Postharvest Browning Research Articles

COMPARISON OF ENZYMES AND FLAVONOIDS RELATED TO POSTHARVEST BROWNING IN THREE LITCHI (LITCHI CHINENSIS SONN.) CULTIVARS

The experiments were performed to compare differences of enzymes and flavonoids related to postharvest browning in three litchi cultivars cv. “Nuomici,”“Heli” and “Feizixiao.” By high-performance liquid chromatograph analysis, the major flavonoids from pericarp tissues were identified as (−)–epicatechin (EC), (−)–epigallocatechin (EGC) and proanthocyanidin A2 (PA2). These flavonoids were ortho dihydric or triatomic phenols serving as potential substrates for enzymatic browning reaction. It was further observed that the similar flavonoid components existed in three cultivars. In addition, comparing three litchi cultivars, cv. “Nuomici” exhibited higher activities of polyphenoloxidase (PPO) and peroxidase (POD) as well as higher contents of potential substrates EC, EGC and PA2, indicating that this cultivar had the stronger capability of enzymatic browning reaction. After the ripe fruits were harvested, cv. “Nuomici” would brown quickly. However, cv. “Heli” possessed the highest EC, EGC and PA2 contents but the lowest PPO and POD activities, and contrarily cv. “Feizixiao” had higher PPO and POD activities but the lowest EC, EGC and PA2 contents, suggesting that both cultivars browned more slowly than cv. “Nuomici” after harvest. PRACTICAL APPLICATIONS Enzymatic browning of pericarp tissues seriously influences the quality of harvested litchi fruit. The browning level of various litchi cultivars is closely correlated with the differences of enzyme activities and flavonoid contents. The aim of the present study was to compare differences of enzymes and flavonoids related to postharvest browning in three common litchi cultivars. This study helped in comprehending the postharvest storage characteristics of different litchi fruits and provided a practical reference for selection and breeding of litchi cultivars with good shelf life.

Effects of a phospholipase D inhibitor on postharvest enzymatic browning and oxidative stress of litchi fruit

Membrane lipid degradation catalyzed by phospholipase D (PLD) results in postharvest browning and senescence of litchi fruit. The effects of n-butanol, a specific PLD inhibitor, on enzymatic browning and oxidative stress during storage of litchi fruit at room temperature were evaluated. n-Butanol-treated fruit had a lower browning index and disease index than untreated fruit. n-Butanol treatment also decreased PLD activity. As a result, the decompartmentalization of litchi polyphenoloxidase and substrates was reduced. The conversion of substrates (−)-epicatechin and procyanidin A 2 into quinones was slowed down and enzymatic browning of litchi pericarp tissues was lower after 6 d storage. Additionally, n-butanol-treated fruit possessed significantly lower malondialdehyde contents than untreated fruit after 4 d storage. Analysis of antioxidative enzyme activities showed that n-butanol treatment inhibited oxidative stress mainly by maintaining high catalase activity in litchi pericarp tissues. Consequently, senescence of litchi fruit during storage was moderated.

Post-harvest browning syndrome and other qualities and defects in Backhousia myrtifolia

SummaryBackhousia myrtifolia is a species native to Australia that shows potential as a cut flower crop. During Spring and Summer, it bears numerous small florets with prominent white sepals and glossy deep-green foliage. B. myrtifolia is harvested either when tight white buds are present in the centre of the star-shaped sepals, or following bud burst, after the petals and stamens have abscised to leave only the sepals.Wilting and brown-to-black discolouration of the flowers and foliage can markedly reduce stem quality. Several forms of discolouration were characterised over the 2004 – 2006 flowering seasons and were collectively termed ‘post-harvest browning syndrome’. Further research based on the symptomatology described herein is required to elucidate the causal agent(s).

Recent advances in extending the shelf life of fresh Agaricus mushrooms: a review

Postharvest browning of Agaricus mushrooms is a severe problem that reduces the shelf life of harvested mushrooms because of their continued respiration and biochemical activity. There are no simple answers and no single treatment is known to limit overall quality deterioration. However, there are several strategies that are being implemented in order to reduce the rate of respiration for mushrooms. Packaging technology is the common denominator that allows us to implement these strategies and thus is key to quality preservation. In this review, first, the major factors involved in postharvest quality deterioration are discussed and then technological advances/methods used to counteract these hurdles are presented.

