Recent advances and current status of the use of heat treatments in postharvest disease management systems: Is it time to turn up the heat?

Advances in propolis and propolis functionalized coatings and films for fruits and vegetables preservation

Propolis, as a natural active substance, is rich in polyphenols, with low toxicity, antioxidant, antifungal and antibacterial properties, which can be applied to the post-harvest preservation of fruits and vegetables. Propolis extracts and propolis functionalized coatings and films have exhibited good freshness in various types of fruits and vegetables as well as fresh-cut vegetables. They are mainly used to prevent water loss after harvesting, to inhibit the infestation of bacteria and fungi after harvesting and to enhance the firmness and apparent quality of fruits and vegetables. Moreover, propolis and propolis functionalized composites have a small or even insignificant effect on the physicochemical parameters of fruits and vegetables. Furthermore, how to cover the special smell of propolis itself so that it does not affect the flavor of fruits and vegetables, and the application of propolis extract in wrapping paper and packaging bag of fruits and vegetables, are worthwhile to further investigate.

Biocontrol potential of Trichoderma harzianum CGMCC20739 (Tha739) against postharvest bitter rot of apples

This study investigated the biocontrol ability of Trichoderma harzianum CGMCC20739 (Tha739) against apple bitter rot caused by Colletotrichum gloeosporioides. In vitro tests, Tha739 inhibited the mycelial growth of C. gloeosporioides. Microscopic observation showed that Tha739 grew in parallel with, coiled around, and deformed the hyphae of C. gloeosporioides. Tha739-derived metabolites decreased the conidia production of C. gloeosporioides. In vivo tests, the lesion diameters of wounded apples treated with Tha739 1 h before C. gloeosporioides were lower than those of wounded apples treated with Tha739 after pathogen inoculation. In addition, compared with the apples inoculated with C. gloeosporioides only, the disease index of unwounded apples inoculated with Tha739 and C. gloeosporioides decreased by 2.17-fold. Furthermore, compared with the control, the total soluble solid contents of apples treated with Tha739 were 9.02 % and 1.54 % higher at 1 and 3 d, respectively. The titratable acidity contents of apples treated with Tha739 were 10.02 % and 14.58 % higher than those in the control at 1 and 3 d after treatment, respectively. The soluble sugar content and weight loss in Tha739 treatment group and control were not significantly different. The results showed that Tha739 could control apple bitter rot and maintain the nutritional quality of the fruit. Thus, T. harzianum Tha739 is a potentially biocontrol agent for harvested apples.

Hot Air Treatment Elicits Disease Resistance against Colletotrichum gloeosporioides and Improves the Quality of Papaya by Metabolomic Profiling

Forced air heat treatment could induce defenses to protect fruit from pathogen attacks and has been applied as an alternative to methyl bromide for phytosanitary treatment before exportation. However, few studies were reported on the regulation mechanism of antifungal effect and delayed physiological disorders of papaya by heat treatment. Therefore, we aim to explore the fruit's resistance to pathogens and the inhibition of physiological disorders by metabolomic profiling. In our study, papaya fruits were treated with 47.2°C for 30, 60, and 90 min by forced hot air treatment. The disease resistance against Colletotrichum gloeosporioides, quality parameters, and metabolites of papaya fruits were measured during 10 days of storage after heat treatment by metabolomic profiling. Papaya fruits after 30 and 60 min heat treatment had higher firmness, a delayed degreening and yellowing (lower a value) process, and a higher lightness (L) and hue angle (h) during storage. Heat treatment also delayed ripening, inhibiting the growth of C. gloeosporioides and softening of papaya. Metabolites and enzymes inhibited ROS scavenging, depressed ABA-regulated respiratory, and activated phenylpropanoid metabolism. Our study provides a broad picture of fruit resistance to pathogens and the inhibition of physiological disorders by metabolomic profiling, which is induced by heat treatment.

Recent advances in research on biocontrol of postharvest fungal decay in apples

Apple is the largest fruit crop produced in temperate regions and is a popular fruit worldwide. It is, however, susceptible to a variety of postharvest fungal pathogens, including Penicillium expansum, Botrytis cinerea, Botryosphaeria dothidea, Monilia spp., and Alternaria spp. Decays resulting from fungal infections severely reduce apple quality and marketable yield. Biological control utilizing bacterial and fungal antagonists is an eco-friendly and effective method of managing postharvest decay in horticultural crops. In the current review, research on the pathogenesis of major decay fungi and isolation of antagonists used to manage postharvest decay in apple is presented. The mode of action of postharvest biocontrol agents (BCAs), including recent molecular and genomic studies, is also discussed. Recent research on the apple microbiome and its relationship to disease management is highlighted, and the use of additives and physical treatments to enhance biocontrol efficacy of BCAs is reviewed. Biological control is a critical component of an integrated management system for the sustainable approaches to apple production. Additional research will be required to explore the feasibility of developing beneficial microbial consortia and novel antimicrobial compounds derived from BCAs for postharvest disease management, as well as genetic approaches, such as the use of CRISPR/Cas9 technology.

