Dharini Sivakumar

Shelf life extension of fresh fruit and vegetables by chitosan treatment

ABSTRACT Among alternatives that are currently under investigation to replace the use of synthetic fungicides to control postharvest diseases in fresh produce and to extend their shelf life, chitosan application has shown promising disease control, at both preharvest and postharvest stages. Chitosan shows a dual mode of action, on the pathogen and on the plant, as it reduces the growth of decay-causing fungi and foodborne pathogens and induces resistance responses in the host tissues. Chitosan coating forms a semipermeable film on the surface of fruit and vegetables, thereby delaying the rate of respiration, decreasing weight loss, maintaining the overall quality, and prolonging the shelf life. Moreover, the coating can provide a substrate for incorporation of other functional food additives, such as minerals, vitamins, or other drugs or nutraceutical compounds that can be used to enhance the beneficial properties of fresh commodities, or in some cases the antimicrobial activity of chitosan. Chitosan coating has been approved as GRAS substance by USFDA, and its application is safe for the consumer and the environment. This review summarizes the most relevant and recent knowledge in the application of chitosan in postharvest disease control and maintenance of overall fruit and vegetable quality during postharvest storage.

Effect of different post-harvest treatments on overall quality retention in litchi fruit during low temperature storage

Summary Freshly-harvested litchi (Litchi chinensis Sonn., L) fruit, of the cultivar ‘Mauritius’, were subjected to 5 min post-harvest dip treatments in aqueous solutions of: potassium metabisulphite, or Vapogard , or Chitosan or combined treatments of: potassium metabisulphite + Vapogard , or Chitosan + potassium metabisulphite, or Anolyte + Triton X-100 + Chitosan, or ammonia + Carnauba wax. Standard commercial sulphur dioxide fumigation was included as a comparative control. After treatment, fruit were held at 1°C, 95% RH for 21 d to simulate refrigerated sea shipment conditions, then held at 18°C, 80% RH for 2 d. Several parameters were used to evaluate fruit quality. Combined post-harvest dip treatment with potassium metabisulphite + Vapogard retained fruit marketability most effectively, preventing severe browning post-harvest diseases, and retaining fruit firmness. Potassium metabisulphite + Vapogard dip treatment also revealed superior eating quality, with a 19.5% soluble solids concentration, 0.2% titratable acidity and a decline in anthocyanin concentration. Fruit fumigated with sulphur dioxide showed increased weight loss with intensified micro-cracks on the pericarp. Chitosan was most effective in reducing the total microbial fructoplane population compared to other treatments. Penicillium expansum Link. and Cladosporium spp. were identified as the predominant fungi on litchi fruit used in this trial.

Avocado Fruit Quality Management during the Postharvest Supply Chain

Avocados are a popular subtropical fruit of high economic importance, and the European Union is the biggest importer of the bulk of the fruit coming from countries such as South Africa, Chile, and Israel. The fruit is highly nutritious, being rich in vitamins A, B, C, minerals, potassium, phosphorus, magnesium, iron, and antioxidants. The biggest challenge is that the fruit is highly susceptible to qualitative and quantitative postharvest losses. Successful maintenance of avocado fruit quality during the supply chain depends on many aspects, including adequate orchard management practices, harvesting practices, packing operations, postharvest treatments, temperature management, transportation and storage conditions, and ripening at destination. Postharvest losses are mostly attributed to flesh softening, decay, physiological disorders, and improper temperature management. Management of the supply chain is solely done to provide the fruit with the most favorable conditions to extend storage life, and retain quality and nutritional attributes of the fruit. The focus of this review is therefore to study the findings that have emanated from research done to retain overall avocado fruit quality and to reduce postharvest losses during the supply chain through the adoption of appropriate and novel postharvest technologies.