Identification of an Alkylhydroquinone from Rhus succedanea as an Inhibitor of Tyrosinase and Melanogenesis

The alkylhydroquinone 10'(Z)-heptadecenylhydroquinone [HQ17(1)], isolated from the sap of the lacquer tree Rhus succedanea, was found to inhibit the activity of tyrosinase and to suppress melanin production in animal cells. The IC50 of HQ17(1) as a tyrosinase inhibitor was 37 microM versus 70 microM for hydroquinone (HQ), a known inhibitor of tyrosinase and melanogenesis. For the inhibition of melanin production in mouse B16 melanoma cells, the EC50 of HQ17(1) was 40 microM versus 124 microM for HQ. HQ17(1) induced much less oxidative stress than did HQ. The effectiveness in inhibiting melanin production could be mimicked by intermittent exposure of cells to HQ17(1). The potent inhibitory effects of HQ17(1) on tyrosinase activity and melanin production are likely due to its heptadecenyl chain, which facilitates retention of the compound in cell membrane compartments and may impede oxidation of the hydroquinone ring. As tyrosinase activity accounts for postharvest browning of botanical products and animal skin melanogenesis, HQ17(1) could be useful for the preservation of these products or as a skin-whitening cosmetic.

Effect of 60Co γ-irradiation on postharvest quality and selected enzyme activities of Pleurotus nebrodensis

Freshly harvested Pleurotus nebrodensis fruit bodies were exposed to four different doses (0.8–2.0 kGy) of 60Co γ-irradiation and various physiological changes associated with postharvest deterioration, as well as the activities of selected enzymes (proteinase, polyphenoloxidase, superoxide dismutase, catalase) thought to play a role in the process of deterioration, were monitored during 22 days of subsequent storage at 4 °C and 65–70% relative humidity. An irradiation dose of 1.2 kGy significantly delayed (by 6–9 days) the onset of fruit body softening, splitting and browning compared with non-irradiated controls and test samples subjected to lower or higher irradiation doses. Irradiation with 1.2 and 1.6 kGy also had a positive effect on other indicators of mushroom tissue senescence, resulting in smaller decreases in soluble protein levels and more protracted increases in proteinase activity. Peak levels of polyphenoloxidase activity, widely recognized as causing postharvest browning of mushroom tissue, were also significantly lower ( P < 0.05) in fruit bodies exposed to 1.2 kGy compared with non-irradiated controls. Our data increase our understanding of the effects of γ-irradiation on the biochemical changes associated with postharvest deterioration in P. nebrodensis, and improve the prospects of more targeted strategies for extending the shelf life of both this and other mushrooms.

Identification of (−)-epicatechin as the direct substrate for polyphenol oxidase from longan fruit pericarp

Postharvest browning of longan fruit results in a short life and a reduced commercial value. The experiments were conducted to separate, then purify and finally identify the polyphenol oxidase (PPO) substrates that cause longan fruit to brown. PPO and its substrates were, respectively, extracted from longan fruit pericarp tissues. The substrate for longan PPO was separated and purified using polyamide column chromatography, Sephadex LH-20 column chromatography and silica gel column chromatography, respectively. The substrate was further identified by 0.5% FeCl 3 solution and enzymatic reaction with longan PPO. On the bases of UV, 1H NMR, 13C NMR, and ESI-MS data, the direct substrate for the PPO from pericarp tissues of longan fruit was identified to be (−)-epicatechin. Furthermore, the contents of (−)-epicatechin of pericarp tissues of longan fruit of two major cultivars were determined by high performance liquid chromatography (HPLC). The HPLC analysis exhibited that the contents of (−)-epicatechin of fruit pericarp of ‘Shixia’ and ‘Chuliang’ were 0.26 and 0.56 mg/g on fresh weight (FW) basis at harvest and 0.15 and 0.09 mg/g FW after 3 days of storage. The more rapid decrease in the (−)-epicatechin content of ‘Chuliang’ was due to the oxidization catalyzed by PPO, which was in agreement with the higher browning index.

