Increase In Polyphenol Oxidase Activity Research Articles

Effects of chitosan coating on shelf life of cold-stored litchi fruit at ambient temperature

Postharvest pericarp browning of litchi fruit results in an accelerated loss in shelf life and a reduced commercial value. Visual quality was lost in only 6 h at ambient temperature when fruit were removed from storage at 2 °C, due to browning. The experiment was conducted to test the role of chitosan coating in inhibiting skin browning and extending shelf life of cold-stored litchi fruit at ambient temperature. Litchi fruit were treated with 2 g chitosan/100 g solution and then stored for 20 days at 2 °C and 90–95% relative humidity (RH), prior to shelf life evaluation at 25 °C and 80–90% RH. Changes in polyphenol oxidase (PPO) activity, anthocyanin concentration, colour index, eating quality and concentrations of total soluble solids and titratable acidity were measured. The effects of chitosan coating on disease incidence were also evaluated. Application of chitosan coating delayed the decrease in anthocyanin content, the increase in PPO activity and the changes in colour index and eating quality, reduced the decrease in concentrations of total soluble solids and titratable acidity, and partially inhibited decay. The results suggested that treatment with chitosan coating exhibited a potential for shelf life extension at ambient temperature when litchi fruit were removed from cold storage.

Bruising injury of persimmon ( Diospyros kaki cv. Fuyu) fruits

This study was performed to monitor the deterioration of bruised persimmon ( Diospyros kaki cv. Fuyu) fruits. Freshly harvested fruits were bruised by dropping them from a height of 50 cm onto a steel board and then stored at 0 or 20 °C in temperature controlled chambers for up to 4 weeks. Immediately after the bruising, no visible injury on the fruits was evident, but the fruits deteriorated rapidly during storage. The skin tissues of the fruits stored at 20 °C became more reddish with the duration of the storage, but no such changes were found with the fruits stored at 0 °C. The increase in redness of the skin tissues appeared to be associated with storage temperature, but not with the bruising. The skin tissues also became darker when stored at 20 °C than at 0 °C and this tendency was more obvious with the bruised fruits. Flesh firmness decreased rapidly during storage except for the non-bruised fruits stored at 0 °C. Even the non-bruised fruits rapidly lost their flesh firmness at 20 °C. No significant changes in lipid peroxidation, as expressed by malondialdehyde production, were found between the bruised and the non-bruised fruits during the storage either at 0 °C or at 20 °C. This implies that the fruit deterioration caused by bruising is not due to the consequences of lipid peroxidation. Polyphenol oxidase activity increased more rapidly in the bruised fruits than in the non-bruised fruits during storage. The bruising had more effect on increasing polyphenol oxidase activity than did the storage temperature. Although the increase in polyphenol oxidase activity appeared to be associated with the visual deterioration of the bruised fruits, it did not exactly correspond to the physical deterioration. These results indicate that polyphenol oxidase is not the only factor influencing the deterioration associated with bruising. Cell wall hydrolases are currently being assayed to determine if they also contribute the deterioration following bruising.

Effects of chitosan coating on quality and shelf life of peeled litchi fruit

Litchi pulp is very perishable and thus has a short shelf life, with marketers and consumers alike desiring a longer period. The current study was conducted to investigate the effects of chitosan coating on quality maintenance and shelf life extension of peeled fruit of cv. Huaizhi. Manually peeled litchi fruits were treated with aqueous solutions of 0%, 1%, 2% or 3% of chitosan, placed into trays over-wrapped with plastic film, and then stored at −1 °C. Changes in sensory quality in terms of taste and colour scales and weight loss were evaluated. Polyphenol oxidase (PPO) and peroxidase (POD) activities were also measured. Application of chitosan coating retarded weight loss and the decline in sensory quality, with higher contents of total soluble solids, titratable acid, and ascorbic acid, and suppressed the increase in activities of PPO and POD. The results showed that application of chitosan coating effectively maintained quality attributes and extended shelf life of the peeled fruit.

