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Hidemi Izumi and Akihiro Suzuki

The effect of electrolyzed water on bacterial count was evaluated on CA/MA stored carrot shreds. Electrolyzed water (pH 6.8) containing 50 ppm available chlorine, was generated by electrolysis of 2.5% NaCl solution using an electrolyzed neutral water generator, Ameni Clean (Matsushita Seiko, Osaka, Japan). Electrolyzed water treatment reduced counts of total bacteria and lactic acid bacteria on surface of carrot shreds by about 1 log CFU/g as compared to water-rinsed control. Microbial population increased on treated carrot shreds stored in air or 3% O2 atmosphere at 10 or 20 °C. The increasing count of lactic acid bacteria was less on electrolyzed water treated samples than on control samples during storage at 10 °C. Electrolyzed water did not affect respiration rate of carrot shreds during storage at 10 and 20 °C. For MA study, the treated carrot shreds were packaged and stored in a polymeric film in which the O2 and CO2 concentrations equilibrated to about 10% and 3% at 10 °C and about 6% and 7% at 20 °C, respectively. The lactic acid bacterial count on shreds in MAP was lower with electrolyzed water treated samples than water treated controls during storage at 10 and 20 °C.

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Yuji Nakata and Hidemi Izumi

‘Minomusume’ strawberries were stored in high CO2 atmospheres (20%, 30%, and 40%) by means of a controlled atmosphere (CA) and active modified atmosphere packaging (MAP) for 10 days at 5 °C. The CA of 20% to 40% CO2 was effective in delaying an increase in fungal count and preventing the external formation of mold mycelia, but a CA of >30% CO2 induced black discoloration on the surface of strawberry due to CO2 injury. When strawberry fruit were stored in a MAP flushed with either air or high CO2, all packages approached an equilibrium of ≈20% CO2 and 2% O2 by the end of storage. Fungal counts of strawberry fruit stored in a MAP remained constant throughout the storage period and the diversity of fungal flora was partially similar regardless of the difference in the MAP method. Visual quality (mold incidence and severity of black discoloration) and physicochemical quality (weight loss, firmness, pH, and total ascorbic acid content) were unaffected by CO2 atmospheres as the flushing gas during active MAP storage, except that the fruit in a MAP flushed with 20% and 30% CO2 were firmer than those with air and 40% CO2. After transfer to ambient conditions for 6 days at 10 °C, however, external formation of mold mycelia identified as Botrytis cinerea and surface black discoloration were induced in strawberry fruit in MAP flushed with 30% and 40% CO2.

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Hidemi Izumi and Alley E. Watada

Physiology and quality of CaCl2 treated or nontreated `Elite' zucchini squash slices were monitored during storage in air, low O2 (0.25, 0.5 and 1%) or high CO2 (3, 6, and 10%) atmosphere at 10C. O2 consumption and CO2 production were reduced under low O2 and high CO2 atmospheres and the reduction was greater with low O2. C2H4 production was reduced with low O2 and initially with high CO2. After day 2 or 4, C2H4 production under high CO2 increased with the increase being greater at the lower CO2 level. The amount and severity of injury/decay were less under low O2 and high CO2 than air atmosphere. Slices stored under 0.25% O2 atmosphere had less weight loss and injury/decay and greater shear force and ascorbic acid content than those held in air atmosphere. Microbial count, pH, and color were affected by the low O2 only on the last day. CaCl2 had no additive effect.

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Hidemi Izumi, Takeshi Yamashita and Maki Inada

Ferulic acid agent (2% of ferulic acid), fumaric acid agent (20% of fumaric acid), mustard extract agent (10% of allyl isothiocyanate), and calcined calcium agent (91% of calcium) were assessed for reduction of endogenous microbial population on fresh-cut lettuce, cabbage, and cucumber in the preliminary study. In seeking effective minimum concentration, a 0.5% ferulic acid agent or 1.0% fumaric acid agent applied on lettuce, 0.1% mustard extract agent on cabbage, and 0.05% calcined calcium agent on cucumber reduced mesophilic aerobic bacteria (MAB) and coliform group (coliforms) by about 0.5 to 1.5 logs relative to water-dipped control. The efficacy of these antimicrobial agents with subsequent washing treatments with electrolyzed water (13 ppm of available chlorine) or ozonated water (5 ppm of ozone) on endogenous microorganism were evaluated with fresh-cut vegetables stored in MA package for 4 days at 10 °C. With lettuce, the fumaric acid agent followed by electrolyzed water treatment was the most effective in reducing counts of MAB, coliforms, and psychrotrophic aerobic bacteria (PAB) for the first 2 days of storage. This treatment eliminated gram-positive bacteria such as the genus Curtobacterium and gram-negative bacteria such as the genus Stenotrophomonas. With cucumber, fumaric acid agent or calcined calcium agent with sequential washing with electrolyzed water reduced counts of MAB, coliforms, PAB and lactic acid bacteria during 4 days of storage, with the reduction being greater with fumaric acid agent than with calcined calcium agent. With cabbage, the combinations of the agents and washing treatments had no pronounced effect when compared with water treatment.

