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。     

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。     

臭氧结合超声协同低浓度次氯酸钠复合处理对冰鲜鸡腿的保鲜效果

为降低肉鸡宰后鸡体表面初始菌数,延长冰鲜鸡货架期,探究臭氧水处理（ozone,OZ）、超声协同次氯酸钠处理（ultrasound assisted sodium hypochlorite,SH-US）、臭氧结合超声协同低浓度次氯酸钠复合处理（ultrasound assisted sodium hypochlorite and ozone,SH-US-OZ）3种减菌方式对鸡腿表面减菌效果和对其托盘包装贮藏期间保鲜效果的影响。结果表明,3种减菌处理均可以显著降低冰鲜鸡腿表面初始微生物数量（P<0.05）,其中,SH-US-OZ复合处理减菌效果最好。该处理将初始菌落总数从5.72(lg(CFU/g))降低到4.25(lg(CFU/g)),减菌率为96.6%,有效延缓了微生物在贮藏期间的生长速率、提升了鸡腿贮藏期间的表面亮度值和感官品质、减少了贮藏损失和挥发性盐基氮含量。虽然该复合处理组增加了脂质氧化程度、降低了表面红度值,但未引起感官劣变。因此,SH-US-OZ复合处理在减少次氯酸钠使用的基础上具有显著的减菌和保鲜效果,有效保持鸡腿贮藏期间的品质,将货架期延长至5 d以上。     

臭氧水处理结合气调包装对鲜切生菜保鲜效果的影响

研究臭氧水处理结合气调包装对鲜切生菜在4℃贮藏下的保鲜效果。结果表明,臭氧水处理结合气调包装相比于对照组可以有效抑制鲜切生菜组织中细菌的生长繁殖、水分的流失、叶的降解以及多酚氧化酶的活性,降低鲜切生菜腐败、萎蔫、黄化、褐变的速度,维持鲜切生菜的感官品质,同时也有效抑制了鲜切生菜中VC的氧化分解,延长了货架期,使鲜切生菜在贮藏第14天仍具商品价值。另外,研究结果显示在适当低浓度(5%~10%)的O2和CO2比例范围内,经过长时间(6d以上)贮藏后,不同的气调比例对鲜切生菜品质没有显著的影响。     

不同清洗方式对青椒保鲜效果的影响

以青椒为对象,采用自来水、臭氧水、次氯酸钠、二氧化氯和超声波对青椒进行清洗,研究不同清洗方式对青椒保鲜效果的影响。贮藏期间,每2 d测定失重率、可滴定酸含量、可溶性固形物含量、抗坏血酸含量、叶绿素含量和菌落总数等指标。结果表明,臭氧水、次氯酸钠、二氧化氯和超声波清洗能使青椒在贮藏过程中保持较好的感官品质,减缓营养物质可溶性固形物、叶绿素、抗坏血酸含量的下降,抑制可滴定酸含量和细菌菌落总数的增加。5种清洗方式中,使用臭氧水清洗对青椒的保鲜效果最佳,贮藏至10 d仍有商品价值和食用价值,可用于青椒保鲜。     

超声波处理结合纳米包装对鲜切生菜品质的影响

运用超声波清洗结合纳米包装技术对鲜切生菜进行保鲜贮藏,通过测定贮藏期间生菜的主要品质、生理和微生物指标以探讨其保鲜作用。结果表明,纳米包装在抑制生菜质量损失,保持叶绿素、还原糖、VC含量方面效果都要优于超声波作用,而超声波处理（240 W、10 min、20 ℃）在抑制生菜酶活和表面微生物上的作用要较纳米包装好;超声波处理结合纳米包装对生菜的保鲜效果最佳,能够降低质量损失率,较好地保叶绿素和还原糖含量,控制微生物的生长,抑制多酚氧化酶和过氧化物酶活性,从而延缓衰老和褐变。经感官评定发现,超声波处理结合纳米包装的鲜切生菜在（4±0.5）℃、相对湿度85%～95%的贮藏环境中贮藏15 d后仍有商品价值。     