Combination of 1-methylcyclopropene treatment and controlled atmosphere storage retains overall fruit quality and bioactive compounds in mango

BACKGROUND Postharvest application of fungicide prochloraz and hot-water dip are commercially practiced to control postharvest diseases in mangoes. Owing to the increasing consumer demand for organically produced fruit, the search for natural environmentally friendly alternative products and processes has become important for the fruit industry. This study evaluated the combined effect of 1-methylcyclopropene (1-MCP) (500 nL L⁻¹) and controlled atmosphere storage conditions (CA-1, 5% O₂ + 5% CO₂ or CA-2, 3% O₂ + 8% CO₂) on the maintenance of fruit quality and bioactive compounds on hot-water treated mangoes (cv. Kent) during postharvest storage. RESULTS In comparison to the 1-MCP + CA-1 treatment, 1-MCP + CA-2 reduced the incidence of anthracnose, weight and firmness loss; delayed the skin and flesh colour development; prevented the increase of soluble solids concentration/titratable acidity ratio, ethanol and acetaldehyde content; and maintained the ascorbic acid, carotenoid, total phenolic and flavonoid contents, and antioxidant scavenging activity in hot-water treated mangoes. The untrained panel preferred 1-MCP + CA-2 treated fruit to the fruit subjected to other postharvest treatments adopted in this investigation. CONCLUSION Our investigation suggests that the combined effect of 1-MCP and CA-2 storage can be recommended as an alternative treatment to replace prochloraz application for hot-water treated mangoes and can be adopted commercially for organic export markets.

Natural Occurrence, Analysis, and Prevention of Mycotoxins in Fruits and their Processed Products

Mycotoxins are small toxic chemical products formed as the secondary metabolites by fungi that readily contaminate foods with toxins in the field or after harvest. The presence of mycotoxins, such as aflatoxins, ochratoxin A, and patulin, in fruits and their processed products is of high concern for human health due to their properties to induce severe acute and chronic toxicity at low-dose levels. Currently, a broad range of detection techniques used for practical analysis and detection of a wide spectrum of mycotoxins are available. Many analytical methods have been developed for the determination of each group of these mycotoxins in different food matrices, but new methods are still required to achieve higher sensitivity and address other challenges that are posed by these mycotoxins. Effective technologies are needed to reduce or even eliminate the presence of the mycotoxins in fruits and their processed products. Preventive measures aimed at the inhibition of mycotoxin formation in fruits and their processed products are the most effective approach. Detoxification of mycotoxins by different physical, chemical, and biological methods are less effective and sometimes restricted because of concerns of safety, possible losses in nutritional quality of the treated commodities and cost implications. This article reviewed the available information on the major mycotoxins found in foods and feeds, with an emphasis of fruits and their processed products, and the analytical methods used for their determination. Based on the current knowledge, the major strategies to prevent or even eliminate the presence of the mycotoxins in fruits and their processed products were proposed.

An overview on litchi fruit quality and alternative postharvest treatments to replace sulfur dioxide fumigation.

Litchi fruit quality is determined by chemical parameters, color, fruit composition (vitamins and minerals) and aroma volatiles. Globally there are growing concerns regarding the use of “sulfiting” agents in fresh fruits and vegetables. Consequently, new restrictive U.S. Food and Drug Administration regulations require its declaration. Sulfur dioxide (SO2), used as a fumigant for litchi, has been officially defined as a pesticide. Detectable levels must be ≤ 10 ppm as specified by the EU. Although an alternative sulfiting agent, Na2S2O5 impregnated pads, showed promising control of decay and color retention, its usage is sometimes limited since the active concentration depends on the type of cultivar. This review summarises the developments in finding appropriate alternative technologies to replace SO2 fumigation.

Bioactive Compounds and Fruit Quality of Green Sweet Pepper Grown under Different Colored Shade Netting during Postharvest Storage.

UNLABELLED In this study, influence of 3 types of photo-selective nets (pearl, red and yellow) and a standard black net on marketable yield, fruit quality and bioactive compounds after postharvest storage was investigated. Percentage marketable fruits were higher in green sweet peppers produced under the pearl nets. Fruits produced under the pearl nets showed higher fruit mass, firmness, chlorophyll content, ascorbic acid content, antioxidant scavenging activity after postharvest storage. Red/far red photon ratio under the pearl net could have improved the ascorbic acid content and the antioxidant scavenging activity in green peppers. Green sweet peppers grown under the pearl nets had higher hue values and maintained green color longer. Our results showed the impact of modified light quality on the bioactive compounds of green sweet pepper during postharvest storage. PRACTICAL APPLICATION Green sweet peppers are rich in phytochemicals. Marketability of green sweet peppers is affected partially due to ripening after postharvest storage and decay. Maintenance of green color, fruit mass, firmness, and nutritional composition are important parameters that attract consumers. This research shows the influence of light quality during production on the fruit quality parameters and bioactive compounds after postharvest storage.