Effects of low-temperature acclimation on browning of litchi fruit in relation to shelf life

SummaryPostharvest pericarp browning of litchi fruit results in an accelerated loss in shelf life and reduced commercial value. Visual quality was lost in only 6.h at room temperature after fruit were removed from storage at 2°C, due to browning. Cultivar ‘Huaizhi’ fruit stored for 2 d at 8°C, for 26 d at 2°C, followed by 2 d storage at 15°C prior to a shelf-life evaluation at 23–258C, 80–90% r.h. were compared with continuous storage for 30 d at 2°C. Changes in polyphenol oxidase (PPO), anthocyanin, membrane leakage, colour, eating quality, total soluble solids, titratable acidity, and ascorbic acid were measured. The effects of temperature conditioning on disease incidence was also evaluated. Application of low-temperature acclimation delayed the decrease in anthocyanin content, the increases in PPO activity and membrane leakage, the changes in colour and eating quality, and partially inhibited decay of fruit. The results suggested that potential exists for shelf-life extension at ambient temperature when fruit are acclimated.

BIOCHEMICAL CHANGES ASSOCIATED WITH CHILLING IN PINEAPPLE FRUIT

Pineapple (Ananas comosus [L.] Merr.) fruit of variable cultivar ('Smooth Cayenne' and PRI hybrid '73-50') and maturity were stored at chilling temperatures to investigate the mechanism for blackheart inducement and development. When chilled for three weeks at 13degreesC followed by 7 days storage at 25degreesC, fruit of both cultivars developed significantly increased polyphenol oxidase (PPO) activities concurrently with blackheart symptoms. Fruit stored continuously at 25degreesC developed no blackheart. There was no correlation between peroxidase activity (POD) and blackheart development for either cultivar. The influence of fruit maturity on blackheart development was also investigated, by storing 'Smooth Cayenne' fruit of six maturity ranges for 3 weeks at 10degreesC, or for 3 weeks at 10degreesC followed by 7 days at 25degreesC. Immature fruit developed negligible blackheart, while fruit of mid-range maturity were susceptible, the latter also developed increased PPO activity after 4 weeks. Over mature fruit developed a translucent breakdown of the pulp, rather than blackheart. Differences in subsequent fruit susceptibility to blackheart were not consistent with PPO activities at harvest. Total phenol concentration increased with fruit maturity, but high phenol concentration was not consistent with increased blackheart incidence. There was no significant difference in ascorbic acid levels at harvest between the maturity ranges. The suggestion in the literature that ascorbic acid level at harvest indicates susceptibility to blackheart is not support by our data.

Blackheart development following chilling in fruit of susceptible and resistant pineapple cultivars

Smooth Cayenne, a widely grown commercial cultivar of pineapple (Ananas comosus L. Merr.), is susceptible to the internal browning disorder known as blackheart (also referred to as endogenous brown spot or internal browning). This disorder is induced by chilling and results in browning of the flesh and core of the fruit due to the oxidation of phenolic substances by the enzyme polyphenol oxidase. The hybrid pineapple cultivar Hawaiian Gold (53-116) is reported to be resistant to blackheart. Fruit of both Hawaiian Gold and Smooth Cayenne were stored for 14 days at 0, 2, 4, 6, 10 and 23˚C, followed by 7 days at 23˚C. Blackheart symptoms were observed in the flesh of Smooth Cayenne fruit chilled at 10˚C and they were progressively less severe at lower chilling temperatures, with no symptoms observed in the flesh of fruit chilled at 0˚C. Increased blackheart symptoms were observed in the core of the fruit at temperatures below 6˚C. Blackheart symptoms were not observed in the flesh of Hawaiian Gold fruit chilled at any of the temperatures tested, but some symptoms were observed in the core tissue at temperatures between 0 and 6˚C. Increased polyphenol oxidase activity was induced by chilling in the flesh of Smooth Cayenne fruit but not in the flesh of Hawaiian Gold. The levels of phenolics and juice pH were similar in the 2 cultivars. The results indicate that Hawaiian Gold fruit are resistant to blackheart in the flesh, at chilling temperatures of between 0 and 23˚C. The unexpected observation that blackheart symptoms were restricted to the core of both Smooth Cayenne and Hawaiian Gold fruit following chilling at 0˚C may have useful implications for the pineapple-processing industry.

Effects of chitosan coating on postharvest life and quality of longan fruit

Abstract The effects of chitosan coating in extending postharvest life of longan fruits and maintaining their quality were investigated. The fruits were treated with aqueous solutions of 0.5, 1.0 and 2.0% chitosan, respectively, and then stored at 2°C and 90% relative humidity. Changes in respiration rate, polyphenol oxidase (PPO) activity, colour, eating quality, and weight loss were measured. The effect of chitosan coating on disease incidence was also evaluated. The application of chitosan coating reduced respiration rate and weight loss, delayed the increase in PPO activity and the changes in colour, and eating quality, and partially inhibited decay of fruit during storage. Furthermore, increasing the concentration of chitosan coating enhanced the beneficial effects of chitosan on postharvest life and quality of the fruit.

