Matrix effects on the antimicrobial capacity of silver based nanocomposite absorbing materials

The suitability of cellulose/silver nanocomposites to decrease the microbial loads in absorbent materials was studied during the shelf-life of minimally processed foods. Cellulose/silver nanocomposites were synthesised by means of reduction by UV/heat of silver nitrate adsorbed on fluff pulp cellulose fibres. Minimally processed fruits and meat products were packaged in trays containing commercial absorbent pads or silver loaded absorbers, and stored during 10 days at 4 °C. The synthesised antimicrobial nanocomposites were useful to control the population of spoilage-related microorganisms in absorbent pads, being particularly effective in contact with low-protein food products. In contact with silver loaded absorbers, counts of total viable microorganisms and yeasts and moulds were reduced up to 99.9% in juices from kiwi fruit and melon; in drip from poultry and beef meat, microbial loads (total viable counts, lactic acid bacteria) were constantly 90% below the controls. Consequently, silver based absorbent materials could be especially designed to improve hygienic conditions during the manipulation and storage of minimally processed fruit cuts and meat products, but matrix effects must be taken into account.     

Behaviour of Brochothrix thermosphacta in presence of other meat spoilage microbial groups

The microbial flora of fresh meat stored aerobically at 5 degrees C up to spoilage was enumerated and collected in order to have mixed spoilage bacterial groups to be used in competition tests against Brochothrix thermosphacta. The bacterial groups collected as bulk colonies were identified by PCR-DGGE followed by partial 16S rDNA sequencing. The predominant bacteria associated with the spoilage of the refrigerated beef were B. thermosphacta, Pseudomonas spp, Enterobacteriaceae and lactic acid bacteria (LAB). The interactions between B. thermosphacta and the other spoilage microbial groups were studied in vitro at 5 degrees C. The results showed that a decrease of the growth of B. thermosphacta was evidenced in presence of LAB at 5 degrees C while the bacterium is the dominant organism when inoculated with mixtures of Pseudomonas spp., LAB and Enterobacteriaceae. A better understanding of bacterial meat spoilage interactions may lead to improved quality of fresh meat stored in refrigerated conditions.     

冷藏温度下真空包装牛肉微生物及品质变化

为研究真空包装冷却牛肉贮藏过程中微生物和各品质指标的变化,确定理化指标和微生物指标的相关性,测定了于4℃贮藏的真空包装冷却牛肉在0、7、13、21、28、38 d的菌落总数、乳酸菌、假单胞菌、热杀索丝菌、肠杆菌5个微生物指标及pH值、挥发性盐基氮、系水力和色差值4个品质指标的变化情况,并确定了各指标随贮藏时间的动态变化规律及相关性。结果表明,在贮藏期间,菌落总数和乳酸菌的变化趋势相同,假单胞菌、热杀索丝菌和肠杆菌等生长迅速;pH值为先下降后上升趋势;色差值a*值、C*ab初期上升,后期小幅下降;挥发性盐基氮值初期平稳上升,后期快速增大;系水力逐步上升。菌落总数与乳酸菌呈现极显著相关的关系(P<0.01),与挥发性盐基氮值、a*值、b*值、C*ab及系水力显著相关(P<0.05)。由此可知,微生物的生长引起牛肉品质变化,挥发性盐基氮值、a*值、b*值、C*ab可以作为判断真空包装牛肉腐败指标。     

Lactic Acid Concentration and Microbial Spoilage in Anaerobically and Aerobically Stored Ground Beef

Lactic acid concentration of coarsely ground beef, packaged in low oxygen permeability casings, is inversely related to sensory acceptability of the meat following regrinding and aerobic storage for six additional days. Samples, reground and stored aerobically after periods of anaerobic storage, were assayed for total aerobic bacterial counts, percentage of gram-positive microflora, and pH. Lactic acid concentration ranged from 130 to 1055 mg per 100g ground beef and increased with anaerobic storage. During 6 days of aerobic storage, both increases and decreases in concentration were noted and related to changes in microbial flora. A positive correlation was found between the proportion of gram-positive bacteria (lactic acid bacteria) and lactic acid and pH.     

