Article pubs.acs.org/JAFC
Postharvest Exogenous Application of Abscisic Acid Reduces Internal Browning in Pineapple Qin Zhang,† Yulong Liu,† Congcong He, and Shijiang Zhu* Guangdong Province Key Laboratory of Postharvest Physiology and Technology of Fruits and Vegetables, College of Horticulture, South China Agricultural University, Guangzhou, Guangdong 510642, China ABSTRACT: Internal browning (IB) is a postharvest physiological disorder causing economic losses in pineapple, but there is no effective control measure. In this study, postharvest application of 380 μM abscisic acid (ABA) reduced IB incidence by 23.4− 86.3% and maintained quality in pineapple fruit. ABA reduced phenolic contents and polyphenol oxidase and phenylalanine ammonia lyase activities; increased catalase and peroxidase activities; and decreased O2·−, H2O2, and malondialdehyde levels. This suggests ABA could control IB through inhibiting phenolics biosynthesis and oxidation and enhancing antioxidant capability. Furthermore, the efficacy of IB control by ABA was not obviously affected by tungstate, ABA biosynthesis inhibitor, nor by diphenylene iodonium, NADPH oxidase inhibitor, nor by lanthanum chloride, calcium channel blocker, suggesting that ABA is sufficient for controlling IB. This process might not involve H2O2 generation, but could involve the Ca2+ channels activation. These results provide potential for developing effective measures for controlling IB in pineapple. KEYWORDS: abscisic acid, antioxidant systems, internal browning, pineapple, phenolic compounds, quality
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INTRODUCTION Internal browning (IB), also referred to as blackheart, is a physiological disorder of pineapple (Ananas comosus L.) that often occurs during postharvest processes. The affected fruit develop browning spots or areas mainly in the flesh surrounding the core with no obvious external damage, hence the name. Most cultivars of pineapple are susceptible to internal browning;1 therefore, the losses due to this disorder are often heavy in production countries.2,3 For example, it brings about US$1.3 million in annual losses to the Australian pineapple industry,4 and it could cause even heavier losses to the Chinese pineapple industry, as over 90% of total production in China is from the susceptible cultivar “Comte de Paris”. Over the years, various methods have been tried to control IB, including preharvest application of potassium 5 or calcium6 and postharvest use of calcium,1,7 strontium chloride,1 modified atmosphere,7,8 1-methylcyclopropene,9 waxing,2 and heat treatment.7,10 However, to date, not a single effective way has been found to be commercially useful, mainly because of their relatively low efficacies. Take the most extensively studied calcium application, for example. Although some contributions reported that calcium was effective in reducing IB incidence, whether applied preharvest6,11 or postharvst,1,12 others did not show any effects7,13 or could not confirm the effects.14 This implies a complex nature of IB, as harvested pineapple could either develop IB symptoms under low temperature (LT; 10 °C or lower)1,2,4−6,15 or at ambient temperature (AT; 20 °C or higher).15,16 The LT-caused IB could be related to chilling injury,4 while the IB occurred in AT could be the manifestation of senescence. However, the fact plant hormone gibberellins (GAs) are involved in this disorder could make things simpler because exogenous GAs treatment induced IB,15,17 and this is true for pineapple stored either at LT or AT (20 °C −25 °C).15 In addition, endogenous GAs levels were found to be positively correlated to IB incidence.15 It is not known whether abscisic © 2015 American Chemical Society
acid (ABA), the antagonist of GAs, can inhibit IB. It is likely that ABA could inhibit IB developed as a result of chilling under LT, as ABA has been widely confirmed to induce chilling tolerance in plants. 18,19 In addition, ABA applied in combination with calcium hydroxide and wax sprays significantly reduced pineapple IB severity under LT.20 Because LT storage alone can effectively inhibit development of IB for sufficiently long,16 from the industry point of view, it is not necessary to use ABA to control IB of pineapple stored in LT. On the other hand, pineapple is mostly transported and sold under AT in China and other developing countries that produce it; therefore, it is of great value to develop IB control measures for pineapple stored and shipped under AT. This study investigated effects of application of ABA on IB development in AT, aiming to develop an effective alternative to control IB. In addition, this research investigated the mechanism of ABA in controlling IB to help understand the role of exogenous ABA.