Effect of a biocontrol agent (Bacillus subtilis) and modified atmosphere packaging on postharvest decay control and quality retention of litchi during storage

The efficacy of biological control and two types of modified atmosphere packaging (MAP) alone and in combinations was evaluated under cold storage as well as simulated market-shelf conditions to control decay and pericarp browning on litchi cv. ‘McLean’s Red’. Fruits were dipped for 2 min at 15°C inBacillus subtilis or prochloraz separately, packed in MAP [low density polyethylene (LDPE) or polypropylene (PP)], heat sealed and stored at 2°C and 90% r.h. for 18 days followed by 2 days at 14°C and 75% r.h. to simulate market-shelf conditions. A commercially adopted sulfur dioxide treatment was included as a comparative control. Fruits treated withB. subtilis + PP or prochloraz + PP and stand-alone PP treatment did not show decay or browning at 2°C. Decay and browning were controlled significantly after 2 days at 14°C inB. subtilis + PP or prochloraz + PP treatments. However, the prochloraz + PP affected the natural pinkish-red color of the pericarp and gave higher h° (hue angle) values. The stand-alone PP treatment (∼14% O2, ∼5% CO2) showed 11.3% decay due mainly toAlternaria alternata andCladosporium spp. at 14°C. The effectiveness of the MAP was improved at 14°C whenB. subtilis was combined with PP, controlling decay and pericarp browning and retaining the fruit color and quality.B. subtilis survived in PP at 2° and 14°C, but not in LDPE. Stand-alone LDPE (∼3% O2, ∼10% CO2) and combination treatmentsB. subtilis + LDPE or prochloraz + LDPE failed to control decay and pericarp browning. Higher yeast populations were observed in LDPE orB. subtilis + LDPE at both 2° and 14°C.Candida, Cryptococcus andZygosaccharomyces spp. were the predominant yeasts in all LDPE treatments.

Effect of modified atmosphere packaging on the quality and bioactive compounds of Chinese cabbage (Brasicca rapa L. ssp. chinensis)

BACKGROUND The perishability of Brassica chinensis poses a major challenge to distribution and marketing. The aim of this work was to select a suitable modified atmosphere packaging to retain the overall quality and bioactive compounds during storage. RESULTS Four types of biorientated polypropylene packaging (BOPP)--BOPP03, BOPP04, BOPP05 and BOPP06--with different perforations were evaluated regarding the maintenance of quality parameters (weight loss, leaf yellowing, colour L*, C*, h°), decay, chlorophyll a, chlorophyll b, bioactive compounds (carotenoids, ascorbic acid, total phenolic compounds), antioxidant scavenging activity, overall appearance and odour evaluation, at 10°C at 2, 4, 6, 8 and 10 days. Leaves were packed in BOPP (two 2-mm holes) and packed and unpacked leaves were included for comparison. The modified atmosphere created (2% O2 and 7% CO2) inside the BOPP05 reduced leaf yellowing (higher h°), improved the overall appearance with acceptable odour, moderately maintained chlorophyll a and b, bioactive compounds and antioxidant scavenging activity, and remained marketable for up to 10 days at 10°C. Gas composition within the packages influenced the retention of bioactive compounds and overall quality. CONCLUSION Application of BOPP05 is a promising method for extending the shelf life of B. chinensis leaves in order to promote its utilisation and commercialisation via urban fresh-produce markets.

Influence of Heat Treatments on Quality Retention of Fresh and Fresh-Cut Produce

Postharvest decay and insect infestation are two major causes that contribute towards higher postharvest losses during the fresh produce supply chain. Although decay and pest infestation could be controlled successfully via pesticide applications, the use of chemicals at the postharvest stage is becoming limited due to the strict regulations regarding pesticide residue levels enforced by importing countries. Heat treatments are environmentally friendly and recommended as alternative treatments to replace pesticide applications, especially with regard to fresh produce. These treatments help to eradicate pathogens or pests that are present on the fruit surface while maintaining the overall quality of the fresh produce during the supply chain. Browning is regarded as an economically important physiological disorder that causes detrimental effects on the quality maintenance of fresh-cut produce. Contamination of fresh produce by foodborne pathogens could occur at any stage during the production, harvesting, postharvest chain, or processing, and heat treatments could be recommended as an antibrowning or disinfection treatment for the fresh-cut industry. In light of the above, this review summarizes the effects of postharvest heat treatments on postharvest decay, insect infestation, physiological disorders, fruit ripening, retention of color, and bioactive compounds.