Hongyin Zhang

Effects of Chitin and Its Derivative Chitosan on Postharvest Decay of Fruits: A Review

Considerable economic losses to harvested fruits are caused by postharvest fungal decay during transportation and storage, which can be significantly controlled by synthetic fungicides. However, considering public concern over pesticide residues in food and the environment, there is a need for safer alternatives for the control of postharvest decay to substitute synthetic fungicides. As the second most abundant biopolymer renewable source in nature, chitin and its derivative chitosan are widely used in controlling postharvest decay of fruits. This review aims to introduce the effect of chitin and chitosan on postharvest decay in fruits and the possible modes of action involved. We found most of the actions discussed in these researches rest on physiological mechanisms. All of the mechanisms are summarized to lay the groundwork for further studies which should focus on the molecular mechanisms of chitin and chitosan in controlling postharvest decay of fruits.

Biocontrol of postharvest gray and blue mold decay of apples with Rhodotorula mucilaginosa and possible mechanisms of action

The efficacy of Rhodotorula mucilaginosa against postharvest gray mold, blue mold and natural decay development of apples and the possible mechanisms involved were investigated. The decay incidence and lesion diameter of gray mold and blue mold of apples treated by R. mucilaginosa were significantly reduced compared with the control fruits, and the higher concentration of R. mucilaginosa, the better the efficacy of the biocontrol. R. mucilaginosa also significantly reduced the natural decay development of apples following storage at 20°C for 35 days or at 4°C for 45 days followed by 20°C for 15 days. Germination and survival of spores of Penicillium expansum and Botrytis cinerea were markedly inhibited by R. mucilaginosa in an in vitro test. Rapid colonization of the yeast in apple wounds was observed whether stored at 20°C or 4°C. In apples, the activities of peroxidase (POD) and polyphenoloxidase (PPO) were significantly induced and lipid peroxidation (malondialdehyde (MDA) content) was highly inhibited by R. mucilaginosa treatment compared with those of the control fruits. All these results indicated that R. mucilaginosa has great potential for development of commercial formulations to control postharvest pathogens on fruits. Its modes of action were based on competition for space and nutrients with pathogens, inducement of activities of defense-related enzymes such as POD, PPO and inhibition of lipid peroxidation (MDA content) of apples, so as to enhance the resistance and delay the ripening and senescence of apples.

Control of postharvest pear diseases using Rhodotorula glutinis and its effects on postharvest quality parameters

Rhodotorula glutinis was evaluated for its activity in reducing postharvest gray mold decay and blue mold decay of pear caused by Botrytis cinerea and Penicillium expansum respectively, and in reducing natural decay development of pear fruits, as well as its effects on postharvest quality of fruits. There was a significant negative correlation between concentrations of the yeast cells and infectivity of the pathogens. At concentrations of R. glutinis at 5x108 CFU/ml, the gray mold decay was completely inhibited after 7 days incubation at 20 degrees C, while the control fruit had 100% disease incidence and 2.15 cm lesion diameter respectively, at challenged with B. cinerea spores suspension of 1x105 spores/ml; No completely control was got to blue mold, when pear fruits stored at 20 degrees C for 7 d (challenged with P. expansum spores suspension of 5x104 spores/ml), but the decay was distinctly prevented with 20% and 0.60 cm of disease incidence and lesion diameter respectively, while the control fruits were 100% and 2.74 cm, respectively. Rapid colonization of the yeast in wounds was observed during the first 1 d at 20 degrees C, and then the populations stabilized for the remaining storage period. On pear wounds kept at 4 degrees C, rapid colonization of the yeast in wounds was observed during the first 3 d, and then the increase in population density of R. glutinis turned slow, which continued over 6 d after application of the antagonist until it reached a high level. Then, the populations stabilized for the remaining storage period. In the test on PDA plates, R. glutinis significantly inhibit the growth of B. cinerea and P. expansum. Spore germination of pathogens in PDB was greatly controlled in the present of living yeast cell suspensions. R. glutinis significantly reduced the natural development of decay of pear following storage at 20 degrees C for 7 days or at 4 degrees C for 30 days followed by 20 degrees C for 5 days, and did not impair quality parameters, including mass loss, firmness, TSS, ascorbic acid or titratable acidity. Thus, the application of R. glutinis can be an alternative to chemicals for control of postharvest diseases on pear fruits.