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Yukari Murakami, Yoshihiko Ozaki and Hidemi Izumi

The microbiological quality and shelf life of enzyme-peeled fresh-cut persimmon slices were evaluated during storage in a high CO2 controlled atmosphere (CA) and active modified atmosphere packaging (MAP) at 10 °C. Microbial counts of the enzyme-peeled slices were lower in high CO2 atmospheres (10%, 15%, and 20%) than in air during CA storage for 6 days at 10 °C with the 20% CO2 atmosphere being most effective. High CO2 atmospheres did not affect the number of bacterial and fungal species detected in the persimmon slices. The surface color, expressed as C* values, of the peeled side of enzyme-peeled slices was lower in high CO2 than in air after 6 days of CA storage. In contrast, C* values at the cut side were higher for slices stored in 20% CO2 than in air on Day 6. High CO2 atmospheres did not affect other quality of enzyme-peeled slices such as texture, pH, sugar content, and total ascorbic acid content. Based on the optimum 20% CO2 concentration in a CA, enzyme-peeled slices were stored in a MAP flushed with either air or 20% CO2 for 4 days at 10 °C. The CO2 concentration approached an equilibrium of either 5% or 10% after 3 days of storage in packages flushed with either air or 20% CO2, respectively, and the O2 decreased to ≈10% in both packages. Adding 20% CO2 to the MAP was effective in reducing the growth of mesophiles and coliforms but not fungi in enzyme-peeled persimmon slices throughout 4 days of storage. The diversity of bacterial and fungal flora was partially similar between packages flushed with air and 20% CO2. Texture, pH, surface color, sugar content, and total ascorbic acid content of enzyme-peeled persimmon slices were unaffected by air or 20% CO2 as the flushing gas, except that C* values of the enzymatically peeled side on Day 4 were lower for slices flushed with 20% CO2 than air. A 20% CO2 atmosphere is recommended for reducing the microbial population of enzyme-peeled persimmon slices stored at 10 °C and the shelf life of persimmon slices in an active MAP with 20% CO2 is 4 days at 10 °C.

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Yukari Murakami, Yoshihiko Ozaki and Hidemi Izumi

Enzymatic peeling of ‘Fuyu’ and ‘Tone-wase’ persimmon fruit was conducted for production of fresh-cut slices, and the microbiological and physicochemical quality of enzyme-peeled fresh-cut slices was compared with that of slices manually peeled with a knife. The enzymatic peeling process involved a porous treatment of the peel, heating at 100 °C for 45 s, infusion with 3% protopectinase at 37 °C for 3 h, and rinsing under running tap water. Initially, the peel of ‘Fuyu’ persimmon fruit had microbial counts ranging from 3.9 to 4.2 log cfu·g−1 and a diverse microflora. The heating treatment before the enzymatic peeling process reduced the microbial counts in both the peel and flesh of all fruits to levels below the lower limit of detection. After the enzyme infusion followed by gentle rinsing with tap water, microbial counts of enzyme-peeled fruit were close to or below the level of detection. When microbial contamination of enzyme-peeled and knife-peeled ‘Fuyu’ and ‘Tone-wase’ persimmon slices was compared, the bacterial counts and diversity of bacterial and fungal flora were less in enzyme-peeled slices than in knife-peeled slices. With ‘Tone-wase’ slices, the color index, pH, and texture were unaffected by enzymatic peeling, except for surface lightness, which was lower in enzyme-peeled slices than in knife-peeled slices. These results indicate that enzymatic peeling could be an alternative to knife-peeling of ‘Tone-wase’ persimmon fruit for fresh-cut production from the point of microbiological and physicochemical quality.

