Microbial heat resistance of Listeria monocytogenes and the impact on ready-to-eat meat quality after post-package pasteurization

Several methods using bactericides, hydrostatic pressure, and post-package pasteurization technologies to control Listeria monocytogenes (LM) in ready-to-eat meats have been attempted. In addition to controlling LM contamination, any newly developed technology must have minimal effects on organoleptic properties. The objectives of this study were to: (1) determine the heat resistance of LM in two brands (A and B) of bologna differing in formulations, and, (2) evaluate the effects of post-package pasteurization on product quality. Fat content did not affect LM heat resistance in bologna at 55, 60, and 65 °C; however, Brand B bologna had a numerically lower inactivation rate. Microbial heat resistance differed (P < 0.05) with changes in pasteurization temperature. Time and temperature affected (P < 0.05) cook-loss and L^∗ Hunter color value for both bologna brands. These data show that post-package pasteurization is effective but suggest that meat formulations may need modification to prevent development of negative quality characteristics.     

辐照和巴氏杀菌对番茄果浆品质及微生物生长情况的影响

为了探索辐照剂量和巴氏杀菌对番茄果浆的品质和杀菌效果的影响,对番茄果浆进行1、2、3kGy的辐照和巴氏杀菌处理,分别考察处理后的番茄果浆在25℃下的总酸、总糖、pH、花青素、VC含量及大肠菌群数、菌落总数和霉菌总数的变化情况,由此得到最适宜的处理方式.结果表明:辐照处理和巴氏杀菌处理对番茄果浆均起到了较好的杀菌效果,且...     

低温杀菌对真空包装酱牛肉货架期及品质的影响

采用70～75℃或80～85℃的温度热处理30min,可以将酱牛肉中大部分腐败菌杀死,但芽孢尚能存活。低温杀菌以后,真空包装酱牛肉的货架期大大延长,但红度值有所下降。当加热处理温度提高时,在室温贮存时产品中芽孢杆菌的比例有所上升,乳酸菌的比例有所下降,而低温贮存抑制了芽孢杆菌的增殖。     

Possible implications of milk pasteurization on the manufacture and sensory quality of ripened cheese

Cheese made from raw milk represents an important proportion of the traditional cheeses, particularly in South European countries. Besides destruction of pathogenic bacteria, the most significant changes in milk relevant to cheesemaking, which are induced by pasteurization are:

• a partial elimination of the milk microorganisms which may grow in cheese during ripening,

• a partial or total activation or inhibition of the plasmin/plasminogen complex, cathepsin D, lipoprotein lipase and alkaline phosphatase. Enzymes from psychrotrophic bacteria, acid phosphatase and xanthine oxidase, which may be active during ripening, withstand pasteurization.,

• a slight (7%) denaturation of serum proteins and little or no modification of the cheesemaking properties (coagulation, acidification by lactic acid bacteria).

From experimental work carried out on several cheese varieties, comparing pasteurized or microfiltered milk and raw milk cheeses, it was found that facultatively heterofermentative lactobacilli, Micrococcaceae, enterococci, and propionibacteria in Swiss-type cheese, are found at higher levels in raw milk cheese. The main biochemical modification of cheese during ripening concerns the nature and extent of proteolysis. Although there is no clear trend in the breakdown of _s1- and β-caseins, milk pasteurization leads to a significant decrease of the amount of small peptides and free amino acids and to different HPLC profiles. Experiments carried out with sensory analysis show that, in all cases, pasteurized or microfiltered milk cheeses have received lower flavour intensity scores than raw milk cheeses. From this review, it is concluded that the indigenous milk microflora, with its diversity of species and strains, appears to be mainly responsible of the specific sensory properties of raw milk cheeses.     

Effect of combining nisin and/or lysozyme with in-package pasteurization for control of Listeria monocytogenes in ready-to-eat turkey bologna during refrigerated storage

This study investigated the efficacy of in-package pasteurization combined with pre-surface application of nisin and/or lysozyme to reduce and prevent the subsequent recovery and growth of Listeria monocytogenes during refrigerated storage on the surface of low-fat turkey bologna. Sterile bologna samples were treated with solutions of nisin (2 mg/ml=5000 AU/ml), lysozyme (10 mg/ml=80 AU/ml) and a mixture of nisin and lysozyme (2 mg nisin+10mg lysozyme/ml) before in-package pasteurization at 65 degrees C for 32s. In-package pasteurization resulted in an immediate 3.5-4.2 log CFU/cm(2) reduction in L. monocytogenes population for all treatments. All pasteurized treatments also resulted in a significant reduction of L. monocytogenes by 12 weeks compared to un-pasteurized bologna. In-package pasteurization in combination with nisin or nisin-lysozyme treatments was effective in reducing the population below detectable levels by 2-3 weeks of storage. Results from this study could have a significant impact for the industry since a reduction in bacterial population was achieved by a relatively short pasteurization time and antimicrobials reduced populations further during refrigerated storage.     