生鲜牛肉中的腐败微生物概述

生鲜牛肉腐败是一个涉及多种特定微生物相互作用并受多种因素影响的复杂的微生物生态现象。了解牛 肉中微生物的污染源及微生物的多样性对于控制其腐败进程、延长牛肉货架期十分重要。因此,本文对肉牛从 下刀宰杀到包装前所有可能的污染源、污染微生物在种的水平上的分类和多样性、单个菌属及多种微生物作用的 腐败机制等方面对生鲜牛肉中腐败微生物的相关信息进行了系统性分析,初步总结得出活体动物的皮毛及皮毛上 的污染物、去皮用的刀具和剥皮操作工人的手、分割时的工作接触面为生鲜牛肉中微生物的主要污染源;主要 的微生物种类为假单胞菌（Pseudomonas）、肠杆菌（Enterobacteriaceae）、乳酸杆菌及热杀索丝菌（Brochothrix thermosphacta）;不同种类的微生物因利用肉中营养代谢底物的顺序不同而产生不同的腐败现象。期望通过本文的 总结和概述能够为生鲜牛肉腐败微生物的控制提供理论指导。     

Shelf life of fresh foal meat under MAP, overwrap and vacuum packaging conditions

The objective of this study was to investigate the physico-chemical properties, the microbial counts and the sensory properties' changes of foal steaks packed under various conditions. The experimental packaging systems were: (i) vacuum packaging (VP), (ii) overwrap packaging and (iii) two modified atmosphere packaging methods (MAP): high O(2) MAP (80% O(2)+20% CO(2)) and low O(2) MAP (30% O(2)+70% CO(2)). The meat was stored at 2°C during 14days and tested for pH, colour, lipid and protein oxidation, microbial counts and sensory assessment of odour, colour and appearance. Of the two MAP, overwrap and VP, both MAP were the most effective treatments for the inhibition of the total viable counts (TVC), Pseudomonas spp., psychrotrophic aerobic bacteria, lactic acid bacteria, Enterobacteriaceae as well as moulds and yeast. According to the sensory evaluation, foal steaks packed under overwrap and MAP treatments resulted unacceptable after 7days of storage, whereas the vacuum-packed meat was still acceptable. Moreover, the redness value decreased significantly (P<0.001) with all treatments during the storage time, except for the vacuum packs, which increased significantly (P<0.001). Finally, foal steaks from overwrap packaging and MAP conditions had a greater increase of TBAR'S values and carbonyl content during the storage time. High O(2) levels affected foal meat quality negatively, while anaerobic conditions extended the meat's shelf life up to 14days.     

STRATEGIES FOR PROLONGING THE SHELF LIFE OF MINCED BEEF PATTIES

The study of different strategies for prolonging the shelf life of fresh minced beef patties was addressed in this work. Fresh minced beef was supplemented with thymol (THY) at levels of 250, 500 and 750 mg per kg of ground beef. Treated samples were packed using a high barrier film and stored in refrigerated conditions (4C) under ordinary atmosphere packaging and modified atmosphere packaging (MAP) conditions for 16 days. The microbiological quality decay kinetic was determined by monitoring the following microorganisms: Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria, Brochothrix thermosphacta, coliforms and total psychrotrophic viable count. Results show that THY, working alone, was effective on coliforms and Enterobacteriaceae, whereas it does not seem to inhibit to a great extent the growth of the other microbial populations. On the other hand, an increased amount of THY, under MAP conditions, had better effects on the product quality, with a consequent prolongation of the shelf life.

PRACTICAL APPLICATIONS

Great interest is developing in food bio-preservation, because of the ever-increasing needs to protect consumers' health and to valorize the naturalness and safety of food products. However, very few works have been carried out on the applications of bio-preservatives to extend the shelf life of fresh meat products. This study, therefore, was mainly initiated to evaluate the possibility of extending the shelf life of packed fresh meat patties by a combination of thymol (THY) to other extrinsic factors such as storage temperatures and modified atmosphere during packaging. Interesting results were obtained suggesting that THY can perform an efficient synergy with modified atmosphere conditions and could be advantageously utilized by the meat industry.     

