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Hisashi Kato-Noguchi and Alley E. Watada

Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or in air for 7 days at 5 and 15 °C to study the regulation of ethanolic fermentation metabolism. Low-O2 atmospheres of 0.5% and 2% caused increases in ethanol and acetaldehyde concentrations and the activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) compared to air. By day 3, ethanol increased 38-, 25-, 13-, and 9.5-fold; acetaldehyde increased 20-, 13-, 7.7-, and 5.6-fold; ADH increased 7.6-, 6.3-, 3.8-, and 2.7-fold; and PDC increased 4.2-, 3.9-, 2.3-, and 2.2-fold in samples at 0.5% O2 at 15 or 5 °C and at 2% O2 at 15 or 5 °C, respectively, compared with corresponding samples in air. These results indicate that ethanolic fermentation was accelerated more in the 0.5% than in the 2% O2 atmosphere and more at 15 °C than at 5 °C. The acceleration of ethanolic fermentation may allow production of some ATP, which may permit the carrot tissues to survive.

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Hisashi Kato-Noguchi and Alley E. Watada

Although a number of studies have been conducted to evaluate the effect of control and modified atmosphere on the quality and storability of carrot roots (Daucus carota L.) under low O2 atmosphere, little is known about the underling biochemical changes in particular changes in anaerobic respiration. Carrot root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2), or air for 7 days at 5 and 15°C to study the regulation of glycolysis and the accumulation of glycolytic end products, such as ethanol and/or lactic acid. Low O2 atmosphere caused increases in the concentrations of ethanol and acetaldehyde and the activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC). By day 3, ethanol increased 38-, 25-, 13-, and 9.5-fold, acetaldehyde increased 20-, 13-, 7.7-, and 5.6-fold, ADH increased 7.6-, 6.3-, 3.8-, and 2.7-fold, and PDC increased 4.2-, 3.9-, 2.3-, and 2.2-fold for 0.5% O2 at 15 and 5°C, 2% O2 at 15 and 5°C, respectively, compared with corresponding air control. These results shows that the production of ethanol was higher in 0.5% O2 than in 2% O2 at both temperatures. The enhancement of the glycolytic flux under 0.5% O2 indicates that under these conditions the mitochondrial terminal oxydases were restricted, hence, the enhancement of ethanol synthesis, to compensate partly for the decrease in ATP production.

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Hisashi Kato-Novuchi and Alley E. Watada

Carrot (Daucus carota L.) shreds were stored under a continuous flow of 0.5% O2 (balance N2), 2% O2 (balance N2), or air for 9 days at 5C and 15C. The resulting changes in respiration and levels of the glycolytic intermediates were monitored. Low-oxygen atmosphere reduced respiration rate, but the RQ increased. The RQ was higher at 0.5% O2 than at 2% O2 atmosphere at both 5C and 15C. The most significant change in the levels of glycolytic intermediates was the accumulation of fructose 1,6-biphosphate. The level of fructose 1,6-biphosphate at 0.5% O2 was about 2-fold greater than at 2% O2 atmosphere at both 5C and 15C. The level of the other glycolytic intermediates at low-oxygen atmosphere was similar to that held in air atmosphere. These results suggest that phosphofructokinase activity in the tissue of carrots may increase under low-oxygen condition and it may be one of the controlling points in the glycolytic pathway affected by low oxygen concentrations.

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Jin-He Bai and Alley E. Watada

A study was made to determine if induction of modified atmosphere at the time of packaging would be of a benefit to the quality of fresh-cut honeydew cubes because the desired gas levels are not attained immediately or at all during the short holding period in modified-atmosphere packages. Fresh-cut honeydew cubes (2-cm cube) were placed in a plastic container underlaid with a water absorbent packet and the container was sealed with a film. The film is coextruded polystyrene and polyethylene (Cryovac), which had oxygen transmission rates of 1448 and 1903ml/m2 per day per atm at 5 °C and 10 °C, respectively. The sealed packages were given one of the following three treatments: 1) the packages were allowed to form their own natural modified atmosphere (nMAP), 2) the internal atmosphere of the packages was flushed with a gas mixture of 5% O2 + 5% CO2 (iMAP), 3) the film was perforated with a needle to have ten 1.5-mm holes (PFP). The packages were stored at 5 °C, 2 days at 5 °C, and transferred to 10 °C or at 10 °C for 2, 4, 7, 9, or 11 days. Quality attributes and microbial population were analyzed after each holding period. The average gas mixture equilibrated to 7% O2 and 9.5% CO2 in nMAP, was unchanged from the induced atmosphere in iMAP, and was close to the ambient condition (air) in PFP. Honeydew cubes were marketable on days 11, 4, and 4 when held in nMAP; on days 11, 4, and 7 when held in iMAP; and unsalable on days 9, 4, and 7 when held in PFP at 5 °C, 10 °C or transferred to 10 °C, respectively. Development of water-soaked lesions and sour odor were the main factor affecting marketability of the cubes. The decreasing pH, chroma and `L' values and increasing hue angle, mesophilic aerobic microrganism, and yeast population was retarded in both of nMAP and iMAP.