净菜商品化处理中品质变化及其控制的研究

净菜的生产和消费已成为现代社会发展的趋势,但其具有特殊的加工特点,品质维护难度很大,对净菜商品化处理过程中品质变化及其控制措施进行了论述。     

Postharvest ozone application for the preservation of fruits and vegetables

Vegetables and fruits have been recognized as a healthy and nutritive value food, with both a noticeable rise in consumption nowadays and greater frequency of foodborne illnesses associated with fresh produce. Current sanitation disinfectants fail to adequately control common spoilage microorganisms as well as potential harmful human pathogens. Alternative and effective disinfectants are being sought, with ozone being a viable alternative to traditional disinfectants. Despite the considerable commercial interest that ozone has attracted, several contradictions regarding the ozone efficiency are often found in the literature and further research is still needed to explore its potential application in the food industry as sanitizer.     

Microbial and sensory quality of vegetables for soup packaged in different atmospheres

Fresh prepacked vegetables for soup have become very popular on the Italian market, since they are already peeled, cut, washed and ready-to-use. The packaging and the modified atmosphere can prolong their shelf-life and maintain their hygienic, physicochemical and sensory characteristics during storage at + 4°C. The hygienic and sensory quality was evaluated by analysing microbial growth and atmosphere composition at the moment of packaging and at the end or the shelf-life of vegetables prepacked in air on under modified atmospheres, and by determining the browning or blackening of parsley and the loss of carrot exudates. A large number of different groups of microorganisms was found in raw vegetables. In spite of this high starting concentration of microbial flora, the prepackaging systems investigated did not seem to significantly influence their growth during vegetable storage at +4°C. No pathogenic microorganisms were isolated from the prepackaged vegetables. The hygienic quality was similar in all packaging systems used. However, the vegetables packaged in perforated. film kept their sensory characteristics better than those packaged in air or under a modified atmosphere.     

Nitrate-N determination in leafy vegetables: Study of the effects of cooking and freezing

Nitrate upon reduction to nitrite can cause methaemoglobinaemia or act as precursor in the endogenous formation of carcinogenic nitrosamines. The leafy vegetables are the major vehicle for the entry of nitrate into the human system. The present study was conducted to establish a flow injection analysis (FIA) technique to investigate the nitrate-N contents of four commonly consumed fresh leafy vegetables (Chinese cabbage, celery, lettuce and English cabbage) from market in Fiji. Two extraction techniques (activated carbon and alkaline extraction) were assessed to extract nitrate-N and the activated carbon extraction was preferred over alkaline extraction and applied. The recoveries of spiked nitrate-N in vegetable matrices ranged from 90.40% to 112.80% in activated carbon extraction with an average of 100.62%. The effects of cooking (boiling, baking and frying) and deep-freezing on the nitrate-N contents were also studied. Nitrate contents in selected leafy vegetables were determined by FIA coupled with Greiss protocol involving sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride as color reagents. Nitrate was determined in the linear range from 1.0 to 20.0 mg L⁻¹ with the method detection limit of 0.042 mg L⁻¹ (0.34 mg kg⁻¹). The results of the study show that nitrate contents in fresh leafy vegetables ranged from 1297 to 5658 mg kg⁻¹. Boiling reduces nitrate content by 47–56% whereas frying in Soya bean oil elevates nitrate content by as much as 159–307%. No significant change was observed in nitrate content after baking. The deep-freezing of the selected leafy vegetables shows that nitrate-N content fluctuates slightly from the original nitrate-N values over the seven day period. The FIA throughput was 38 samples h⁻¹.     

Effect of processing and storage conditions on the microbiological quality of minimally processed vegetables

The microbiological contamination of minimally processed vegetables was measured before and after processing and at different times and storage temperatures (5 and 10 days at 4 and 20 °C). To evaluate the efficacy of the overall process the water used for washing and rinsing the vegetables during the various phases of the operation were also examined. Thanks to the high quality of the vegetables at origin, simple chlorine treatment was sufficient to achieve a satisfactory reduction in coliforms, Escherichia coli, coliphages and saprophytic flora, thus ensuring that all of the freshly packed samples conformed to reference standards and guidelines. This conformity was maintained when the storage instructions indicated on the package (4 °C for 5 days) were followed. However, the persistence of faecal indicators after treatment suggested a potential risk of infection that could increase if the original contamination was higher. Microbiological examination of the water used for preliminary washing and for rinsing was seen to be useful in the assessment of the safety of the vegetables, at origin and after processing. The advantage of choosing coliphages for such monitoring is that they are indicators of viral contamination that can be measured rapidly. Critical points to be checked during the process are the levels of residual chlorine remaining in the washing tanks and the storage temperatures.     

