PA/PE复合膜对鲜切莴笋保鲜效果的影响

为了验证尼龙-聚乙烯（polyamide/polyethylene,PA/PE）复合膜对鲜切莴笋的保鲜效果,将新鲜莴笋切片真空包装后在4 ℃条件下冷藏,不加任何包装的鲜切莴笋同样条件下作空白对照。贮藏期间评价菌落总数、色差、pH值、汁液流失率、VC含量、感官等指标。结果PA/PE组贮藏期达24 d,而不加包装的对照组只有4 d。可见对于鲜切莴笋的贮藏,PA/PE复合膜结合真空包装可明显延长其贮藏期。     

Effect of gamma irradiation on microbial growth and sensory quality of fresh-cut lettuce

Fresh-cut lettuce was irradiated and microbiological and sensory quality was examined during storage at 4 degrees C. Experimental results showed that the number of aerobic mesophilic bacteria on fresh-cut lettuce irradiated with 1.0 kGy was reduced by 2.35 logs and sensory quality was maintained best during storage for 8 days at 4 degrees C. It was indicated that Gompertz model could predict the bacterial number on fresh-cut lettuce if the initial level was known.     

Growth and bacteriocin production by lactic acid bacteria in vegetable broth and their effectiveness at reducing Listeria monocytogenes in vitro and in fresh-cut lettuce

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.     

EHA/PE高阻隔复合膜对鲜切莴笋保鲜效果的影响

为了考察EHA/PE高阻隔复合膜对鲜切莴笋的保鲜效果,采用EHA/PE复合膜真空包装鲜切莴笋,以相同条件处理但不加任何包装的鲜切莴笋作为对照,并于(5±2)℃下冷藏,贮藏期间定期测定菌落总数、色差、p H、汁液流失率、VC、感官评分等指标。结果表明:EHA/PE复合膜包装莴笋的各项指标均显著优于对照组(p<0.05)。未加包装的莴笋在4 d时感官状态已不能接受,菌落总数达(5.91±0.12)CFU,而EHA/PE组感官状态可保持16 d,且第18 d时菌落总数仅为5.69 CFU,水分流失率在16 d时仍小于1.5%,VC含量始终大于5 mg/100 g。可见,EHA/PE高阻隔复合膜可明显延长鲜切莴笋的贮藏期。      

超声-次氯酸钠-植酸联合处理提高鲜切生菜的保鲜效果

本文从自来水、超声波、微酸性电解水、超声波结合微酸性电解水、超声波结合植酸、次氯酸钠结合植酸、超声-次氯酸钠-微酸性电解水联合处理和超声-次氯酸钠-植酸联合处理8种方法中选出对鲜切生菜清洗后抑菌效果最好的方法超声-次氯酸钠-植酸联合处理,测定该方法处理后的鲜切生菜在贮藏期间的品质指标,以无菌蒸馏水作为对照。探讨超声-次氯酸钠-植酸联合处理对鲜切生菜表面大肠杆菌O157:H7抑菌效果和贮藏品质的影响。结果表明,超声-次氯酸钠-植酸联合处理的抑菌效果最好,抑菌率达到99.97%。处理后的鲜切生菜在贮藏第14 d,质量损失率为3.45%,总色差为5.39,Vc含量为2.93 mg/100 g,叶绿素含量为0.56 mg/g,水分含量为90.54%,均优于对照组;与对照组相比,过氧化物酶和多酚氧化酶活性被有效抑制,总酚含量保持较高的水平。因此,超声-次氯酸钠-植酸联合处理有利于提高鲜切生菜表面大肠杆菌O157:H7的抑菌效果和改善鲜切生菜的贮藏品质。综上表明,超声-次氯酸钠-植酸联合处理可以有效提高鲜切生菜的保鲜效果,延长货架期。     

臭氧水处理鲜切生菜贮藏期间的品质变化

研究了臭氧水处理鲜切生菜在 4℃贮藏期间的细菌总数、大肠菌群、PPO活性、Vc含量、失重率和感官质量的变化。试验结果表明 ,与对照相比 ,采用 0 1 8μg/L臭氧水处理可使鲜切生菜中细菌总数下将 1 5个数量级、大肠菌群数低于 3 0× 1 0 - 2 /g ,PPO活性被抑制、Vc损失减少 ,失重率降低 ,同时 ,贮藏至 9天 ,感官质量明显优于对照组。     

