Mario Schirra

Host-pathogen interactions modulated by heat treatment

Prestorage heat treatment appears to be a promising method of postharvest control of decay. Heat treatments against pathogens may be applied to fresh harvested commodities by hot water dips, by vapour heat, by hot dry air or by a very short hot water rinse and brushing. Heat treatments have a direct effect slowing germ tube elongation or of inactivating or outright killing germinating spores, thus reducing the effective inoculum size and minimising rots. Heat treatment can also indirectly affect decay development via physiological responses of the fruit tissue. These responses include inducing antifungal-like substances that inhibit fungal development in the fruit tissue, or enhancing wound healing. Heat treatment can induce PR proteins such as chitinase and β-1,3 glucanase, stabilise membranes, elicit antifungal compounds, or inhibit the synthesis of cell wall hydrolytic enzymes (polygalacturonases), and delay the degradation rate of pre-formed antifungal compounds that are present in unripe fruit. Additionally, curing, as a heat treatment can cause the disappearance of wax platelets normally present in untreated fruit and make the fruit surface relatively homogeneous. Thus, cuticular fractures, microwounds and most stomata are partially or completely filled, and early-germinated spores are encapsulated and inactivated by molten wax. The occlusion of possible gaps for wound pathogens as well as the encapsulation and inactivation of early-germinated spores have been considered as additional factors in fruit protection against decay.

Control of Postharvest Diseases of Fruit by Heat and Fungicides: Efficacy, Residue Levels, and Residue Persistence. A Review

Extensive research has been done in recent years to reduce the heavy dependence on chemical fungicides to control postharvest diseases and disorders of horticultural crops. Alternative strategies were based on improved cultural practices, biological control, plant-defense promoters, and physical treatments such as UV illumination, radiofrequency treatment, heat therapy, and storage technologies. Among these, postharvest heat treatments such as hot water dips, short hot water rinsing and brushing, and hot air conditioning have reduced rot development and enhanced fruit resistance to chilling injury in sensitive cultivars while retaining fruit quality during cold storage and shelf life. Additive or synergistic increases in effectiveness were observed by integrating heat therapy with various chemical compounds, thus leading to significant reductions in the application of active ingredients to protect produce from decay. This paper highlights the knowledge on this topic with emphasis on heat therapy effects and factors affecting the uptake, persistence, and performance of fungicide residues when they are applied in combination with hot water.

Residues of azoxystrobin, fenhexamid and pyrimethanil in strawberry following field treatments and the effect of domestic washing.

Residues of the pesticides azoxystrobin, fenhexamid and pyrimethanil were determined in strawberry after field treatment. The effect of ‘home’ washing with tap water and a commercially available vegetable detergent on residue levels was also studied. After treatment, azoxystrobin and pyrimethanil residues on strawberry were on average 0.55 and 2.98 mg kg−1, respectively, values below the maximum residue level (MRL) fixed by the European Union (2.0 and 5 mg kg−1, respectively), while fenhexamid residues were on average 2.99 mg kg−1, which is very close to the MRL of 3.0 mg kg−1, but some samples were over the MRL. Thereafter, all residues declined, with a half-life of about 8 days (azoxystrobin and fenhexamid) and 4.8 days (pyrimethanil). Washing the fruit with tap water reduced the residues of azoxystrobin and fenhexamid but did not affect pyrimethanil residues. Finally, when fruits were washed with a commercial detergent, greater amounts were removed (about 45% of azoxystrobin and pyrimethanil and 60% of fenhexamid).