Comparing equivalent thermal, high pressure and pulsed electric field processes for mild pasteurization of orange juice. Part I: Impact on overall quality attributes

Mild heat pasteurization, high pressure processing (HP) and pulsed electric field (PEF) processing of freshly squeezed orange juice were comparatively evaluated examining their impact on microbial load and quality parameters immediately after processing and during two months of storage. Microbial counts for treated juices were reduced beyond detectable levels immediately after processing and up to 2 months of refrigerated storage. Quality parameters such as pH, dry matter content and brix were not significantly different when comparing juices immediately after treatment and were, for all treatments, constant during storage time. Quality parameters related to pectinmethylesterase (PME) inactivation, like cloud stability and viscosity, were dependent on the specific treatments that were applied. Mild heat pasteurization was found to result in the most stable orange juice. Results for HP are nearly comparable to PEF except on cloud degradation, where a lower degradation rate was found for HP. For PEF, residual enzyme activity was clearly responsible for changes in viscosity and cloud stability during storage.

Industrial relevance

Development of mild processing technologies with a minimal impact on fruit juice can be considered as a true alternative of fresh fruit. The present work presents a fair comparison of mild heat treated, high pressure (HP) and pulsed electric field (PEF) processed orange juice as an alternative for thermal pasteurization. Orange juices were monitored during two months of storage.     

Nonthermal plasma for pesticide and microbial elimination on fruits and vegetables: an overview

Nonthermal plasma (NTP) is defined in terms of partly ionised gas which overall temperature is quite low because the stored energy is mostly in free electrons. Applications of NTP have been expanded to new areas of food applications such as the microbial inactivation and also the elimination of pesticide and toxic chemical residues in food such as fruits and vegetables while nutritional content and key characteristics are still preserved. Plasma treatment has successfully decreased the concentrations of pesticides by about 45‐71%. In this article, NTP technologies as well as investigations about applying of NTP for removing pesticide residues and improving microbial safety in fresh produce are described. Potential applications of NTP in food processing together with some of their challenges and limitations are also discussed.     

果蔬压差膨化过程中水分迁移的机理分析

水分的除去是食品干燥工业中最重要的指标之一,果蔬物料在干燥脱水中各工艺阶段的水分散失情况的确定,将有助于制定准确的工艺参数。果蔬压差膨化是一种新型的果蔬干燥工艺,通过以低温高压膨化设备为研究对象,根据其工艺参数并利用热力学相关定律,分析并计算出整个膨化操作过程中水分的迁移情况。结合示意图,给出了膨化过程中物料各阶段含水量。并根据分析,给出影响产品质量的冷凝水的处理方法,为果蔬压差膨化的工艺完善提供了理论基础。     

Anti-inflammatory effects of phytochemicals from fruits,vegetables, and food legumes: A review

Inflammation is the first biological response of the immune system to infection, injury or irritation. Evidence suggests that the anti-inflammatory effect is mediated through the regulation of various inflammatory cytokines, such as nitric oxide, interleukins, tumor necrosis factor alpha-α, interferon gamma-γ as well as noncytokine mediator, prostaglandin E₂. Fruits, vegetables, and food legumes contain high levels of phytochemicals that show anti-inflammatory effect, but their mechanisms of actions have not been completely identified. The aim of this paper was to summarize the recent investigations and findings regarding in vitro and animal model studies on the anti-inflammatory effects of fruits, vegetables, and food legumes. Specific cytokines released for specific type of physiological event might shed some light on the specific use of each source of phytochemicals that can benefit to counter the inflammatory response. As natural modulators of proinflammatory gene expressions, phytochemical from fruits, vegetables, and food legumes could be incorporated into novel bioactive anti-inflammatory formulations of various nutraceuticals and pharmaceuticals. Finally, these phytochemicals are discussed as the natural promotion strategy for the improvement of human health status. The phenolics and triterpenoids in fruits and vegetables showed higher anti-inflammatory activity than other compounds. In food legumes, lectins and peptides had anti-inflammatory activity in most cases. However, there are lack of human study data on the anti-inflammatory activity of phytochemicals from fruits, vegetables, and food legumes.     