Effect of wounding on phenolic enzymes in six minimally processed lettuce cultivars upon storage.

The effect of wounding on polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonia-lyase (PAL) was studied in six minimally processed lettuce (Lactuca sativa L.) cultivars upon storage for 7 days at 5 degrees C (Iceberg Mikonos (IM), I. Green Queen (IGQ), I. Asdrúbal (IA), Little Gem Sandra (LGS), Romaine Cazorla (RC), and R. Modelo (RM)). Wounding of lettuce tissue midribs (because of minimal processing) caused an exponential increase in PPO activity due to the activation process from latent to fully active PPO by following first order kinetics in the time range from 3.7 days (LGS) to 6.3 days (RC). However, total PPO activity (active plus latent) remained constant. Isoform pattern of PPO changed upon storage probably because of posttranslational processes. POD activity linearly increased with induction of new POD isoenzymes. PAL activity presented a typical bell-shaped induction pattern in four cultivars. Only IM and IGQ showed a second induction response which has not been previously described in the literature. IM was the cultivar most susceptible to browning and RC was the cultivar least susceptible. However, no clear correlation was observed between browning and any of the biochemical and physiological attributes investigated (PPO, PAL, and POD activities, total and individual phenols accumulation, and ascorbic acid content).

Characterization of polyphenol oxidase in coffee

Polyphenol oxidase (PPO) was characterized in partially purified extracts of leaves (PPO-L) and fruit endosperm (PPO-E) of coffee ( Coffea arabica L.). PPO activity was higher in early developmental stages of both leaves and endosperm of fruits. Wounding or exposure of coffee leaves to methyl jasmonate increased PPO activity 1.5–4-fold. PPO was not latent and was not activated by protease treatment. PPO activity was stimulated 10–15% with sodium dodecyl sulphate (SDS) at 0.35–1.75 mM, but at higher concentrations activities were similar to the control samples, without detergent. Prolonged incubation of extracts with trypsin or proteinase K inhibited PPO activity but pepsin had no effect. Inhibition of PPO with proteinase K was increased in the presence of SDS. PPO activity from both tissues was optimal at pH 6–7 and at an assay temperature of 30°C. Activity was highest with chlorogenic acid as substrate with a K m of 0.882 mM (PPO-L) and 2.27 mM (PPO-E). Hexadecyl trimethyl-ammonium bromide, polyvinylpyrrolidone 40, cinnamic acid and salicylhydroxamic acid inhibited PPO from both tissues. Both enzymes were inactivated by heat but the activity in endosperm extracts was more heat labile than that from leaves. The apparent M r determined by gel filtration was 46 (PPO-L) and 50 kDa (PPO-E). Activity-stained SDS–polyacrylamide gel electrophoresis (PAGE) gels and western blots probed with PPO antibodies suggested the existence of a 67 kDa PPO which is susceptible to proteolytic cleavage that generates a 45 kDa active form.

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.

Browning susceptibility of minimally processed Baby and Romaine lettuces

This study was conducted to determine the effects of cultivar, tissue susceptibility and storage temperature on the keeping quality of minimally processed Baby and Romaine lettuces. Midrib and photosynthetic tissues were lightly processed and stored for up to 7 days at 5 °C and 13 °C. Changes in L* and a* values and absorbance at 430 nm were compared. The relationship between polyphenols, phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) activities and browning was examined. Measurements of L* and a* values on midribs showed that browning discoloration was the same for Baby as for Romaine lettuces and there was no relationship for temperature. In addition, L* and a* values in photosynthetic tissue indicated a decrease in green pigmentation during storage, especially at 13 °C. For both kinds of tissue at the end of cold storage an increase in soluble brown polymers was detected. In midribs, total phenolics increased significantly throughout the storage period because of the tissue-wounding response. The photosynthetic tissue had a higher phenolic content than the midrib one. For both kinds of tissue an increase in PPO activity occurred throughout cold storage. On the other hand, PAL activity in midrib tissue only increased initially, followed by a slow decline to reach normal levels. Browning potential estimated by L* values correlated significantly (P>95%) with PPO activity and with absorbance at 430 nm for Romaine lettuce. Based on colour and browning potential no differences between Romaine and Baby lettuce cultivars were observed. However, photosynthetic tissue was the most suitable tissue for the preparation of minimally processed salad mixes because of its high phenolic content.