Efficacy of Pichia caribbica in controlling blue mold rot and patulin degradation in apples

The efficacy of Pichia caribbica in controlling postharvest blue mold and natural decay development of apples and degrading the patulin produced by Penicillium expansum was investigated. The decay incidence of the blue mold of apples treated by P. caribbica was significantly reduced compared with the control samples, and the higher the concentration of P. caribbica, the better the efficacy of the biocontrol. P. caribbica significantly controlled the natural decay development of apples following storage at 20°C for 35days or 4°C for 45 days followed by 20°C for 15 days. Germination of spores and growth of P. expansum were markedly inhibited by P. caribbica in in vitro testing. Rapid colonization of apple wounds by the yeast was observed in fruit stored at 20°C or 4°C. After incubation with P. caribbica at 20°C for 15 days, patulin production by P. expansum in apples was significantly reduced compared with the control. In vitro testing indicated that P. caribbica can degrade patulin directly.

Biological control of postharvest blue mold of oranges by Cryptococcus laurentii (Kufferath) Skinner

Cryptococcus laurentii (Kufferath) Skinner was evaluated for its activity in reducing postharvest blue mold decay of oranges caused by Penicillium italicum in vitro and in vivo. The results showed that washed cell suspensions of yeast provided control of blue mold decay better than yeast in culture broth. Autoclaved cell culture and cell-free culture filtrate failed to provide protection against the pathogen. The concentrations of antagonist had significant effects on biocontrol effectiveness. When the washed yeast cell suspension reached the concentration of 1 × 109 CFU/ml, challenged with pathogen spore suspension at 1 × 104 spores/ml, the blue mold decay was completely inhibited during 5 days of incubation at 20 °C. No complete control was obtained when oranges were stored at 4 °C for 30 days, but the decay was distinctly prevented. Efficacy of C. laurentii was maintained when applied simultaneously or prior to inoculation with P. italicum. Efficacy was reduced when C.laurentii was applied after inoculation. In drop-inoculated wounds of oranges, the populations of C.laurentii increased by approximately 50-fold during the first 24 h at 20 °C. The maximum yeast populations, approximately 250-fold over the initial populations, were reached 15 days after inoculation at 4 °C.

Biocontrol of postharvest blue mould rot of pear by Cryptococcus laurentii

Summary Cryptococcus laurentii was evaluated for its activity in reducing postharvest blue mould decay of pear caused by Penicillium expansum. Washed cell suspensions of yeast controlled blue mould better than yeast in culture broth. Treatment of wounds with autoclaved cultures or cell-free culture filtrate did not prevent decay. There was a negative correlation between concentrations of the yeast cells and infectivity of the pathogens: at concentrations of yeast at or above 1 × 109 colony forming units (CFU) ml–1 and pathogen spores suspension of 5 × 104 spores ml–1, blue mould was completely inhibited after 7 d of incubation at 25°C, and was almost inhibited after 30 d incubation at 2°C followed by 7 d at 20°C. The interval between inoculation with the pathogen and application of the antagonist significantly influenced the efficacy of biocontrol. Efficacy was maintained when C. laurentii was applied simultaneously or prior to inoculation with P. expansum but reduced if applied after inoculation with P. expansum. Rapid colonization of the yeast in wounds was observed during the first 3 d at 20°C, and then the populations stabilized for the remaining storage period. On pear wounds kept at 4°C, the increase in population density of C. laurentii was lower than at 20°C, but rose over 15 d after application of the antagonist to approx. 107 CFU wound–1.

