Shimshon Ben-Yehoshua

Effects of superatmospheric oxygen levels on postharvest physiology and quality of fresh fruits and vegetables

Abstract Exposure to superatmospheric O 2 concentration may stimulate, have no effect, or reduce rates of respiration and ethylene production, depending on the commodity, maturity and ripeness stage, O 2 concentration, storage time and temperature, and concentrations of CO 2 and C 2 H 4 present in the atmosphere. In some plant organs, cyanide-resistant respiration is enhanced by elevated O 2 atmospheres. Ripening of mature-green, climacteric fruits was slightly enhanced by exposure to 30–80 kPa O 2 , but levels above 80 kPa retarded their ripening and caused O 2 toxicity disorders on some fruits. High O 2 concentrations enhance some of the effects of ethylene on fresh fruits and vegetables, including ripening, senescence, and ethylene-induced physiological disorders (such as bitterness of carrots and russet spotting on lettuce). While superatmospheric O 2 concentrations inhibit the growth of some bacteria and fungi, they are much more effective if combined with elevated (15–20 kPa) CO 2 , which is a fungistatic gas.

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.

Reducing chilling injury and decay of stored citrus fruit by hot water dips

Abstract The effect of hot water dips (53 °C, 2–3 min) on chilling injury (CI) and decay of various citrus fruits was compared with the effect of curing (36 °C, 72 h). Experiments were conducted with grapefruit ( Citrus paradisi Macf., cv. Marsh), lemon ( Citrus limon . Burm., cv. Eureka), oroblanco ( C. grandis Osb. × C. paradisi , cv. Oroblanco, syn. Sweety) and kumquat ( Fortunella margarita Swingle, cv. Nagami). Prestorage hot water dips reduced significantly the sensitivity of all these fruits to CI. Subsequent sealing of hot water-dipped fruit improved the positive effect but was not essential for the success of treatment. In our experiments, addition of fungicides (imazalil or thiabendazole, 1000 ppm) to the hot dip did not increase significantly the CI-reducing effect, but prevented fruit decay. Hot water dip also reduced decay of citrus fruits stored both at low and optimal temperatures, demonstrating an effect comparable to that of curing. An increased level of putrescine was observed in hot water-dipped grapefruit and lemons. Compared with curing, hot water dip was much easier to implement and could be combined with regular packing-house treatment procedures.

Effects of various heat treatments on the induction of cold tolerance and on the postharvest qualities of 'Star Ruby' grapefruit.

Abstract We examined the effects of various heat treatments on the induction of cold tolerance in red grapefruit ( Citrus paradisi cv. Star Ruby) and evaluated their effects on various other postharvest quality parameters such as decay development, weight loss, peel color, and juice total soluble solids (TSS) and acid content. Various heat treatments, including prestorage conditioning regimes of 3 days at 21°C and 7 days at 16°C, a hot water dip (HWD) at 53°C for 2 min, a hot water brushing (HWB) treatment at 60°C for 30 s, and curing (3 days at 36°C) achieved 70–90% reduction in the chilling injury (CI) index, as compared with control untreated fruit, following 6 weeks of cold storage at 2°C and an additional week at 20°C. Of the various treatments that induced cold tolerance, only HWB significantly reduced postharvest decay development. Conditioning and curing, which required longer exposure periods of 3–7 days at relatively high temperatures, significantly increased fruit weight loss, enhanced peel color alteration, and increased the juice TSS/acid ratios. On the other hand, the short postharvest heat treatments, including the HWD at 53°C for 2 min and the HWB at 60°C for 30 s, did not affect fruit weight loss, color, or TSS and acidity levels. Overall, it is concluded that short postharvest heat treatments, including either HWD or HWB are preferable, since they effectively induce tolerance to cold temperatures in ‘Star Ruby’ grapefruit without impairing any other postharvest qualities. Of these treatments, the new HWB is faster and could be used to clean and disinfect the fruit, and simultaneously to enhance its CI tolerance.

Effect of combined application of heat treatments and plastic packaging on keeping quality of ‘Oroblanco’ fruit (Citrus grandis L.×C. paradisi Macf.)

