Preharvest application of abscisic acid promotes anthocyanins accumulation in pericarp of litchi fruit without adversely affecting postharvest quality

Pericarp colour of litchi fruit is an important quality attribute that determines its market value and consumer acceptance. Plant growth regulators (PGR) such as abscisic acid (ABA) and ethephon are known to play important roles in peel colour development during maturation and ripening of non-climacteric fruits (e.g. grape and litchi). Our aim was to investigate the effects of preharvest application of ABA, ethephon and their combination on pericarp colour and fruit quality of litchi (cv. Calcuttia) and also to assess the potential effects on postharvest performance of fruit. Exogenous application of ABA (150 or 300 mg L⁻¹) at the colour-break stage significantly increased the concentration of total anthocyanins and cyanidin-3-O-rutinoside, the major anthocyanin contributing ∼71–96% of the total anthocyanins, in litchi pericarp compared to ethephon (500 μL L⁻¹). Among different anthocyanins quantified, the relative contribution of cyanidin-3,5-diglucoside to the total anthocyanins was significantly higher in all PGR-treated fruit compared to the control, but the concentration of cyanidin-3-O-glucoside was specifically enhanced by ABA. No significant effect on the concentrations of epicatechin, and quercetin-3-O-rutinoside was observed in response to PGR treatments. Ethephon (500 μL L⁻¹) treatment did not significantly increase the anthocyanin levels in pericarp, but it caused more degradation of chlorophyll pigments than control. Aril quality with regard to firmness, soluble solids and acidity was not significantly affected by PGR treatments, except that ethephon-treated fruit showed significant softening and lower acidity. Postharvest changes in fruit quality attributes including pericarp browning during cold storage at 5 °C for 14 d were mainly related to the storage duration effect, rather than PGR treatment. In conclusion, ABA treatment (150 or 300 mg L⁻¹) at the colour-break stage enhanced anthocyanins accumulation in litchi pericarp without adversely affecting postharvest quality and storage stability for 14 d.     

Physiological and biochemical profiles of imported litchi fruit under modified atmosphere packaging

Although sophisticated packaging materials can be used to minimise postharvest changes of litchi fruit, no work has documented the effect of different modified atmosphere packaging on biochemical composition of litchi aril and pericarp tissue. Therefore, the aim of this study was to detail not only the changes in weight and colour, but also individual sugars, organic acids and anthocyanin concentrations using various packaging materials. Non-acid- and SO₂-free fruit cv. Mauritius, imported from Israel, were packed using four different packaging films viz. micro-perforated polypropylene (PP), PropaFresh™ PFAM (PF), NatureFlex™ NVS (NVS), Cellophane™ WS (WS) and unwrapped, and stored at 13 °C for 9 days. Concentrations of CO₂ and ethylene were greater in WS packs during storage followed by NVS, PF and PP films, respectively. Weight loss of fruit stored in PF film was lower than for other treatments. The PF treatment better maintained sugars, organic acids in aril and pericarp tissue and individual anthocyanins in pericarp. These results indicate that PropaFresh™ PFAM was the best packaging film to maintain physiological and biochemical properties in litchi fruit.     

生物抑制剂处理结合低温冷藏对龙眼保鲜质量的影响

以提高龙眼的保鲜质量和商品率为目的，采用生物抑制剂处理龙眼进行低温气调保鲜。采用正交试验方法，分析了生物抑制剂对龙眼果皮褐变和保鲜效果的影响。结果表明，在相同的低温气调保鲜条件下，采用生物抑制剂处理，可更有效地抑制龙眼保鲜过程的呼吸作用，有效降低了酶活性的变化，延缓了龙眼果实的衰老与果皮褐变，保鲜时间长，且更好地保留了果实的营养成分，商品率高。     

Phomopsis longanae Chi-induced pericarp browning and disease development of harvested longan fruit in association with energy status

The effects of Phomopsis longanae Chi infection on browning development and disease incidence in relation to energy status in pericarp of harvested longan fruit were investigated. Longan fruit were inoculated for 5 min with P. longanae at 10⁴ spores mL⁻¹, while fruit dipped in sterile deionized water were used as control. These fruits were stored at (28 ± 1) °C and 90% relative humidity for up to five days. The results showed that the browning index, disease incidence, cellular membrane permeability and AMP content increased but the contents of ATP and ADP, and energy charge decreased in pericarp of longan fruit infected by P. longanae. It was suggested that P. longanae infection caused energy deficiency in longan fruit, possibly resulting in accelerated senescence and decreased resistance to pathogen, and thus promoted browning development and disease occurrence.     

