Effects of post-harvest treatment using chitosan from Mucor circinelloides on fungal pathogenicity and quality of table grapes during storage

Pichia anomala Induced With Chitosan Triggers Defense Response of Table Grapes Against Post-harvest Blue Mold Disease

To study the mechanism by which Pichia anomala induced with chitosan (1% w/v) controls blue mold disease in table grapes caused by Penicillium expansum, this study evaluated alterations in three yeast enzymatic activities. The changes in the five primary disease defense-related enzymes and two non-enzyme activities of table grapes were assayed. The results of the study showed that chitosan (1% w/v) significantly increased the yeast β-1,3-glucanase, catalase (CAT), and malondialdehyde (MDA) activities. Furthermore, P. anomala alone or induced with chitosan (1% w/v) significantly increased the table grapes enzymatic activities of Polyphenol oxidase (PPO), phenylalanine (PAL), peroxidase (POD), and catalase (CAT) compared to the control. The RT-qPCR results also confirmed that the genes of these major disease defense enzymes were up-regulated when the table grapes were treated with P. anomala. The highest results were recorded when the fruit was treated by yeast induced with chitosan (1% w/v). The phenolic compounds, in addition to their nutritional value, can also increase the antimicrobial properties of table grapes. The current experiment determined that the total phenol and flavonoid contents of table grapes showed the highest results for fruits treated by P. anomala induced with chitosan compared with the control. Generally, the increment of these fruit enzymatic and non-enzymatic activities shows improved table grape defense against the pathogenic fungus. The induction of the yeast with chitosan also increases its bio-control efficacy against the pathogen. This study will enable future detailed investigation in the yeast pathogen control mechanisms and the use of yeasts as bio-pesticides.

Ultrasonic and osmotic pretreatments followed by convective and vacuum drying of papaya slices

BACKGROUND

Papaya fruit is highly nutritive, but very fragile, and thus has a limited shelf life. Drying is essential to preserve it for longer durations. In this work, osmotic dehydration (OD) with and without ultrasound (US) was applied to papaya slices as a pretreatment in conjugation with vacuum (VD) and convective air drying (AD). Drying was carried out in a novel dryer. Moisture content, drying time, water activity, total color change, total phenolic content, radical scavenging activity, texture, and Fourier-transform infrared (FTIR) spectrums were evaluated for fresh and dried papaya slices.

RESULTS

It was observed that US-assisted osmotic dehydration (USOD) followed by VD had the lowest drying time with highest retention of phenols and antioxidants as compared to other drying techniques. Higher phenols and antioxidants in US-pretreated samples were attributed to the release of trapped intra-cellular polyphenols by cavitation. However, the color characteristics and texture of OD pretreatment followed by convective AD slices were found to be better. Color retention could be due to carotenoid preservation, which would be degraded in other treatments, whereas lower brittleness was associated with lower pectin. Infrared spectroscopy confirmed the retention of phytochemicals and antioxidants in dried papaya slices that were subjected to pretreatment.

CONCLUSION

Pretreatment before drying enhances the end product quality of dried papaya slices. The results of this study highlight that USOD-VD is effective for nutrition preservation while OD-AD is suitable for preserving physical characteristics. © 2020 Society of Chemical Industry.

Characterization and antifungal activity of chitosanase produced by Pedobacter sp. PR-M6

To investigate the temperature requirements of chitosanase activity, as well as the degradation patterns generated by enzyme-induced chitosan oligomer hydrolysis, Pedobacter sp. PR-M6 was inoculated onto 0.5% colloidal chitosan medium agar plates. Cell growth was higher at 30 °C than at 20 °C during the initial 2 days of incubation. The protein content rapidly increased on day 1 at both temperatures and then it slowly increased at 20 °C and slowly decreased at 30 °C during the following 5 days of incubation. In order to characterize the electrophoretic pattern, Pedobacter sp. PR-M6 was cultured in 1% powder chitosan medium at 20 °C and 30 °C for 5 days after incubation and analyzed by SDS-PAGE. Four bands were visible, corresponding to ct1 (25 kDa), ct2 (17 kDa), ct3 (15 kDa), and ct4 (14 kDa), at both 20 °C and 30 °C. The optimal conditions for the activity of chitosanase produced from Pedobacter sp. PR-M6 were 60 °C and 1.81 enzyme units/mg protein. Two major isozyme bands (ct3 and ct4) exhibited their strongest chitosanase activity at 50 °C in SDS-PAGE gel. The reaction products generated from (GlcN)₂-(GlcN)₅ substrates at 60 °C after a 1 h incubation were investigated by thin-layer chromatography. Low-molecular weight chitosan and oligochitosan (LCOC) and soluble chitosan showed antifungal activity against A. brassicicola, B. cinerea, F. solani, and R. solani. LCOC exhibited higher antifungal activity than soluble chitosan. Moreover, LCOC treatments (500 ppm and 1000 ppm) inhibited conidia germination in A. brassicicola.