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MATERIALS AND METHODS Plant Materials and Treatment. Pineapple (Ananas comosus L. cv “Comte de Paris”) fruit of “Queen” group at 70% maturity (commercial maturity in China, with fruit being green with a trace of yellow) were collected from a commercial plantation in Xuwen County, Guangdong Province and transported 300 km to Guangdong Province Key Laboratory of Postharvest Physiology and Technology of Fruits and Vegetables, College of Horticulture, South China Agricultural University, Guangzhou, Guangdong Province. Fruit uniform in size (average weight about 500 g) and free of physical injury or Received: Revised: Accepted: Published: 5313
December 28, 2014 May 25, 2015 May 26, 2015 May 26, 2015 DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
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Journal of Agricultural and Food Chemistry
for 15 min at 4 °C, and the supernatant (enzyme extract) was used for PAL assays. A 3 mL reaction mixture contained 0.4 mL of enzyme extract, 1.6 mL of 0.1 mM sodium borate, pH 8.8, supplemented with 5 mM dithiothreitol and 1 mL of 0.02 M Lphenylalanine as substrate. The mixture was incubated at 38 °C for 3 h. PAL activity was expressed as the difference in optical density at 290 nm before and after incubation. One unit was defined as an increase in A290 of 0.01 h−1. Assay of Total Phenolic Compounds (TPC). The contents of TPC were detected using Folin−Ciocalteu reagent according to the method described previously.23 The absorbance at 765 nm was measured and used to calculate the phenolic contents using gallic acid (GA) as a standard. Results were calculated and expressed as milligrams of GA equivalent (GAE) per gram of fresh samples. Determination of O2·−, H2O2, and MDA. The contents of superoxide radicals (O2·−), hydrogen peroxide (H2O2), and MDA were determined according the method described by Li et al.24 with modification. First, 0.5 mL of the same supernatant as for measuring PPO, POD, and CAT was reacted with 1 mL of hydroxylamine hydrochloride for 1h, then 1 mL of paminobenzenesulfonic acid and 1 mL of α-naphthylamine were added, and the solution was kept at 25 °C for 20 min. The absorbance at 530 nm was measured, and the result was expressed as nmol/min·gFW. The H 2 O 2 content was determined as a H2O2−titanium complex resulting from the reaction of tissue−H2O2 with titanium tetrachloride. Absorbance values at 415 nm were calibrated to a standard curve generated using known concentrations of H2O2. The MDA content was determined following the method described by Li et al.24 Statistical Analyses. The experiments were repeated two or three times with similar results. There were three replications for analysis of each parameter. Data were analyzed by one-way analysis of variance (ANOVA). Mean separations were performed using the least significant difference method (LSD test). Statistically significant differences were assumed when their P values were ≤0.01.