Involvement of ethylene in browning development of controlled atmosphere-stored ‘Empire’ apple fruit

‘Empire’ apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] are susceptible to development of chilling injury, expressed as firm flesh browning, during controlled atmosphere (CA) storage. Because of this susceptibility, fruit are typically stored at 2–4 °C, but the incidence of flesh browning can be increased by 1-methylcyclopropene (1-MCP) treatment at these temperatures. In this study, flesh browning development has been investigated in relationship to ethylene production, internal ethylene concentration (IEC), flesh firmness, total phenolic concentrations, and the activities of polyphenol oxidase (PPO) and peroxidase (POX) in the flesh tissues. Fruit were harvested from two orchards, either untreated or 1-MCP treated, and then stored under CA conditions at either 0.5 or 4 °C. Fruit were removed from storage at 1.5-month intervals for 10.5 months. 1-MCP treated apples were firmer than those of untreated apples, and had lower IECs, at all removals. Flesh browning incidence and severity developed earlier in 1-MCP-treated apples than untreated apples stored at either temperature. Total phenolic concentrations differed by orchard, but no major differences in concentrations were detected between untreated and 1-MCP treated apples. However, PPO activities were higher in the flesh of 1-MCP treated apples than untreated apples from both orchards and at both storage temperatures. POX activity was not consistently affected by 1-MCP treatment or storage temperature. Overall, our results suggest that inhibited ethylene production, either as a result of storage at 0.5 °C, or by treatment with 1-MCP at either temperature, may cause stress and damage to cells and result in higher PPO activity that leads to progressive flesh browning development during CA storage.     

1-MCP extends the storage and shelf life of mangosteen (Garcinia mangostana L.) fruit

Mangosteen (Garcinia mangostana L.) fruit were harvested when the peel (pericarp) was light greenish yellow with scattered pinkish spots. Fruit were exposed to 1 μL L⁻¹ 1-methylcyclopropene (1-MCP) for 6 h at 25 °C and were then stored at 25 °C (control) or 15 °C. The 1-MCP treatment only temporarily delayed softening of the fruit flesh, during storage. Storage life, defined as the time until the pericarp was dark purple, was much longer in fruit stored at 15 °C than in fruit stored at 25 °C. It was also longer in 1-MCP treated fruit (storage life at 15 °C: control 18 d, 1-MCP-treated fruit 27 d). The 1-MCP treatment also increased the length of shelf life, defined as the time until the pericarp turned blackish purple or showed calyx wilting, at 25 °C. 1-MCP treatment reduced ethylene production. It also reduced pericarp levels of 1-aminocyclopropane-1-carboxylic acid (ACC), and the pericarp activities of ACC synthase (ACS) and ACC oxidase (ACO). In the fruit flesh, in contrast, 1-MCP did not affect ACC levels and ACS activity, but the treatment reduced ACO activity. Taken together, both the storage life and the shelf life of the fruit were extended by the 1-MCP treatment. A decrease in ACO activity largely accounted for the effects of the 1-MCP on ethylene production in the pericarp.     

The effects of nitric oxide and nitrous oxide on enzymatic browning in longkong (Aglaia dookkoo Griff.)

The effect of nitric oxide and nitrous oxide on pericarp browning of longkong fruit was studied. The fruit was either dipped for 5 min in 0.25 mM sodium nitroprusside (SNP), a nitric oxide donor, or continually exposed to 90% nitrous oxide (N₂O) vapour for 3 h and was compared to the untreated fruit (control). The fruits were then stored at 13 °C and RH of 90 ± 5%. The fruit treated for 3 h with nitrous oxide vapour had delayed pericarp browning with higher phenolic compounds. However, these fruit showed lower levels of phenylalanine ammonia lyase, polyphenol oxidase and peroxidase than the control fruit and those treated with 0.25 mM SNP. Therefore, we conclude that nitrous oxide delays browning and reduces the activities of browning enzymes in longkong pericarp.     

