotenoids, leading to the color changed from green to yellow.

Low temperature modulates natural peel degreening in lemon fruit independently of endogenous ethylene.

Peel degreening is an important aspect of fruit ripening in many citrus fruit, and previous studies have shown that it can be advanced by ethylene treatment or by low-temperature storage. However, the important regulators and pathways involved in natural peel degreening remain largely unknown. To determine how natural peel degreening is regulated in lemon fruit (Citrus limon), we studied transcriptome and physiochemical changes in the flavedo in response to ethylene treatment and low temperatures. Treatment with ethylene induced rapid peel degreening, which was strongly inhibited by the ethylene antagonist, 1-methylcyclopropene (1-MCP). Compared with 25 ºC, moderately low storage temperatures of 5-20 °C also triggered peel degreening. Surprisingly, repeated 1-MCP treatments failed to inhibit the peel degreening induced by low temperature. Transcriptome analysis revealed that low temperature and ethylene independently regulated genes associated with chlorophyll degradation, carotenoid metabolism, photosystem proteins, phytohormone biosynthesis and signalling, and transcription factors. Peel degreening of fruit on trees occurred in association with drops in ambient temperature, and it coincided with the differential expression of low temperature-regulated genes. In contrast, genes that were uniquely regulated by ethylene showed no significant expression changes during on-tree peel degreening. Based on these findings, we hypothesize that low temperature plays a prominent role in regulating natural peel degreening independently of ethylene in citrus fruit.

Light Regulation of Carotenoid Biosynthesis in the Peel of Mandarin and Sweet Orange Fruits.

Carotenoids are the pigments responsible for the coloration of the peel and pulp of Citrus fruits. Light is one of the major environmental factors influencing coloration and carotenoid content and composition of fleshy fruits and therefore their commercial and nutritional quality. Agronomical observations indicate that citrus fruits exposed to sunlight develop a brighter peel coloration than shaded fruit inside the tree canopy. In the present study, the effect of light deprivation on carotenoid profile, and in the expression of genes of carotenoid metabolism and their precursors have been analyzed in fruits of Clemenules mandarin (Citrus clementine) and Navelina orange (Citrus sinensis). Fruit shading accelerated peel degreening, chlorophyll degradation, and reduced chloroplastic-type carotenoids. Time-course shading experiments revealed that the stage of fruit ripening appears to be determinant for the effect of darkness in carotenoid biosynthesis. Fruit shading produced a down-regulation of the expression of key carotenoids biosynthetic genes (PSY, PDS, ZDS1, LCY2a, LCY2b, and CHX). However, expression of MEP pathway genes (DXS, HDR1, and GGPPS1) and the carotenoid cleavage dioxygenase, CCD4b1, responsible of the formation of the apocarotenoid β-citraurin, were not substantially affected by dark-grown conditions. The content of abscisic acid (ABA), an end product of the carotenoid pathway, was not affected by the light regime, suggesting that effect of shading on the precursor’s pool is not sufficient to impair ABA synthesis. A moderate increase in total carotenoid and in the expression of biosynthetic genes was observed in mature dark-grown mandarin and orange fruits. Collectively, results suggest that light stimulates carotenoid biosynthesis in the peel of citrus fruits but a light-independent regulation may also operate.

Natural Variation Underlies Differences in ETHYLENE RESPONSE FACTOR17 Activity in Fruit Peel Degreening.

Through natural or human selection, many fleshy fruits have evolved vivid external or internal coloration, which often develops during ripening. Such developmental changes in color are associated with the biosynthesis of pigments as well as with degreening through chlorophyll degradation. Here, we demonstrated that natural variation in the coding region of the gene ETHYLENE RESPONSE FACTOR17 (ERF17) contributes to apple (Malus domestica) fruit peel degreening. Specifically, ERF17 mutant alleles with different serine (Ser) repeat insertions in the coding region exhibited enhanced transcriptional regulation activity in a dual-luciferase reporter assay when more Ser repeats were present. Notably, surface plasmon resonance analysis showed that the number of Ser repeats affected the binding activity of ERF17 to the promoter sequences of chlorophyll degradation-related genes. In addition, overexpression of ERF17 in evergreen apples altered the accumulation of chlorophyll. Furthermore, we demonstrated that ERF17 has been under selection since the origin of apple tree cultivation. Taken together, these results reveal allelic variation underlying an important fruit quality trait and a molecular genetic mechanism associated with apple domestication.