disease symptoms were selected, with the crown being half-cut and sprayed with a fine mist of solution of diphenylene iodonium (DPI) (5 μM), ABA (95 or 380 μM), tungstate (TS) (50 μM), or lanthanum chloride (LaCl3) (50 μM), each containing 0.01% Tween 80, until runoff and air-dried. For the combination of DPI with ABA, LaCl3 with ABA, and TS with ABA, pineapples were permitted to dry at AT for 6 h before being treated further. The control fruit were sprayed in the same way with distilled water containing 0.01% Tween 80. Each treatment was applied to three replications, each containing 20 fruit. Following treatment, pineapples were wrapped with perforated polyethylene film and kept at 20 °C in the dark at 95% RH. Samples of pulp tissues were collected at 6 h, 12 h, 24 h, 3 days, 6 days, 9 days, and 12 days; frozen in liquid nitrogen; and stored at −80 °C. Internal Browning Incidence Assessment. Three fruit from each treatment, one from each replicate, were cut every 3 days for monitoring the development of IB. Upon obvious onset of browning in flesh or core of pineapples from any treatment, all the other fruit, 45−60 fruit per treatment, were then cut for observation of IB. IB incidence was calculated as percentage of fruit with symptoms of IB, irrespective of the size of the browning on cut surface. The strict standard is used because fruit with slight or severe browning are all affected fruit in the eyes of consumers. Therefore, the commercial value is lost upon the appearance of the first trace of internal browning. Determination of Soluble Solids, Titratable Acids, and Ascorbic Acid. Pineapple flesh (100 g) was cut into small pieces, homogenized, and filtered. The filtrate was used for measuring soluble solids concentrations (SSC), titratable acid (TA), and ascorbic acid (AsA) contents according to methods described by Lu et al.21 Assay of Enzyme Activity. Polyphenol oxidase (PPO), peroxidase (POD), and catalase (CAT) were extracted and activity was assayed according to the methods we described previously with modification.22,23 Frozen pineapple flesh (1 g) were ground in liquid nitrogen to fine powder and then homogenized in 4 mL of precooled 0.05 mM potassium phosphate buffer, pH 7.8, containing 5% (w/v) polyvinylpyrrolidone. The homogenate was centrifuged at 15 000g for 20 min at 4 °C. The supernatant, referred to as the crude enzyme extract, was used to assay the activity of enzymes. For PPO assay, a 3 mL reaction mixture contained 2 mL of 50 mM phosphate buffer, pH 7.8, 0.9 mL of 10 mM pyrocatechol, and 0.1 mL of crude enzyme extract. PPO activity was expressed as units of grams per fresh weight (FW). One unit was defined as an increase in A398 of 0.01 min−1. For POD assay, a 3 mL reaction solution consisted of 0.1 mL of 1% (v/v) guaiacol (1%), 0.1 mL of 0.46% H2O2, 2.7 mL of 0.1 M potassium phosphate buffer, pH 7.8, and 0.1 mL of enzyme extract. The enzyme activity was detected by following the change in optical density at 470 nm due to the oxidation of guaiacol. One unit of POD activity was defined as an increase in A470 of 0.01 min−1. For CAT assay, a 3 mL reaction mixture contained 2.9 mL of 15 mM H2O2 in 0.05 M potassium phosphate buffer, pH 7.8, and 0.1 mL of enzyme extract. Catalase activity was expressed in units of grams per FW, where one unit of CAT activity was defined as causing an increase in A240 of 0.01 min−1. Phenylalanine ammonia lyase (PAL) was extracted and the activity determined according to the method described previously.23 Frozen pineapple flesh (1 g) was homogenized in 4 mL of precooled 0.05 M sodium borate buffer, pH 7.0, in an ice−water bath. The homogenate was centrifuged at 15 000g
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RESULTS Effect of ABA on Pineapple IB Incidence. The first experiment conducted in November 2012 showed that ABA at 95 and 380 μM reduced IB incidence by 2.8% and 25%, respectively, with 380 μM ABA treatment being statistically significantly different from the control (P ≤ 0.01) (Figure 1). Therefore, 380 μM was used in a series of experiments that followed over a period of two years to check whether ABA works for fruit harvested from different seasons. As is shown in Figure 2, exogenous application of ABA at 380 μM obviously inhibited IB development for pineapple harvested in different seasons and different years, with the IB incidence being reduced by 70.83% for the trial in June 2013, 58.00% for September 2013, 23.40% for November 2013, 86.30% for June 2014, and 36.60% for September 2014 (Figure 2). Although there were big variances for fruit from different batches or seasons, the difference between the ABA-treated fruit and the water-treated control reached statistically significant levels for all batches (P < 0.01). Effects of ABA on Quality of Pineapple. The timecourse changes of the SSC, TA, and AsA were similar, with the values rising to a peak on day 3 and then declining during the remaining time (Figure 3A). Compared with the control, ABAtreated fruit were almost the same as the control in SSC 5314
DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
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to IB, DPI, an important ROS generation inhibitor, was applied to pineapple before treatment with ABA. The DPI plus ABA treatment increased IB incidence by only 3.3% compared with treatment with ABA alone, while it significant reduced IB occurrence, by 23.3%, compared with the control (P ≤ 0.01) (Figure 6). Effect of LaCl3 on ABA-Induced Resistance to IB. To investigate the effect of blocking of the calcium channel, harvested pineapple fruit were treated with LaCl3 alone or LaCl3 plus ABA. Compared with the control, LaCl3 treatment increased IB incidence by 13.4%, although the difference did not reach a statistically significant level (P < 0.01). The combination treatment significantly reduced IB incidence by 20% and 36.4%, compared with the control and LaCl3 treatment, respectively (P < 0.01) (Figure 7). Effects of TS on Efficacy of ABA. To show what role endogenous ABA plays, especially whether it adds to the effects of exogenous ABA, the TS, inhibitor of ABA biosynthesis, was applied before the pineapple was exposed to ABA. When pineapple was treated with TS alone, the IB incidence was only slightly higher than the control (Figure 8). However, the combination of TS and ABA treatment reduced IB incidence by 23% compared with the control (P < 0.01), suggesting that exogenous ABA can work alone in controlling IB.