Microbial shelf life determination of vacuum-packaged fresh beef treated with polylactic acid, lactic acid, and nisin solutions.

The effectiveness of polylactic acid, lactic acid, nisin, and combinations of the acids and nisin on extending the shelf-life of raw beef was determined. Fresh beef pieces (5 by 5 by 2.5 cm) were dipped in a solution of 2% low molecular weight polylactic acid (LMW-PLA), 2% lactic acid (LA), 200 IU of nisin per ml, or the combinations of nisin in either 2% LMW-PLA or 2% LA. The samples were then drip-dried, vacuum-packaged, and stored at 4 degrees C for up to 56 days. The beef surface pH values and numbers of psychrotrophic aerobic bacteria, psychrotrophic and mesophilic Enterobacteriaceae, Pseudomonas, and Lactobacillus were determined weekly for 56 days. The average surface pH values of the beef samples treated with 2% LMW-PLA or the combination of 200 IU of nisin per ml and 2% LMW-PLA were significantly reduced to 5.19 and 5.17, respectively, at day 0 (P < or = 0.05), while those decontaminated with 2% LA or 200 IU of nisin per ml in 2% LA solution were significantly decreased from 5.62 to 4.98 and 4.96, respectively. The 2% LMW-PLA, 2% LA, or the combinations of each acid and nisin showed immediate inhibitory effects on psychrotrophic aerobic bacteria (1.94, 2.36, 2.59, and 1.76 log reduction, respectively), psychrotrophic Enterobacteriaceae (1.37, 1.86, 1.77, and 1.35 log reduction, respectively), mesophilic Enterobacteriaceae (1.00, 1.00, 0.82, and 0.68 log reduction, respectively), and Pseudomonas (1.77, 1.57, 1.76, and 1.41 log reduction, respectively) on fresh beef (P < or = 0.05). The reduction was evident up to 56 days as seen by the numbers of Enterobacteriaceae and Pseudomonas (P < or = 0.05). Because there was no interaction between treatments and storage times, the data in each period were combined and presented as effect of treatments on overall microbial counts of fresh beef. It was found that 2% LMW-PLA, 2% LA, and the combinations of each acid and nisin significantly lowered the population of the above organisms compared with the untreated control, water, or nisin alone (P < or = 0.05).     

冷鲜牛肉贮藏中菌群结构及优势菌致腐性的分析

为探究牛肉在0?℃冷藏下微生物菌群变化和优势腐败菌,采用培养依赖的16S rRNA结合高通量测序技术分析牛肉样品的微生物多样性变化。通过定期测定接种牛肉汁的生长、感官、蛋白酶活性、pH值和挥发性盐基氮（total volatile basic nitrogen,TVB-N）值,分析分离株的致腐特征。结果表明,牛肉冷藏中感官品质保持良好,15?d出现异味,18?d有腐臭味。而样品中菌落总数第3天快速上升,15?d菌落总数为8.73（lg（CFU/g））,之后呈现稳定,假单胞菌（Pseudomonas spp.）、热死环丝菌（Brochothrix thermosphacta）、肠杆菌（Enterobacter）和乳酸菌4 种分离培养基中细菌与菌落总数增长趋势相似,其中假单胞菌增长最快,肠杆菌数和乳酸菌数生长最慢。两种菌群鉴定结果显示,冷鲜牛肉初始微生物构成复杂,包括热死环丝菌、不动杆菌属（Acinetobacter spp.）、气单胞菌属（Aeromonas spp.）和假单胞菌等多种菌属构成,而腐败末期菌群构成趋于单一,假单胞菌和热死环丝菌为优势腐败菌,特别是莓实假单胞菌（P. fragi）。将腐败分离株10?株假单胞菌、4?株热死环丝菌和1?株蜂房哈夫尼菌（Hafnia alve）接种于冷藏的牛肉汁,发现假单胞菌和蜂房哈夫尼菌的接种组感官评分、pH值和TVB-N值高于热死环丝菌,且假单胞菌有较强的蛋白酶活性。研究表明,结合感官和微生物评价冷鲜牛肉贮藏期为15?d,且菌群多样性下降,假单胞菌和热死环丝菌是优势腐败菌,其中假单胞菌致腐性较强。     