含钙离子壳聚糖涂膜对鲜切莴苣的保鲜性研究

制备氯化钙(CaCl2)质量浓度分别为0、2 g/100 mL、4 g/100 mL、6 g/100 mL的壳聚糖/CaCl2溶液,将其对鲜切莴苣进行涂膜处理,考察该膜对鲜切莴苣的保鲜性。结果发现,随着贮藏期延长,壳聚糖/CaCl2涂膜能一定程度的保持鲜切莴苣的感官品质、抑制色度,失重率、硬度和VC含量下降,从而延长鲜切莴苣的货架寿命。结果表明,CaCl2质量浓度为4 g/100 mL的壳聚糖涂液处理的鲜切莴苣的各项指标最好,使鲜切莴苣的保质期延长到2 d。     

清洗方式对鲜切生菜保鲜效果的影响

以静电水、臭氧水、次氯酸钠水、电解水、自来水对生菜切割后进行处理,研究不同处理方式对贮藏过程中其品质变化的影响。结果表明,这5种处理方式对鲜切生菜失重率的影响不大;臭氧水、次氯酸钠水、电解水处理能够显著延缓鲜切生菜VC、叶绿素含量的下降,在贮藏过程中保持了较好的感官品质。在上述5种处理方式中臭氧水对后期的保鲜效果最佳,是切割蔬菜贮藏前推荐的处理方式,鲜切菜产品贮藏到第12天仍有商品价值。     

Allicin Inhibits Microbial Growth and Oxidative Browning of Fresh-Cut Lettuce (Lactuca sativa) During Refrigerated Storage

Fresh-cut lettuce has a short shelf life since it is very perishable and susceptible to enzymatic browning. The aim of this study was to examine the effectiveness of allicin treatment in prolonging the shelf life of fresh-cut lettuce (Lactuca sativa L. var. angustana Irish). Fresh-cut lettuce slices were treated with water (control), 0.2 and 1 % of allicin solutions, respectively, and stored at 4 °C, >90 % relative humidity. Sensory parameters, microbiological indicators, and physiological indices were determined at 0, 2, 4, and 6 days of storage. The sensory analyses revealed that allicin inhibited the color change and maintained the visual quality of lettuce slice without impairing flavor. Allicin treatment delayed microbial growth at cold storage, as evidenced by the lowered total viable counts (decreased by 2.52 log cfu/g) and yeast and mold counts (decreased by 1.59 log cfu/g) after 6 days in 1 % allicin-treated samples compared to control samples. In addition, differences between lettuce treated with 1 % allicin and control slices in objective color (total color change, chrome, and hue angle), total phenolic compounds and quinones content, activities of browning-related enzymes, and antioxidative enzymes suggested that allicin had antioxidative properties. Conclusively, it was demonstrated for the first time that allicin effectively protected fresh-cut lettuce from tissue browning and microbiological spoilage. These findings indicate that allicin has great potential as a natural additive to extend the shelf life of fresh-cut lettuce.     

高氧气调包装对鲜切莴苣抗氧化活性的影响

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。     

鲜切生菜在贮藏期间的微生物生长模型

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。     

Consumer acceptance of raw apples treated with an antibacterial solution designed for home use.