IDENTIFICATION OF PROCYANIDIN A2 AS POLYPHENOL OXIDASE SUBSTRATE IN PERICARP TISSUES OF LITCHI FRUIT

Postharvest browning of litchi fruit results in short shelf life and reduced commercial value. Experiments were conducted to separate, purify and identify polyphenol oxidase (PPO) substrates that cause litchi fruit to brown. PPO and its substrate were extracted from the pericarp tissues of litchi fruit. The litchi PPO substrate was purified using polyamide column, silica gel column and Sephadex LH-20 column chromatography. The browning substrate was selected by a 0.5% FeCl 3 solution and then identified using a partially purified litchi PPO. Analyses of ultraviolet spectrometry, nuclear magnetic resonance and electrospray ionization mass spectrometry indicated that the PPO substrate was procyanidin A2. The substrate can be oxidized to o-quinones by litchi PPO and then form brown-colored by-products, resulting in pericarp browning of harvested litchi fruit.

CONTROL OF POSTHARVEST BROWNING OF LYCHEE FRUIT USING ASCORBIC ACID

Effect of ascorbic acid on controlling of postharvest browning of lychee fruit (cv. Khom) was studied. Fruit were dipped in 0.5 and 1.0 M ascorbic acid solutions for 10 and 30 minutes and then stored at 5°C and 90-95% RH. Ascorbic acid treatments reduced browning of lychee pericarp with 1.0 M ascorbic acid giving the best control of browning. The treatments with ascorbic acid resulted in reductions in total phenolic compound content as well as pH value of lychee peel which are related to browning disorder as indicated by the browning score. Also ethylene production and loss of weight were low following ascorbic acid treatments. However, the storage life of lychee fruit treated with ascorbic acid was only 28 days due to rapid deterioration from fungal infection.

Identification of (−)-epicatechin as the direct substrate for polyphenol oxidase isolated from litchi pericarp

Abstract Postharvest browning of litchi fruit results in a short life and a reduced commercial value. The experiments were conducted to separate, purify and identify the polyphenol oxidase (PPO) substrates that cause litchi fruit to brown. PPO and its substrates were, respectively, extracted from fruit pericarp tissues. The substrates for litchi PPO were separated and purified using polyamide column chromatography, silica gel column chromatography and preparative thin layer chromatography. The substrate was further identified by 0.5% FeCl3 solution and enzymatic reaction with litchi PPO. On the basis of UV, 1H NMR, 13C NMR, and ESI-MS data, the direct substrate for the PPO from litchi fruit pericarp tissues was identified to be (−)-epicatechin.

Prevention of Agaricus bisporus postharvest browning with tyrosinase inhibitors

Postharvest browning of Agaricus bisporus mushrooms is a severe problem that reduces the shelf life of harvested mushrooms. Mushroom browning occurs mainly as a result of tyrosinase activity, an enzyme belonging to the polyphenol oxidase (PPO) family and known to be a key enzyme in melanin biosynthesis. An ethanolic extract from licorice roots ( Glycyrrhiza glabra) and [3-(2,4-dihydroxyphenyl propionic acid)] (DPPacid) isolated from fig leaves and fruit have been shown to inhibit tyrosinase activity. Adding these inhibitors to sliced mushrooms had a very strong inhibitory effect on browning, but pre-storage immersion of intact mushroom in the licorice extract did not prevent browning after 8 days storage at 4 °C. By contrast, treatment with DPPacid at 1 μg/mL reduced browning by half. Measurement of inhibitor uptake by mass spectra (MS) and assay of tyrosinase activity indicated that penetration into the mushroom tissue was inadequate for tyrosinase inhibition. Moreover, DPPacid was found to be unstable in the mushroom tissue and within a short time it was, presumably, metabolised.

Weak Organic Acids and Inhibitors of pH Homeostasis Suppress Growth of Penicillium Infesting Litchi Fruits

AbstractTo prevent the rapid postharvest browning, litchi fruits can be fumigated with SO2, followed by a hydrochloric acid (HCl) dip to restore their red colour. Most fungal decay agents are sensitive to SO2 fumigation or acidification but the treated fruits are highly sensitive to infection by Penicillium commune and closely related species. The present study examined whether the addition of weak organic acids or pH homeostasis inhibitors, alone and in combination, could effectively control fungal growth under the physiological conditions that are relevant to litchi fruits. It was found that the fungus can proliferate in culture at pH &gt; 2.5 and is capable of either alkalizing or acidifying the medium, depending on the initial pH and the extent of growth inhibition. Propionic, sorbic and decanoic acids progressively inhibited fungal growth at decreasing pH, presumably by inducing acid stress. Likewise, the inhibitors of pH homeostasis, omeprazole and erythrosin B, inhibited fungal growth, and their efficacy was significantly increased at lower pH and in combination with weak organic acids. Litchi fruits treated with sorbic acid in the presence of HCl were significantly less prone to decay by Penicillium. This study shows that it is possible to utilize low pH as a lever to prevent fungal development.

