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  • Author or Editor: Elhadi Yahia x
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The effectiveness of some poststorage treatments in enhancing the flavor components of low-ethylene controlled-atmosphere (LCA) stored `McIntosh' apples (Malus domestica Borkh.) was investigated. Fruits were stored for 9 months in LCA at 3.3C and then exposed to air at 20C and to air, simulated LCA, 100% O2, or light at 3.3C for up to 4 weeks. Respiration and ethylene production indicated that apples were still in the early stage of ripening after 9 months of storage in LCA. Gas chromatographic analysis for 13 odor-active volatiles revealed the presence of eight. Air at 20C after LCA significantly increased the production of some odor volatiles, while light for up to 3 weeks only slightly increased their concentration. Poststorage exposure to air or 100% O2 at 3.3C for up to 4 weeks was not effective in enhancing volatile formation.

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Grapes (Vitis vinifera L. cv. Thompson Seedless) were packed in low density (LDPE) and high density (HDPE) polyethylene bags (Bag size: 25×25 cm containing 300 g of fruit). LDPE and HDPE films had a thickness of 38.7 and 28.2 μm, water permeability of 960 and 720 g/m2.hr.atm., and O2 permeability of 7030 and 3700 cc/m2.day.atm., respectively. Carbon dioxide gas (400 cc) was introduced to the bag immediately after sealing, after 2 weeks. and/or after 4 weeks. Fruits were evaluated after 3 months at 0°C. CO2 was about 30% immediately after introducing the gas but its concentration was reduced to less than 1% within 3 to 4 days. O2 was maintained very high (higher than 10%) in all packages. Water loss and shriveling were very low. However, decay incidence was high in all packages. In-package atmospheric conditions were not appropriate in all treatments to suppress decay activities. Further studies will be carried out with films less permeable to atmospheric gases, and fruits will be evaluated after shorter storage periods.

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`Keitt' mangoes (Mangifera indica L.) were stored for 0 to 5 days at 20C in a continuous flow of an insecticidal low-O2 atmosphere (0.2% to to 0.3%, balance N2). Fruit were evaluated every day after exposure to a low-O2 atmosphere and again after being held in air at 20C for 5 days. There was no fruit injury, organoleptic fruit quality was not lowered due to the low-O2 atmosphere, and fruit ripened normally. These results indicate that applying low-O2 atmospheres postharvest can be used to control insects in mangoes.

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Hot chile peppers are the main element that characterizes the Mexican cuisine and culture for at least the past 8 centuries. The components responsible for chile hot flavor, capsaicinoids, are synthesized through the shikimic acid pathway. Their degradation is thought to be aided by the action of peroxidases. This work describes the evolution of capsaicinoids during the development of the fruit in three varieties of hot chile widely used in Mexico: `Habanero', `Arbol', and `Piquin', and its relation with the activity of peroxidases in these fruits. Plants were seeded and transplanted in a greenhouse and fruit were harvested after 10, 20, 30, 40, 50, and 60 days from fruit set. At 60 days from fruit set fruit were completely red and senescent. Total capsaicinoids, capsaicin, and dihidrocapsaicin were detected and quantified using HPLC. The activity of peroxidases was followed using spectrophotometry. Capsaicinoids were higher in the fruit of `Habanero', followed by `Arbol', and then by `Piquin'. Capsaicin was higher than dihidrocapsaicin in the three varieties. Capsaicinoids, capsaicin, and dihidrocapsaicin increased continuously and reached a peak at 50 days after fruit set in the varieties `Habanero' and `Arbol' and after 40 days in `Piquin', and then started to decline. Peroxidases had a maximum activity at pH 6.0, ≈1.0 mM of capsaicin, and 1.0–1.5 mM of H2O2. The activity of peroxidases was slightly high after 10 days from fruit set, decreased, and started to increase again after 50 days from fruit set, which might be related to the evolution of the capsaicinoids.

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We have shown in research work also presented in this meeting that insecticidal controlled atmospheres at high temperatures are very efficient in causing in vitro mortality of eggs and third instar larvas, and in vivo mortality of third instar larvas of Anastrepha ludens and A. obliqua. In this work we are reporting on their effect on the quality of mango fruit. Fruit of the cultivar `Manila' were exposed to 0% O2 + 50% CO2 at 40, 42, 43, 44, 45, 46, 47, 48, and 49°C and 50% relative humidity for 160 min, after which they were stored at 10 °C for 20 days and evaluated at different intervals. Fruit exposed at 44°C or more had heat injury, while those exposed at 43°C or less did not show any injury and had similar or better quality than the control. On the basis of our previous results on insect mortality and on the resulted fruit quality reported here (heat injury, color, texture, weight loss), we conclude that 0% O2 + 50% CO2 at 43°C or less for 160 min can be used for the control of A. ludens and A. obliqua in mangoes.

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Papaya (Carica papaya L., cv. Sunrise) fruits were exposed to a continuous flow of an atmosphere containing <0.4% 02 (the balance being N2) for 0 to 5 days at 20C. Decay was a major problem, and some fruit had developed off-flavors after 3 days in low O2 plus 3 days in air at 20C. The intolerance of the fruit to low O2 correlates with an increase in the activity of pyruvate decarboxylase and lactate dehydrogenase but not with the activity of alcohol dehydrogenase. Insecticidal O2 (< 0.4%) atmospheres can be used as a quarantine insect control treatment in papaya for periods <3 days at 20C without the risk of significant fruit injury.