Comparison of culture-dependent and independent techniques for characterisation of the microflora of peroxyacetic acid treated,vacuum-packaged beef

The diversity of microflora associated with peroxyacetic acid (POAA) treated and untreated beef was investigated by 16S rDNA gene cloning, DGGE analysis and conventional bacterial cultivation. Following vacuum packaging, POAA treated and untreated meat samples were stored for up to 18 weeks at −1.5 °C. Each culture independent method showed Carnobacterium spp. to predominate on both POAA treated and untreated meat. However, 16S rDNA gene analysis also detected the presence of psychrotolerant Clostridium spp. in the POAA-treated beef. Culture-dependent analysis did not distinguish Carnobacterium spp. from Lactobacilli. Although culture-dependent analysis showed an increase in the ratio of Enterobacteriaceae to lactic acid bacteria from weeks 6–18 in the POAA treated compared with the untreated meat, the numbers of Enterobacteriaceae were significantly less on POAA treated than on untreated meat. The combination of data collected by culture-dependent and independent techniques provided the most robust approach for elucidating the efficacy of chemical sanitization of chilled vacuum-packaged beef. If conventional cultivation is used for monitoring bacterial spoilage of vacuum-packaged chilled meats it is recommended that culture methods specific for Carnobacterium and Clostridium spp. should be included in order to provide a more complete indication of microbial diversity.     

基于宏转录组学解析不同贮藏时期冷鲜滩羊肉微生物代谢过程

以托盘密封包装的冷鲜滩羊肉表面微生物为研究对象,利用宏转录组学技术解析0、4、8 d三个贮藏时期微生物基因组差异转录、代谢途径与3 个贮藏时期微生物群落演替的关系。结果表明：3 个贮藏时期的冷鲜滩羊肉微生物差异表达基因数分别为429、15、1 529 个。通过对这些微生物差异表达基因进行KEGG代谢途径富集分析发现,参与核苷酸代谢、脂质代谢、能量代谢、碳水化合物代谢以及氨基酸代谢相关过程的差异表达基因显著富集,说明这几种代谢途径在滩羊肉微生物的演替过程中占据重要地位。在3 个贮藏时期,变形菌门都是优势微生物,变形菌门下的假单胞菌属和肠杆菌科利用贮藏环境中的氧气与滩羊肉中的葡萄糖为碳源,迅速生长繁殖,成为最主要的优势微生物。随贮藏时间延长,氧气被消耗殆尽,且滩羊肉的pH值降低,使得乳酸菌迅速生长,成为仅次于假单胞菌、肠杆菌的优势微生物。研究结果可以为冷鲜滩羊肉贮藏期间微生物及肉品质量预报、控制技术研发提供理论参考。     

包装方式对牛排贮藏期间微生物数量和演替的影响

为研究包装方式对牛排贮藏期间的品质、微生物数量和演替的影响，牛排分别采用50% O2气调包装（50% O2＋30% CO2＋20% N2）和真空包装在0～4 ℃下贮藏21 d，并检测贮藏期间pH值、肉色、微生物数量和微生物多样性。结果表明：50% O2气调包装组比真空包装具有更好的护色效果；贮藏21 d时，与真空包装组相比，气调包装组菌落总数、乳酸菌数和假单胞菌数降低；两种包装的微生物多样性均随时间延长呈现先升高后降低的趋势，且真空包装牛排比50% O2气调包装牛排具有更复杂的微生物多样性；牛排的初始微生物主要由不动杆菌属、苍白杆菌属、栖热菌属和金黄杆菌属组成，随着贮藏时间的延长，肉食杆菌属逐渐成为真空包装牛排的优势菌群，而环丝菌属、沙雷氏菌属和乳杆菌属则成为50% O2气调包装牛排的优势菌群；贮藏7～14 d是牛排中微生物种类产生变化的关键时间点；相比于真空包装牛排，50% O2气调包装牛排中的微生物群落具有更低的糖代谢和更高的蛋白质代谢能力。本研究结果明确了不同贮藏方法下牛排的品质变化和微生物的演替规律，为定向抑制牛排中的微生物、延长产品货架期提供了参考。     