Comparative study of the banana pulp browning process of 'Giant Dwarf' and FHIA-23 during fruit ripening based on image analysis and the polyphenol oxidase and peroxidase biochemical properties.

This work presents a novel method to associate the polyphenol oxidase (PPO) and the peroxidase (POD) activities with the ripening-mediated color changes in banana peel and pulp by computational image analysis. The method was used to follow up the de-greening of peel and browning of homogenized pulp from 'Giant Dwarf' (GD: Musa AAA, subgroup Cavendish) and FHIA-23 (tetraploid hybrid, AAAA) banana cultivars. In both cultivars, the color changes of peel during the ripening process clearly showed four stages, which were used to group the fruit into ripening stages. The PPO and POD were extracted from pulp of fruit at these ripening stages, precipitated, and partially purified by gel filtration chromatography. Moreover, the pulp browning was digitally monitored after homogenization for a span time of up to 120min. The browning level was higher for GD than FHIA-23 tissues. This fact correlated with an 11.7-fold higher PPO activity in the GD cultivar, as compared with that of FHIA-23. POD activity was 8.1 times higher for GD as compared that that of FHIA-23.

The Effect of Postharvest UV-C Treatment and Associated with Different Storage Conditions on the Quality of Tahitian Limes (Citrus latifolia)

Tahitian limes (Citrus latifolia) were exposed to 0 and 7.2 kJm-2 UV-C. After treatments, it was stored for 28 days in air at 20°C, 80% RH (control) and in air containing <0.005 or 0.1 μL.L−1 ethylene at 20°C and 100% RH. Weight loss, peel colour, calyx abscission, ethylene production, respiration rate, soluble solids content (SSC), titratable acidity (TA) and acceptability index were assessed. The UV-C light treatment significantly affected the quality of lime during storage. UV-C treatment significantly affected peel degreening at 20°C in all storage conditions, whereas treated limes showed significantly lower in peel degreening than the control. These effects reduced over the storage time, with the exception of fruits stored in <0.005 μL.L-1 ethylene which still produced a significantly higher in Hue value after 21 days storage relative to the control. UV-C treatment affected ethylene production during storage under all storage conditions. This effect also diminished with storage time. UV-C treatment did not affect the respiration rate, SSC or TA for all storage conditions. The UV-C treated limes had higher acceptability index than untreated limes up to 14 days storage at 20°C. Storage conditions significantly affected ethylene production, with limes that stored in air exhibiting higher ethylene production than fruits stored in the <0.005 or 0.1 μL.L-1 ethylene atmosphere. Storage conditions also significantly affected weight loss, with fruits stored in air showing greater weight loss compared to the other storage conditions. The results suggest that a pre-storage UV-C treatment, followed by storage in less than 0.1 μL.L-1 ethylene atmosphere improves the quality of limes postharvest.

Involvement of an ethylene response factor in chlorophyll degradation during citrus fruit degreening.

Chlorophyll degradation naturally occurs during plant senescence. However, in fruit such as citrus, it is a positive characteristic, as degreening is an important colour development contributing to fruit quality. In the present work, Citrus sinensis Osbeck, cv. Newhall fruit was used as a model for chlorophyll degradation. An ethylene response factor, CitERF13, was isolated and its transcriptional changes were closely correlated with fruit peel degreening during development or in response to ethylene. Dual-luciferase and yeast one-hybrid assays, as well as motif mutation, indicated that CitERF13 directly binds to the CitPPH promoter and enhances its activity. Transient and stable over-expression of CitERF13 resulted in rapid chlorophyll degradation in Nicotiana tabacum leaves and led to accumulation of pheophorbide (Pheide) a, a metabolite of pheophorbide hydrolase (PPH). Similar results were observed from transient transformation of CitERF13 in citrus fruit peel. Moreover, this function of CitERF13 was conserved within Arabidopsis and tomato, as the homologs AtERF17 and SlERF16 similarly acted as activators of PPH genes and accelerators of chlorophyll degradation.