INHIBITION OF MUSHROOM BROWNING

Postharvest browning of mushrooms is a rapid process, resulting in decreased commercial value. The process may be initiated by enzymatic oxidation of phenols such as tyrosine, to form brown pigments (melanin) or by non-enzymatic phenol oxidation induced by different factors, including bacteria. Plant extracts and their active constituents, possessing potent tyrosinase inhibitory activities, previously isolated in our group, were tested for their ability to inhibit mushroom browning. Sliced mushroom caps were treated with different concentrations of licorice root extract, or with 3-(2,4-dihydroxyphenyl propionic acid) -DPPacid (isolated from fig leaves), with or without pretreatment with H 2 O 2 , and then stored at 20°C for two days. Browning was inhibited with an IC 50 of 0.1 ppm for licorice extract and 0.18 ppm for DPPacid, without H 2 O 2 pre-treatment. Treatment of whole mushrooms with either licorice or DPPacid did not prevent browning, whereas treatment with 5% H 2 O 2 prevented intact cap browning for 10 days at 4°C. This treatment caused an immediate decrease by three orders of magnitude in the number of colony forming units (CFU), from 491 to 0.37 CFU/Cm 2 . In conclusion, increased shelf life of intact mushrooms might be achieved by treatment with H 2 O 2 followed by DPPacid or for cut mushrooms by licorice extract or DPPacid alone.

Effect of oxalic acid on control of postharvest browning of litchi fruit

Litchi ( Litchi chinensis Sonn.) fruit, cv. Huaizhi, was treated with 2 and 4 mM oxalic acid and stored at room temperature to investigate the effect of oxalic acid on pericarp browning. The results showed that the pericarp browning indices of the fruit, treated with both oxalic acid concentrations, were significantly lower than that of the control, due to increase of membrane integrity, inhibition of anthocyanin degradation, decline of oxidation, and maintanance of relatively low peroxidase activity in the fruit during storage. It appears that application of oxalic acid can effectively control the pericarp browning of litchi fruit during postharvest storage.

Role of peroxidase in anthocyanin degradation in litchi fruit pericarp

Postharvest browning of litchi fruit pericarp is a major problem, resulting in accelerated shelf life and reduced commercial value of the fruit. The browning was generally thought to be a rapid degradation of red pigments caused by polyphenol oxidase (PPO) and peroxidase (POD). This work is conducted to understand the role of POD in anthocyanin degradation in litchi pericarp, which is less understood than PPO. POD activity in the pericarp increased consistently with skin browning index during storage of litchi fruit, but was negatively associated with anthocyanin concentration. Although POD cannot directly oxidize litchi anthocyanin in the presence of H2O2 in vitro, the anthocyanin content decreased rapidly after the addition of guaiacol solution, which indicated that the anthocyanin degradation by POD exhibited a coupled oxidation mechanism. Furthermore, anthocyanidin, produced by hydrolysis of the purified anthocyanin, could act as a substrate of POD. Thus, enzymatic browning of litchi fruit pericarp caused by POD may involve an anthocyanase–anthocyanin–phenolic–H2O2 reaction.

Purification and structural analysis of anthocyanins from litchi pericarp

Litchi fruit peel anthocyanins were extracted with 0.5 M HCl, and then purified by an Amberlite XAD-7 column and Sephadex LH-20 column chromatography. The major part of the anthocyanins of litchi pericarp, which (94.3% of total), was obtained. Furthermore, the partially purified anthocyanin was identified as cyanindin-3-rutinoside, with a molecular weight of 595, using HPLC equipped with mass spectrometry. The results corroborate the previous observation of Zhang, Pang, Ji, and Jiang (2001 Food Chemistry, 75, 217–221), who suggested that nonenzymatic degradation of anthocyanins could participate in postharvest browning of litchi pericarp.