An antibacterial treatment consisting of 1.5% lactic acid plus 1.5% hydrogen peroxide at 40 degrees C for 15 min was effective in reducing foodborne bacterial pathogens on raw apples. However, the effects of this treatment on an apple's sensory characteristics and the extent of consumers' willingness to use the treatment at home were not known. This study was undertaken to determine the sensory acceptability and chemical characteristics (pH, soluble solids, and total acidity) of apples subjected to the sanitizing treatment and to obtain information on consumers' purchase behavior, apple handling and consumption practices, and willingness to use an antibacterial treatment. Untrained consumers (n = 80) evaluated the appearance, color, aroma, flavor, texture, and overall appeal of untreated (control) and treated Red Delicious apples that had been stored at 5 degrees C for 0, 6, and 10 days. Panelists used a nine-point hedonic scale (1 = "dislike extremely"; 5 = "neither like nor dislike"; 9 = "like extremely") to evaluate sensory acceptability. Treatment and storage had no significant effect on the appearance, color, or aroma of the samples. Flavor ratings ranged from 6.2 ("like slightly") to 7.0 ("like moderately"). There was no significant difference among any of the control and treated apples stored for 0 days or among those stored for 6 days. Although apples stored for 10 days received the lowest ratings (6.2 to 6.3), they still had an acceptable flavor (6, "like slightly"), and panelists could not perceive differences between the control samples and the treated samples on day 10. The same trends were noted in texture ratings and in overall liking ratings. Treatment and storage had a minimal effect on pH (range, 3.96 to 4.02), soluble solids (range, 11.8 to 12.9 degrees Brix), and total acidity (range, 0.20 to 0.23% malic acid), which are important for apple flavor. Many consumers (87%) were concerned about fruit safety, and 53.2% were willing to try an antibacterial treatment at home. However, 74% would not be willing to use it if a 15-min heating-and-soaking step were required. Implementation of the treatment may be more feasible in the packinghouse than in the home.     

高氧气调包装对鲜切莴苣呼吸和酶活性的影响

以空气包装的鲜切莴苣为对照,研究了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期间呼吸强度和酶活性的变化。结果表明:高氧气调包装对鲜切莴苣呼吸和酶活性影响显著,60%O2﹢20%CO2﹢20%N2和100%O2高氧气调包装显著抑制鲜切莴苣的呼吸,且100%O2气调包装的抑制效果优于60%O2﹢20%CO2﹢20%N2气调包装;60%O2﹢20%CO2﹢20%N2和100%O2高氧气调包装促进SOD酶活性的上升、抑制O2-.生成量的增加和PPO、PAL酶活性的上升。     

Slicing under chlorinated water improves the disinfection of fresh-cut romaine lettuce

The aim of this study was to determine whether the timing or mode of application influences the antimicrobial efficacy of a sodium hypochlorite solution against microorganisms on fresh-cut Romaine lettuce. Lettuce leaves were treated with a solution of sodium hypochlorite containing 70 mg liter(-1) free chlorine prior to slicing (WLS), while submerged in the solution (CWS), or after slicing (PCS), the last being common practice in the fresh-cut industry. Immediate antimicrobial effects were determined from analyses performed directly after treatment, while delayed effects were derived from analysis of packaged samples stored at 4 and 15°C. Experiments were performed with both uninoculated and inoculated whole leaves, using Escherichia coli O157:H7 from a type collection as an inoculum. The CWS treatment provided the greatest initial reductions in aerobic plate counts of E. coli O157:H7 populations, followed by PCS and WLS. The advantage afforded by the CWS approach was maintained over 10 days in storage at 4°C. In addition, it was noted that the visual quality attributes of the fresh-cut lettuce from the CWS approach were better than those from the other two treatments. These results collectively suggest that slicing lettuce under a sanitizer solution could provide better disinfection of fresh-cut Romaine lettuce than the current practice of washing with sanitizer after cutting has taken place.     

Sensorial and chemical quality of gamma-irradiated fresh-cut iceberg lettuce in modified atmosphere packages

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.     

高压对鲜切生菜感官品质的影响

以结球生菜为材料,研究高压处理(50～200MPa处理1～20min)对鲜切生菜感官品质(褐变、水浸、香气、质地、味道)的影响,采用灰色关联度分析方法进行综合评价。结果表明：高压处理对鲜切生菜的感官品质产生不同的影响。50MPa、5min高压处理的鲜切生菜的感官质量与理想感官质量性状的灰色关联度最大,该处理改善了鲜切生菜的感官品质,口感更甜;随着压力的增大、处理时间的延长,鲜切生菜的感官品质变差,200MPa处理20min的鲜切生菜出现异味、高韧度、严重水浸与褐变。     

Combination of hot-water surface pasteurization of whole fruit and low-dose gamma irradiation of fresh-cut cantaloupe