Chilling injury in mango fruit peel: Cultivar differences are related to the activity of phenylalanine ammonia lyase

In mango (Mangifera indica) cv. Nam Dok Mai fruit, stored at 4 °C, peel browning occurred within 9 d, while no browning was found in cv. Choke Anan fruit stored at 4 °C for 30 d. During 6 d of shelf life at 27-28 °C, following various periods of low temperature storage, the peel browning in cv. Nam Dok Mai (if not yet maximal) became worse, whereas little browning was observed in cv. Choke Anan fruit. The pulp of the fruit of both cultivars did not show browning during the 4 °C storage, but the pulp of cv. Nam Dok Mai exhibited some browning during shelf life if the fruit had been stored at 4 °C for more than 18 d. Peel and pulp color were not correlated with total free phenolics. A high correlation coefficient was observed between peel browning and PAL activity in the peel, while a very low correlation was found with peel catechol oxidase activity. The browning in the pulp was not correlated with the measured enzyme activities. The data therefore show a relation between PAL activity in the peel and low temperature-induced peel browning.     

荔枝果皮褐变机理研究进展

通过酶促褐变、失水褐变、花色苷降解致褐、病菌致褐、呼吸强度和乙烯释放增加等其他因素综述了有关荔枝果皮褐变机理方面的研究进展.     

Maturity and cooling rate affects browning,polyphenol oxidase activity and gene expression of ‘Yali’ pears during storage

Browning is the main physiological disorder of ‘Yali’ pear (Pyrus bretschneideri Rehd) during storage. In this study, the relationships between browning development in fruit from different harvest dates, and cooled either rapidly or slowly, with polyphenol oxidase (PPO) activity and isozymes, and PPO gene expression has been investigated. Development of browning was highest in late-harvest fruit in both core and flesh tissues and was higher in rapidly cooled than slowly cooled fruit. Mid-harvest fruit had the lowest browning incidence and PPO activity of core tissue was higher than in flesh and seeds, while the peak of PPO activity in mid-harvest fruit was the lowest. Six PPO isoenzymes were detected in fruit, three bands A, B and E in flesh and core tissues, three bands C, D and F in the seeds. The intensity of PPO isoenzyme staining of bands A and B in pulp and core was similar to that of PPO activity and browning incidence. PPO gene expression increased and then decreased in core tissues. Trends of expression were similar to those of PPO activity. Rapid cooling promoted the expression PPO. The results suggest PPO plays an important role in ‘Yali’ pear browning during storage.     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.     

Use of chlorine dioxide fumigation to alleviate enzymatic browning of harvested ‘Daw’ longan pericarp during storage under ambient conditions

Pericarp browning reduces both the shelf-life and market value of harvested longan fruit stored at room temperature. Our study investigated the efficiency of chlorine dioxide (ClO₂) fumigation at reducing pericarp browning of longan (Dimocarpus longan Lour.) cv. Daw. Fresh longan fruit were fumigated with 0 (control), 2.5, 5, 10 and 25 mg/L ClO₂ for 10 min, before being packed in cardboard boxes, and stored at 25 ± 1 °C, RH 82 ± 5% for 7 days. Fruit treated with ClO₂ had a lower browning index, but higher hue angle (true color), L* (lightness) and b* (yellowness) values than non-treated fruit. The 10 and 25 mg/L ClO₂ treatments were the most effective at extending shelf-life from 1 to 5 days, compared with the control, by reducing pericarp browning, the activities of polyphenol oxidase (PPO) and peroxidase (POD), disease development and by maintaining the highest total phenolic content. However, quality acceptance of fruit treated with 10 mg/L ClO₂ was higher than fruits treated with 25 mg/L, as determined by odor and flavor. Consequently, ClO₂ fumigation at a concentration of 10 mg/L was considered to be the most effective treatment to reduce pericarp browning of longan, whilst maintaining fruit quality.     