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DISCUSSION Internal browning has been regarded as one of the major problems of the pineapple industry. Over the past 30 years, many researchers have been trying to develop techniques to control it, but they have not found a commercially effective measure. In this study, it was shown that exogenous ABA treatment is effective in inhibiting IB development for storage at 20 °C and that it works well for pineapple harvested in different seasons (Figures 1 and 2). This result is inspiring for two reasons. First, it allows the industry to extend this technique to packing houses because of the decreased ABA production cost as a result of improvement of ABA production methods.25 Second, it provides a good perspective for studying and unraveling the nature of IB. In this study, over a period of two years, experiments were conducted with “spring pineapple”, pineapple harvested in period from March to June, and “autumn/winter pineapple”, the fruit harvested in period from September to February. However, no experiment was conducted in the summer because farmers do not produce pineapple during that period because pineapple is not profitable in the presence of many other fancy fruits produced in the summer. The industry has long noticed that the spring pineapple is less susceptible to IB than autumn/ winter pineapple. This study also showed that the efficacy of ABA in controlling IB is obviously higher for spring pineapple than for autumn/winter pineapple (Figure 2). The difference in IB incidence between spring and autumn/winter pineapples could be related to the weather, as the autumn/winter pineapple is exposed to the high temperature and rainfall during development in summer, while the spring pineapple develops in mild temperature and dry season in Xuwen County, Guangdong Province, the major pineapple production area in China. The fact that the fruit develops faster in summer and slower in winter might contribute to the different IB incidences. This could also account for the difference in effects of ABA. How temperature and rainfall during fruit development influence IB incidence and ABA effects remains to be elucidated.
Figure 1. Effect of exogenous ABA at different concentrations on internal browning incidence of harvested pineapple fruit stored at ambient temperature (20 °C). Pineapples were harvested in November 2012 and sprayed with distilled water or ABA solution at 95 μM (ABA95) or 380 μM (ABA380). IB incidence (A) was evaluated and pictures (B) were taken 12 days after treatment. Significance of differences between the control and the treatment is indicated by letters above the bars (P ≤ 0.01). Standard errors are shown.
contents, while they had 4.5% and 25.7% more contents of TA and AsA, respectively, than the control at the end of storage (Figure 3B,C). Effect of ABA on TPC Contents and Related Enzymes Activities. The control increased dramatically in contents of TPC and activities of PAL and PPO during the first 9 days, whereas those of the ABA-treated fruit increased much less (Figure 4). As a result, the ABA-treated fruit had much lower TPC contents and enzyme activities during the last 6 days of storage, especially on day 9, when those with ABA treatment were 12.2%, 29.0%, and 32.6% lower than the control in TPC, PAL, and PPO, respectively. Effects of ABA on Activities of CAT and POD and Levels of ROS and MDA. During storage, CAT activity in pineapple decreases with time, while POD activity first rose to a peak, and then decreased. ABA-treated fruit showed CAT and POD activities higher than that of the control, and they had lower levels of O2·−, H2O2, and MDA during the whole storage period (Figure 5). Role of ROS in ABA-Induced Resistance to IB. To investigate whether ROS plays a role in ABA-induced resistance 5315
DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
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Figure 2. Effects of exogenous ABA treatment on IB incidence of pineapple fruit harvested in different seasons. Fruit were sprayed with distilled water or 380 μM ABA solution before storage at 20 °C. IB incidence was evaluated at 12, 9, 9, 12, and 9 days for trials conducted in June 2013, September 2013, November 2013, June 2014, and October 2014, respectively. Significance of differences between the control and the treatment is indicated by letters above the bars (P ≤ 0.01). Standard errors are shown.