Recent advances and future perspective of essential oils in control Colletotrichum spp.: A sustainable alternative in postharvest treatment of fruits

The world population growth has raised concerns about food security. Agricultural systems are asked to satisfy a growing demand for food with increasingly limited resources, and simultaneously still must reduce the impacts on the environment. This scenario encourages the search for safe and sustainable production strategies. Reducing losses in the production process can be one of the main ways to guarantee food safety. In fruticulture, it is estimated that more than 50% of the production can be lost between harvest and the final consumer due to postharvest diseases caused by phytopathogenic fungi. The fungi of the genus Colletotrichum are opportunistic and are associated with several diseases, being the anthracnose the most relevant in terms of the quality and yield losses in fruit species around worldwide. To control these diseases, the use of synthetic fungicides has been the main instrument utilized, however, because of their phytotoxicity to human health, the environment, and strong selection pressure imposed by continuous applications, the fungicides have caused resistance in the pathogen populations. So reducing the excessive application of these products is indispensable for human health and for sustainable Agriculture. Towards this purpose, research has been carried out to identify the phytopathological potentiality of essential oils (EOs) extracted from plants. Therefore, this review aims to contribute to the formation of knowledge bases, about the discoveries, recent advances, and the use of EOs as a strategy to alternatively control fungal disease caused by Colletotrichum spp. in postharvest fruits. Here, we provide valuable information exploring the application potential of essential oils as commercially useful biorational pesticides for food preservation, contributing to sustainable production and global food security.

Biological and chemical characterization of antimicrobial activity in Arthrobacter spp. isolated from disease-suppressive compost

Antagonistic bacteria can act as biocontrol agents against various phytopathogens. Recently, Arthrobacter spp. demonstrated antifungal activity, but were not further characterized. In this study, the antimicrobial activity of Arthrobacter humicola strains M9-1A, M9-2, and M9-8, and Arthrobacter psychrophenolicus strain M9-17 were evaluated against nine plant pathogens in vitro, and their cell-free filtrates were additionally assessed for inhibition of Alternaria alternata and suppression of black mold disease on tomato fruit. Results indicated that A. humicola M9-1A and A. psychrophenolicus M9-17 were the most inhibitory, reducing growth of seven of the pathogens studied. Cell-free filtrates of A. psychrophenolicus M9-17 reduced the growth of most pathogens. All cell-free bacterial filtrates, except those from A. humicola M9-2, suppressed black mold on tomato fruit. Disk diffusion assays with ethyl acetate soluble culture filtrate extracts of all bacteria reduced the mycelial growth of A. alternata. Clear inhibition zones were observed for A. psychrophenolicus M9-17 extracts using drop bioassays. The antifungal compound N-acetyltryptamine was purified and characterized from the A. psychrophenolicus M9-17 cell-free ethyl acetate soluble extract. This study suggests that antibiosis may play a key role in the antimicrobial activity of Arthrobacter spp.

Eco-friendly management of postharvest fungal decays in kiwifruit

Kiwifruit is purchased by consumers worldwide and is increasing in demand. Unfortunately, kiwifruit is susceptible to postharvest decay caused by a variety of fungal pathogens, including Botrytis cinerea, Penicillium expansum, Alternaria alternata, Botryosphaeria dothidea, and Diaporthe spp. Among these pathogens, B. cinerea is the most prevalent and devastating. Infections by these fungal pathogens result in a deterioration in fruit quality and a reduction in marketable yield. Eco-friendly methods to control kiwifruit postharvest decay have been explored as alternatives to the use of synthetic fungicides. In this review, we provide an overview and discuss the virulence and pathogenesis of fungi that are causal agents of kiwifruit decay, especially B. cinerea, including recent molecular and genomic studies. Advances in pre- and postharvest measures for postharvest decay management, including biological control, physical applications, the use of natural compounds and plant hormones, and the use of combined methods, are also reviewed. Eco-friendly control measures are a critical component of an integrated management approach for sustainable production of kiwifruit. The need for further research on the use of microbial consortia for the management of postharvest diseases of kiwifruit is also discussed.