Carnauba Wax and Modified Atmosphere in Refrigerated Preservation of ‘Tahiti’ Acid Limes

Peel yellowing and loss of fruit mass reduce the useful life of acid limes and limit their commercialization. The goal of the present study was to prolong the post-harvest preservation of acid limes using wax and packaging. Fruits were harvested, selected, disinfected, treated with fungicide, coated with Carnauba wax and placed in cardboard boxes wrapped with different plastic packaging. A fruit lot treated only with wax coating was used as a control. The fruits were stored at 10°C for 24 days followed by 6 days at 20°C. The gas atmosphere inside the packages was analysed during storage. The loss of mass, color index, titratable acidity, and total chlorophyll, ascorbic acid, soluble solids, acetaldehyde and ethanol concentrations of the fruits were measured. The combined use of wax coating and plastic Cryovac® D-955 (Cryovac Brasil Ltda, São Paulo, Brazil) and Vegetal Pack® (Eletropolimeros do Brasil Ltda, São Paulo, Brazil) films resulted in better post-harvest preservation of acid limes compared with only wax coating because the combined treatment maintained the green peel color following 30 days of storage in addition to resulting in lower loss of mass and maintaining chemical characteristics adequate for commercialization. The LDPE (low density polyethylene) and Xtend® packaging (Stepac Brasil Ltda, São Paulo, Brazil), although they prevented peel degreening, did not result in an adequate atmosphere to maintain the quality of limes due to the accumulation of high concentrations of acetaldehyde and ethanol, especially for the LDPE packaging. LDPE drastically changed the atmosphere surrounding the fruit, resulting in loss of the characteristic pulp color, in addition to conferring an alcohol odor. Copyright © 2015 John Wiley & Sons, Ltd.

DELAYED COLOR BREAK IN 'TARDIVO', A LATE RIPENING MANDARIN MUTANT, IS RELATED TO A DEFECTIVE ETHYLENE RESPONSE

Delaying peel senescence in clementine mandarins is of paramount importance in the citrus industry because it extends the harvesting period and improves the shelf life of the fruits. Gibberellins and ethylene treatments have been used for delaying or accelerating color development in citrus fruit peel, respectively, indicating a prominent role of these hormones in the regulation of the external ripening process. Late ripening mutants constitute an extremely useful tool to decipher the molecular bases regulating the timing and the rate of color development in citrus fruits. Although the causes for these phenotypes may be diverse, there is recent evidence in the literature linking delayed degreening with altered ethylene sensitivity. ‘Tardivo’ is a late ripening mutant of clementine mandarin that displays a delay in peel degreening, color development and expression of carotenoids biosynthetic genes. In the present work we have explored if this phenotype is associated with altered sensitivity to ethylene. Therefore, we have examined the expression of genes involved in carotenoids, ABA biosynthesis, and ethylene signaling and biosynthetic pathways in response to ethylene. The results indicated that ‘Tardivo’ fruits displayed a transient response to ethylene but it was unable to sustain subsequent ethylene-induced gene expression. It is then concluded that the delay in color development of ‘Tardivo’ mandarin may be related to a defective sensitivity or response to ethylene.

Altered sensitivity to ethylene in ‘Tardivo’, a late‐ripening mutant of Clementine mandarin

'Tardivo' mandarin is a mutant of 'Comune' Clementine with a delay in peel degreening and coloration, allowing late harvesting. In this work, we have explored if the late-harvesting phenotype of 'Tardivo' mandarin is related to altered perception and sensitivity to ethylene. The peel degreening rate was examined after a single ethephon treatment or during a continuous ethylene application in fruits at two maturation stages. In general, ethylene-induced peel degreening was considerably delayed and reduced in fruits of 'Tardivo', as well as the concomitant reduction of chlorophyll (Chl) and chloroplastic carotenoids, and the accumulation of chromoplastic carotenoids. Analysis of the expression of genes involved in Chl degradation, carotenoids, ABA, phenylpropanoids and ethylene biosynthesis revealed an impairment in the stimulation of most genes by ethylene in the peel of 'Tardivo' fruits with respect to 'Comune', especially after 5 days of ethylene application. Moreover, ethylene-induced expression of two ethylene receptor genes, ETR1 and ETR2, was also reduced in mutant fruits. Expression levels of two ethylene-responsive factors, ERF1 and ERF2, which were repressed by ethylene, were also impaired to a different extent, in fruits of both genotypes. Collectively, results suggested an altered sensitivity of the peel of 'Tardivo' to ethylene-induced physiological and molecular responses, including fruit degreening and coloration processes, which may be time-dependent since an early moderated reduction in the responses was followed by the latter inability to sustain ethylene action. These results support the involvement of ethylene in the regulation of at least some aspects of peel maturation in the non-climacteric citrus fruit.