Combined effect of natural essential oils, modified atmosphere packaging, and gamma radiation on the microbial growth on ground beef

Selected Chinese cinnamon, Spanish oregano, and mustard essential oils (EOs) were used in combination with irradiation to evaluate their ability to eliminate pathogenic bacteria and extend the shelf life of medium-fat-content ground beef (23% fat). Shelf life was defined as the time when the total bacterial count reached 10(7) CFU/g. The shelf life of ground beef was determined for 28 days at 4 degrees C after treatment with EOs. The concentrations of EOs were predetermined such that sensory properties of cooked meat were maintained: 0.025% Spanish oregano, 0.025% Chinese cinnamon, and 0.075% mustard. Ground beef samples containing EOs were then packaged under air or a modified atmosphere and irradiated at 1.5 kGy. Ground beef samples (10 g) were taken during the storage period for enumeration of total mesophilic aerobic bacteria, Escherichia coli, Salmonella, total coliforms, lactic acid bacteria, and Pseudomonas. Mustard EO was the most efficient for reducing the total mesophilic aerobic bacteria and eliminating pathogenic bacteria. Irradiation alone completely inhibited the growth of total mesophilic aerobic and pathogenic bacteria. The combination of irradiation and EOs was better for reducing lactic acid bacteria (mustard and cinnamon EOs) and Pseudomonas (oregano and mustard EOs). The best combined treatment for extending the shelf life of ground beef for up to 28 days was EO plus irradiation (1.5 kGy) and modified atmosphere packaging.     

Effect of Co2 or vacuum packaging on normal and high pH meat shelf-life

In order to extend meat shelf-life, normal-pH and high-pH beef steaks were packaged under vacuum or in 100% C 0 2 atmosphere. Microbiological, colour (L*, a*, b*)
and reflectance (R630-R580 values) characteristics were measured.
After packaging under vacuum, Enterobacteriaceae, Brochothrix thermosphacta and Pseudomonas numbers were 10- to 100-fold greater on high-pH meat than on
normal-pH meat.
Packaging under C 0 2 improved the shelf-life of meat, particularly that of high-pH meat up to 42 days. For both high- and normal-pH meats, the bacterial flora was
composed only of lactic acid bacteria. Normal-pH meat in C 0 2 atmosphere and vacuum packaging had a purple colour. After C02-pack opening the meat colour
became bright red and R630- R580 measurements were high, whereas after opening of vacuum packaging R630-R580 decreased rapidly with increasing aerobic exposure.
High-pH meat became paler with increasing storage time in C02. Simultaneously R630-R580 values increased and the pH fell. In addition it lost less exudate and
oxidized less in air than the normal-pH meat under the same conditions.     

Formation of biogenic amines and relation to microbial flora and sensory changes in smoked turkey breast fillets stored under various packaging conditions at 4 degrees C