Alternative Management Approaches of Citrus Diseases Caused by Penicillium digitatum (Green Mold) and Penicillium italicum (Blue Mold)

Green mold (Penicillium digitatum) and blue mold (Penicillium italicum) are among the most economically impactful post-harvest diseases of citrus fruit worldwide. Post-harvest citrus diseases are largely controlled with synthetic fungicides such as pyrimethanil, imazalil, fludioxonil, and thiabendazole. Due to their toxic effects, prolonged and excessive application of these fungicides is gradually restricted in favor of safe and more eco-friendly alternatives. This review comprehensively describes alternative methods for the control of P. digitatum and P. italicum: (a) antagonistic micro-organisms, (b) plant extracts and essential oils, (c) biofungicides, (d) chitosan and chitosan-based citrus coatings, (e) heat treatments, (f) ionizing and non-ionizing irradiations, (g) food additives, and (h) synthetic elicitors. Integrating multiple approaches such as the application of biocontrol agents with food additives or heat treatments have overcome some drawbacks to single treatments. In addition, integrating treatment approaches could produce an additive or synergistic effect on controlling both molds for a satisfactory level of disease reduction in post-harvest citrus. Further research is warranted on plant resistance and fruit-pathogen interactions to develop safer strategies for the sustainable control of P. digitatum and P. italicum in citrus.

Biological control of postharvest fungal decays in citrus: a review

Citrus (Citrus spp.) species produce a variety of fruits that are popular worldwide. Citrus fruits, however, are susceptible to postharvest decays caused by various pathogenic fungi, including Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii, Aspergillus niger, and Aspergillus flavus. Decays resulting from infections by these pathogens cause a significant reduction in citrus quality and marketable yield. Biological control of postharvest decay utilizing antagonistic bacteria and fungi has been explored as a promising alternative to synthetic fungicides. In the present article, the isolation of antagonists utilized to manage postharvest decays in citrus is reviewed, and the mechanism of action including recent molecular and genomic studies is discussed as well. Several recently-postulated mechanisms of action, such as biofilm formation and an oxidative burst of reactive oxygen species have been highlighted. Improvements in biocontrol efficacy of antagonists through the use of a combination of microbial antagonists and additives are also reviewed. Biological control utilizing bacterial and yeast antagonists is a critical component of an integrated management approach for the sustainable development of the citrus industry. Further research will be needed, however, to explore and utilize beneficial microbial consortia and novel approaches like CRISPR/Cas technology for management of postharvest decays.

Hurdle Effect of Hot Air Impingement Drying and Surfactant-Sanitizer Wash on Removal of Listeria innocua from Fresh Apples

ABSTRACT

This study investigated the decontamination efficacy of washing treatments for whole fresh apples by using washes containing surfactants, lauric arginate, sodium dodecyl sulfate, and Tween 20, combined with peracetic acid (PAA), followed by hot air impingement drying. Whole fresh apples of selected varieties (Gala and Granny Smith) were inoculated with Listeria innocua (7 log CFU/mL) by using a dipping method, and then dried and subjected to wash treatments with selected washing solutions (H2O, PAA, PAA-lauric arginate, PAA-sodium dodecyl sulfate, and PAA-Tween 20), followed by hot air impingement drying at two different temperature and time conditions, 93°C for 60 s or 121°C for 25 s. The H2O and PAA wash followed by hot air impingement drying led to a maximum 1.5-log reduction of L. innocua on the fruit surface. Adding surfactants increased the effectiveness of washing and drying treatments, resulting in an approximate 2.2-log reduction. Surfactants increased the spreadability and evaporation rate of the washing solutions. Posttreatment changes in apple firmness were assessed during a 21-day storage at 4 and 21°C. The hot air impingement drying had no adverse effect on the firmness of the apples and did not show any further reduction in L. innocua. Washing apples with solutions containing surfactants combined with PAA followed by hot air impingement drying helped to reduce the microbial loads to some extent and may help to reduce drying times significantly.