Chitosan, a Biopolymer With Triple Action on Postharvest Decay of Fruit and Vegetables: Eliciting, Antimicrobial and Film-Forming Properties

Chitosan is a natural biopolymer from crab shells that is known for its biocompatibility, biodegradability, and bioactivity. In human medicine, chitosan is used as a stabilizer for active ingredients in tablets, and is popular in slimming diets. Due to its low toxicity, it was the first basic substance approved by the European Union for plant protection (Reg. EU 2014/563), for both organic agriculture and integrated pest management. When applied to plants, chitosan shows triple activity: (i) elicitation of host defenses; (ii) antimicrobial activity; and (iii) film formation on the treated surface. The eliciting activity of chitosan has been studied since the 1990's, which started with monitoring of enzyme activities linked to defense mechanisms (e.g., chitinase, β-1,3 glucanase, phenylalanine ammonia-lyase) in different fruit (e.g., strawberry, other berries, citrus fruit, table grapes). This continued with investigations with qRT-PCR (Quantitative Real-Time Polymerase Chain Reaction), and more recently, with RNA-Seq. The antimicrobial activity of chitosan against a wide range of plant pathogens has been confirmed through many in-vitro and in-vivo studies. Once applied to a plant surface (e.g., dipping, spraying), chitosan forms an edible coating, the properties of which (e.g., thickness, viscosity, gas and water permeability) depend on the acid in which it is dissolved. Based on data in literature, we propose that overall, the eliciting represents 30 to 40% of the chitosan activity, its antimicrobial activity 35 to 45%, and its film-forming activity 20 to 30%, in terms of its effectiveness in the control of postharvest decay of fresh fruit. As well as being used alone, chitosan can be applied together with many other alternatives to synthetic fungicides, to boost its eliciting, antimicrobial and film-forming properties, with additive, and at times synergistic, interactions. Several commercial chitosan formulations are available as biopesticides, with their effectiveness due to the integrated combination of these three mechanisms of action of chitosan.

Postharvest Techniques to Prevent the Incidence of Botrytis Mold of ‘BRS Vitoria’ Seedless Grape under Cold Storage

‘BRS Vitoria’ (Vitis spp.) is a novel hybrid seedless table grape recommended for cultivation in tropical and subtropical areas, especially for overseas export. The main postharvest disease of this cultivar is botrytis or gray mold (Botrytis cinerea), which occurs even under low temperatures in cold chambers. Sulfur dioxide (SO2) release pads have been used to control this disease under cold storage, but some grape cultivars are sensitive to certain levels of this compound. The objective of this work was to evaluate different types of SO2 generator pads in order to prevent the incidence of gray mold of ‘BRS Vitoria’ seedless grape, as well to avoid other grape injuries during cold storage. Grape bunches were harvested when fully ripened (16°Brix) from a commercial field trained on overhead trellis and located at Marialva, state of Parana (PR) (South Brazil). Grapes were packed into carton boxes and subjected to the following SO2 pad treatments (Uvasys®, Cape Town, South Africa) in a cold chamber (2 °C): (a) control; (b) SO2 slow release pad; (c) SO2 dual release pad; (d) SO2 dual release–fast reduced pad; (e) SO2 slow release pad with grapes inoculated with B. cinerea; (f) SO2 dual release pad with grapes inoculated with B. cinerea; and (g) SO2 dual release–fast reduced pad with grapes inoculated with B. cinerea. After a 50-day cold chamber period, the grape boxes were kept for 7 days at room temperature at 25 °C. A randomized design was used with seven treatments and four replications, with five bunches per plot. The incidence of gray mold on grapes was evaluated after the 50-day cold storage and after the 7-days-at-room-temperature periods, as well other grape physicochemical variables, such as shattered berries, stem browning, bunch mass, bunch mass loss, skin color, soluble solids (SS), titratable acidity (TA), and SS/TA. The dual release pads were more efficient in preventing the incidence of gray mold and mass loss in ‘BRS Vitoria’ seedless grapes than the slow release pads in both storage periods. The incidence of shattered berries was lower when any type SO2 pad was used during cold storage, and no effects were observed on stem browning, firmness, or berry skin color of ‘BRS Vitoria’ grapes.

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.

Edible coating composed of chitosan and Salvia fruticosa Mill. extract for the control of grey mould of table grapes

BACKGROUND

Consumer concerns regarding high-quality produce, free of pesticide residues, direct research towards disease management strategies that minimise or even exclude the use of synthetic chemistries in crop production. The efficacy of a chitosan-based edible coating combined with the acetonic extract of Salvia fruticosa Mill. (ASF) was assessed against the grey mould of table grapes.