清洗方式对空心菜采后保鲜效果的影响

以空心菜为对象,研究不同清洗方式(次氯酸钠溶液,有效氯浓度为100 mg/L;臭氧水,活性氧浓度1. 8 mg/L;超声波清洗,40 Hz、0. 33 W/cm~2)对空心菜采后贮藏保鲜效果的影响。结果表明,这3种清洗处理有利于保持空心菜的感官品质,维持较低的菌落总数水平,延缓叶绿素、Vc等含量下降,其中臭氧水清洗保鲜效果最好,相对于对照组货架期有效地延长了3 d。     

现代果蔬贮藏保鲜技术研究进展

综述了国内外有关果蔬贮藏保鲜的新技术及研究进展情况,包括天然果蔬保鲜剂的应用、利用调压技术贮藏、臭氧及负氧离子保鲜、利用生物技术保鲜、静电场处理贮藏、低剂量辐射处理和紫外线处理保鲜以及细胞水结构化气调保鲜等国内外近几年发展起来的现代果蔬贮藏保鲜技术.     

超市销售条件下贮藏温度对洁净生菜保鲜效果的影响

本试验研究了模拟超市销售条件下生菜的贮藏与保鲜,超市生菜保鲜和贮藏夏天用的是(22±2)℃,冬天用的是(17±2)℃。结果表明,塑料薄膜包装的生菜低温(17±2)℃下贮藏,可以降低生菜的呼吸强度和蒸腾作用,减少还原糖、抗坏血酸、和叶绿素含量的损失,从而有利于生菜品质的保持和货架期的延长。     

臭氧对冷却肉的保鲜效果

通过实验测定冷却猪肉在贮藏期间的感官品质、微生物和理化指标来评价臭氧的保鲜效果，结果表明，臭氧处理可有效地改善冷却猪肉在贮藏期的保鲜效果，且对冷却猪肉的保鲜效果随其浓度的增加而增加，臭氧的有效保鲜浓度为4mg／L。     

Elimination by ozone of Shigella sonnei in shredded lettuce and water

Several outbreaks of shigellosis have been attributed to the consumption of contaminated fresh-cut vegetables. The minimal processing of these products make it difficult to ensure that fresh produce is safe for consumer. Chlorine-based agents have been often used to sanitize produce and reduce microbial populations in water applied during processing operations. However, the limited efficacy of chlorine-based agents and the production of chlorinated organic compounds with potential carcinogenic action have created the need to investigate the effectiveness of new decontamination techniques. In this study, the ability of ozone to inactivate S. sonnei inoculated on shredded lettuce and in water was evaluated. Furthermore, several disinfection kinetic models were considered to predict S. sonnei inactivation with ozone. Treatments with ozone (1.6 and 2.2 ppm) for 1 min decreased S. sonnei population in water by 3.7 and 5.6 log cfu mL(-1), respectively. Additionally, it was found that S. sonnei growth in nutrient broth was affected by ozone treatments. After 5.4 ppm ozone dose, lag-phases were longer for injured cells recovered at 10 degrees C than 37 degrees C. Furthermore, treated cells recovered in nutrient broth at 10 degrees C were unable to grow after 16.5 ppm ozone dose. Finally, after 5 min, S. sonnei counts were reduced by 0.9 and 1.4 log units in those shredded lettuce samples washed with 2 ppm of ozonated water with or without UV-C activation, respectively. In addition, S. sonnei counts were reduced by 1.8 log units in lettuce treated with 5 ppm for 5 min. Therefore, ozone can be an alternative treatment to chlorine for disinfection of wash water and for reduction of microbial population on fresh produce due to it decomposes to nontoxic products.     

新型鸡肉制品防腐保鲜剂研究

通过多种防腐保鲜方法的综合使用,尽量少地破坏鸡肉原有的风味口感和营养成分,并达到保鲜的效果。对大肠杆菌以及总菌数进行检测,得出以下结论:通过臭氧杀菌和乳酸链球菌素等多种保鲜手段的综合运用,可以在降低杀菌温度的同时保证杀菌效果。     

