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Yiping Gong, Peter M.A. Toivonen, O.L. Lau and Paul A. Wiersma

Apple fruits (Malus domestica Borkh. cv. Braeburn) harvested from two orchards (A and B) on the same day were stored in air or pretreated in air for 0, 2 (2dCA) or 4 weeks (4dCA) before moving into controlled atmosphere (CA) storage with 1.5% O2 + 5% CO2. During storage at 1 °C for 9 weeks in air and/or CA, changes of pyruvate decarboxylase (PDC) activity, alcohol dehydrogenase (ADH) activity, acetaldehyde (AA) and ethanol (EtOH) concentrations in flesh tissue were assayed in addition to the incidence of Braeburn browning disorder (BBD). Immediate introduction to CA conditions induced the development of BBD with the highest incidence 62.2%, however delaying application of CA for 2 and 4 weeks reduced the incidence of BBD to 38.5% and 27.0%. The development of disorder in grower B was less than in grower A. 2dCA and 4dCA treatments did not influence PDC activity compared with treatment of CA. However, ADH activity and the accumulation of AA and EtOH in treatments of 2dCA and 4dCA were markedly lower than those in CA. The accumulation of AA in grower B was lower than grower A. The results of this study suggest that the delayed application of CA reduced BBD and this may be due to reduced anaerobic metabolism of fruits in the delayed CA.

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J.P. Mattheis and D.A. Buchanan

Apple fruit storage lie is prolonged by low-oxygen cold storage, however, ethanol accumulates when oxygen concentration is reduced below the Pasteur point, Upon return to aerobic conditions, dissipation of ethanol occurs due to physical (evaporation) and biochemical processes. Oxidation of ethanol by apple fruit occurs at a slow rate, but ethanol also serves es a substrate for fruit volatile synthesis. This study was conducted to determine changes in concentrations of ethanol and other non-ethylene apple fruit volatiles following periods of anaerobiosis. `Delicious' apples were obtained from a commercial warehouse and stored at 0.05% O2, 0.2% CO2 and 1 C. One day following return to ambient oxygen conditions, several volatiles were identified from anaerobic fruit that were nor produced by the control fruit. All were eaters that contained an ethyl group as the alcohol-derived portion, These included ethyl acetate, ethyl butyrate, ethyl 2-methyl butyrate, ethyl hexanoate and ethyl octanoate. Several esters produced by the controls were not detectable from anaerobic fruit including butyl butyrate, butyl 2-methyl butyrate, propyl hexanoate and 3-methyl butyl hexanoate. After 7 days ripening at 20 C, the amount of ethanol and the additional ethylesters was reduced in anaerobic fruit. Synthesis of esters produced by control fruit but nor by anaerobic fruit during the initial volatile sampling had resumed after 7 days.

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A.A. Kader, D. Ke, M. Mateos and E. Yahia

Fruits of `Bartlett' pear (Pyrus communis L.) at green (preclimacteric) and yellow (postclimacteric) stages were kept in 0.25% O2 (balance N2), 80% CO2 (balance O2), or 0.25% O2 + 80% CO2 (balance N2) for 1, 2, or 3 days followed by transfer to air at 20C for 3 days to study the effects of these controlled atmosphere (CA) treatments on anaerobic products and enzymes. All the three CA treatments caused greater accumulation of ethanol, acetaldehyde, and ethyl acetate than the air control. The postclimacteric pears were more sensitive to CA treatments as indicated by occurrence of skin browning, enhanced activity of pyruvate decarboxylase, and higher concentrations of the anaerobic volatiles. For the preclimacteric pears, the 0.25% O2 treatment dramatically increased alcohol dehydrogenase (ADH) activity, which was associated with the induction of one ADH isozyme. Exposure of preclimacteric pears to 80% CO2 slightly increased ADH activity while treatment with 0.25% O2 + 80% CO2 resulted in lower AD11 activity than 0.25% O2 alone.

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Junqin Zong, Yanzhi Gao, Jingbo Chen, Hailin Guo, Yi Wang, Fan Meng, Yiwei Jiang and Jianxiu Liu

tolerant citrus genotype ‘Carrizo’ citrange ( Poncirus trifoliata × Citrus sinensis ), supporting the idea of synergistic action in the positive antioxidant response ( Arbona et al., 2008 ). Similar to anaerobic metabolism, differential responses of

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Charles F. Forney and Michael A. Jordan