Repeated treatment of apple fruit with 1-methylcyclopropene (1-MCP) prior to controlled atmosphere storage

The effect of multiple 1-MCP treatments prior to the establishment of controlled atmosphere (CA) storage on the quality of ‘McIntosh’ and ‘Empire’ apples [Malus × sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] was investigated. Fruit were harvested on three occasions over a 1 week period, and at each harvest cooled overnight and 1-MCP applied the following day. Fruit from the first or second harvests were treated again or for the first time when fruit from each successive harvest was treated. CA conditions were established after the last 1-MCP treatment and fruit were stored for up to 8 months. Delays in 1-MCP application generally resulted in progressively higher internal ethylene concentrations (IECs) at the time of treatment and lower firmness both at the time of treatment and after storage. Multiple 1-MCP applications kept IECs low and maintained firmness compared with single applications that were applied after 4 d. For ‘McIntosh’, external CO₂ injury was more prevalent after storage if fruit were treated without delays after harvest for earlier harvests while later harvests were less affected. For ‘Empire’, flesh browning was more prevalent in fruit from later harvests and 1-MCP treated fruit had higher levels than untreated fruit. Either early 1-MCP treatment or multiple treatments reduced senescent breakdown in ‘McIntosh’, and core browning and greasiness in ‘Empire’.     

不同梨果实褐变特异性分析

以黄金梨、大香水、新梨七号为试材,研究了贮藏后梨褐变不同部位酚类物质含量和种类、多酚氧化酶(PPO)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)的活性及可溶性蛋白的关系。结果表明,梨果实中的酚类物质以绿原酸为主,果实褐变与酚类物质含量和多酚氧化酶活性,特别是二者在果实中不同部位的分布特性有关。黄金梨果心与其他部位比较具有较高的酚类物质含量和PPO活性。由果皮至果心CAT活性依次降低,而果皮中POD活性极大地高于其他部位。SOD的活性与褐变的直接关系不明显。     

Effect of adenosine triphosphate on changes of fatty acids in harvested litchi fruit infected by Peronophythora litchii

Recent investigations have shown that disease development of harvested horticultural crops may be attributed to a limited availability of energy or low energy production. In this study, litchi fruit were treated with 1.0 mM adenosine triphosphate (ATP) or 0.5 mM 2,4-dinitrophenol (DNP) and then half of the ATP-treated fruit were inoculated with Peronophythora litchii. The composition and contents of fatty acids (FAs) and esterase activity in litchi fruit during storage were investigated. Free fatty acids (FFAs) in all fruit increased over storage, especially in the P. litchii-inoculated fruit. In particular, the content of saturated FAs increased faster than unsaturated FAs. In polar lipids (PL), a decrease in the amount of C18:3 and an increase in the amount of C16:0 or C18:0 was found during storage, while the proportions of C16:0, C18:0 and C18:1 in neutral lipid (NL) gradually increased but the proportions of C18:3 decreased during storage. The proportion of C18:2 increased within the first four days and then decreased. Exogenous ATP treatment suppressed the release of FFAs and increased the contents of each FA in PL, indicating a slower hydrolysis of lipids. ATP treatment also delayed the increase in the proportion of C18:0 in NL. Further analysis showed that the double bond index (DBI) of litchi fruit decreased in all fractions of FAs and ATP treatment can slow the decrease in DBI. In addition, lower esterase enzyme activity was detected in all ATP-treated fruit. Treatment with DNP (a respiration uncoupler) increased esterase activity. P. litchii-inoculated fruit after ATP treatment also exhibited similar trends in delaying the release of FFAs. Enhanced disease resistance of litchi fruit by ATP could involve the levels of FAs and esterase activity.     

Defense responses of tomato fruit to exogenous nitric oxide during postharvest storage

Nitric oxide (NO), an important signalling molecule, has shown diverse physiological functions in plants. We investigated physiological responses of harvested tomato fruit (Solanum lycopersicum cv. Ailsa Craig, AC) to NO treatment. NO released by 1 mM sodium nitroprusside (SNP) aqueous solution could effectively retard pericarp reddening of tomato fruit, suppress ethylene production, and influence quality parameters during storage. The activity of antioxidant enzymes in NO-treated tomato fruit was higher in the late storage period compared to the control. RT-PCR analysis showed that expression of six genes related to fruit ripening was regulated by NO treatment, resulting in an increase in resistance of tomato fruit to gray mold rot caused by Botrytis cinerea. Our results demonstrated that application of NO could be a potential method for treating harvested fruit in order to delay ripening, maintain quality and enhance resistance of fruit to fungal pathogens.     