The present study evaluated: (1) the formation of biogenic amines (BAs) in smoked turkey fillets during storage under aerobic and modified atmosphere packaging (MAP) conditions at 4 degrees C, (2) the relation of BAs to microbial and sensory changes in turkey meat and (3) the possible role of BAs as indicators of poultry meat spoilage. Smoked sliced turkey fillets were stored in air and under vacuum, skin and two modified atmospheres (MAP), M1 (30% CO(2)/70% N(2)) and M2 (50% CO(2)/50% N(2)), at 4+/-0.5 degrees C, for a period of 30 days. The BAs determined were: tryptamine, tyramine, histamine, putrescine, cadaverine, spermidine and spermine. Low levels of BAs were observed throughout the entire storage period, with the exception of histamine, tyramine and tryptamine, for which higher concentrations were recorded. Values for these three BAs were the highest for air-packaged samples (32.9, 25.0 and 4.1mg/kg, respectively) and the lowest for skin-packaged samples (11.9, 4.3 and 2.8 mg/kg, respectively) after 30 days of storage. All microorganism populations increased throughout the storage period, except for Pseudomonas spp. and Enterobacteriaceae, in skin-packaged fillets and modified atmosphere M2, which remained under the method detection limit (<1logCFU/g) until day 30 of storage. Pseudomonas spp. and Enterobacteriaceae for the rest of the packaging treatments remained below 5logCFU/g throughout storage. On the other hand, lactic acid bacteria were dominant throughout the storage period, regardless of the packaging conditions reaching 8.9logCFU/g on day 30 of storage. Mesophiles reached 7logCFU/g after ca. 19-20 days for the air and skin packed samples, 22-23 days for the M2 and vacuum packed samples and 25-26 days for the M1 packed samples. BA values for tryptamine, histamine and tyramine correlated well with both microbiological and sensory analyses data. Tryptamine, histamine and tyramine may be used as chemical indicators of turkey meat spoilage.     

气调包装对烤鸭腿货架期及微生物多样性的影响

为延长烤鸭腿货架期、保持其食用品质并阐明烤鸭腿冷藏过程中的菌群演替规律,本实验以托盘包装为对照组,研究了0～4 ℃条件下两种气调包装（100%（体积分数,下同）N2、50% CO2＋50% N2）对烤鸭腿贮藏过程中微生物（菌落总数、乳酸菌数、肠杆菌科数）、硫代巴比妥酸反应产物值及感官特性的影响,并通过高通量测序分析了贮藏过程中烤鸭腿的微生物多样性。结果表明：与托盘包装和100% N2包装相比,50% CO2＋50% N2包装显著抑制了烤鸭腿微生物的生长（P＜0.05）,使其货架期接近21 d,并抑制了其脂肪氧化（P＜0.05）,较好地维持了烤鸭腿的品质和感官特性。贮藏时间和包装方式对贮藏后期烤鸭腿的菌群结构有明显影响,泛菌属、类香味菌属、假单胞菌属和不动杆菌属为50% CO2＋50% N2包装烤鸭腿中的优势菌群,索丝菌属、泛菌属、假单胞菌属、肉食杆菌属和明串珠菌属为100% N2包装烤鸭腿中的优势菌群,优势菌群的不同是导致不同包装方式烤鸭腿间货架期产生差异的主要原因。     

Development of the aerobic spoilage flora of chilled rabbit meat

Even though worldwide production of rabbit meat is over 1,000,000ton, little information is available on rabbit meat microbiology. This paper reports on the microflora developing on chill-stored rabbit carcasses. Four different lots of 24h post-mortem rabbit carcasses dressed and kept at 0°C in a medium-size abattoir were collected and evaluated for sensory, physicochemical and microbiological changes during aerobic storage at 3±1°C. Mean initial pH value (pH(24)), extract-release volume (ERV) and lactate content of Biceps femoris muscle, were 6.26±0.20, 13.50±3.50ml and 0.70±0.07%, respectively. As with other muscle foods kept chilled in air, pH increased and ERV and lactate decreased as storage progressed. Initial levels (logcfu/g) of aerobes (APC), psychrotrophic flora, Pseudomonas spp., Brochothrix thermosphacta, lactic acid bacteria, Enterobacteriaceae and yeasts were 4.76±0.31, 4.81±0.81, 3.39±1.12, 2.01±0.92, 2.76±0.51, 0.49±0.45 and 3.46±0.32, respectively. Pseudomonads, most of them fluorescent, and to a lesser extent B. thermosphacta and yeasts grew faster than the remaining microorganisms and became predominant at the end of the shelf life. Carcasses spoiled when mean APC, psychrotrophic and pseudomonads numbers were ca. 8logcfu/g, their mean shelf life being estimated at 6.8 days. A lot of DFD-like rabbit carcasses, with higher pH and lower ERV values but similar microbial loads to normal meat, developed a strong putrid odour after 4 days.     