Improvements in methods for disinfecting fresh-cut cantaloupe could reduce spoilage losses and reduce the risk of foodborne illness from human pathogen contamination. The objective of this study was to investigate the feasibility of using hot-water treatment in combination with low-dose irradiation to reduce native microbial populations while maintaining the quality of fresh-cut cantaloupe. Whole cantaloupes were washed in tap water at 20 or 76 degrees C for 3 min. Fresh-cut cantaloupe cubes, prepared from the washed fruit, were then packaged in clamshell containers, and half the samples were exposed to 0.5 kGy of gamma radiation. Native microflora populations and sensory qualities were evaluated during the subsequent 7 days of storage at 4 degrees C. The hot-water surface pasteurization reduced the microflora population by 3.3 log on the surface of whole fruits, resulting in a lower microbial load on the fresh-cut cubes compared with cubes cut from fruit treated with cold water. Irradiation of cubes prepared from untreated fruit to an absorbed dose of 0.5 kGy achieved a low microbial load similar to that of cubes prepared from hot-water-treated fruit. The combination of the two treatments was able to further reduce the microflora population. During storage, the headspace atmosphere of the packages was not significantly influenced by any of the treatments. Color, titratable acidity, pH, ascorbic acid, firmness, and drip loss were not consistently affected by treatment with irradiation, hot water, or the combination of the two. Cubes prepared from hot-water-treated whole fruit had slightly lower soluble solids content. The combination of hot-water pasteurization of whole cantaloupe and low-dose irradiation of packaged fresh-cut melon can reduce the population of native microflora while maintaining the quality of this product.     

Behavior of Listeria monocytogenes and Aeromonas spp. on fresh-cut produce packaged under equilibrium-modified atmosphere.

Storage experiments were conducted to follow the behavior of pathogens on fresh-cut vegetables (trimmed brussels sprouts, grated carrots, shredded iceberg lettuce, and shredded chicory endives) packaged under an equilibrium-modified atmosphere (EMA) (2 to 3% O2, 2 to 3% CO2, and 94 to 96% N2) and stored at 7 degrees C. As a comparison, fresh-cut vegetables were also packaged in a perforated high-barrier film (air conditions) and stored at 7 degrees C. In a first step, the shelf life of the vegetables in the two kinds of packages was determined by evaluating the microbiological quality as well as the sensorial quality (appearance, taste, and odor). In general, sensorial properties were faster in limiting the shelf life than microbiological criteria. The shelf life of the vegetables stored under an EMA was extended by 50% or more, compared with the air-stored vegetables. In a second storage experiment, the four fresh-cut vegetables were inoculated with a cocktail of psychrotrophic pathogens (Listeria monocytogenes, Aeromonas caviae [HG4]) and A. bestiarum (HG2) before packaging under an EMA and air at 7 degrees C. The inoculated pathogens were more influenced by the type of vegetable than by the type of atmosphere. No growth was detected on the brussels sprouts or on carrots (L. monocytogenes). Aeromonas spp. had a higher growth rate than L. monocytogenes on the shredded chicory endives and shredded iceberg lettuce at 7 degrees C.     

Survival and growth of Escherichia coli O157:H7 inoculated onto cut lettuce before or after heating in chlorinated water, followed by storage at 5 or 15 degrees C

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.     

ACCEPTABILITY OF LETTUCE TREATED WITH A LACTIC ACID AND HYDROGEN PEROXIDE ANTIBACTERIAL SOLUTION

Whole iceberg lettuce heads were treated with 1.5% lactic acid plus 2.0% hydrogen peroxide solution (antibacterial solution) at 22C for 5 min. They were then either rinsed by immersing in running tap water for 5 min or neutralized with 2.5% sodium bicarbonate solution at 22C for 5 min followed by rinsing (immersion in running tap water) for 10 min, draining, and storing in sealed plastic containers at 5C for 0, 6, and 10 days along with untreated controls. The antibacterial treatment resulted in marginally acceptable lettuce at day 0; neutralization resulted in acceptable lettuce at day 0 but unacceptable after 6 and 10 days. Consumers indicated willingness to purchase an antibacterial solution to treat lettuce at home as well as lettuce pretreated at the packinghouse/processing plant; they were willing to pay at least 3 to 5 cents more per head for pretreated lettuce. Antibacterial treatment plus neutralization provided acceptable lettuce if used in less than 6 days.