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鲜切生菜在贮藏期间的微生物生长模型 总被引:12,自引:1,他引:12
主要研究了在 0℃、4℃和 2 5℃贮藏温度下鲜切生菜中细菌的生长趋势和感官质量的变化。研究结果表明 ,实验中所建立的Gompertz模型能有效地拟合在不同贮藏温度下鲜切生菜中细菌总数的动态变化 ,从而能预测不同贮藏温度下、不同贮藏时间内鲜切生菜中的细菌总数 ,为快速、有效地评估鲜切生菜的货架期和微生物安全性 ,提供了一个方便有效的方法。同时探讨了鲜切生菜中细菌总数与细胞组织腐烂的关系 ,即当细菌总数≤ 1 0 6 cfu/ g ,鲜切生菜的细胞组织不会腐烂。 相似文献
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A study was conducted to investigate the effects of various doses of irradiation on the quality of fresh-cut iceberg lettuce and to determine a suitable maximum dose. Fresh-cut iceberg lettuce packaged in film bags was exposed to 0, 1, 2, 3, and 4 kGy of gamma radiation and stored at 3 degrees C for 14 days. CO2 levels were higher and O2 levels were lower in packages containing irradiated lettuce than in those containing nonirradiated lettuce for most of the storage period. Comparison with nonirradiated lettuce indicated that total ascorbic acid (ascorbic acid plus dehydroascorbic acid) content and firmness were not significantly influenced by irradiation at 1 or 2 kGy. The overall visual appearance was best for lettuce irradiated at 1 or 2 kGy. This improved quality may be related to the high CO2 and low O2 levels observed for the irradiated samples. Electrolyte leakage for lettuce increased with higher radiation doses and was correlated (R2 = 0.99) with a soggy appearance. The leakage for lettuce irradiated at > or = 2 kGy was significantly more extensive than that for nonirradiated lettuce. The irradiation of fresh-cut lettuce in modified atmosphere packages at doses of 1 kGy and perhaps 2 kGy for safety enhancement and quality improvement is feasible. 相似文献
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An antibacterial treatment consisting of 2% hydrogen peroxide at 50 degrees C for 60 s was evaluated for its effects on the sensory quality of fresh-cut iceberg lettuce. Treated lettuce was packaged in polyethylene film by a protocol used in the fresh-cut produce industry and then stored along with untreated controls for 3, 10, and 15 days at 5 degrees C. Gas chromatographic analysis confirmed that the desired initial volume (approximately 6 liters) and oxygen gas content (approximately 10%) were maintained during storage. Consumers from the local community who were the primary shoppers for their households and who purchased and ate lettuce regularly evaluated the appearance, color, aroma, flavor, and texture of the lettuce and their overall liking of the lettuce. Forty consumers were recruited to evaluate processing replication 1 on 26 April, and another 40 were chosen to evaluate processing replication 2 on 3 May. Because replication differences were observed in instrumental color measurements and in mean sensory ratings, replications were not pooled for the two test dates. Lettuce purchased for processing replication 2 was considerably greener than that used in replication 1. Overall, the antibacterial treatment was more effective than the control treatment in maintaining sensory quality over 15 days of storage, provided that the lettuce was initially intensely green. Three-fourths of the participants indicated that they would be willing to buy precut packaged lettuce that had already been treated at the packinghouse or processing plant with an antibacterial solution, and of these participants, 62.5% indicated that they would be willing to pay 5 to 10 cents more per bag. 相似文献
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The fresh-cut fruit and vegetable industry is searching for alternatives to replace chemical treatments with biopreservative approaches that ensure the safety of the product and fulfil consumer preferences for minimally processed foods. In this study, the use of bacteriocins produced by lactic acid bacteria has been tested as a substitute for chemical disinfection of fresh-cut iceberg lettuce. First, the ability of several non-plant origin bacteriocinogenic strains (nisin Z(+), plantaricin C(+), lacticin 481(+), coagulin(+) or pediocin PA-1(+)) to grow in a lettuce extract at 4 degrees C, 10 degrees C and 32 degrees C was tested. All strains were able to grow, but bacteriocin production was