Figure 3. Effects of exogenous ABA treatment on soluble solid concentrations (SSC) (A), TA (B), and AsA (C) contents of harvested pineapple fruit. Fruit were sprayed with distilled water or 380 μM ABA solution before storage at 20 °C. The samples were from experiments conducted in June 2013.
not affect SSC contents (Figure 3). These results indicate that ABA maintained the quality of harvested pineapple. Development of internal browning involves oxidation of phenolic compounds by PPO.28 In this study, ABA-treatment reduced PPO activity (Figure 4) and inhibited internal browning (Figures 1 and 2), consistent with previous studies that show activities of PPO were positively correlated with severity of IB in pineapple.15,29 This result suggests that ABA could control IB by inhibiting enzymatic oxidation of phenolic compounds. How ABA inhibited PPO activities remains to be
Different studies varied or even conflicted regarding the effects of exogenous ABA on fruit quality such as SSC and TA. Preharvest application of ABA improved color of grapes and increased acidity but reduced SSC contents.25 ABA application to plants increased tomato fruit soluble sugar, while decreasing organic acid concentrations.26 ABA treatment at the color-break stage did not affect postharvest quality attributes such as soluble solids and acidity in litchi fruit.27 In this study, postharvest ABA treatment slowed the decease of TA and AsA levels, while it did 5316
DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
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Figure 4. Effects of exogenous ABA treatment on contents of total phenolic compounds (A) and activities of PAL (B) and PPO (C) of harvested pineapple fruit. Fruit were sprayed with distilled water or 380 μM ABA solution before storage at 20 °C. The samples were from experiments conducted in June 2013.
Figure 5. Effects of exogenous ABA treatment on activities of CAT (A) and POD (B) and contents of O2·− (C), H2O2 (D), and MDA (E) of harvested pineapple fruit. Fruit were sprayed with distilled water or 380 μM ABA solution before storage at 20 °C. The samples were from experiments conducted in June 2013.
ROS molecules are scavenged by various antioxidative defense mechanisms.34 These include enzymatic antioxidant systems, such as SOD, POD, glutathionereductase (GR), and CAT, and nonenzymatic low molecular metabolites, such as AsA and reduced glutathione (GSH).36 Studies with different plants showed ABA increased contents of AsA and activities of CAT and POD.36,37 In this study, ABA elevated levels of AsA (Figure 3) and enhanced activities of CAT and POD (Figure 5A,B), suggesting that it enhanced antioxidant defense system of pineapples. That ABA-treated pineapple had levels of O2·− and H2O2 lower than those of the control (Figure 5C,D) implies the strengthened defense system efficiently scavenged ROS molecules and thus protected the integrity of cells. This is further confirmed by the reduced MDA contents in ABAtreated fruit (Figure 5E), as MDA is used as an indicator of the severity of cell membrane injury.36 These results suggest that ABA protected cell membrane systems through activating the antioxidative defense system to reduce ROSs, which greatly contributed to reduced IB. However, the role of H2O2 seems to be complicated. On the one hand, it acts as a cytotoxic molecule. On the other hand, it can function as a signaling molecule.38 What actual role it plays
elucidated. Phenolics are the prerequisite for the PPO enzymatic browning. In eggplant, although both the phenolic content and PPO activity play important roles in browning of stored fruit, the phenolic compounds play a major role, as the cultivar with higher TPC showed higher browning, although the PPO activity was lower.30 In this study, ABA-treated pineapples had significantly lower TPC, which might be closely related to the lower IB in those fruits. PAL plays an important role in the browning process of fruits and vegetables,31 as it plays a pivotal role in the biosynthesis of phenolics.32 In pistachio (Pistacia vera L.), there was a high positive correlation between PAL activity and total phenolics contents.33 In this study, ABA-treated pineapple showed obviously lower PAL activities (Figure 4), suggesting that ABA could reduce biosynthesis of TPC by decreasing PAL activity. How ABA reduces activities of PAL remains to be studied. The ROS, which include superoxide radicals (O2·−), hydrogen peroxide (H2O2), singlet oxygen ( 1O2), and perhydroxy radical (HO2·−), affect many cellular functions by damaging nucleic acids, oxidizing proteins, and causing lipid peroxidation.34 A strong oxidative burst will cause cellular damage and death.35 Under normal and healthy conditions, the 5317
DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
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Figure 6. Effect of DPI on ABA induced resistance to internal browning in pineapple fruit stored at 20 °C. Fruit were sprayed with distilled water, 380 μM ABA, or 5 μM DPI before treatment with 380 μM ABA. Incidence (A) was evaluated and pictures (B) were taken 9 days after treatment. Significance of differences between the control and the treatment is indicated by letters above the bars (P ≤ 0.01). Standard errors are shown. The experiment was conducted in October 2014.
