The efficacy of the combination of Candida saitoana with 0.2% glycolchitosan (the bioactive coating) as a biocontrol treatment of postharvest diseases of apple and citrus fruit was evaluated in tests with natural inoculations that simulated commercial packinghouse conditions. The growth of C. saitoana in apple wounds and on fruit surfaces was not affected by glycolchitosan. The bioactive coating was more effective in controlling decay of several cultivars of apples (Red Delicious, Rome, Golden Delicious, and Empire) than either C. saitoana or 0.2% glycolchitosan alone. Depending on the apple cultivar used, the bioactive coating was comparable or superior to thiabendazole in reducing decay. The bioactive coating was also superior to C. saitoana in controlling decay of oranges (cvs. Washington navel, Valencia, Pineapple, and Hamlin) and cv. Eureka lemons, and the control level was equivalent to that with imazalil. The bioactive coating and imazalil treatments offered consistent control of decay on Washington navel oranges and Eureka lemons in early and late seasons, while C. saitoana or 0.2% glycolchitosan were most effective on early-season fruit. The combination of C. saitoana with 0.2% glycolchitosan also reduced the incidence of stem-end rot of cv. Valencia oranges, but control was less effective than treatment with imazalil.

Aspire, a formulation of the yeast Candida oleophila registered for postharvest application to citrus for the control of green mold (Penicillium digitatum), competes with the pathogen for nutrients at injuries to prevent infection. A major factor affecting efficacy is how quickly and well the yeast colonizes injuries to the fruit surface, including minor injuries involving only oil vesicles. Colonization of puncture-related injuries that either encompassed oil glands or individually ruptured glands was achieved within 1–2 days at 21°C. Colonization of puncture injuries by C. oleophila was comparable after 2 days at 21 and 30°C, but no colonization occurred at 13°C. Ruptured oil glands were colonized more effectively if treated 7 h after injury rather than immediately. Peel oil was toxic to cells of C. oleophila but not to spores of P. digitatum. Candida oleophila colonized punctures more uniformly than individually damaged oil glands, and provided more effective control of green mold originating at punctures than at oil gland injuries. Incubating treated fruit at 30°C for 2 days before storage at 21°C enhanced the control of green mold, and control was significantly improved by the addition of Aspire in one of two trials.

Stem-end rot (SER) caused by Diplodia natalensis is a major postharvest disease of fresh Florida citrus degreened with ethylene to enhance fruit appearance. Significant increase in disease incidence by the use of ethylene at concentrations above those needed for degreening may be related to the activity of the abscission enzymes, polygalacturonase (PG) and cellulase (CX). Quiescent mycelia of D. natalensis in necrotic tissue on the surface of the calyx and disk (button) at the stem-end of the fruit grow into the fruit upon separation of the button from the fruit during abscission. Activity of the abscission enzymes in oranges was enhanced by high ethylene (0.055 ml l−1), and a larger number of cells were degraded within the abscission layer by their activity than at lower (0.002 ml l−1) more typical degreening concentrations. Commercial enzymes or partially purified preparations of the abscission enzymes added to abscission areas of debuttoned oranges before inoculation with mycelia of D. natalensis caused a significant increase in SER. Fruit dipped in 2,4-dichlorophenoxyacetic acid (2,4-D) or silver thiosulfate (STS) before degreening were more resistant to SER when inoculated following degreening. Addition of these metabolic inhibitors or cycloheximide (CHI) to the fruit abscission zone after removal of the button during early stages of degreening (18 h) with high ethylene also caused a significant reduction in SER. The metabolic inhibitors had no affect on SER if applied at 60 h after terminating the ethylene treatment. Reductions in activity of PG and CX were obtained by applying 2,4-D or STS to fruit before degreening, and STS or CHI to fruit abscission zones at early stages of degreening (18 h).

