用ORP监控鲜切果蔬臭氧水消毒的实验研究

研究了用氧化还原电位(ORP)监控臭氧水对鲜切果蔬的消毒灭菌过程,通过不同ORP的臭氧水消毒实验发现,将鲜切果蔬浸入ORP超过800mV的臭氧水中超过30s可以使细菌总数下降约2个数量级。通过改变臭氧浓度和水温的方法研究了臭氧水ORP的影响因素,得出了提高臭氧气体浓度和低温制冷有利于制取高ORP臭氧水的结论。结果表明,利用ORP监测臭氧水的消毒能力是可行的。     

Performance study of analytical method for ethoxyquin in fruit

A performance study of an analytical method of ethoxyquin (ET) in apples and pears was conducted. In the proposed method, the sample was homogenized with thiourea and ET was extracted with acetone instead of hexane used in the official analytical method for ET, in order to improve the extraction efficiency. Furthermore, dibutyl hydroxytoluene was added in the test solution to prevent the decomposition of ET. For evaluation of the method. ET spiked into apples and pears at the level of 0.2 microgram/g was determined in replicate in six laboratories. Mean recoveries from apple, pear and Japanese pear were 85.3, 83.0 and 83.9%, respectively. Repeatability relative standard deviation values were 3.8-4.7% and reproducibility relative standard deviation values were 7.8-11.3%. The detection limits were 0.001-0.025 microgram/g in the six laboratories; this value may reflect instrument performance. ET spiked into apples and pears at the level of 0.2 microgram/g was detected by both LC/MS and GC/MS.     

Control of foodborne pathogens on fresh-cut fruit by a novel strain of Pseudomonas graminis

The consumption of fresh-cut fruit has substantially risen over the last few years, leading to an increase in the number of outbreaks associated with fruit. Moreover, consumers are currently demanding wholesome, fresh-like, safe foods without added chemicals. As a response, the aim of this study was to determine if the naturally occurring microorganisms on fruit are “competitive with” or “antagonistic to” potentially encountered pathogens. Of the 97 and 107 isolates tested by co-inoculation with Escherichia coli O157:H7, Salmonella and Listeria innocua on fresh-cut apple and peach, respectively, and stored at 20 °C, seven showed a strong antagonistic capacity (more than 1-log unit reduction). One of the isolates, CPA-7, achieved the best reduction values (from 2.8 to 5.9-log units) and was the only isolate able to inhibit E. coli O157:H7 at refrigeration temperatures on both fruits. Therefore, CPA-7 was selected for further assays. Dose-response assays showed that CPA-7 should be present in at least the same amount as the pathogen to adequately reduce the numbers of the pathogen. From the results obtained in in vitro assays, competition seemed to be CPA-7's mode of action against E. coli O157:H7. The CPA-7 strain was identified as Pseudomonas graminis. Thus, the results support the potential use of CPA-7 as a bioprotective agent against foodborne pathogens in minimally processed fruit.     

A bacteriophage JN02 infecting multidrug-resistant Shiga toxin-producing Escherichia coli: isolation,characterisation and application as a biocontrol agent in foods

Bacteriophages are increasingly considered as novel biocontrol agents against Multidrug-resistant (MDR) Shiga toxin-producing Escherichia coli (STEC). In this study, a virulent phage JN02 capable of infecting MDR STEC was isolated, characterised and evaluating its efficacy in reducing MDR STEC in foods. One-step growth and stability assay showed that JN02 had a relatively short latent period (15 min), large burst sizes (69 PFU/cell), and high physicochemical stability (temperature (30–60°C), pH (2–11), 0.1%, 1% pig bile salt, biocides and food additives (100% chloroform, 0.1% acetic acid, 1% potassium sorbate). In spot tests, 18 E. coli strains were sensitive to JN02. In efficiency of plating (EOP), 4 E. coli strains were sensitive to JN02. Electron microscopy and genome sequencing showed that JN02 belongs to the family Myoviridae. Importantly, no known virulence-associated, lysogenic and antibiotic genes were identified in the genome of JN02. Viable cell counts of MDR STEC were significantly (P < 0.05) reduced in milk (no viable counts) and beef samples (1.0–1.9 log₁₀ CFU cm⁻² reduction) when treated with JN02 at 4 °C. The results indicated that JN02 might be a new potential natural biological control agent for MDR STEC in foods.     

