Methyl jasmonate enhances biocontrol efficacy of Rhodotorula glutinis to postharvest blue mold decay of pears

The effect of Rhodotorula glutinis treatment alone or in combination with methyl jasmonate (MeJA) in controlling blue mold decay, the natural fungal decay of pears and the postharvest quality parameters including fruit firmness, total soluble solids, titratable acidity, and ascorbic acid were investigated. The combination of methyl jasmonate (200 μM) and R. glutinis (1 × 10⁸ CFU/ml) was a more effective approach to reduce the disease incidence and lesion diameter of blue mold decay of pears than the application of MeJA or R. glutinis alone after incubation for 7 d at 20 °C. The natural fungal decay of pears treated with the application of R. glutinis combined with MeJA resulted in reduced average decay incidence of 10.42% or 4.16%, respectively, compared with 27.17% or 20.83% in the control fruits following storage at 20 °C for 15 d or 4 °C for 60 d followed by 20 °C for 15 d. The combined treatment did not impair quality parameters of fruits under both conditions.     

苹果采后灰霉病抗性生理差异分析

以‘秦冠’、‘富士’苹果果实为材料,对损伤接种灰葡萄孢(Botrytis cinerea Pers.)后果肉组织抗病相关物质及酶活力变化进行分析测定,揭示苹果采后灰霉病抗性差异的生理机制。结果表明:接种B.cinerea后,两种果实的发病率和病斑直径存在差异,其中‘秦冠’苹果发病率和病斑直径显著小于‘富士’苹果(P0.05);进一步研究发现抗病品种果肉组织中苯丙氨酸解氨酶、过氧化物酶、多酚氧化酶、几丁质酶、β-1,3-葡聚糖酶活力均高于感病品种,从而促进抗病品种果肉中类黄酮和木质素的积累,降低膜脂过氧化程度,减少丙二醛的产生,提高了果实的抗病性,但总酚含量‘秦冠’苹果低于‘富士’苹果。研究结果可以为苹果灰霉病抗性鉴定和筛选抗灰霉病苹果资源提供理论指导。     

Influences of preharvest spraying Cryptococcus laurentii combined with postharvest chitosan coating on postharvest diseases and quality of table grapes in storage

The effects of preharvest spray with Cryptococcus laurentii combined with chitosan coating after harvest on decay and quality of table grapes during storage periods were evaluated in the present study. Preharvest spray with C. laurentii (PreA) significantly decreased decay index (DI), and postharvest chitosan coating (PCC) enhanced the effectiveness of the pre-harvest spray when fruits were stored at 0 °C. PreA combination with PCC increased the activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) of fruit in storage. PreA + PCC treatment was effective in reducing weight loss of fruits by 85% at 17 d storage and 38% at 42 d storage as compared to PreA alone at the same stage. In addition, PreA enhanced the ratio of soluble solids content (SSC) to titratable acid (TA) by 12% at harvest time, 7% at 17 d storage and 25% at 42 d storage, mainly by increasing SSC and decreasing TA in fruit stored at 0 °C. These results suggested that integration of preharvest spray with C. laurentii and postharvest chitosan coating treatment may be a promising management strategy for decay control and quality maintenance of table grapes.     

A combination of marine yeast and food additive enhances preventive effects on postharvest decay of jujubes (Zizyphus jujuba)

We investigated the effects of marine yeast Rhodosporidium paludigenum in combination with a food additive, carboxymethylcellulose sodium (CMC-Na), on prevention of postharvest decay and food quality of Chinese winter jujubes. R. paludigenum (1 × 10⁸ cells/ml) combined with CMC-Na (0.3%) significantly increased the inhibition of black rot on jujubes at 25 °C when compared with R. paludigenum-alone treatment (5.8% vs. 20%, p < 0.05). The combination also reduced natural rot from 86% (control) to 56%. The combination caused transient changes in enzyme activities or contents of some oxidation reactive markers such as peroxidase (POD), superoxide dismutase (SOD), and malondialdehyde (MDA) of jujubes. The combination had no significant effect on the food qualities such as colour (chroma and hue angle), total soluble solid (TSS) and titratable acidity (TA) of the fruit. While enhancing these effects, CMC-Na did not affect the survival of R. paludigenum in nutrient yeast dextrose agar (NYDA) culture. Thus, we conclude that the combination of R. paludigenum and CMC-Na is a promising formulation to control postharvest decay of Chinese winter jujubes.     