Pithy brown core in ‘d’Anjou’ pear (Pyrus communis L.) fruit developing during controlled atmosphere storage at pO2 determined by monitoring chlorophyll fluorescence

Physiological responses and fruit quality of ‘d’Anjou’ pear fruit from five orchard lots were evaluated after cold storage in air or controlled atmospheres (CA) with the O2 concentration based on assessment of fruit chlorophyll fluorescence (CF) or standard conditions (1.5kPa O2). The pCO2 for all CA fruit was 0.5kPa. Softening, acid loss, and peel degreening of all lots were delayed at one or more evaluation dates (2, 4, 6, 8 months) by previous storage at the CF pO2 compared with fruit stored in 1.5kPa O2 or in air. Superficial scald developed on fruit previously stored in air but not on fruit stored in a CA. Pithy brown core developed on fruit from all lots stored at the CF pO2 and on fruit stored at 1.5kPa in 3 of the 5 lots. Pithy brown core incidence decreased with advanced harvest maturity. Post-storage ethylene and CO2 production were in most instances lowest for fruit stored at the CF pO2. A significant relationship between fruit ethanol content and pithy brown core incidence was observed. Results indicate low pO2 storage based on CF monitoring slows fruit ripening relative to fruit stored at 1.5kPa O2, prevents superficial scald development compared with fruit stored in air, however, development of pithy brown core in fruit stored at the CF pO2 was not accompanied by a change in CF.

EXPLORING THE INVOLVEMENT OF ETHYLENE IN THE REGULATION OF COLOR CHANGES IN CITRUS FRUIT

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Postharvest Technology in the Global Market EXPLORING THE INVOLVEMENT OF ETHYLENE IN THE REGULATION OF COLOR CHANGES IN CITRUS FRUIT

EFFECTS OF POSTHARVEST HOT WATER TREATMENT ON PHYSIOLOGICAL AND BIOCHEMICAL PROPERTIES OF 'EKSOTIKA' PAPAYA DURING RIPENING

Effects of postharvest hot water treatment (HWT) on the 'Eksotika' papaya fruit quality during ripening were investigated. HWT is a method for fruit fly disinfestation which is a quarantine requirement for the papaya exportation industries. Fruit were harvested at maturity stage Index 2 (green with a tinge of yellow). One group was treated with hot water at 47±1°C for 10 min and another group was untreated. Fruit were left to ripen at ambient temperature (25°C) and were taken into experiment at Index 2 (Harvest Index), Index 4 and Index 5. Physiological changes including peel colour, weight loss, fruit firmness, total soluble solids (TSS) and pH were determined at the three different ripening indices. Biochemical changes including total sugars and total reducing sugars were also investigated. From the results, both treated and untreated fruit showed normal ripening. There were also no significant differences in weight loss, TSS and pH value between the untreated and treated fruit at the three ripening indices. However, the peel colour changes in untreated fruit were delayed by approximately 1-2 days. At Index 5, the treated fruit was firmer than the untreated fruit. The total sugars and total reducing sugars contents showed no significant difference between the two groups at the three different ripening indices. The reducing sugar content was increased and attained highest value at Index 4. Conversely, the non reducing sugar content was decreased during ripening. Although HWT hastened degreening (of peel), cause slightly firmer fruit when ripe, fruit sweetness was remained unchanged and maintained at a good quality. This suggests that postharvest hot water treatment at the selected temperature can maintain postharvest quality of 'Eksotika' papaya fruit and at the same time prevent it from insect infestation.