Figure 7. Effects of LaCl3, calcium channel blocker, on IB development in harvested pineapple fruit stored at 20 °C. Fruit were sprayed with distilled water, 50 μM LaCl3, or 380 μM ABA following LaCl3 treatment. Incidence (A) was evaluated and pictures (B) were taken 9 days after treatment. Significance of differences between the control and the treatment is indicated by letters above the bars (P ≤ 0.01). Standard errors are shown. The experiment was conducted in September 2013.
depends on the delicate equilibrium between ROS production and scavenging at the proper site and time.39 ABA is a key inducer of H2O2 production in maize leaves under water stress.40 Synthesis of H2O2 is essential for ABA-induced stomatal closure in various species.41 In Arabidopsis, ABAinduced stomatal closure was inhibited by DPI, an inhibitor of NADPH oxidase.42 These suggest that certain functions of ABA depend on H2O2 as a signaling molecule. It is worth investigating whether H2O2 as a signaling molecule is needed by ABA for activating of the antioxidant system that leads to alleviated internal browning. The result showed that the combination of DPI and ABA treatment did not obviously increase IB severity compared with ABA treatment alone (Figure 6), suggesting that H2O2 is not needed by ABA as a signaling molecule to activate the ROS scavenging system and inhibit IB. How ABA activates ROS scavengers, such as POD and CAT, remains to be elucidated. As a second messenger, cytosolic calcium ([Ca2+]cyt) mediates ABA-induced plant’s responses to abiotic stresses, such as chilling43 and heat.44 ABA functions by activating Ca2+-
permeable channels.45 ABA-induced [Ca2+]cyt increases are mediated by Ca2+ influx through plasma membrane Ca2+permeable (ICa) channels and Ca2+ release from internal stores.46 If it is the case in harvested pineapple that ABA controls IB by activating Ca2+-permeable channels, what happens when the channels are blocked would be an interesting question. To address this question, LaCl3, a Ca2+-permeable channels blocker, was applied alone or in combination with ABA to harvested pineapple fruit. The results showed the LaCl3 alone increased the IB incidence by 13.7% compared with the control, indicating that blocking calcium channels was unfavorable for control of IB. However, the combination treatment reduced IB by 33.4% compared with LaCl3 treatment alone (Figure 7), indicating that ABA could reactivate the Ca2+ channels blocked by LaCl3. These results suggest that control of IB by ABA involves activation of Ca2+-permeable channels. 5318
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enzymatic oxidation of phenolics, and enhancing ROSscavenging capability to protect cell membranes. ABA-induced resistance to IB is not dependent on synthesis of H2O2, but could be through activating the Ca2+ channels. ABA is sufficient for controlling IB, and deficiency of ABA in pineapple tissue could induce IB.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 20 38902512/13632355208. Fax: +86 2085288280. E-mail:
[email protected]. Author Contributions †
Q.Z. and Y.L.: These authors contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
This work is supported by Special Fund for Agro-scientific Research in the Public Interest funded by China Ministry of Agriculture (Project 201203021).