Yeast biocontrol of fungal spoilage of pears stored at low temperature

To reduce the use of fungicides, biological control with yeasts has been proposed in postharvest pears. Most studies of antagonists selection have been carried out at room temperature. However, in regions like North Patagonia where fruits are stored at − 1/0 °C during 5-7 months the selection of potential antagonist agents must be carried out at low temperature. In this study, 75 yeast cultures were isolated from healthy pears from two Patagonian cold-storage packinghouses. Aureobasidium pullulans, Cryptococcus albidus, Cryptococcus difluens, Pichia membranifaciens, Pichia philogaea, Rhodotorula mucilaginosa and Saccharomyces cerevisiae yeast species were identified. Additionally, 13 indigenous isolates of Penicillium expansum and 10 isolates of Botrytis cinerea were obtained from diseased pears, characterized by aggressiveness and tested for sensitivity to postharvest fungicides. The yeasts were pre-selected for their ability to grow at low temperature. In a first biocontrol assay using the most aggressive and the most sensitive isolate of each pathogen, two epiphytic isolates of A. pullulans and R. mucilaginosa were the most promising isolates to be used as biocontrol agents. They reduced the decay incidence by P. expansum to 33% and the lesion diameter in 88% after 60 days of incubation in cold. Foreign commercial yeast used as a reference in assays, only reduced 30% of lesion diameter in the same conditions. Yeasts were not able to reduce the incidence of B. cinerea decay. The control activity of the best two yeasts was compared with the control caused by the fungicides in a second bioassay, obtaining higher levels of protection against P. expansum by the yeasts. These two regional yeasts isolates could be promising tools for the future development of commercial products for biological control.     

Salicylic acid enhances biocontrol efficacy of Rhodotorula glutinis against postharvest Rhizopus rot of strawberries and the possible mechanisms involved

The potential of using Rhodotorula glutinis alone or in combination with salicylic acid (SA) for the control of postharvest Rhizopus rot of strawberries, and their effects on enzyme activities of fruits were investigated. The combination of R. glutinis (1 × 10⁸ CFU ml⁻¹) with SA (100 μg ml⁻¹) resulted in a significant reduction in the disease incidence and lesion diameter of Rhizopus rot on the strawberry fruits at 20 °C and 4 °C, and more so than with SA or yeast alone. SA at the concentration of 100–1000 μg ml⁻¹ significantly inhibited spore germination of Rhizopus stolonifer. About 100 μg ml⁻¹ of SA did not inhibit the growth of the antagonistic yeast, and could significantly increase the population growth of R. glutinis in strawberry wounds at 20 °C. SA, combined with R. glutinis, increased the activity of strawberry host defence enzymes (POD) and cell wall lytic enzymes (β-1,3-glucanase).     

植酸结合胶红酵母对桃果采后根霉病的控制

为了寻找一种能够代替化学杀菌剂控制桃果采后病害的方法,研究了植酸与胶红酵母结合使用对桃果采后根霉病的控制效果。结果表明,0.15%植酸与胶红酵母结合使用能显著降低桃果采后根霉病发病率,防治桃果自然腐烂的发生,并且对果实贮藏品质没有产生不利影响;能诱导桃果多酚氧化酶(PPO)、过氧化物酶(POD)活性的提高,同时可以抑制丙二醛(MDA)含量的增加。     

Combination of Kluyveromyces marxianus and sodium bicarbonate for controlling green mold of citrus fruit

Biocontrol efficacy of an antagonistic yeast Kluyveromyces marxianus was evaluated individually or in combination with sodium bicarbonate (SBC) against green mold of citrus fruit caused by Penicillium digitatum. Their effects on postharvest quality of citrus fruit were also investigated. The results indicated that the antagonistic activity of K. marxianus at 1 × 10⁸ CFU/mL on green mold of citrus fruit was enhanced by 2% SBC treatment. In artificial inoculation trials, disease control after 3 and 6 days, respectively, with the mixture of K. marxianus and 2% SBC (18.33%, 58.33%) was significantly improved over that obtained with K. marxianus (41.67%, 70.00%) or SBC (43.33%, 81.67%) alone. The combination of K. marxianus with SBC was as effective as the imazalil treatment in natural infection trials, which gave about 90% control of green mold. Addition of 2% SBC significantly stimulated the growth of K. marxianus in citrus fruit wounds after 72 h. Moreover, K. marxianus, SBC and their combination did not impair quality parameters including weight loss, fruit firmness, total soluble solids, titratable acidity and ascorbic acid at 4 °C for 30 days followed by 20 °C for 15 days. These results suggested that the use of SBC is a useful approach to improve the efficacy of K. marxianus for the postharvest green mold of citrus fruit.     