Methanethiol (MT) is a volatile compound responsible for the unpleasant odor evolved when fresh broccoli (Brassica oleracea L., Italica group) is held under anaerobic conditions. Inductive atmospheres can develop in storage, transportation containers, or modified atmosphere packages, resulting in reduced quality. To determine if related vegetables are capable of producing MT, 12 different vegetables from the genus Brassica were cut into ready-to-eat forms. Fifty-gram samples were sealed in 500-mL glass jars and flushed with N2. After 24 h in the dark at 20 °C, headspace samples from the jars were analyzed for MT and other volatiles. Headspace concentration of MT was greatest in broccoli florets, followed by pak choi (Brassica rapa L., Chinensis group) leaf blades, savoy cabbage (Brassica oleracea L., Capitata group), broccoflower (Brassica oleracea L., Botrytis group), and green and red cabbage (Brassica oleracea L., Capitata group). Broccoli stems, kale (Brassica oleracea L., Acephala group), Brussels sprouts (Brassica oleracea L., Gemmifera group), pak choi petioles, rutabaga (Brassica napus L., Napobrassica group) root, cauliflower (Brassica oleracea L., Botrytis group) florets, Chinese cabbage (Brassica rapa L., Pekinensis group), and kohlrabi (Brassica oleracea L., Gongylodes group) tubers produced <3% of the MT produced by broccoli florets. Green tissues appeared to have a greater capacity to produce MT than nongreen tissues. Anaerobic production of CO2 and ethanol did not relate to the vegetable's ability to produce MT. The production of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) were also induced by the anaerobic conditions. Green cabbage produced the greatest concentration of DMDS, followed by savoy cabbage and broccoli florets. Production of DMTS was similar to the pattern observed for MT, but DMDS production was not highly correlated with MT production.

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Yuehe Huang, David H. Picha and Anthony W. Kilili

`Beauregard' sweetpotato (Ipomoea batatas L. Lam) roots were maintained under different controlled atmospheres ranging from 0% to 21% O2 at 22 °C in two separate trials for 14 days to study changes in activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH). Trial I showed no difference in activities of PDC and ADH between 0% and 1% O2, or among 2%, 5%, and 21% O2. Both PDC and ADH activities were significantly higher at 0% and 1% O2 compared to the 2%, 5%, and 21% O2 atmospheres. In trial II, both enzyme activities were lower at 1.5% O2 than at 0% O2, but higher than at 10% and 21% O2 atmospheres. The combined data of the two trials showed a very strong correlation between PDC and ADH activities (R 2 = 0.86). In addition, a strong correlation existed between PDC activity and acetaldehyde concentration (R 2 = 0.95). The maximal activities were at pH 6.5 for PDC and at pH 8.5 for ADH in the direction of acetaldehyde-to-ethanol. The results suggest that 1.5% O2 is the critical point for the transition from aerobic to anaerobic metabolism in CA storage of sweetpotato roots, and PDC is the key enzyme in alcoholic fermentation.

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Abd. Shukor Rahman

Controlled-atmosphere (CA) storage of fruits employing low O2 and/or elevated CO2 have been used to reduce respiration and other associated metabolic activities. Papaya fruit cv. Eksofika were exposed to 2%, 5%, and 21% (air) O2 for 4 weeks at 12C. The CO2 production rates of fruit previously stored in 2% and 5% O2 were suppressed during storage, but increased upon transfer to air at 20C. Carbon dioxide production rates of low-oxygen stored fruits were slightly lower than the air-stored fruit during transfer to air, indicating a slight residual effect of low O2 on the respiratory activity of the fruit. This was highly evident in fruit stored in 2% O2 for 4 weeks. Ethylene production rates were not affected by prior storage of fruit in low-O2 atmosphere. Anaerobic metabolism did not occur in fruit stored in 2% O2 for 4 weeks, as evidenced by the RQ values close to unity and the absence of ethanol from the headspace of the respired gas. The total sugar content of ripe fruit at color score 5, previously stored in low-O2 atmosphere for 4 weeks, were not significantly different from the air-stored fruit.

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CHLOROPHYLL FLUORESCENCE HarvestWatch is a non-destructive, real-time, chlorophyll fluorescence-based technology that identifies the transitional threshold between aerobic and anaerobic metabolism in apples in low-oxygen storage by a spike in the fluorescence

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Kehua Wang and Yiwei Jiang

.R. 1993 Effects of flooding on carbohydrate and ABA levels in roots and shoots of alfalfa Plant Cell Environ. 16 695 702 Chen, H. Qualls, R.G. 2003 Anaerobic metabolism in the roots of seedlings of the invasive

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Bo Xiao and David Jespersen

, 2007a ). Due to oxygen deficiency in the plant rhizosphere, anaerobic metabolism plays an important role in producing energy for waterlogged plants, especially the activity of fermentation enzymes, including alcoholic dehydrogenase (ADH), pyruvate