Enhancement of biocontrol efficacy of Rhodotorula glutinis by salicyclic acid against gray mold spoilage of strawberries

The control activity of Rhodotorulaglutinis, salicylic acid (SA), alone or in combination, on gray mold spoilage and natural spoilage of strawberries was investigated. R. glutinis as stand-alone treatment, and the combined treatment of SA at 100 microg/mL with R. glutinis significantly reduced the disease incidence and lesion diameter of gray mold spoilage, respectively at both 20 degrees C and 4 degrees C. After 20 d storage at 4 degrees C, the combination of SA and R. glutinis was more effective than R. glutinis or SA alone treatment. At the concentration of 100 microg/mL, SA had no inhibition on the mycelial growth of Botrytiscinerea in PDA, however, it significantly inhibited spore germination of B. cinerea in PDB. The combination of R. glutinis and SA was the most effective treatment in controlling the natural spoilage of strawberries, and resulted in low average natural spoilage incidence in 6.3% or 6.3%, respectively, compared with 37% or 46.7% in the water-treated control fruit following storage at 20 degrees C for 3d or 4 degrees C for 7d followed by 20 degrees C for 2d.

Ascorbic Acid Enhances Oxidative Stress Tolerance and Biological Control Efficacy of Pichia caribbica against Postharvest Blue Mold Decay of Apples

The effect of ascorbic acid (VC) on improving oxidative stress tolerance of Pichia caribbica and biocontrol efficacy against blue mold caused by Penicillium expansum on apples was investigated. P. caribbica showed susceptibility to the oxidative stress in vitro test, and 250 μg/mL VC treatment improved its oxidative stress tolerance. The higher viability exhibited by VC-treated yeast was associated with a lower intracellular ROS level. The activities of antioxidant enzymes of P. caribbica were improved by VC treatment, including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX). Additionally, VC-treated yeast exhibited greater biocontrol activity against P. expansum and faster growth when stored at 25 and 4 °C, respectively, compared to the performance of the non-VC-treated yeast. In response to the VC treatment under oxidative stress, several differentially expressed proteins were identified in P. caribbica, and most of the poteins were confirmed to be related to basic metabolism. Therefore, the application of ascorbic acid is a useful approach to improve oxidative stress tolerance of P. caribbica and its biocontrol efficacy on apples.

Enhanced biocontrol activity of Rhodotorula mucilaginosa cultured in media containing chitosan against postharvest diseases in strawberries: possible mechanisms underlying the effect.

The effect of Rhodotorula mucilaginosa cultured in media containing chitosan on its antogonistic activity against postharvest diseases of strawberries and the possible mechanisms involved are discussed. Two-dimensional gel electrophoresis were applied in the analysis of the proteins of R. mucilaginosa in response to chitosan. Compared with the application of R. mucilaginosa alone, the biocontrol efficacy of the yeast combined with 0.5% chitosan was enhanced greatly, with significant increase in chitinase activity of antagonistic yeast, polyphenoloxidase, peroxidase, phenylalanine ammonia lyase, chitinase and β-1,3-glucanase activity, and with an inhibition of lipid peroxidation of strawberries. The population of R. mucilaginosa harvested from NYDB amended with chitosan at 0.5% increased rapidly in strawberry wounds compared with those harvested from NYDB without chitosan. In the cellular proteome, several differentially expressed proteins were identified, most of which were related to basic metabolism.

Effects of Cryptococcus laurentii (Kufferath) Skinner in combination with sodium bicarbonate on biocontrol of postharvest green mold decay of citrus fruit

The potential of using Cryptococcus laurentii alone or in combination with sodium bicarbonate solution for control of Penicillium digitatum (green mold) on oranges was investigated. Agar disks of C. laurentii NYDA cultures placed on PDA plates seeded with pathogen did not inhibit the growth of P. digitatum. Spore germination of P. digitatum in PDB was significantly controlled in the presence of living C. laurentii cell suspensions. Cryptococcus laurentii significantly controlled green mold on oranges after challenge with 5 × 104 spores/ml of P. digitatum. The higher the concentrations of the antagonist, the lower the disease incidence regardless of whether the fruit was stored at 20°C for 5 days or 2°C for 50 days. The efficacy of C. laurentii for control of green mold was improved when combined with sodium bicarbonate. The combination of sodium bicarbonate and C. laurentii could be an alternative to fungicides for control of postharvest green mold disease on citrus fruits.