Limiting the deterioration of mango fruit during storage at room temperature by oxalate treatment

Effects of oxalate on the incidence of decay and ripening in mango fruit, and its physiological effects on the peel and flesh of mango were investigated after mango fruit (Mangifera indica L.) were dipped in different oxalate solutions for 10 min and then stored at 25 °C. Oxalate application decreased the incidence of decay and delayed the ripening process in mango fruit during storage. Potassium oxalate treatment resulted in increased activities of peroxidase (POD) in both the peel and the flesh and polyphenol oxidase (PPO) in the peel, without activation of phenylalanine ammonia-lyase activity, and elevated total phenolic content in the peel. The physiological effects of oxalate in increasing activities of POD and PPO and elevating total phenolic level could be involved in induced resistance of mango fruit against postharvest disease. Oxalate application could be a promising method to suppress postharvest deterioration and extend the useful shelf-life of mangoes.     

1-MCP对低温贮藏苹果灰霉病抗性的诱导作用

以红富士苹果为试材,研究1-甲基环丙烯（1-methylcyclopropene,1-MCP）对低温贮藏（0±1）℃苹果灰霉病的控制效果及其诱导抗病机理。结果表明：采后1 μL/L 1-MCP处理较对照可显著降低损伤接种苹果灰霉病的发病率,抑制病斑的扩展（P＜0.05）。同时1-MCP处理能够诱导果实中苯丙氨酸解氨酶、多酚氧化酶、过氧化物酶、β-1,3-葡聚糖酶、几丁质酶活性的提高,促进总酚、类黄酮和木质素的积累,降低膜脂过氧化程度,减少丙二醛的产生,从而提高果实的抗病性。研究结果可为1-MCP防治苹果采后病害提供理论依据。     

Peroxidase and polyphenol oxidase thermal inactivation by microwaves in green coconut water simulated solutions

Enzymes from coconut water such as peroxidase (POD) and polyphenol oxidase (PPO) when in contact with oxygen begin reactions causing nutritional and color losses. Solutions simulating the chemical constituents of coconut water were submitted to a batch process in a microwave oven. PPO and POD inactivation data could be characterized by: PPO/water D_93 °C=16.5 s (z=35.5 °C); PPO/sugars D_91 °C=18 s (z=33°C); POD/water D_91.5 °C=44 s (z=24 °C) and POD/sugars D_92 °C=20.5 s (z=19.5 °C). The contact between salts and enzymes promoted a drastic reduction of the initial activity. After the incidence of microwave energy at temperatures above 90 °C, enzymes activity was not detected. These results can indicate an adequate choice of temperature conditions to inactivate coconut water enzymes. The knowledge of how green coconut water constituents influence POD and PPO activity will supply useful information about microwave processing of coconut water.     

Physiological and biochemical responses of grapefruit seed extract dip on ‘Redglobe’ grape

Table grapes (Vitis vinifera cv. Redglobe) were immersed in 1 g L⁻¹ grapefruit seed extract (GSE) for 60 s at 15 °C and then stored at 2 ± 1 °C, and the related physiological effects were investigated. The results showed that GSE treatment lowered the respiration rate and ethylene evolution in the whole cluster. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) were increased and extended by GSE treatment, however, polyphenol oxidase (PPO) activity was suppressed. Furthermore, increase of malondialdehyde (MDA) as well as membrane permeability was delayed in GSE-treated grapes. Total phenolic compounds degradation was substantially lower in GSE-treated grapes than in control. The soluble solids content (SSC) in GSE-treated grapes was always higher than in control, although there was no significant difference at the level of P < 0.05. Our study suggests that GSE might be a promising candidate for extending the postharvest storage time of table grapes.     