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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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Hidemi Izumi, Tetsuya Nakatani and Hiroki Ogikubo

`Sunbest' spinach leaves were stored in air or controlled atmosphere (CA) containing 3%, 6%, and 10% CO2 combined with 0.5% O2 at 0, 10 and 20 °C. Carbon dioxide production and O2 consumption of spinach leaves decreased in CA by about 50%, 40%, and 65% relative to those in air at 0, 10 and 20 °C, respectively. The rates in the different CA were similar. The respiratory quotient (RQ) of spinach leaves held in CA was slightly higher than that held in air at 0 and 20 °C. CA inhibited the growth of aerobic mesophilic bacteria and lactic acid bacteria at all temperatures, with the inhibition being greater in 6% or 10% CO2 with 0.5% O2. The ascorbic acid content at the end of storage was higher in spinach leaves held in air than in CA at all temperatures except 10% CO2 with 0.5% O2 at 20 °C. A slight or no off-odor was emitted by all spinach leaves. At 20 °C, spinach leaves held in 6% and 10% CO2 with 0.5% O2 developed more off-odor than those in air. These results indicate that the CA of 3%-10% CO2 and 0.5% O2 was beneficial in reducing respiration rate and microbial growth of spinach leaves at 0, 10, and 20 °C but accelerated ascorbic acid loss at all temperatures and induced off-odor at 20 °C.

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Hidemi Izumi, Alley E. Watada and Willard Douglas

`Marathon' broccoli (Brassica oleracea L. var. italica) florets were stored in air, low O2(0.25%, 0.5%, and 1 %) or high CO2(3%,6%, and 10%) at 0, 5, and 10C. Oxygen consumption and CO2 production were reduced under low O2 or high CO2atmosphere, the reduction being greater at lower O2 and higher CO2 levels. No differences were found in ethylene production among the different atmospheres. Low O2 and high CO2 retained color of broccoli florets to about the same extent at 10C but had no effect at 0 and 5C. Development of soft rot and browning was suppressed by low O2 or high CO2, but offensive off-odor occurred in 0.25%02 at all temperatures and 0.5% O2 at 10C. These results indicate that the best O2 and CO2 levels seem to be 0.5% O2 and 10% CO2 at 0 and 5C, and 1% O2 and 10% CO2 at 10C.

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Hidemi Izumi*, Moritoshi Tachibana, Chika Yamamoto and Mio Nagano

Fresh-cut cucumber slices were stored at 10 and 20 °C in high CO2 controlled atmospheres (5%, 10%, and 20%) or in MAP of OPP non-perforated and perforated with 50 micro m pores (P-plus) films. In CA storage, respiration rates and surface yellowing of slices were reduced by high CO2 atmospheres at 10°C, but increased with increasing CO2 levels at 20 °C. Counts of mesophiles, psychrotrophs and coliform group on slices stored at 10 °C were not affected by high CO2, except lactic acid bacteria, which the counts increased when stored in 20% CO2. At 20°C, all bacterial counts were higher with slices in 10% or 20% CO2 than those in air or 5% CO2. For MAP study, the used films were non-perforated OPP films (1170 mL/m2/day/atm, O2 permeability) and P-plus films having high (51000 and 74000 mL/m2/day/atm for storage at 10 and 20 °C, respectively) and low (17000 and 51000 mL/m2/day/atm for storage at 10 and 20 °C, respectively) O2 permeability. Cucumber slices were stored in MAP for 7 days at 10 °C and 2 days at 20 °C. The CO2 accumulated to 17.5% and 30% and O2 depleted to 2.5 and 3% at 10 and 20°C, respectively, in the non-perforated OPP film packages. Ethylene accumulated only in non-perforated OPP films at both temperatures. Growth of coliform group at 20 °C and lactic acid bacteria at 10 and 20 °C was greater in slices packaged in non-perforated OPP films than in P-plus films, while growth of mesophiles and psychrotrophs was similar in any packaging films. At the end of storage period, the bacteria isolated frequently from cucumber slices were Enterobacteriaceae and plant pathogenic bacteria. Lactic acid bacteria such as Leuconostoc citreum were detected on slices in non-perforated OPP films.