Monitoring programme on nitrates in vegetables and vegetable-based baby foods marketed in the Region of Valencia,Spain: levels and estimated daily intake

This study was carried out to determine the current levels of nitrates in vegetables and vegetable-based baby foods (a total of 1150 samples) marketed in the Region of Valencia, Spain, over the period 2000–2008, and to estimate the toxicological risk associated with their intake. Average (median) levels of nitrate in lettuce, iceberg-type lettuce and spinach (1156, 798 and 1410 mg kg^?1 w/w, respectively) were lower than the maximum limits established by European Union legislation. Thirteen fresh spinach samples exceeded the regulatory limits. Median nitrate values in other vegetables for which a maximum limit has not been fixed by the European Commission were 196, 203, 1597, 96, 4474 and 2572 mg kg^?1 w/w (for potato, carrot, chard, artichoke, rucola and lamb's lettuce, respectively). The estimated nitrate daily intakes through vegetables consumption for adult, extreme consumers and children were found to be about 29%, 79.8% and 15.1%, respectively, of the acceptable daily intake (3.7 mg kg^?1). The levels (median = 60.4 mg kg^?1 w/w) found in vegetable-based baby foods were, in all cases, lower the maximum level proposed by European Union legislation. The estimated nitrate daily intake through baby foods for infants between 0–1 and 1–2 years of age were 13% and 18%, respectively, of the acceptable daily intake.     

Review: Modified Atmosphere Packaging and its effects on the microbiological quality and safety of produce

Modified Atmosphere Packaging and related technologies are increasingly used to extend shelf-life of fresh produce. This paper reviews the effect of such technology on the spoilage microbiological flora and food-borne pathogens which may be present in produce and also on the organoleptic properties of the product.     

Antioxidant potential,anti-proliferative activities,and phenolic content in water-soluble fractions of some commonly consumed vegetables: Effects of thermal treatment

Thermal treatments associated with food processing can alter the phenolic content of vegetables; yet, the biological properties associated with altered phenolic content have not been well delineated. We assessed the effects of various thermal treatments on total phenolic content, antioxidant and anti-proliferative activities of water-soluble fractions from six commonly consumed vegetables. Phenolic content in the water-soluble fraction of the tested vegetables was in the order of spinach > ‘komatsuna’ > ‘haruna’ > ‘chingensai’ > white cabbage > Chinese cabbage. Total antiradical activity against the DPPH radical was in the order of ‘komatsuna’ > spinach > ‘haruna’ > ‘chingensai’ > white cabbage > Chinese cabbage. Antiradical activity against hydroxyl radicals (deoxyribose assay) was highest for spinach and white cabbage. White cabbage extract showed the highest anti-proliferative activity in HL 60 cells. Normal cooking temperatures detrimentally affected phenolic content as well as antiradical and anti-proliferative activities of juice from most of the vegetables tested. However, mild heating of vegetable juices (50 °C, 10–30 min) preserved 80–100% of phenolic content, and both antioxidant activity and cell proliferation inhibition activities. The degree of thermal processing affects not only the content of phenolic compounds in vegetables but also beneficial biological effects associated with these compounds.     

低温在鲜切果蔬保鲜技术中研究进展

介绍了影响鲜切果蔬品质的因素、鲜切果蔬贮藏过程中发生的不良变化以及国内外对于低温在鲜切果蔬保鲜中的作用机理研究进展。     

Heat treatment of bovine colostrum. I: effects of temperature on viscosity and immunoglobulin G level

The objective of this study was to identify the critical temperature, at or below which heat-treatment of bovine colostrum would produce no significant changes in viscosity, IgG concentration, or Ig activity. Results of preliminary work, using a Rapid Visco Analyzer (RVA) to heat 50-mL aliquots from 6 unique batches of bovine colostrum at 59, 60, 61, 62, and 63°C, suggested that colostrum could be heated to 60°C for up to 120 min without changing viscosity or IgG concentration. This finding was confirmed by heating 50-mL aliquots from 30 unique batches of colostrum in an RVA for 120 min at 60 and 63°C. Heating colostrum to 63°C resulted in an estimated 34% decrease in IgG concentration and 33% increase in viscosity. However, there was no difference in IgG concentration between preheat-treated (73.4 ± 26.5 mg/mL) and post-heat-treated (74.5 ± 24.3 mg/mL) samples after heating colostrum to 60°C in an RVA for 120 min. Similarly, viscosity was unaffected after heating colostrum to 60°C in an RVA for 120 min. High quality colostrum (≥73.0 mg/mL) suffered greater losses of IgG and greater viscosity changes when heated to 63°C than did moderate quality colostrum (<73.0 mg/mL). However, the effects of colostrum quality were minor if high quality colostrum was only heated to 60°C. The results of a bovine viral diarrhea serum neutralization assay suggested that antibody activity was unchanged after heating colostrum to either 60 or 63°C. However, these results were interpreted as being inconclusive due to a high proportion of missing results because of the congealing of many samples after heat treatment. The results of this study indicate that 50-mL volumes of bovine colostrum can be heat treated at 60°C for up to 120 min in an RVA without affecting IgG concentration or viscosity.