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ABBREVIATIONS USED ABA, abscisic acid; GAs, gibberellins; CAT, catalase; PAL, phenylalanine ammonia-lyase; POD, peroxidase; PPO, polyphenol oxidase; SOD, superoxide dismutase; IB, internal browning; MDA, malondialdehyde; TS, tungstate; ROS, reactive oxygen species; AsA, ascorbic acid; TSS, total soluble solids; TA, titratable acids; TPC, total phenolic compounds; FW, fresh weight; O2·−, superoxide radicals; H2O2, hydrogen peroxide; LT, low temperature; AT, ambient temperature; OD, optical density; RH, relative humidity; DPI, diphenylene iodonium
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REFERENCES
(1) Youryon, P.; Wongs-Aree, C.; McGlasson, W. B.; Glahan, S.; Kanlayanarat, S. Alleviation of internal browning in pineapple fruit by peduncle infiltration with solutions of calcium chloride or strontium chloride under mild chilling storage. Int. Food Res. J. 2013, 20 (1), 239−246. (2) Rohrbach, K. G.; Paull, R. E. Incidence and severity of chilling induced browning of waxed ‘Smooth Cayenne’ pineapple. J. Am. Soc. Hortic. Sci. 1982, 107, 453−457. (3) Smith, L. G. Cause and development of blackheart in pineapple. Trop. Agric. 1983, 60 (1), 31−35. (4) Ko, H. L.; Campbell, P. R.; Jobin-Decor, M. P.; Eccleston, K. L.; Graham, M. W.; Smith, M. K. The introduction of transgenes to control blackheart in pineapple (Ananas comosus L.) cv. Smooth cayenne by microprojectile bombardment. Euphytica 2006, 150 (3), 387−395. (5) Soares, A. G.; Trugo, L. C.; Botrel, N.; Souza, L. F.; da, S. Reduction of internal browning of pineapple fruit (Ananas comosus L.) by preharvest soil application of potassium. Postharvest Biol. Technol. 2005, 35 (2), 201−207. (6) Herath, H. M. I.; Bandara, D. C.; Banda, D. M. G. A. Effect of pre-harvest calcium fertilizer application on the control of internal browning development during the cold storage of pineapple ″Mauritius″ (Ananas comosus L. Merr.). J. Hortic. Sci. Biotechnol. 2003, 78 (6), 762−767. (7) The, P. M. P; Goncalves, N. B.; Pinto, N. A. V. D. Effect of a combination of calcium chloride, modified atmosphere and hot water treatment on internal browning in pineapple cv. Smooth Cayenne. Revista Brasileira de Armazenamento 2005, 30 (1), 1−7 in Portuguese with English abstract.
Figure 8. Effects of sodium tungstate dehydrate (TS), inhibitor of ABA biosynthesis, on IB development in harvested pineapple fruit stored at 20 °C. Fruit were sprayed with distilled water, 50 μM TS, or 380 μM ABA following TS treatment. Incidence (A) was evaluated and pictures (B) were taken 9 days after treatment. Significance of differences between the control and the treatment is indicated by letters above the bars (P ≤ 0.01). Standard errors are shown. The experiment was conducted in November 2013.
To check how important ABA is for pineapple to keep healthy during storage, TS, the inhibitor of ABA biosynthesis, was applied to harvested pineapples. The results showed that TS alone slightly aggravated IB symptoms compared with the control, while the combination of TS and ABA treatment effectively inhibited IB development (Figure 8). This result is consistent with that of Pusittigul et al.15 which showed that aggravated IB in pineapple coincided with decreased ABA contents. This implies that sufficient ABA content is necessary for controlling IB and that the deficiency or degradation of endogenous ABA during storage process could result in development of IB. In conclusion, ABA induced resistance to IB and maintained quality of harvested pineapples. ABA reduced IB development by reducing biosynthesis of phenolic substrates, inhibiting 5319
DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
Article
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DOI: 10.1021/jf506279x J. Agric. Food Chem. 2015, 63, 5313−5320