The role of polyphenol oxidase and peroxidase in the browning of water caltrop pericarp during heat treatment

The mechanism of browning involving enzymatic browning was investigated in the pericarp of water caltrop, an Asian vegetable popular for its taste and medicinal properties. Polyphenol oxidase (PPO) and peroxidase (POD) activities were determined in pericarp at various times and temperatures. Water caltrop consisted of 44.22% moisture content, 37.23% crude fibre, and 2.63% crude protein. PPO and POD activities dropped from 62 and 38 units/g sample, respectively, as water temperature was increased from 30 to 80 °C. Optimum pH and temperature for PPO activity was at pH 5.0, 25–45 °C, and POD activity peaked at 60 °C. High PPO and POD activities at 40–50 °C resulted in degradation of phenolic compounds, which led to increased aggregation of browning pigments and discolouration (lower L-values) of the pericarp. Enzymatic browning was determined as the major factor in the browning discolouration of heat-treated water caltrop pericarp.     

Kinetic characterisation and thermal inactivation study of polyphenol oxidase and peroxidase from table grape (Crimson Seedless)

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from a table grape (Crimson Seedless) using Triton X-114 and characterized using spectrophotometric methods. Both PPO and POD were activated by acid shock. However, in the presence of the anionic detergent sodium dodecil sulphate (SDS), PPO was activated whereas POD was inactivated. The enzymes were kinetically characterized and both followed Michaelis–Menten kinetics, although with different values of their kinetic parameters. The V_m/K_m ratio showed that Crimson Seedless grape PPO presents a similar affinity for 4-tert-butyl-catechol (TBC) whether activated by acid shock (0.018 min⁻¹) or SDS (0.023 min⁻¹). With regards to POD, the K_m and V_m values for 2,2′-azinobis(3-ethylbenzothiazolinesulphonic acid) (ABTS) were 0.79 mM and 1.20 μM/min, respectively. In the case of H₂O₂, the K_m and V_m value were 0.4 mM and 0.93 μM/min, respectively. PPO and POD showed similar thermostability, losing >90% of relative activity after only 5 min of incubation at 78 °C and 75 °C, respectively. In addition, PPO´s activation energy was similar to that obtained for POD (295.5 kJ/mol and 271.9 kJ/mol, respectively).     

Polyphenol oxidase from bayberry (Myrica rubra Sieb. et Zucc.) and its role in anthocyanin degradation

Polyphenol oxidase (PPO) was extracted from bayberry (Myrica rubra Sieb. et Zucc. cv. Biqi), and its partial biochemical characteristics were studied. Stable and highly active PPO extracts were obtained using insoluble polyvinylpolypyrrolidone (PVPP) in sodium phosphate, pH 7.0, buffer. The highest PPO activity was observed in the ripe fruits. Optimum pH and temperature for bayberry PPO activity were pH 6.0 and T = 30 °C with 0.1 M catechol as substrate. PPO showed activity using the substrates of catechol, gallic acid and protocatechuic acid, but no activity with the substrates (+)-catechin, p-coumaric acid or caffeic acid. K_m and V_max values were 313 mM and 3.26ΔOD/min/g FW, respectively, with catechol as the substrate. Bayberry PPO did not act directly on cyanidin 3-glucoside but the rate of anthocyanin degradation was stimulated by the addition of gallic acid.     

Purification and characterisation of a polyphenol oxidase from Boletus erythropus and investigation of its catalytic efficiency in selected organic solvents

Polyphenol oxidase (PPO) was purified from Boletus erythropus using a Sepharose 4B-L-tyrosine-p-amino benzoic acid affinity column. Optimum pH and temperature were found to be 8.0 and 20 °C, respectively, using 4-methylcatechol as a substrate. The enzyme was extremely stable between pH 3.0 and 9.0 after 24 h incubation at 4 °C. B. erythropus PPO was also quite stable between 10 and 30 °C after 4 h incubation. The K_m and V_max values were calculated as 2.8 mM and 1430 U/mg protein by Lineweaver–Burk curve, respectively. The enzyme activity was inhibited by sodium metabisulfite, ascorbic acid, sodium azide and benzoic acid. It was seen that the mushroom PPO was an effective biocatalyst in selected organic solvents, such as dichloromethane, dichloroethane and toluene, when catechin was used as a substrate. All data support that B. erythropus has a highly active PPO, possessing similar biochemical and kinetic characteristics to other plant PPOs.     