Role of anthocyanins, polyphenol oxidase and phenols in lychee pericarp browning

Postharvest browning of lychee fruits is investigated in relation to anthocyanins, polyphenol oxidase (PPO) and phenols, using a purified PPO, anthocyanin extract and phenolic extract. Lychee PPO cannot oxidise the degradation of anthocyanins, but the presence of phenolic extract stimulates pigment degradation by PPO, leading to the development of brown pigments. The absorbance at 410 nm of the reaction solution is correlated well with the peel browning index. Pyrogallol, catechol and 4-methylcatechol are good stimulators, but no action with chlorogenic acid, p-cresol, resorcinol or tyrosine is observed. A decrease in the ascorbic acid content of lychee pericarp is associated with an increase in the peel browning index, and the addition of ascorbic acid to the reaction mixture exerts a preventive action on the anthocyanin degradation. Data here suggest that anthocyanins, PPO and phenols contribute to lychee pericarp browning involved in anthocyanin–PPO–phenol reactions. © 2000 Society of Chemical Industry

Postharvest Browning of Litchi Fruit by Water Loss and its Prevention by Controlled Atmosphere Storage at High Relative Humidity

Postharvest browning of litchi fruit caused by water loss was investigated in relation to anthocyanin content, polyphenol oxidase (PPO) activity, pH value, and membrane permeability. Total anthocyanin concentration decreased with pericarp desiccation. Fruit stored at 90% relative humidity (RH) had the lowest loss of total anthocyanins over the storage period, while total anthocyanin content of fruit stored at 60 and 70% RHs significantly declined. Polyphenol oxidase activity with 4-methylcatechol as a substrate tended to increase with reduced storage RH, but no activity towards anthocyanins was detected. Furthermore, in the presence of 4-methylcatechol, the oxidation of anthocyanins by PPO was observed. The pH value was initially low, and then increased with pericarp desiccation, which was associated with increased PPO activity. Conversely, the integrity of membrane systems, which increased with reduced storage RH and increased storage time, showed that membrane structure became more vulnerable. These results indicate that oxidation of both phenolic and anthocyanins by PPO seems to affect the response of litchi fruit to water loss in terms of browning, and suggest that substrate-enzyme contact should be emphasized as this could promote enzymatic reaction leading to browning. Storage at 1°C under controlled atmosphere (3–5% O2and 3–5% CO2) at 90% RH gave good browning control and fruit quality maintenance.

Calcium Chloride Added to Irrigation Water of Mushrooms (Agaricus Bisporus) Reduces Postharvest Browning

ABSTRACTThe influence of 0.3% CaCl2 added to irrigation water on mushroom tyrosinase activity and postharvest browning was examined. Calcium concentration of mushrooms was significantly increased with the addition CaCl2 to irrigation water but had no effect on inherent tyrosinase activity but reduced postharvest browning. The CaCl2 had even more pronounced improvement in shelf life as indicated by reduced browning following a standard bruising treatment. Transmission electron micrographs indicate that increased levels of calcium in mushrooms irrigated with CaCl2may have decreased browning by increasing vacuolar membrane integrity; thereby reducing the opportunity for tyrosinase to react with its substrates.

Postharvest Browning of Rambutan is a Consequence of Water Loss

Rambutan (Nephelium lappaceum L.) rapidly lose their attractive appearance after harvest due to a superficial pericarp browning. Storage at high humidity minimizes fruit desiccation and may, therefore, delay browning onset. This paper examines the effect of reduced water loss rate on browning that may occur with time. Rambutan fruit pericarp browning beyond a commercially saleable level occurred at a weight loss of 25% to 40%. This depended on duration and storage relative humidity (RH). Skin browning was 50% greater on the red (R 134) than the yellow (R 156) cultivar at 60% RH. There was a storage time × RH interaction in the development of browning such that browning was observed earlier at lower RHs. Skin browning and spintern (soft spine) browning developed independently. Cracks appeared on the surface of fruit with increased weight loss. Browning occurrence was consistent with increased total phenolic compound levels in the pericarp. Water loss precedes browning occurrence and, over time, water loss is related to browning. Water stress appeared to affect rambutan pericarp tissue in much the same manner as senescence.