Combinations of various heat treatments with individual fruit sealing, packaging in polyethylene liners or waxing were tested as means to control pathological and physiological spoilage of ‘Oroblanco’ fruit (Citrus grandis L.×C. paradisi Macf.). The following heat treatments were used: curing at 36°C for 72 h, hot water dip at 52°C for 2 min or ‘hot drench brushing’ at 52, 56 or 60°C for 10 s. The standard packinghouse treatment included waxing with addition of thiabendazole (TBZ) and 2,4-d isopropyl ester. The fruit was stored for 2 weeks at 1°C (simulated low-temperature quarantine treatment), followed by 12–13 weeks at 11°C (simulated sea transportation to Japan) and 1 additional week at 20°C (simulated retail shelf-life period). The lowest weight loss and the highest firmness were observed with individually sealed fruit. Polyethylene liners were usually more efficient for weight loss control than waxing. However, the liner packaging enhanced the risk of postharvest disease development, if not accompanied by appropriate decay-controlling measures. Applying TBZ, hot water dip or curing controlled the development of postharvest pathogens, especially that of Penicillium molds. In another trial, both hot drench brushing at 56 or 60°C and hot water dip reduced decay incidence. Hot drench brushing at 60°C and hot water dip slowed fruit softening and reduced buttons abscission. In addition, the hot drench brushing at 60°C significantly delayed the loss of ‘Oroblanco’ green rind color, especially at the stylar and stem ends of the fruit. The hot dip at 52°C inhibited yellowing only when combined with individual seal-packaging.

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.

Involvement of limonene hydroperoxides formed after oil gland injury in the induction of defense response against Penicillium digitatum in lemon fruit.

The effects of wounding oil glands of lemon [Citrus limon (L.) Burm.] fruit were investigated. Young mature-green lemons demonstrated significantly lower decay incidence than older yellow fruit when their oil glands were punctured in the presence of postharvest wound pathogen Penicillium digitatum Sacc. Contact with the released gland content on the green lemon surface reduced the viability of P. digitatum spores approximately twice. Wounding caused rapid production of limonene hydroperoxides that persisted for only a few minutes. The magnitude depended on the physiological maturity of the fruit; mature-green fruit produced much higher levels than did yellow lemons. Furthermore, wounding of the oil glands or injection of limonene hydroperoxides into the lemon peel elicited the production of the citrus fruit phytoalexins, scoparone and scopoletin, to levels known to be effective in reducing decay caused by P. digitatum. The mature-green fruit produced about twice as much of these phytoalexins as the older yellow fruit. This induced defensive elicitation of phytoalexin production, as well as the direct effects of these antifungal compounds, markedly inhibited the pathogen in mature-green fruits but was ineffective in older yellow ones.

Quality of lemons sealed in high-density polyethylene film during long-term storage at different temperatures with intermittent warming

Storage of lemons is designed to extend the marketing of fruit throughout the year, from the main harvest season in the winter until late summer, which is a period of short supply in the market. This work was concerned with physiological and chemical attributes of stored lemons either seal-packaged in high-density polyethylene plastic film (HDPE), or left unwrapped, during storage at 13, 8 and 2°C. Intermittent warming (IW) was used to prevent chilling injury at the lower temperatures. Differences between fruit subjected to the two treatments which produced longest storage (sealed at 13°C and non-sealed at 2°C with IW) are discussed. Both treatments are recommended for adoption in commercial practice.

Comparative Effects of Applying Imazalil By Dipping or By Incorporation Into the Plastic Film On Decay Control, Distribution and Persistence of This Fungicide in Shamouti Oranges Individually Seal-Packaged

Seal-packaging presents another practical way of providing fungicides to individual fruits by incorporating the fungicide in the packaging film. Imazalil-containing film prevented the development of Penicillium digitatum and significantly inhibited that of Diplodia natalensis and Alternaria citri in petri dishes; this indicates that imazalil exerts its action through the vapor phase. Film containing imazalil (at concentration of 2000μg/g) markedly reduced the decay of Shamouti oranges inoculated with P. digitatum if the sealing was done immediately following the inoculation, and only slightly if sealing was delayed 24 h. Disinfection with sodium orthophenylphenate combined with sealing in imazalil-containing film provided further reduction in decay, even if the film was applied 24 h after inoculation. The effectiveness of fungi cides, whether applied to the fruit directly or in the film, was not affected by sealing. Distribution of imazalil among the film, flavedo and albedo was monitored through out the storage period of sealed fruit. The film could serve as a reservoir releasing the fungicide gradually, so that its antifungal activity may replace that previously provid ed by waxing without the risk of excessive toxic residues.

RETRACTED CHAPTER: Apharsemon, Myrrh and Olibanum: Ancient Medical Plants

Among the most reputed ancient medical plants were the: olibanum – frankincense, derived from Boswellia spp., myrrh, derived from Commiphoras spp., both from southern Arabia and the Horn of Africa, and apharsemon of Judea, derived from Commiphora gileadensis that had its origin also in these territories. The demand for these medical plants that were also important spices was met by scarce and limited sources of supply. The incense trade and trade routes were developed to carry this precious cargo over long distances through many countries to the important foreign markets of Egypt, Mesopotamia, Persia, Greece, and Rome. The export of the frankincense and myrrh made Arabia extremely wealthy, so much so that Theophrastus, Strabo, and Pliny all referred to it as Felix (fortunate) Arabia. At present, this export hardly exists, and the spice trade has declined to around 1,500 t, coming mainly from Somalia; both Yemen and Saudi Arabia import rather than export these frankincense and myrrh.