Influence of Postharvest Hot Water Treatment on Nutritional and Functional Properties of Kumquat (Fortunella japonica Lour. Swingle Cv. Ovale) Fruit

The present study investigated the influence of a hot water dip (HWD) for 2 min at 50 degrees C, a standard and effective treatment for postharvest decay control of citrus fruit, on the nutritional and health-related properties of kumquats. The results show that most of the parameters examined, including titratable acidity, soluble solids content, maturity index, glucose, fructose, sucrose, ascorbic acid, dehydroascorbic acid, alpha- and gamma-tocopherols, beta-carotene, zeaxantin, rhoifolin, and antioxidant activity, were not significantly affected by treatment. The levels of beta-cryptoxanthin, narirutin, and total flavonoids increased after HWD, whereas lutein and total phenols decreased. The concentration of the essential oil and the relative percentage of the individual components of the essential oil were not affected by HWD except for the minor compound p-menta-1,5-dien-1-ol, which increased after HWD. After storage, lower levels of glucose, total sugars, beta-carotene, beta-cryptoxanthin and lutein were recorded in HWD fruit. A decrease in antioxidant activity and increases in alpha-tocopherol and total vitamin E were found both in control and HWD fruit. The influence of HWD at 50 degrees C for 2 min on individual nutraceuticals and health-related properties was thus generally low and may depend on storage conditions.

Chilling injury and residue uptake in cold-stored 'Star Ruby' grapefruit following thiabendazole and imazalil dip treatments at 20 and 50°C.

‘Star Ruby’ grapefruit (Citrus paradisi Macf.) were harvested from November through June and subjected to a 3-min dip in water at room temperature (20°C) with or without 1200 or 200 mg:l imazalil (IMZ) or thiabendazole (TBZ) at 50°C. Fruit were then stored at 2°C and 90‐95% relative humidity (RH) for 6 weeks and 1 additional week at 20°C and approximately 80% RH to simulate a marketing period (SMP). Fruit harvested in April and June and treated with 1200 mg:l TBZ at room temperature or with 200 mg:l at 50°C contained higher levels of TBZ residue than fruit picked in November and January. Fruit uptake of IMZ was not affected by harvest date. Within each date, conventional treatments with IMZ or TBZ fungicides at room temperature and treatment at 50°C produced similar levels of residues in most samples. Susceptibility to chilling injury (CI) was highest in fruit harvested in November and January, lower in April and negligible in June. Water dips at 50°C significantly reduced CI, the extent depending on harvest date and storage duration. The influence of 1200 mg:l IMZ dips at 20°C on CI control was not significant in most samples. Treatments with 200 mg:l IMZ at 50°C produced effects in CI control similar to that of water dips at 50°C. Beneficial effects were also achieved after treatment with 1200 mg:l TBZ at 20°C, although its efficacy in reducing CI was markedly improved with reduced doses (200 mg:l) at 50°C.

Epicuticular changes and storage potential of cactus pear (Opuntia ficus-indica Miller (L.)) fruit following gibberellic acid preharvest sprays and postharvest heat treatment

Abstract Cactus pear [Opuntia ficus-indica Mill. (L.) cv. Gialla] fruit were treated 10 weeks after the second induced-bloom flush with 10 ppm gibberellic acid (GA3) or were heated at 37°C for 30 h under saturated humidity after harvest. The two treatments were also combined before storage at 6°C for 45 days plus 4 additional days at 20°C to simulate a marketing period (SMP). Fruit not treated with GA3 and unheated were used as controls. GA3 spray delayed fruit ripening as evaluated by peel colour change and scanning electron microscopic observations of epicuticular wax morphology, decreased ethanol levels in the flesh during storage and SMP, and reduced decay development during storage. Postharvest heat treatment (HT) reduced decay during storage and SMP, retained visual quality of fruit, prevented chilling injury and resulted in a higher ethylene production rate after SMP in comparison with untreated fruit. The combined treatments (GA3+HT) did not produce any further beneficial effects in chilling injury and decay control or in maintaining fruit quality. Heat treatment caused a partial melting of the epicuticular wax layers. This caused the disappearance of platelets normally present on the skin surface of unheated fruit and sealed micro-wounds and cracks. The covering of wounds and cracks by melted wax following heat treatment was considered a contributing factor in protection against wound pathogens.

Synthesis and Inhibitory Activity of 7-Geranoxycoumarin against Penicillium Species in Citrus Fruit.