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`Hass' avocado (Persea americana Mill.) fruit were kept in air, 0.25% O2 (balance N2), 20 % O2 + 80% CO2, or 0.25% O2 + 80% CO2 (balance N2) at 20C for up to 3 days to study the regulation of fermentative metabolism. The 0.25% 02 and 0.25% 02 + 80% CO2 treatments caused accumulations of acetaldehyde and ethanol and increased NADH concentration, but decreased NAD level. The 20% O2 + 80% CO2 treatment slightly increased acetaldehyde and ethanol concentrations without significant effects on NADH and NAD levels. Lactate accumulated in avocadoes kept in 0.25 % 02. The 80% CO, (added to 0.25% O2) did not increase lactate concentration and negated the 0.25% O2-induced lactate accumulation. Activities of PDC and LDH were slightly enhanced and a new isozyme of ADH was induced by 0.25% O2, 20% O2 + 80% CO2, or 0.25 % O2 + 80% CO2; these treatments partly reduced the overall activity of the PDH complex. Fermentative metabolism can be regulated by changes in levels of PDC, ADH, LDH, and PDH enzymes and/or by metabolic control of the functions of these enzymes through changes in pH, ATP, pyruvate, acetaldehyde, NADH, or NAD. Chemical names used: alcohol dehydrogenase (ADH), adenosine triphosphate (ATP), lactate dehydrogenase (LDH), nicotinamide adenine dinucleotide (NAD), reduced NAD (NADH), pyruvate decarboxylase (PDC), pyruvate dehydrogenase (PDH).

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Changes in fermentation volatiles and enzymes were studied in preclimacteric and postclimacteric `Bartlett' pears (Pyrus communis L.) kept in air, 0.25% O2, 20% O2 + 80% CO2, or 0.25% O2 + 80% CO2 at 20C for 1, 2, or 3 days. All three atmospheres resulted in accumulation of acetaldehyde, ethanol, and ethyl acetate. The postclimacteric pears had higher activity of pyruvate decarboxylase (PDC) and higher concentrations of fermentation volatiles than those of the preclimacteric fruit. For the preclimacteric pears, the 0.25% O2 treatment dramatically increased alcohol dehydrogenase (ADH) activity, which was largely due to the enhancement of one ADH isozyme. Exposure to 20% O2 + 80% CO2 slightly increased ADH activity, but the combination of 0.25% O2 + 80% CO2 resulted in lower ADH activity than 0.25% O2 alone. For the postclimacteric pears, the three atmospheres resulted in higher PDC and ADH activities than those of air control fruit. Ethanolic fermentation in `Bartlett' pears could be induced by low O2 and/or high CO2 via 1) increased amounts of PDC and ADH; 2) PDC and ADH activation caused by decreased cytoplasmic pH; or 3) PDC and ADH activation or more rapid fermentation due to increased concentrations of their substrates (pyruvate, acetaldehyde, or NADH).

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Winter squash are grown in northwestern Mexico for export to distant markets. During transport, fruits deteriorate and develop fungal rots. Squash (Cucurbita maxima Duch. `Delica') was given hot-water dips at 50C for 0, 3, 6, 9, and 12 min and stored at 10 and 20C with 75% RH for 4, 8, and 12 weeks. The highest weight loss (11.3%) was in fruits without hot water treatment stored at 20C for 12 weeks—weight losses were 3.6%, 7.2%, and 10.2% in the 4-, 8-, and 12-week storage periods, respectively. At 10C, the weight losses were 3.4%, 6.8%, and 7.6% for the same periods, respectively. ß-carotene content increased from 36.2 to 54.2 mg/100 g after 4 and 8 weeks of storage, respectively, but declined to 42.8 mg/100 g after 12 weeks. Chlorophyll content decreased as temperature and storage period increased, changing from 16.7 to 10.8 mg·liter-1 at 10 and 20C and from 16.9 to 15.8 mg·liter-1 and 8.8 mg·liter-1 at 4, 8, and 12 weeks, respectively. Fruits had decay caused by Rhizopus and Aspergillus. Weight loss, ß-carotene and chlorophyll contents, and decay were not affected by length of hot-water treatment. General appearance was better in fruits stored at 10 than at 20C.

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There is a continuous need for the monitoring of agrochemicals in foods. For this purpose, there is a need for sensitive and inexpensive techniques. The recent use of immunoassays for the detection and quantification of environmental residues is advantageous as being specific, sensitive, fast, and potentially inexpensive compared to traditional methods. In this work, we have used an immunoassay method to quantify 13 pesticides in eight fresh and processed fruits and vegetables consumed in northwestern Mexico. The concentrations detected were much lower than the maximum permitted levels in all products analyzed. Minimum concentration detected was 0.1 ppb of chlorothalonil in tomato fruit. The maximum concentration detected was 386 ppb of benomyl in Mexican-produced apples.

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