Shrivel development in kiwifruit

Shrivel is a potential storage quality problem for kiwifruit. ‘Zesy003’ (commonly called Gold9) is a newly released, yellow-fleshed Actinidia chinensis cultivar that tends to shrivel more than other commercialised cultivars. Water loss and shrivel in Gold9 fruit were investigated during storage at 1 °C for up to 14 weeks and shelf-life at 20 °C. In addition, the water status of ripe fruit was quantified by magnetic resonance imaging and the capacity of a crude outer pericarp cell wall extract to swell. Shrivelled Gold9 fruit had 1–6% weight loss, although 6% weight loss did not always result in shrivel. Three weeks of storage resulted in fruit taking longer to shrivel during shelf-life, with a concomitant higher weight loss by the time the fruit was shrivelled. In contrast, 14 weeks of storage resulted in fruit that shrivelled more rapidly in shelf-life at a lower weight loss. At any given time after harvest, fruit with more severe shrivel tended to be softer than less shrivelled fruit. Shrivel therefore appears associated with fruit softening. Outer pericarp tissue from ripe Gold9 fruit had lower water mobility and a greater capacity to swell than pericarp from other kiwifruit cultivars. It is concluded that shrivel is not determined simply by an absolute amount of water loss. The development and ease of expression of shrivel in Gold9, and possibly other kiwifruit, is influenced by softening and the water characteristics of the fruit outer pericarp when soft.     

Magnetic resonance imaging provides spatial resolution of Chilling Injury in Micro-Tom tomato (Solanum lycopersicum L.) fruit

Magnetic resonance imaging (MRI) was used to monitor internal changes in harvested tomato (Solanum lycopersicum L. cv. Micro-Tom) fruit. Measurements of ethylene evolution, respiration, and ion leakage indicated that the fruit developed chilling injury (CI) after storage at 0 °C. Unlike these measurements, MRI provided spatially resolved data. The apparent diffusion coefficient (ADC), which is an indication of water mobility in tissues, was calculated from MRIs of the different parts of the fruit. Storage for 1 or 2 weeks at 0 °C caused no difference in the ADCs (D-values) in the pericarp, but it did lead to higher values in the inner tissues i.e., the columella and locular region compared to non-chilled fruit (P < 0.05). Changes in inner fruit D-values after 1 and 2 weeks of chilling at 0 °C were similar to changes in respiration, ethylene production and ion leakage which increased (P < 0.05) compared to the non-chilled controls. Most CI studies of tomato fruit used pericarp tissue. Our data indicate that columella tissue changes occur in response to chilling injury in tomato fruit and suggest that more caution is needed when interpreting data from experiments commonly used to study this phenomenon.     

Influence of exogenous ethylene during refrigerated storage on storability and quality of Actinidia chinensis (cv. Hort16A)

The kiwifruit industry was established on fruit of Actinidia deliciosa (‘Hayward’), which is known as a climacteric fruit with high sensitivity to ethylene. In recent times fruit from Actinidia chinensis have become a substantial component of the kiwifruit market. There is limited information about the sensitivity of A. chinensis to ethylene during refrigerated storage and hence current ethylene management practices for A. chinensis mimic those established for A. deliciosa. This research aimed to quantify the effect of ethylene during refrigerated storage on A. chinensis (‘Hort16A’) quality (firmness, colour and total soluble solids). Three grower lines were stored at 1.5 °C, 95% RH with ethylene in the range of 0.001-1 μL L⁻¹ applied to the environment after 3 weeks of storage for the remainder of storage (17 weeks). Fruit quality was assessed at regular intervals. Loss of firmness was found to be very sensitive to ethylene, with significant differences between fruit stored in 0.001 μL L⁻¹ (as a control) and 0.1 μL L⁻¹ occurring after 2 weeks of exposure. Fruit exposed to 1 μL L⁻¹ ethylene not only rapidly softened, but also increased in hue angle (greenness) and reduced in lightness (darkened) further reducing the quality of the yellow coloured kiwifruit cultivar. Total soluble solids were not heavily influenced by ethylene exposure, with grower differences being maintained throughout the experiment. This work demonstrates that A. chinensis (cv. Hort16A) fruit firmness and colour will be influenced by the ethylene conditions in a commercial storage environment by advancing ripening and senescence.