predominantly detected at 32 degrees C. Addition of bacteriocinogenic supernatants (nisin(+), coagulin(+) and a nisin-coagulin(+) cocktail) to tryptic-soy agar plates inoculated with Listeria monocytogenes reduced Listeria counts by approximately 1-1.5 log units compared with the control plates without bacteriocin, after 48 h of storage at 4 degrees C. The effect of washing with bacteriocin-containing solutions on survival and proliferation of Listeria monocytogenes was also evaluated in fresh-cut lettuce packaged in macro-perforated polypropylene bags and stored for 7 days at 4 degrees C. Washing fresh-cut lettuce with these solutions decreased the viability of Listeria monocytogenes by 1.2-1.6 log units immediately after treatment, but, during storage at 4 degrees C, bacteriocin treatments only exerted minimal control over the growth of the pathogen. Natural microbiota were little affected by bacteriocins during storage. 相似文献
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Recent studies showed that sodium acid sulfate (SAS) and levulinic acid (LA) in combination with sodium dodecyl sulfate (SDS) was effective in inactivating human pathogens on Romaine lettuce. The present study investigated the effects of LA and SAS in combination with SDS (as compared with citric acid and chlorine) on the inactivation of E. coli O157:H7 and sensory quality of fresh-cut Iceberg lettuce in modified atmosphere packages during storage at 4 °C. Results showed that LA (0.5% to 3%) and SAS (0.25% to 0.75%) with 0.05% SDS caused detrimental effects on visual quality and texture of lettuce. LA- and SAS-treated samples were sensorially unacceptable due to development of sogginess and softening after 7 and 14 d storage. It appears that the combined treatments caused an increase in the respiration rate of fresh-cut lettuce as indicated by higher CO(2) and lower O(2) in modified atmosphere packages. On the positive side, the acid treatments inhibited cut edge browning of lettuce pieces developed during storage. LA (0.5%), SAS (0.25%), and citric acid (approximately 0.25%) in combination with SDS reduced population of E. coli OH157:H7 by 0.41, 0.87, and 0.58 log CFU/g, respectively, while chlorine achieved a reduction of 0.94 log CFU/g without damage to the lettuce. Therefore, compared to chlorine, LA and SAS in combination with SDS have limited commercial value for fresh-cut Iceberg lettuce due to quality deterioration during storage. 相似文献
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研究4℃、10% O2结合不同体积分数CO2(10%~50% CO2)处理对鲜切结球莴苣的主要品质和生理指标变化的影响。结果表明:高体积分数CO2导致了细胞膜通透性增加;10% O2+30% CO2气体组合显著抑制了多酚氧化酶、过氧化物酶和过氧化氢酶的活性,延缓了组织的衰老和褐变,并较好地保持了鲜切结球莴苣中叶绿素、VC和还原糖含量。感官评价结果表明,在10% O2+30% CO2气体组合条件下,鲜切结球莴苣贮藏15d仍具有商品价值。 相似文献
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This study determined the effects of mild heat and chlorine treatment followed by storage for up to 18 days at 5 degrees C or 7 days at 15 degrees C on the survival and growth of Escherichia coli O157:H7 inoculated onto fresh-cut iceberg lettuce. The efficacy of treatment with 20 ppm chlorine in killing the pathogen on lettuce at 50 degrees C was determined. Treatment of lettuce with 20 ppm chlorine at either 20 or 50 degrees C did not result in significantly greater reductions in populations of E. coli O157:H7 compared to respective treatments in water without chlorine. The pathogen steadily decreased in viability on treated lettuce throughout subsequent storage at 5 degrees C for 18 days. The population increased by 2.3 to 3.2 log10 CFU/g within 2 days, then continued to increase at a slower rate through 7 days of storage at 15 degrees C. At 4 and 7 days, significantly (alpha = 0.05) higher populations were reached on lettuce that had been treated at 50 degrees C, compared to respective samples that had been treated at 20 degrees C, regardless of the presence of 20 ppm chlorine in the treatment water. Treatment of lettuce with 20 ppm chlorine at 50 or 20 degrees C before or after inoculation with E. coli O157:H7 did not have a marked influence on behavior of the pathogen during subsequent storage at 5 or 15 degrees C. 相似文献