Ozone inactivation of norovirus surrogates on fresh produce

Preharvest contamination of produce by foodborne viruses can occur through a variety of agents, including animal feces/manures, soil, irrigation water, animals, and human handling. Problems of contamination are magnified by potential countrywide distribution. Postharvest processing of produce can involve spraying, washing, or immersion into water with disinfectants; however, disinfectants, including chlorine, have varying effects on viruses and harmful by-products pose a concern. The use of ozone as a disinfectant in produce washes has shown great promise for bacterial pathogens, but limited research exists on its efficacy on viruses. This study compares ozone inactivation of human norovirus surrogates (feline calicivirus [FCV] and murine norovirus [MNV]) on produce (green onions and lettuce) and in sterile water. Green onions and lettuce inoculated with FCV or MNV were treated with ozone (6.25 ppm) for 0.5- to 10-min time intervals. Infectivity was determined by 50% tissue culture infectious dose (TCID(50)) and plaque assay for FCV and MNV, respectively. After 5 min of ozone treatment, >6 log TCID(50)/ml of FCV was inactivated in water and ～2-log TCID(50)/ml on lettuce and green onions. MNV inoculated onto green onions and lettuce showed a >2-log reduction after 1 min of ozone treatment. The food matrix played the largest role in protection against ozone inactivation. These results indicate that ozone is an alternative method to reduce viral contamination on the surface of fresh produce.     

Bactericidal effects of lettuce after subsequent washing with hypobromous acid and sodium hypochlorite

Sodium hypochlorite (NaClO) is widely used as a sanitizer to maintain microbial safety of lettuce; however, NaClO treatment is insufficient on pathogen reduction due to its high instability for an extended storage time. Hypobromous acid (HOBr) as another sanitizer, relatively stable in processing conditions, was applied to lettuce. The numbers of total aerobic bacteria, Escherichia coli, Salmonella Typhimurium, and Staphylococcus aureus were evaluated on lettuce treated with NaClO and HOBr. The population of 4 selected bacteria on lettuce reduced more than 2.5 log CFU/g. Bactericidal effect maintained for 10 days in combined treatment with 100 mg/L NaClO followed by 200 mg/L HOBr, while the population of the bacteria without HOBr treatment increased. Combined treatment on lettuce can give synergistic effect on reducing microbial population. Residual bromine was not detected on the lettuce treated with HOBr after washed with water for 30 s, indicating that bromine was effectively washed away.     

USE OF OZONE TO INACTIVATE MICROORGANISMS ON LETTUCE

When ozone (1.3 mM) was bubbled for 3 min in a mixture of shredded lettuce and water, counts ofmesophilic andpsychrotrophic bacteria decreased 1.4 and 1.8 log₁₀ cfu/g, respectively. Counts of these microorganisms on lettuce, from a different batch, decreased 3.9 and 4.6 log, respectively, during 5 min of ozone treatment. Shredded lettuce was treated with gaseous ozone, or mixed with aqueous solution of ozone (1:20 w/w) with or without bubbles. For effective delivery of ozone, stirring (low and high speed), sonication or stomaching was applied during the ozonation. Washing the lettuce with water only decreased total count on shredded lettuce by 0.74–1.0 log cfu/g. When lettuce in a treatment chamber was flushed with gaseous ozone, the total count decreased 0.85 log cfu/g, but when vacuum was applied before the ozone flush, the total count decreased 0.96 log cfu/g. Bubbling ozone in water-lettuce mixture while sonicating, high-speed stirring, or before stomaching inactivated 1.4, 1.9 and 1.9 log cfu/g, respectively. In conclusion, bubbling gaseous ozone in water is the most effective ozonation method. Efficient ozone delivery to microorganisms on lettuce requires a combination of ozone bubbling and high-speed stir.     

Effect of ozone and calcium lactate treatments on browning and texture properties of fresh‐cut lettuce

The effects of three treatments, 1 mg L^?1 ozone at 18–20 °C, 15 g L^?1 calcium lactate (CLac) at 50 °C and a combination thereof, were compared on fresh‐cut lettuce over 10 days of refrigerated storage. Respiration rate, browning and texture were examined as main quality indicators. The use of ozone produced a significantly (P < 0.05) higher oxygen decline than the use of CLac (from day 3 to day 10). At the end of storage, CLac (alone or combined with ozone) samples had higher oxygen content (～9%) than ozone samples (～6%). Enzymatic activity decreased significantly (P < 0.05) in ozone samples. Polyphenol oxidase activity in fresh‐cut lettuce treated with ozone (alone or combined with CLac) showed lower values on day 1 (<2500 units g^?1) and at the end of storage (<3000 units g^?1) than CLac samples (4000–4800 units g^?1). Ozone also reduced peroxidase activity to ～300 units g^?1 after treatment. Finally, pectin methylesterase activity was also reduced with ozone, showing a negative effect on textural properties. Data suggested that CLac maintained quality markers better than treatments with ozone and ozone/CLac combination over 10 days of storage. Copyright © 2006 Society of Chemical Industry     