Distribution of salmonella strains in farrow-to-finish pig herds: a longitudinal study

The aims of this study were to investigate patterns of Salmonella shedding in finishing pigs and to study the role of the sow in the transmission of Salmonella to her offspring. In each of the three herds (A, B, and C), one cohort of sows (n = 34, n = 40, n = 32, respectively) together with three piglets of their offspring (n = 102, n = 120, n = 96, respectively) were selected. Individual fecal and blood samples were taken from the sows at different times during one production cycle and from the piglets from weaning until slaughter. At slaughter, contents from the jejunum, colon, and mesenteric lymph nodes were collected. Fecal samples, as well as the jejunum, colon, and mesenteric lymph node samples collected at slaughter, were submitted to a qualitative Salmonella analysis. Isolates were characterized by random amplified polymorphic DNA, and if necessary, further characterization was done by pulsed-field gel electrophoresis. In herds A and B, Salmonella shedding began in the nursery. A significant increase in the number of Salmonella shedders was seen after transferring pigs to the growing unit in herd B (P = 0.003) and to the finishing unit in herds A (P < 0.001) and B (P = 0.013). None of the fattening pigs in herd C were shedding Salmonella. This study reveals that transferring pigs is an important trigger to induce Salmonella shedding, leading to horizontal spread. Direct transmission of Salmonella from the sows to their piglets could not be demonstrated, but the similarities between the isolates found in the sows and those found during the nursery and finishing periods and at slaughter suggested indirect transmission.     

茉莉酸甲酯预处理对鲜切火龙果品质和 抗氧化活性的影响

目的研究茉莉酸甲酯(Me JA)预处理对鲜切火龙果在10℃,4 d贮藏期间品质和抗氧化活性的影响。方法完整火龙果先用浓度分别为0、1、10和100μmol/L的Me JA熏蒸,再进行鲜切处理,测定其贮藏期间的品质和理化指标。结果 100μmol/L的Me JA熏蒸处理能最显著地诱导鲜切火龙果贮藏期间总酚、总黄酮等次级代谢产物的积累,提高鲜切火龙果贮藏期间DPPH自由基清除能力。Me JA预处理能有效地促进鲜切火龙果贮藏期间超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽还原酶(GR)等抗氧化酶活性的提高。同时,Me JA预处理抑制了可滴定酸(TA)含量的下降,对可溶性固形物(TSS)、维生素C含量无不良影响。结论 100μmol/L的Me JA预处理能较好地保持鲜切火龙果的品质,并有效地提高其抗氧化能力,最终提高鲜切火龙果的营养品质。     

超高压对鲜切猕猴桃果片多聚半乳糖醛酸酶及品质的影响

采用超高压处理对鲜切猕猴桃片进行保鲜,研究了超高压处理对贮藏期间多聚半乳糖醛酸酶活性、果片硬度、可溶性果胶和VC含量的影响。研究结果表明:猕猴桃片采用600MPa压力、30℃下加压10min后,在4℃条件下贮藏9d,与未超高压处理的对照组相比,超高压处理的鲜切猕猴桃片多聚半乳糖醛酸酶活性较低,果片硬度、可溶性果胶含量、VC含量和可溶性果胶变化不显著;600MPa超高压处理可通过抑制多聚半乳糖醛酸酶活性而维持果片硬度,同时可有效控制VC的损失。     

基于核酸适体微球的沙门氏菌检测方法研究

目的:研究基于核酸适体的微球芯片系统应用于沙门氏菌检测的可行性。方法:采用偶联有沙门氏菌适体的微球作为载体,以荧光作为检测信号建立微球芯片体系,并优化影响检测结果的各项因素。结果:通过此方法检测20份水产样品,6份检出沙门氏菌,检出率为30%。结论:建立的检测体系能实现对沙门氏菌的快速,准确的检测,且具有较高的特异性。      

Effect of drying method on the sorption characteristics of model fruit powders

Pectin-sugar gels were dehydrated with four different drying methods: freeze, microwave, vacuum and conventional drying to a moisture content of about 5%. The effect of the drying method on the water sorption properties of dehydrated products was evaluated at 25 °C. Freeze-dried gel adsorbed more water vapour than microwave-dried gel, which had a higher sorption capacity than vacuum- and conventional-dried product. The sorption isotherms were in agreement with the reported shape for high sugar foodstuffs. Three different equations proposed in the literature (GAB, Oswin, Hasley) were used to fit the sorption data. The GAB equation gave the best fit to the experimental data. The porosity of the dehydrated products depended on the drying method, ranging between 0.2 and 0.5. Freeze- and vacuum-dried pectin developed the highest porosity, whereas the lowest porosity was obtained using conventional and microwave drying. Hunter colour parameters (L, a, b) also depended on the drying method. The colour of freeze- and vacuum-dried pectin was close to that of commercial pectin, while the colour of the conventional- and microwave-dried product changed significantly.     