HIGHLIGHTS

Postharvest heat treatments to inhibit Penicillium digitatum growth and maintain quality of Mandarin (Citrus reticulata blanco)

Use of fungicides is a common practice as a postharvest treatment to control fruit decay. Nowadays, environment friendly technologies, such as heat treatments, are viable replacements. This study evaluated the effects of post-harvest heat treatments (traditional and microwave-assisted) on mandarins intentionally inoculated with Penicillium digitatum. For the studied heat treatments, the target temperature was 50 °C, which was held for 2.5 min. After heating, mandarins were cooled and stored at 25 °C for 13 days. MW treatments effectively prevented mold growth during storage, while HW only delayed it. Control mandarins (without treatment) showed the highest significant weight loss. Neither thermal treatment nor storage affected fruit juice pH (p > 0.05). Treated mandarins had a significantly lower vitamin C content than control fruits throughout storage, and all mandarins lost firmness by the 13^th day (p < 0.05). Control and MW-treated mandarins had lower citric acid content; however, they retained color, total soluble solids (TSS) and had a higher maturity index. While HW mandarins did not have changes in citric acid content, they had higher TSS, and lower maturity index. MW-assisted treatments were effective at inactivating molds and helped retain some nutritional and physical-chemical characteristics of mandarins. However, juice of MW-treated mandarins was not preferred by judges in the sensory tests, the juice was rated lower than that obtained from the other treatment. Postharvest heat treatments may constitute a helpful application to control mandarin’ fungal decay.

The Combination of Hot Air and Chitosan Treatments on Phytochemical Changes during Postharvest Storage of 'Sanhua' Plum Fruits

Plum fruits would become putrid quickly after harvest. In order to prolong postharvest life, 'Sanhua' plum fruits were treated by hot air combined with a chitosan coating, and stored at low temperature. Fruit firmness, total soluble solids, total phytochemical contents were evaluated along with total antioxidant activities and phytochemical components. Results showed that hot air treatment delayed softening process of plum fruit. The total phenolics and flavonoids accumulated and antioxidant activities increased in both control and treatment samples during storage. These values in the samples treated with hot air and chitosan were all higher than control and hot air treatments. Phytochemicals of epicatechin, cyanidin, pelargonidin, and hesperetin were all upregulated by hot air and chitosan treatment, especially epicatechin. This suggested that chitosan might play an important role in regulating phytochemical profiles of 'Sanhua' plum fruits during storage.

Hot air treatment reduces postharvest decay and delays softening of cherry tomato by regulating gene expression and activities of cell wall-degrading enzymes

BACKGROUND

Fruit softening facilitates pathogen infection and postharvest decay, leading to the reduction of shelf-life. Hot air (HA) treatment at 38 °C for 12 h is effective in reducing postharvest disease and chilling injury of tomato fruit. To explore the effect and mechanism of HA treatment on reducing postharvest decay and softening of cherry tomato, fruit at the mature green stage were treated with HA and then stored at 20 °C for 15 days. Changes in natural decay incidence, firmness, cell wall compositions, activities and gene expression of cell wall-degrading enzymes of cherry tomatoes were assessed.

RESULTS

HA treatment reduced natural decay incidence, postponed the firmness decline, inhibited the respiration rate and ethylene production, and retarded pectin solubilisation and cellulose degradation of cherry tomatoes. Enzymatic activities and gene expression of pectin methylesterase, polygalacturonase, cellulase and β-galactosidase were inhibited by HA treatment. In addition, the gene expression of LeEXP1 was reduced, while LeEXT was up-regulated after HA treatment.

CONCLUSIONS

Our findings suggested that HA treatment could inhibit cell wall degradation and postpone softening of cherry tomatoes by regulating gene expression and activities of cell wall-degrading enzymes, resulting in the reduction of postharvest decay. © 2017 Society of Chemical Industry.

The impact of the postharvest environment on the viability and virulence of decay fungi

Postharvest decay of fruits, vegetables, and grains by fungal pathogens causes significant economic losses. Infected produce presents a potential health risk since some decay fungi produce mycotoxins that are hazardous to human health. Infections are the result of the interplay between host resistance and pathogen virulence. Both of these processes, however, are significantly impacted by environmental factors, such as temperature, UV, oxidative stress, and water activity. In the present review, the impact of various physical postharvest treatments (e.g., heat and UV) on the viability and virulence of postharvest pathogens is reviewed and discussed. Oxidative injury, protein impairment, and cell wall degradation have all been proposed as the mechanisms by which these abiotic stresses reduce fungal viability and pathogenicity. The response of decay fungi to pH and the ability of pathogens to modulate the pH of the host environment also affect pathogenicity. The effects of the manipulation of the postharvest environment by ethylene, natural edible coatings, and controlled atmosphere storage on fungal viability are also discussed. Lastly, avenues of future research are proposed.