ABSTRACTThe survival and growth of Salmonella spp., Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus on peeled Hamlin orange were examined. Fruits were peeled by infusing the peel with water to assist hand removal. The peeled oranges had an average pH of 6.0–6.5 at the surface and 3.8 in the juice. After surface inoculation, peeled fruits were incubated for up to 14 days. Growth was observed with all tested pathogens only at the abusive storage temperature (24°C). Refrigeration (4 or 8°C) effectively inhibited the growth of all pathogens and caused population reduction of Salmonella spp. and S. aureus.

Citrus fruit surface microbial populations were evaluated following various packingline processes of seven Florida commercial packinghouses. At each packinghouse, six fruits (oranges or tangerines) were collected at each of four sampling points. The sampling was conducted in duplicate; thus, 336 fruit were evaluated during this survey. Average aerobic plate counts and yeast and mold counts on fruit surfaces before washing were about 4.0 log CFU/cm2 and 3.3 log CFU/cm2, respectively, and were reduced to 2.1 log CFU/cm2 and 1.3 log CFU/cm2, respectively, by packinghouse processing. Waxing alone reduced the average fruit surface aerobic plate counts and coliform counts from 3.7 log CFU/cm2 and 35.2 most probable number (MPN)/cm2, respectively, to 2.6 log CFU/cm2 and 1.4 MPN/cm2. No Escherichia coli was recovered from fruit at the end of packinghouse processing, and no salmonellae were found on fruit during the entire processing. In an inoculation study to test the effect of packinghouse processes, test organism E. coli was applied to fruit to achieve a high level (4.8 log CFU/cm2) of contamination. The average E. coli count was reduced about 2.4 log cycles by washing and rinsing with potable water (40 psi, 25 degrees C) for about 30 s. The combination of washing and waxing significantly reduced the inoculated level of E. coli from 4.8 to 1.4 log CFU/cm2.

Peeling and storage characteristics of citrus fruit infused with water or enzyme solution were compared. Fruit were vacuum- or pressure-infused with water or water-containing pectinase. The enzyme treatment did not affect peeling times of white or red grapefruit, oranges, or tangelos. Pressure and vacuum infusion methods produced similar results. Grapefruit and oranges infused with water had significantly less juice leakage and were firmer than fruit infused with enzyme. Microbial levels and respiration rates and ethylene emanation during storage were the same for enzyme- and water-treated fruit.

A postharvest peel disorder, morphologically similar to chilling injury (CI), was detected on nonchilled `Marsh' white grapefruit ( Citrus paradisi Macf.). Like CI, the disorder was characterized by pitting of the peel caused by the collapse of oil gland clusters. This disorder is distinguished from CI in that pitting developed within the first 10 days of postharvest storage on fruit held at high (21.0C), but not low (4.5C), temperatures and on waxed fruit, but not unwaxed fruit. Pathogens isolated from pitted fruit were similar to those of nonpitted fruit. No preharvest pitting or visual clues of fruit susceptibility were observed.

An enzymatic peeling process is currently used to produce peeled citrus fruit that are convenient for consumption. By this process, fruit are scored and infused with pectinase or pectinase and cellulase solution and are incubated at 20 to 45C for 0.5 to 2 h. While enzyme solution apparently weakens of the albedo and thus improves separation of the fruit from its peel, we expect that enzyme infused into the flesh reduces storage quality. In these studies, fruit were vacuum- or pressure-infused with or without pectinase in water. The time required to peel white `Marsh' and `Ruby Red' grapefruit infused with solution containing enzyme were only 10% to 20% less than for fruit infused with water alone. `Hamlin' orange and `Orlando' tangelo peeling times were not improved by enzyme treatment. This suggests that water is the primary operative component of the enzyme solution and that the enzyme is an active, but nonessential, supplement. For white grapefruit and oranges stored at 5, 10, 15, or 25C, nonenzyme-treated fruit had significantly less juice leakage than enzyme-treated fruit. For example, 0.2% and 5.0% of the peeled fruit weight was lost by non-enzymatically and enzymatically peeled fruit, respectively, for vacuum-infused oranges stored at 5C for 7 days. Moreover, the enzyme treatment significantly reduced firmness, as determined by a sensory panel. Microbial levels and rates of respiration and ethylene emanation during storage were not significantly affected by enzyme treatment. Similar results were found for vacuum- and pressure-infused fruit.