Effects of chitosan coating on enzymatic browning and decay during postharvest storage of litchi (Litchi chinensis Sonn.) fruit

Abstract Litchi (Litchi chinensis Sonn. cv. Huaizhi) fruit were treated with aqueous solutions of 1.0 or 2.0% chitosan coating 1 h after dipping in 0.1% thiabendazole (TBZ), and then stored at 4°C and 90% relative humidity (RH). Changes in browning, anthocyanins, flavonoids, total phenolic contents, polyphenol oxidase (PPO) and peroxidase (POD) activities, and weight loss were measured. The effects of chitosan coating on decay control were also evaluated. The application of chitosan coating delayed changes in contents of anthocyanin, flavonoid, total phenolics, delayed the increase in PPO activity, reduced weight loss, and partially inhibited the increase in POD activity. All these changes corresponded to changes in browning. The application of chitosan coating partially inhibited decay of fruit during storage. However, increasing the concentration of chitosan coating did not significantly increase the beneficial effects of chitosan on browning and decay of the fruit.

ダイコンの赤心症発生に及ぼすホウ素およびリン酸施用の影響

Effects of boron and phosphate applied to the different kinds of soils and solution culture on the internal browning of roots in summer-sown Japanese radish were investigated. With hydroponics, the relationship between the incidence of internal browning and polyphenol concentrations and polyphenol oxidase activity in roots was also examined.1. Borax, applied to the brown lowland soils (sand) and medium and coarse-textured yellow soils (sandy loam), was effective in reducing internal browning and increasing boron concentrations in the roots, but that applied to the andosols (loam) was ineffective. Super phosphate application which increased phosphorus concentrations in the roots was effective in decreasing internal browning even in andosols.2. The occurrence of internal browning induced by the absence of boron in the hydroponic solution was severe at 29 °C as compared to 21 °C, although boron concentration in the root was relatively high at the higher temperature. These results suggest that the occurrence of internal browning can not be explained merely by concentrations of boron in the roots.3. The polyphenol oxidase activity but not the polyphenol concentrations in the roots increased in the absence of boron in the hydroponic solution. Therefore, the internal browning is considered to be caused by the increased polyphenol oxidase activity in response to the boron deficiency in the root.In the presence of boron in the solution, the internal browning did not occur, irrespective of phosphorus concentrations in the solution. On the other hand in the absence of boron, the occurrence of internal browning and polyphenol oxidase activity in the roots decreased with the increase in phosphate levels.

Behaviour of Polyphenol Oxidase, IAA Oxidase and Catalase in Germinating Rice in Relation to Salt Tolerance

Activities of the enzymes polyphenol oxidase, indole-3-acetic acid (IAA) oxidase and catalase were compared from endosperms and embryoaxes of germinating rice (Oryza sativa) seeds of two sets of cultivars differing in salt tolerance, raised under increasing levels of NaCl salinity. Salt sensitive cvs. Ratna and Jaya were characterized by higher polyphenol oxidase activity in embryoaxes under salinisation as compared to salt tolerant cvs. CSR-1 and CSR-3. In endosperms of salt sensitive cultivars the enzyme activity decreased under salinisation whereas in tolerants it increased due to salinity. In vitro studies using desalted enzyme extracts showed a continuous increase in polyphenol oxidase activity with increasing concentration of NaCl (0–1000 mM) in the reaction medium. IAA oxidase activity increased due to salinity in embryoaxes of both sets of cultivars, the effect was greater in sensitive cultivars than tolerants. NaCl when incorporated in the reaction medium caused decrease in IAA oxidase activity. Activity of catalase decreased with increase in salinity with greater decrease in sensitive cultivars than tolerants. Results suggest possible different behaviours of oxidative enzymes in germinating seeds of rice cultivars differing in salt tolerance and that salt tolerance ability is associated with lower polyphenol oxidase and IAA oxidase activities and higher catalase activity in embryoaxes under salinisation.