INFLUENCE OF CUT AND PACKAGING FILM ON SENSORY QUALITY OF FRESH-CUT BUTTERHEAD LETTUCE (LACTUCA SATIVA L., CV. WANG)

ABSTRACT

The purpose of the present work was to study the influence of cut (manual and using a sharp knife) and packaging film (bioriented polypropylene and polyolefin PD‐961) on the sensory quality of fresh‐cut butterhead lettuce stored under passive modified atmosphere at 5C. Results showed that lettuce cut by hand had a lower respiration rate and deterioration rate than those cut with a knife. This difference could be attributed to a difference in the level of wounding, which can be explained by the fact that cutting by hand caused the tear to follow the naturally weaker areas of the lettuce, leading to less tissue damage than that engendered by the use of a sharp knife.

PRACTICAL APPLICATIONS

Results suggest that lettuce leaves cut by hand showed a lower sensory deterioration rate than those cut with a sharp knife. While not industrially applicable, the cutting of lettuce by hand might be appealing to small ventures such as buffets, restaurants and catering services. The sensory analysis carried out suggests that the use of polyolefin PD‐961 is preferred over bioriented polypropylene for packaging fresh‐cut lettuce, in view of achieving a better quality of the produce.     

Decontamination of lettuce using acidic electrolyzed water

The disinfectant effect of acidic electrolyzed water (AcEW), ozonated water, and sodium hypochlorite (NaOCl) solution on lettuce was examined. AcEW (pH 2.6; oxidation reduction potential, 1140 mV; 30 ppm of available chlorine) and NaOCl solution (150 ppm of available chlorine) reduced viable aerobes in lettuce by 2 log CFU/g within 10 min. For lettuce washed in alkaline electrolyzed water (AIEW) for 1 min and then disinfected in AcEW for 1 min, viable aerobes were reduced by 2 log CFU/g. On the other hand, ozonated water containing 5 ppm of ozone reduced viable aerobes in lettuce 1.5 log CFU/g within 10 min. It was discovered that AcEW showed a higher disinfectant effect than did ozonated water significantly at P < 0.05. It was confirmed by swabbing test that AcEW, ozonated water, and NaOCI solution removed aerobic bacteria, coliform bacteria, molds, and yeasts on the surface of lettuce. Therefore, residual microorganisms after the decontamination of lettuce were either in the inside of the cellular tissue, such as the stomata, or making biofilm on the surface of lettuce. Biofilms were observed by a scanning electron microscope on the surface of the lettuce treated with AcEW. Moreover, it was shown that the spores of bacteria on the surface were not removed by any treatment in this study. However, it was also observed that the surface structure of lettuce was not damaged by any treatment in this study. Thus, the use of AcEW for decontamination of fresh lettuce was suggested to be an effective means of controlling microorganisms.     

Ozone and Chlorine Treatment of Minimally Processed Lettuce

ABSTRACT The objectives of this research were to determine the effectiveness of ozone in combination with chlorine on the microbiological and sensory attributes of lettuce as well as the quality of the water used for processing commercial lettuce salad. Iceberg lettuce was inoculated with 8.0 log CFU/g microorganisms isolated from spoiling lettuce, treated with combinations of chlorine and ozone, and analyzed microbiologically. Commercial salads rinsed with chlorine, ozone, or a mixture were evaluated for sensory acceptability. Chlorine, ozone, and chlorine-ozone reduced aerobic plate count up to 1.4, 1.1, and 2.5 log, respectively. As determined by appearance, commercial lettuce salads treated with chlorine, ozone, or a combination had a shelf life of 16, 20, or 25 d, respectively. Using an ozone-chlorine or ozone rinse for commercial lettuce salads, there were no visible turbidity changes in process water. The quality of the water remained constant for longer periods of time making it available for longer reuse. Therefore, chlorine-ozone combinations may have beneficial effects on the shelf life and quality of lettuce salads as well as on the water used for rinsing or cleaning the lettuce.