鲜切藕片褐变程度的数学模型研究

利用测色色差计,研究了鲜切藕片在贮藏过程中的褐变程度和各色泽参数间的变化以及各色泽参数与鲜切藕片褐变程度之间的相关关系.研究结果表明:L*、b*、DL*、Db*、DE*、C*值与鲜切藕片褐变程度之间呈一定的相关性;L*、DL*、b*、DE*、C*的显著性水平为P<0.01,Db *显著性水平为P<0.05,a*、Da*、h与褐变程度的相关性不显著(P0.05);其中,DL*值与褐变程度的相关性系数最大,其线性回归方程为Y=-0.469X-11.688(R2=0.953),通过该方程预测的褐变程度与实际的褐变程度基本一致,表明该方程可应用于对鲜切藕片褐变程度的判断分级.     

Effect of hot water and hydrogen peroxide treatments on survival of salmonella and microbial quality of whole and fresh-cut cantaloupe

Cantaloupe melon has been associated with outbreaks of salmonellosis. Contamination might be introduced into the flesh from the rind by cutting or by contact of cut pieces with contaminated rinds. Our objectives were to investigate the efficacy of hot water or hot 5% hydrogen peroxide treatments in reducing the population of native microflora and inoculated Salmonella on cantaloupe rind and transfer to fresh-cut tissue during cutting. Whole cantaloupes, inoculated with a cocktail of Salmonella serovars to give 4.6 log CFU/cm2 and stored at 5 or 20 degrees C for up to 5 days, were treated with hot water (70 or 97 degrees C) or 5% hydrogen peroxide (70 degrees C) for 1 min at 0, 1, 3, or 5 days postinoculation. Aerobic mesophilic bacteria and yeast and mold on treated whole melon and fresh-cut pieces were significantly (P < 0.05) reduced by all three treatments. Treatments with hot water (70 and 97 degrees C) caused a 2.0- and 3.4-log CFU/cm2 reduction of Salmonella on whole cantaloupe surfaces irrespective of days of postinoculation storage prior to treatment up to 5 days at 5 or 20 degrees C, respectively. Treatment with 5% hydrogen peroxide (70 degrees C) caused a 3.8-log CFU/cm2 reduction of Salmonella. Fresh-cut pieces prepared from untreated inoculated melons and those treated with 70 degrees C hot water were positive for Salmonella. However, fresh-cut pieces prepared from inoculated whole melon dipped in water (97 degrees C) or hydrogen peroxide (70 degrees C) for 60 s were negative for Salmonella, as determined by dilution plating onto agar medium, but were positive after enrichment at days 3 and 5 of storage at 5 degrees C. The ability to detect Salmonella in fresh-cut pieces was dependent on the initial level of inoculation. The results of this study indicate that the use of hot water (97 degrees C) or heated hydrogen peroxide to reduce the population of Salmonella on contaminated whole cantaloupes will enhance the microbial safety of the fresh-cut product.     

Partial characterization and in vitro evaluation of a lytic bacteriophage for biocontrol of Campylobacter jejuni in mutton and chicken meat

Campylobacter jejuni is a major foodborne pathogen causing acute bacterial enteritis worldwide. Screening of novel bacteriophages as biocontrol tools to eliminate C. jejuni in food during pre- and postharvest is an emerging research field. In this study, we partially characterized C. jejuni bacteriophage CJ01 for potential use as biocontrol agent. Transmission electron microscopy revealed bacteriophage CJ01 belonged to the Myoviridae family with a genome size of approximately 136 kb. The results of host range assay revealed CJ01 was able to infect C. jejuni and C. lari strains, with burst size about 35 phages per infected cell and latent period of 30 min. The effectiveness of bacteriophage CJ01 (with 100 multiplicity of infection = 100) was determined in mutton and chicken meat artificially contaminated with C. jejuni. The amount of C. jejuni in treated mutton and chicken meat were significantly reduced by 1.70 log CFU/g and 1.68 log CFU/g, respectively, after 48 hr stored at refrigeration temperature (4°C). The data presented here suggest that bacteriophage CJ01 can be used as a postharvest biocontrol agent.     