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Hisashi Kato-Noguchi and Alley E. Watada

This study was undertaken to determine the effect of low-O2 atmosphere on the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), which can activate the enzyme pyrophosphate-dependent:phosphofructokinase (PPi-PFK) to catalyze the reaction from fructose 6-phosphate to fructose 1,6-bisphosphate (Fru-1,6-P2). Fru-2,6-P2 remained unchanged in carrot (Daucus carota L.) root shreds stored under air, but it increased 3.0- and 5.3-fold at 2% and 0.5% O2 atmosphere, respectively, at 5C, and the increases were almost twice as great at 15C. The concentration of PPi ranged from 17 to 33 nmol·g-1 fresh weight, which is more than sufficient for the PPi-PFK to proceed. Thus, low-O2 atmosphere appeared to hasten glycolysis of carrot shreds by increasing Fru-2,6-P2, which activated PPi-PFK toward glycolysis.

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Hidemi Izumi, Alley E. Watada, and Ling Qi

Respiration of carrot slices, sticks, and shreds was monitored during storage in air, low O2 (0.5%, 1%, and 2%) or high CO2 (3%, 6%, and 10%) atmospheres at 0, 5, and 10°C. The respiration pattern differed with temperature and type of cuts. At 10°C, the rates of all cuts decreased with time. At the lower temperatures, the rate of sticks and shreds increased with the increase being greater at 5°C. Carbon dioxide production and O2 consumption of all cuts were lower when stored in either reduced O2 or elevated CO2 relative to those in air. Reduction was the greatest with cuts held in 0.5% O2 or 10% CO2 at 0°C. Low O2 was more effective than high CO2 atmosphere in reducing the rate at 10°C, but not at other temperatures. Respiratory quotient (RQ) of shreds were higher when held in low O2 and lower when held in high CO2 relative to those in air. RQ of other cuts were affected, but not consistently. The Q10 of all cuts ranged from 1.9 to 7.4 in the 0 to 10°C range and was lower with cuts in low O2 and greater with cuts in high CO2.

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Hisashi Kato-Noguchi and Alley E. Watada

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Nithiya Rattanapanone, Yuen Lee, Tianxia Wu, and Alley E. Watada

The marketable period of fresh-cut `Tommy Atkins' and `Kent' mango cubes was 3 to 5 days at 10 °C and 5 to 8 days at 5 °C. The marketable period was extended by 1 to 2 days when cubes were held in a 4 kPa O2 + 10 kPa CO2 or 2 kPa O2 + 10 kPa CO2 (balance N2) atmospheres, depending on cultivar and temperature. Variations in texture (shear force), pH, and soluble solids were greater among cubes from different mango lots than among cubes held at different temperatures or atmospheres. Yeast count increased more with time than did the total mesophilic aerobic count, and the increase was less under controlled atmosphere (CA) than in air at 10 °C. The CA was beneficial in maintaining quality of the cubes; however, low temperature was more effective than CA.

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Yasuo Tatsumi, Alley E. Watada, and Peter P. Ling

Water jet technology to slice carrots or salt treatment prior to slicing was studied to minimize the unappealing whitish tissue noted with carrot sticks. The water jet was a fine stream with 378,950 kPa force. Salt treatment consisted of immersing carrots in NaCl solution ranging from 0.0 to 1.0 M concentration for 3 to 20 hours. Subsequently, the carrots were sliced, stored at 5 C, and analyzed. Carrot sticks sliced with the water jet had a greater amount of white tissue than those sliced with a knife. Scanning electron microscopy showed that the water jet caused grooves on the cut surface, which exposed many layers of cells to dehydrate rapidly. The grooves probably can be minimized by increasing the speed of slicing. Salt treatments of 0.5 to 1.0 M concentration caused 3 to 10 percent weight loss when treated for 20 hours at 5 C or 3 hours at 20 C. Carrot sticks with increased weight loss had less whitish tissue and had an appearance of freshly cut sticks; however, the textural quality decreased.

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Hidemi Izumi, Nathanee P. Ko, and Alley E. Watada

Quality and physiology of carrot shreds were monitored during storage in air, low O2 (0.5%, 1%, and 2%), or high CO2 (3%, 6%, and 10%) at 0, 5, and 10C to evaluate the response to controlled-atmosphere (CA) storage. Oxygen uptake and CO2 production from respiration were reduced under low-O2 or high-CO2 atmosphere, the reduction being greater at lower O2 and higher CO2 levels. The respiratory quotient was about 1 with samples in air, more than 1 in low-O2, and less than 1 in high-CO2 atmosphere during storage at all temperatures. No differences were found in ethylene production, which were less than 0.2 μl·kg–1·h–1 with all samples. The CA containing 0.5% O2 and 10% CO2 reduced weight loss and formation of white-colored tissue and decreased pH, but did not affect microbial count and texture at all temperatures. Off-odor and black root rot were not detected in both CA and air atmospheres.