Combined effect of gamma irradiation,ascorbic acid,and edible coating on the improvement of microbial and biochemical characteristics of ground beef

This study was conducted to evaluate the combined effect of gamma irradiation and the incorporation of natural antimicrobial compounds in cross-linked films on the microbiological and biochemical characteristics of ground beef. Medium-fat (23% fat) ground beef patties were divided into three separate treatment groups: (i) control samples without additives, (ii) ground beef samples containing 0.5% (wt/wt) ascorbic acid, and (iii) ground beef samples containing 0.5% ascorbic acid and coated with a protein-based cross-linked film containing immobilized spice powders. Meat samples were irradiated at doses of 0, 1, 2, and 3 kGy and stored at 4 +/- 2 degrees C. Microbial growth (based on total aerobic plate counts [APCs] and total coliforms) was evaluated, as were the content of thiobarbituric acid-reactive substances (TBARS) and that of free sulfydryl groups. At the end of the storage period, Enterobacteriaceae, presumptive Staphylococcus aureus, presumptive Pseudomonas spp., Brochothrix thermosphacta, and lactic acid bacteria were enumerated. Regardless of the treatment group, irradiation significantly (P < or = 0.05) reduced the APCs. Irradiation doses of 1, 2, and 3 kGy produced immediate APC reductions of 2, 3, and 4 log units, respectively. An APC level of 6 log CFU/g was reached after 4, 7, and 10 days for samples irradiated at 1, 2, and 3 kGy, respectively. Lactic acid bacteria and B. thermosphacta were more resistant to irradiation than were Enterobacteriaceae and Pseudomonas. The TBARS and free sulfydryl contents were stabilized during postirradiation storage for samples containing ascorbic acid and coated with the protein-based cross-linked film containing immobilized spice powders.     

Bacterial populations associated with bulk packaged beef supplemented with dietary vitamin E

Five Simmentaler type calves were fed diets supplemented with 500 mg vitamin E per day and five fed control diets, Rump steaks from each carcass were PVC-overwrapped and bulk packaged in 100% CO2 or 20% CO2:80% O2. Bulk packs were stored up to 42 days at 4 degrees C and PVC-overwrapped samples subsequently displayed up to 7 days at 4 degrees C. After display the Aerobic Plate Count (APC) of steaks was determined and four colonies were randomly selected from the highest dilution APC plates showing growth. A total of 627 colonies were obtained. Gram-reaction, catalase, oxidase, morphology and motility of the isolates were determined. The gram-negative and gram-positive isolates were then identified using a dichotomous identification key. Enterobacteriaceae, Pseudomonas spp. and Acinetobacter spp. predominated on rump steaks from both feeding treatments and in packaging treatments. After 42 days bulk storage Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria and Acinetobacter spp. predominated in 20% CO2:80% O2 and 100% CO2 bulk packaging. Enterobacteriaceae, Pseudomonas spp. and Acinetobacter spp. predominated on rump steaks, from both feeding and packaging treatments, during the aerobic display period of 7 days.     

Shelf life of beef from local Spanish cattle breeds stored under modified atmosphere

Beef steaks from six Spanish cattle breeds (Asturiana de los Valles, Morucha, Parda Alpina, Pirenaica, Rubia Gallega and Retinta) were packaged under modified atmosphere (60% O(2), 30% CO(2) and 10% N(2)). Water loss, pH, thiobarbituric acid values (TBA), aerobic plate counts, lactic acid bacteria and Enterobacteriaceae counts, CIE L*a*b* colour values and the sensory properties of odour and colour were recorded before packaging (day 0) and after 5, 10 and 15 days of storage. A significant interaction (P<0.05) between breed and storage time was found for all variables, except water loss. Values of pH were between 5.3 and 5.6; maximum water loss (2.64%) was reached after 10 days of storage; aerobic plate counts, lactic acid bacteria and Enterobacteriacea counts were lower than 10(7) CFU/g, and L* increased with storage time while a* decreased (P<0.05). The maximum shelf life of beef assessed by sensory evaluation (regarding colour and odour degradation) was between days 5 and 10 in meat from Retinta breed and between days 10 and 15 in meat from the other breeds, shelf life was probably limited by lipid oxidation.