RESULTS

HPLC-SPE-NMR and q-NMR analyses defined major constituents of ASF to be the flavonoids hispidulin, salvigenin and cirsimaritin and the diterpenes carnosic acid, carnosol and the 12-methoxycarnosic acid. The extract was found to be efficacious in reducing spore germination and mycelial growth of Botrytis cinerea in vitro at 10 and 25 °C. However, the combination of the ASF with chitosan 1% (w/v; CHIT) significantly improved fungal inhibition. Similarly, in fruit inoculation trials at 10 °C, the efficacy of the combined application of the ASF at 500 mg L^-1 with CHIT against grey mould was statistically equal to the synthetic fungicide thiabendazole, ranging from 98.4% to 92.7% at 12 and 21 days post-inoculation, respectively. Furthermore, chitosan coating alone and in combination with ASF decreased the rate of fruit weight loss during cold storage, while preserved soluble solids content and titratable acidity. Chitosan-based coatings did not affect quality attributes and the bioactive compounds in table grapes.

CONCLUSION

The combined application of the ASF in the form of an edible coating with chitosan could effectively control B. cinerea without deteriorating quality and physico-chemical properties of grapes. © 2016 Society of Chemical Industry.

Modeling and optimization of degree of folate grafted on chitosan and carboxymethyl-chitosan

Chitosan is a cationic polysaccharide with great properties and so is considered as an attractive biopolymer. However, chitosan shows its antibacterial activity only in acidic environment and this restricts its uses. So water-soluble chitosan derivatives such as carboxymethyl chitosan could be good candidates for such biomedical applications. Modified chitosan with hydrophobic functional groups such as folate (FA) is able to make self-assembled nanoparticles in aqueous media. One of the most important factors affecting the properties of resulting nanoparticles such as size, morphology, amount and efficiency of drug loading and also drug release profile is the amount of FA groups grafted on the chitosan chains. In this study FA modified chitosan and carboxymethyl chitosan have been synthesized using folic acid, N-hydroxy succinimide (NHS), N, N-dicyclohexylcarbodiimide (DCC) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The effect of molecular weight, degree of substitution of carboxymethyl hydrophilic group and primary molar ratio of folic acid to chitosan/carboxymethyl chitosan (CMCS) on degree of substitution of folate functional groups grafted on chitosan chains was modeled using a statistical software package (Design of Expert 8, Trial version). Degree of substitution of grafted folate was measured using UV/Vis spectroscopy. Results show that degree of substitution of CMC and molar ratio of folic acid to chitosan/carboxymethyl chitosan has direct effect on substitution degree of folate and molecular weight has an inverse impact. Also results show that molar ratio of folic acid to chitosan/(CMCS) has the most effect on substitution degree of folate and the proposed model is statistically valid to predict degree of substitution of FA groups on chitosan chains.

Efficacy of a coating composed of chitosan from Mucor circinelloides and carvacrol to control Aspergillus flavus and the quality of cherry tomato fruits

Cherry tomato (Lycopersicon esculentum Mill) fruits are susceptible to contamination by Aspergillus flavus, which may cause the development of fruit rot and significant postharvest losses. Currently there are significant drawbacks for the use of synthetic fungicides to control pathogenic fungi in tomato fruits, and it has increased the interest in exploring new alternatives to control the occurrence of fungal infections in these fruits. This study evaluated the efficacy of chitosan (CHI) from Mucor circinelloides in combination with carvacrol (CAR) in inhibiting A. flavus in laboratory media and as a coating on cherry tomato fruits (25°C, 12 days and 12°C, 24 days). During a period of storage, the effect of coatings composed of CHI and CAR on autochthonous microflora, as well as on some quality characteristics of the fruits such as weight loss, color, firmness, soluble solids, and titratable acidity was evaluated. CHI and CAR displayed MIC valuesof 7.5 mg/mL and 10 μL/mL, respectively, against A. flavus. The combined application of CHI (7.5 or 3.75 mg/mL) and CAR (5 or 2.5 μL/mL) strongly inhibited the mycelial growth and spore germination of A. flavus. The coating composed of CHI (3.75 mg/mL) and CAR (2.5 or 1.25 μL/mL) inhibited the growth of A. flavus in artificially contaminated fruits, as well as the native fungal microflora of the fruits stored at room or low temperature. The application of the tested coatings preserved the quality of cherry tomato fruits as measured by some physicochemical attributes. From this, composite coatings containing CHI and CAR offer a promising alternative to control postharvest infection caused by A. flavus or native fungal microflora in fresh cherry tomato fruits without negatively affecting their quality over storage.