Abstract A naturally occurring compound with strong antifungal activity was isolated from the flavedo tissue of “Star Ruby” grapefruits (Citrus paradisi) and identified as 7-geranoxycoumarin. A high yield strategy for its synthesis was found and its antifungal activity against Penicillium italicum and P. digitatum assessed by in vivo and in vitro test.

Simultaneous amperometric detection of ascorbic acid and antioxidant capacity in orange, blueberry and kiwi juice, by a telemetric system coupled with a fullerene- or nanotubes-modified ascorbate subtractive biosensor

Four fullerenes- or nanotubes-modified graphite sensor-biosensor systems (SBs), coupled with a dual-channel telemetric device, based on an ascorbate oxidase (AOx) biosensor, were developed for on line simultaneous amperometric detection of ascorbic acid (AA) and antioxidant capacity in blueberry, kiwi and orange juice. Fullerene C60 (FC60), fullerene C70 (FC70), single-walled carbon nanotubes (SWCN) and multi-walled carbon nanotubes (MWCN) increased the sensitivity of graphite toward AA and phenols 1.2, 1.5, 5.1 and 5.1 times respectively. Fullerenes combined with AOx improved the selectivity toward AA more than nanotubes, being able to hold a higher number of AOx molecules on the biosensor surface. The SBs work at an applied potential of +500 mV, in a concentration range between the LOD and 20 μM, with a response time of two minutes. The LOD is 0.10, 0.13, 0.20 and 0.22 μM for SBs modified with FC60, FC70, SWCN and MWCN respectively. Biosensors register lower AA currents than the sensors due to the enzyme capability to oxidize AA before it reaches the transductor surface. Phenols currents registered by sensors and biosensors did not differ. Based on the difference between sensor and biosensor recorded currents a AA selectivity index was developed as an indicator of specificity toward AA and of the capacity to distinguish between AA and phenols contribution to the antioxidant capacity. This value is almost zero for fullerene-modified SBs, 0.13 and 0.22 for SWCN- and MWCN-modified SBs respectively. The results of juices analysis performed with SBs were in accordance with reference methods.

New Ultralow-Cost Telemetric System for a Rapid Electrochemical Detection of Vitamin C in Fresh Orange Juice

Ascorbic acid (AA), one of the principal micronutrients in horticultural crops, plays a key role in the human metabolism, and its determination in food products has a great significance. Citrus fruits are rich in AA, but its content is highly susceptible to change during postharvest processing and storage. We present a new ultralow-cost system, constituted of an amperometric microsensor composed of three rod carbon electrodes connected to a telemetric device, for online detection of AA in orange juice, as an alternative to conventional analytical methods. The in vitro calibration, ranged from 0 to 5 mM, and AA juice content was calculated by adding low volumes of sample into an acetate buffer solution at a constant potential of +120 mV vs carbon pseudoreference. This new approach, which is simple, expandable, and inexpensive, seems appropriate for large scale commercial use.

Improving storability of 'Tarocco' oranges by postharvest hot-dip fungicide treatments

Abstract The effectiveness of postharvest water dip, with or without thiabendazole (TBZ) or Kilol DF-100 (DF) fungicide treatments, at 52 °C on the keeping quality of ‘Tarocco’ oranges during two months storage at 8 °C and subsequent one week of simulated shelf-life at 20 °C was investigated in comparison to water dip with or without TBZ and DF at 25 °C. Considerable control of chilling injury and decay occurred both during storage and simulated shelf-life with 52 °C water dipping. TBZ fungicide was also effective in disease and disorders control, its efficacy being greatly enhanced when used in hot solution. Beneficial effects were also produced by DF applied alone or in combination with TBZ, but to a lesser extent at 25 °C. Respiration rate and ethanol amount in the juice were significantly affected by dip temperature and by treatments, while endogenous ethylene did not. Mean values of electrolyte leakage of flavedo peel discs from fruit dipped at 52 °C during storage were significantly lower than those dipped at 25 °C. After simulated shelf-life, values tended to level out. No detrimental effects on quality characteristics of fruits occurred as a consequence of prestorage dip treatment in water alone at 52 °C or with fungicide solutions.