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Effects of storage temperature (1, 5, and 10 degrees C) on growth of microbial populations (total aerobic bacteria, coliform bacteria, Bacillus cereus, and psychrotrophic bacteria) on acidic electrolyzed water (AcEW)-treated fresh-cut lettuce and cabbage were determined. A modified Gompertz function was used to describe the kinetics of microbial growth. Growth data were analyzed using regression analysis to generate "best-fit" modified Gompertz equations, which were subsequently used to calculate lag time, exponential growth rate, and generation time. The data indicated that the growth kinetics of each bacterium were dependent on storage temperature, except at 1 degrees C storage. At 1 degrees C storage, no increases were observed in bacterial populations. Treatment of vegetables with AcEW produced a decrease in initial microbial populations. However, subsequent growth rates were higher than on nontreated vegetables. The recovery time required by the reduced microbial population to reach the initial (treated with tap water [TW]) population was also determined in this study, with the recovery time of the microbial population at 10 degrees C being <3 days. The benefits of reducing the initial microbial populations on fresh-cut vegetables were greatly affected by storage temperature. Results from this study could be used to predict microbial quality of fresh-cut lettuce and cabbage throughout their distribution. 相似文献
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The influence of ultrasound (US) treatment in combination with modified atmosphere packaging on microbial loads and quality attributes of fresh-cut lettuce was investigated during storage at 4 °C for up to 15 days. Fresh-cut lettuces were sonicated for different durations (0, 5, 10 and 15 min) by US (20 kHz, 226 W cm−2) and then packed in active modified atmosphere packaging (MAP). Results showed that US treatment combined with modified atmosphere effectively inhibited growth of bacteria, mold and yeast during storage. The US treatment for 10 min combined with MAP reduces mass losses and colour change, inhibits POD and PPO activities, conserves ascorbic acid and chlorophyll contents and maintains water distribution in fresh-cut lettuce. These results illustrated that US treatment combined with modified atmosphere was an effective preservation method to improve storage quality of fresh-cut lettuce. 相似文献
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Improving the microbial safety while maintaining quality of fresh fruits and vegetables will increase consumer confidence in fresh produce. This study was conducted to investigate the effects of irradiation at 1 kGy, a dose that potentially inactivates E. coli O157:H7 by 5 logs, on the quality of 13 common fresh-cut vegetables: iceberg, romaine, green and red leaf lettuce, spinach, tomato, cilantro, parsley, green onion, carrot, broccoli, red cabbage, and celery. The results showed that the appearance of irradiated samples was similar to the nonirradiated ones except that irradiated carrots, celery, cilantro, and green onions had higher appearance scores than corresponding nonirradiated vegetables. There was no difference in the instrumental texture between irradiated samples and nonirradiated ones. The aroma of several irradiated vegetables was significantly better than controls after 14-d storage, because these control samples decayed or senesced. The 1 kGy irradiation did not affect vitamin C content of most vegetables; however, irradiated green and red leaf lettuce had 24% to 53% lower vitamin C contents than the controls. Our results suggest that most fresh-cut fruits and vegetables tested can tolerate up to 1 kGy irradiation without significant losses in any of the quality attributes. 相似文献
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Cross-contamination of lettuce with Escherichia coli O157:H7 总被引:2,自引:0,他引:2