鲜切马铃薯褐变程度数学模型研究

利用测色色差仪,研究鲜切马铃薯经保鲜处理后在不同贮藏温度下贮藏过程中色差值的变化及其与褐变程度的关系,建立褐变程度数学模型.研究结果表明:贮藏温度愈高、贮藏时间愈长,褐变愈严重,总色差值△E愈大,且△E3.5可作为评断鲜切马铃薯是否具有商品性的界限值.实验中所建立的二元二次方程Y=-0.00095A2-0.26B2+0.0145AB +0.059A+ 1.572B-0.563,经验证实验表明可用于预测不同贮藏温度、不同贮藏时间内鲜切马铃薯的褐变程度,从而为鲜切马铃薯的快速分级,提供一个方便有效的方法.     

鲜切马铃薯褐变程度数学模型研究

利用测色色差仪,研究鲜切马铃薯经保鲜处理后在不同贮藏温度下贮藏过程中色差值的变化及其与褐变程度的关系,建立褐变程度数学模型。研究结果表明:贮藏温度愈高、贮藏时间愈长,褐变愈严重,总色差值ΔE愈大,且ΔE3.5可作为评断鲜切马铃薯是否具有商品性的界限值。实验中所建立的二元二次方程Y=-0.00095A2-0.26B2+0.0145AB+0.059A+1.572B-0.563,经验证实验表明可用于预测不同贮藏温度、不同贮藏时间内鲜切马铃薯的褐变程度,从而为鲜切马铃薯的快速分级,提供一个方便有效的方法。      

Calculation method for designing a multi-plate freeze-concentrator for concentration of fruit juices

The aim of this work is to establish a calculation method for designing and sizing of equipment for film freeze-concentration of fruit juices. The various steps are outlined of an algorithm that uses the characteristics of the juice as inputs.The calculation method assumes that the amount of fruit juice, its concentration (^°Brix), and its sugar composition (% of fructose, glucose and sucrose) are known. Using pre-set (constant) values for the flow of concentrated juice and for the heat flow, the algorithm predicts the values of the main unknowns: the concentration of impurities in the ice, the concentration of sugars in the final concentrate, the heat-exchange surface needed, the amount of ice obtained, and the duration of the concentration step.Using this calculation method, one can estimate the size of the equipment and its operational costs, which can be used to analyse the economic viability compared to alternative processes.     

Effect of hot water surface pasteurization of whole fruit on shelf life and quality of fresh-cut cantaloupe

ABSTRACT:  Cantaloupes are associated with recent outbreaks of foodborne illnesses and recalls. Therefore, new approaches are needed for sanitization of whole and cut fruit. In the present study, whole cantaloupes were submerged into water in the following 3 conditions: 10 °C water for 20 min (control), 20 ppm chlorine at 10 °C for 20 min, and 76 °C water for 3 min. Populations of microflora were measured on the rinds of the whole cantaloupes. Quality and microbial populations of fresh-cut cantaloupes prepared from whole fruit were analyzed after 1, 6, 8, 10, 13, 16, and 20 d of storage at 4 °C. The hot water significantly reduced both total plate count (TPC) and yeast and mold count on rind of whole fruits while chlorine or cold water wash did not result in a significant reduction of microbial population. Fresh-cut pieces prepared from hot water-treated cantaloupes had lower TPC than the other 2 treatments in the later storage periods (days 13 to 20) in 2 of 3 trials. The hot water treatment of whole fruits was inconsistent in reducing yeast and mold count of fresh-cut pieces. Soluble solids content, ascorbic acid content, fluid loss, and aroma and appearance scores were not consistently affected by either hot water or chlorine treatment. Our results suggested that hot water pasteurization of whole cantaloupes frequently resulted in lower TPCs of fresh-cut fruit during storage and did not negatively affect quality of fresh-cut cantaloupes.     

荔枝的冷却方式选择

通过比较真空预冷、水冷和强制通风对荔枝的冷却效果,选择出它的最佳冷却方式。结果表明,真空预冷、水冷却和强制通风都适用于荔枝;而用冷水对荔枝冷却时,在指定时间内的终温最低,能满足正常商业需求,因此,水冷应为荔枝的最佳冷却方式。