Combined effect of temperature and pulsed electric fields on apple juice peroxidase and polyphenoloxidase inactivation

Pulsed electric fields (PEF) were applied to freshly prepared apple juice using a laboratory scale continuous PEF system to study the feasibility of inactivating peroxidase (POD) and polyphenoloxidase (PPO). Square wave PEF using different combinations of electric field strength, pre-treatment temperature and treatment time were evaluated in this study and compared to conventional pasteurisation (72 °C; 26 s). Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed the highest level of decrease in the enzymatic activity of 71% and 68%, for PPO and POD, respectively, were obtained by using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. This level of inactivation was significantly higher (P < 0.05) than that recorded in juice processed by conventional mild pasteurisation where the activity of PPO and POD decreased by 46% and 48%, respectively. The kinetic data for the inactivation of both enzymes could be described using a 1st-order model (P < 0.001).     

Carotenoids of yeasts isolated from the Brazilian ecosystem

The carotenoid composition of pigmented yeasts isolated in Brazil was studied. The yeasts were cultured in yeast malt broth at 200 rpm, 25 °C, for 5 days, without illumination. Open column, thin layer and high performance liquid chromatography were used to separate, identify and quantify the carotenoids. The major pigments found in these yeasts were torulene and β-carotene. β-Carotene predominated in Rhodotorula graminis-125, Rhodotorula glutinis and Sporobolomyces roseus, while torulene was the principal carotenoid in Rhodotorula mucilaginosa. The yeast R. glutinis had the highest total carotenoid production (881 μg/l), followed by R. graminis (594 μg/l), Rhodotorula mucilaginosa-137 (590 μg/l), Rhodotorula mucilaginosa-108 (562 μg/l) and Rhodotorula mucilaginosa-135 (545 μg/l). Rhodotorula minuta and S. roseus had the lowest carotenoid contents (168 and 237 μg/l, respectively). In μg/g of dry cells, R. glutinis had a total carotenoid concentration of 132 μg/g.     

Effect of pre- and postharvest salicylic acid treatment on ethylene production,fungal decay and overall quality of Selva strawberry fruit

The effect of salicylic acid (SA) treatment at different concentrations and growth stages of strawberry (Fragaria ananassa cv. Selva) fruit on postharvest ethylene production, fungal decay and overall quality index was studied. SA at all concentrations effectively reduced fruit ethylene production and fungal decay and retained overall quality. Treatment of plants at vegetative stage and fruit development stage followed by postharvest treatment of fruits with 1 and 2 mmol L⁻¹ was the most effective strategy, whilst with decrease in treatment time the effects of treatment decreased. Single stage treatment strategy of fruits with 2 mmol L⁻¹ SA at postharvest stage was most effective. Postharvest treatment with 4 mmol L⁻¹ SA slightly damaged the fruits and was less effective than 2 mmol L⁻¹ in retaining fruit quality.     

Effect of nanocomposite-based packaging on postharvest quality of ethylene-treated kiwifruit (Actinidia deliciosa) during cold storage

A novel nanocomposite-based packaging (NCP) was prepared by blending polyethylene (PE) with nano-Ag, nano-TiO₂ and montmorillonite. The effects of NCP on the quality parameters of ethylene-treated mature kiwifruit were investigated during the 42 d of storage at 4 °C. The results showed that adding nanoparticles to the PE significantly decreased the oxygen, water vapor permeability and longitudinal strength, and inhibited spore germination. The weight loss, softening, color variation and soluble solid content of kiwifruit were significantly inhibited by 22.67%, 124.84%, 23.46% and 14.42% respectively, which indicated that NCP could delay the ripening of kiwifruit. However, ascorbic acid and total phenols contents in NCP-treated fruit were increased compared with the controls. Additionally, kiwifruit in NCP exhibited 57.44% lower headspace ethylene concentration, 29.44% for malondialdehyde (MDA), lower polyphenol oxidase (PPO) activity and higher peroxidase (POD) activity than the controls. These results suggest that NCP may be a useful technique to reduce fruit decay and maintain quality in kiwifruits during postharvest storage.