Ethylene treatment of citrus fruit to improve rind color (degreening) significantly enhances the incidence of stem-end rot caused by Diplodia natalensis and stimulates disease development. In an effort to identify the role of excessive exogenous ethylene in pathogenesis, tissue exposed to different ethylene and air atmospheres was taken from the base of citrus fruit adjacent to the abscission area at the point of fungal ingress and examined for the presence of fungal inhibitors and lignin. The major inhibitor, identified as scoparone (6,7-dimethoxycoumarin), accumulated most extensively in tissue taken from asymptomatic fruit receiving either high ethylene treatments (55 mul L-1) followed by low inoculum levels, or low ethylene treatments (2 mul L-1) followed by high inoculum levels. Accumulation of lignin, extracted from the same tissue and measured as lignothioglycolic acid, followed a response pattern similar to that observed for scoparone. Evidence for some role of scoparone and lignin in fruit resistance was indicated by the correlation between enhanced accumulation of these inhibitors and the lack of decay. However, other factors affected by high ethylene play a role in disease development since levels of inoculum that induced little disease at low ethylene were capable of causing decay at high ethylene. Sensitivity of D. natalensis to scoparone was reduced and its growth rate was increased when the fungus was grown in high-ethylene atmospheres. One role of such ethylene atmospheres in inducing extensive Diplodia stem-end rot could be that of stimulating more rapid growth of the fungus and invasion of tissue in spite of the presence of threshold inhibitory levels of scoparone.

The fungicides thiabendazole (TBZ) or imazalil were applied at 1 g·liter -1 at 24 or 53C to `Marsh' and `Redblush' grapefruit (Citrus paradisi Macf.) to reduce fruit susceptibility to chilling injury (CI) and decay. Generally, there was more CI and decay on `Marsh' grapefruit than on `Redblush'. Severity of CI was lower in grapefruit that had been dipped at 53C than at 24C. Fruit dipped in fungicides had less CI than fruit dipped in water alone. Imazalil was more effective in reducing CI than TBZ. Fungicides reduced decay at both temperatures, and imazalil was better than TBZ. Chemical names used: 2-(4-thiazolyl)benzimidazole (thiabendazole, TBZ); 1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl] -1H -imidazole (imazalil).

Imazalil applied to citrus fruit after harvest moved into the rind while the fruit were wet from the treatment. Imazalil was absorbed by the epicuticular wax and cuticle within a wetness period lasting 1-3 min, but less than 1% of it moved through the cuticle during this period. However, 30-45 min after fruit were dipped in imazalil (1,000 μg/ml) for 15 sec, the fungicide was recovered from tissue deeper than 1 mm into the rind. About 40% of the applied imazalil remained on the fruit surface after the fruit dried. At comparable treatment concentrations and times, significantly more imazalil adhered to fruit that were dipped than to fruit treated with a nonrecovery spray over brushes saturated with the fungicide (...)

The ED 50 values of imazalil ranged from 27 to 146 ng/ml, with a mean of 55. These values are less than those reported with biotypes collected in California citrus packinghouses, where ED 50 values were near 1,000 ng/ml after intensive commercial use of imazalil

Etude de l'efficacite d'une serie de desinfectants (ClO2, composes ammonium quaternaire, orthophenylphenate de Na, acide peracetique) en pulverisations ou en trempages vis-a-vis de cette bacterie contaminant les agrumes

Fresh citrus fruit is a most appealing and healthful food that many people pay a premium to enjoy. Most consumers take for granted the availability of fresh, high quality grapefruit, oranges, and specialty fruits. The per capita consumption of fresh citrus fruit in the United States in 1983 was 14.4 kg (Florida Crop and Livestock Reporting Service 1984)