Ultrastructure of wheat straw cell wall delignified byPleurotus ostreatus

Transmission electron microscopy of wheat straw cell wall incubated with Pleurotus ostreatus in the presence of glucose or sunflower oil reveals different degradation patterns. Lower lignin content and increased polyphenol-oxidase activity correspond to peculiar features of the substrate at ultrastructural level. Differentiation between cellulose and lignin degradation by electron microscopy might represent a valuable tool to monitor biological delignification during industrial hydrolysis of ligno-cellulose.

Ultrastructure of wheat straw cell wall delignified by Pleurotus ostreatus

Transmission electron microscopy of wheat straw cell wall incubated with Pleurotus ostreatus in the presence of glucose or sunflower oil reveals different degradation patterns. Lower lignin content and increased polyphenol-oxidase activity correspond to peculiar features of the substrate at ultrastructural level. Differentiation between cellulose and lignin degradation by electron microscopy might represent a valuable tool to monitor biological delignification during industrial hydrolysis of ligno-cellulose.

Fenóis, peroxidase e polifenoloxidase na resistência do cafeeiro a Meloidogyne incognita

Plântulas dos cultivares Mundo Novo, de Coffea arabica, suscetível, e Apoatã, de Coffea canephora, resistente, foram inoculadas com ovos de Meloidogyne incognita raça 2, e avaliadas em duas fases do ciclo de desenvolvimento do parasito, isto é, na de penetração de larvas e na de fêmeas com ovos. Não foram observadas diferenças quanto ao desenvolvimento radicular e da parte aérea entre plântulas inoculadas e não inoculadas, nas duas avaliações. Nos dois cultivares, houve aumento no teor de fenóis nas plântulas inoculadas na primeira avaliação, e, na segunda, apesar de os valores terem sido maiores, foram iguais entre plântulas inoculadas e seus respectivos controles. O 'Mundo Novo' apresentou sempre maior conteúdo de fenóis que o 'Apoatã' e somente houve aumento na sua atividade de peroxidase na primeira avaliação. Na segunda, a atividade dessa enzima foi maior do que na primeira, porém igual entre plântulas inoculadas e seus controles. O 'Apoatã' sempre teve maior atividade de peroxidase, e apenas houve aumento da atividade de sua polifenoloxidase na primeira avaliação, sendo que nesse cultivar a atividade dessa enzima sempre foi maior do que no 'Mundo Novo'. Cromatografias em camada delgada de celulose mostraram que em nenhum deles houve variações quantitativas de fenóis entre as plantas inoculadas e não inoculadas. Ambos, 'Mundo Novo' e 'Apoatã', apresentaram 23 compostos fenólicos em comum e, nove e onze não comuns respectivamente.

Enzyme activities and polyphenols related to mesocarp discolouration of avocado fruit

Avocado fruit showing severe symptoms of the mesocarp discolouration disorder exhibited significantly higher extractable activities of soluble polyphenol oxidase and peroxidase, as well as higher levels of total phenols, hydroxycinnamic acids and proanthocyanidins, when compared to healthy fruit. However, l-phenylalanine ammonia-lyase activity was very variable, and no significant differences were observed between healthy and affected fruit. Extraction of healthy, but not severely affected, fruit in the presence of 0.1 % SDS resulted in increased polyphenol oxidase activity reflecting the release of bound and/or latent enzyme. Qualitative differences between healthy and affected fruit included different patterns of polyphenol oxidase multiple forms and different polyphenol profiles. The pattern of polyphenol oxidase multiple forms from SDS-extracted healthy fruit was similar to that from mildly affected fruit not extracted with detergent.

Ethylene Concentration and Polyphenol Oxidase Activity in Mango (Mangifera indica L.) Fruit Abscission

Summary Young fruit abscission in mango was found to be associated with an increased polyphenol oxidase activity, similar to the response of peroxidase activity, for both Haden and Sensation cultivars. The former, which is more prone to abscission, also had a higher activity for both enzymes compared with the latter cultivar. Ethylene production was increased in the abscised fruit of the Haden cultivar only. The possible association with phenol synthesis and the phenylalanine ammonia-lyase enzyme is discussed.

Presence of auxin protectors inEriophyes inducedZizyphus stem galls

3 auxin protectors, which were o-dihydroxyphenols of high molecular weight, were isolated fromZizyphus gall tissues. An increase in polyphenol oxidase activity in the gall tissue was observed which probably led to the production of high levels of auxin protectors. This prevented IAA oxidation, resulting in hyperauxinity and auxin-autotrophy.