Contamination of produce by bacterial pathogens is an increasingly recognized problem. In March 1999, 72 patrons of a Nebraska restaurant were infected with enterohemorrhagic Escherichia coli (EHEC) O157:H7, and shredded iceberg lettuce was implicated as the food source. We simulated the restaurant's lettuce preparation procedure to determine the extent of possible EHEC cross-contamination and growth during handling. EHEC inoculation experiments were conducted to simulate the restaurant's cutting procedure and the subsequent storage of shredded lettuce in water in the refrigerator. All lettuce pieces were contaminated after 24 h of storage in inoculated water (2 x 10(9) CFU of EHEC per 3 liters of water) at room temperature or at 4 degrees C; EHEC levels associated with lettuce increased by > 1.5 logs on the second day of storage at 4 degrees C. All lettuce pieces were contaminated after 24 h of storage in water containing one inoculated lettuce piece (approximately 10(5) CFU of EHEC per lettuce piece) at both temperatures. The mixing of one inoculated dry lettuce piece with a large volume of dry lettuce, followed by storage at 4 degrees C or 25 degrees C for 20 h resulted in 100% contamination of the leaves tested. Microcolonies were observed on lettuce stored at 25 degrees C, while only single cells were seen on leaves stored at 4 degrees C, suggesting that bacterial growth had occurred at room temperature. Three water washes did not significantly decrease the number of contaminated leaves. Washing with 2,000 mg of calcium hypochlorite per liter significantly reduced the number of contaminated pieces but did not eliminate contamination on large numbers of leaves. Temperature abuse during storage at 25 degrees C for 20 h decreased the effectiveness of the calcium hypochlorite treatment, most likely because of bacterial growth during the storage period. These data indicate that storage of cut lettuce in water is not advisable and that strict attention must be paid to temperature control during the storage of cut lettuce. 相似文献
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研究60% O2+20% CO2+20% N2和100% O2高氧气调包装的鲜切莴苣在4℃贮藏14d期间抗氧化能力的变化,以空气包装的鲜切莴苣为对照。结果表明:高氧气调包装对鲜切莴苣的抗氧化活性有明显影响,60% O2+20% CO2+20% N2和100% O2高氧气调包装抑制了VC及其对DPPH自由基清除率的下降,促进类胡萝卜素及其对DPPH自由基清除率的下降,促进了多酚及其对DPPH自由基清除率的上升,从而抑制了鲜切莴苣抗氧化活性的下降。统计分析表明,VC与DPPH自由基清除能力间呈显著的线性正相关关系,相关系数为0.8745,说明高氧气调包装抑制鲜切莴苣抗氧化活性的下降与其抑制VC含量的下降有关。 相似文献
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Iceberg lettuce is a major component in vegetable salad and has been associated with many outbreaks of foodborne illnesses. In this study, several combinations of lactic acid and hydrogen peroxide were tested to obtain effective antibacterial activity without adverse effects on sensory characteristics. A five-strain mixture of Escherichia coli O157:H7, Salmonella enterica serotype Enteritidis, and Listeria monocytogenes was inoculated separately onto fresh-cut lettuce leaves, which were later treated with 1.5% lactic acid plus 1.5% hydrogen peroxide (H2O2) at 40 degrees C for 15 min, 1.5% lactic acid plus 2% H2O2 at 22 degrees C for 5 min, and 2% H2O2 at 50 degrees C for 60 or 90 s. Control lettuce leaves were treated with deionized water under the same conditions. A 4-log reduction was obtained for lettuce treated with the combinations of lactic acid and H2O2 for E. coli O157:H7 and Salmonella Enteritidis, and a 3-log reduction was obtained for L. monocytogenes. However, the sensory characteristics of lettuce were compromised by these treatments. The treatment of lettuce leaves with 2% H2O2 at 50 degrees C was effective not only in reducing pathogenic bacteria but also in maintaining good sensory quality for up to 15 days. A < or = 4-log reduction of E. coli O157:H7 and Salmonella Enteritidis was achieved with the 2% H2O2 treatment, whereas a 3-log reduction of L. monocytogenes was obtained. There was no significant difference (P > 0.05) between pathogen population reductions obtained with 2% H2O2 with 60- and 90-s exposure times. Hydrogen peroxide residue was undetectable (the minimum level of sensitivity was 2 ppm) on lettuce surfaces after the treated lettuce was rinsed with cold water and centrifuged with a salad spinner. Hence, the treatment of lettuce with 2% H2O2 at 50 degrees C for 60 s is effective in initially reducing substantial populations of foodborne pathogens and maintaining high product quality. 相似文献