Inhibition, survival and growth of Listeria monocytogenes on poultry as influenced by buffered lactic acid treatment and modified atmosphere packaging.

The effect of the treatment with various concentrations (2%, 5% and 10% w/v) of lactic acid/sodium lactate buffer (pH 3.0), modified atmosphere (MAP) packaging (90% CO2 and 10% O2) and 10% (w/v) lactic acid/sodium lactate buffer (pH 3.0) combined with MAP on Listeria monocytogenes Z7 serotype 1 and on the shelf life of chicken legs stored at 6 degrees C was investigated. The initial contamination level of L. monocytogenes on the chicken legs surface was 8.3 x 10(2) cfu/cm2 of skin. After 2 days of storage at 6 degrees C the number of L. monocytogenes on legs treated with 2%, 5%, 10% lactic acid/sodium lactate buffer (pH 3.0) and 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP was significantly lower than the initial number of L. monocytogenes. Later, growth of L. monocytogenes was observed. After 13 days of storage at 6 degrees C the number of L. monocytogenes on legs treated with 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP was still similar to the initial number. Legs treated with 2%, 5%, 10% lactic acid/sodium lactate buffer (pH 3.0), MAP and 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP, have a shelf life at 6 degrees C of respectively 8, 9, 10, 13 and 17 days. This means a prolongation of 2, 3, 4, 7 and 11 days, respectively for storage at 6 degrees C. The antimicrobial effect of lactic acid buffer systems (pH 3.0) increased with increasing concentrations of lactic acid in the buffered system. The best results were obtained by the combined use of 10% acid/sodium lactate buffer (pH 3.0) and MAP.     

Quality attributes of farmed eel (Anguilla anguilla) stored under air, vacuum and modified atmosphere packaging at 0 degrees C

The shelf life of fresh eel in various packaging conditions of atmospheric air, vacuum and modified atmosphere packaging (MAP) (40% CO(2), 30% N(2) and 30% O(2)) at 0 degrees C was investigated. All raw eel samples received acceptable sensory scores during the first 11+/-1 days of storage in atmospheric air, 11+/-1 days of storage in vacuum and finally 18+/-1 days of storage in MAP conditions. Using the microbial quality indicators the shelf life of eel packed in air, vacuum and MAP was estimated to be more than 18, 28 and 34 days, respectively. The main spoilage microorganisms under MAP conditions were lactic acid producing bacteria followed by Shewanella spp., pseudomonads, Enterobacteriaceae and yeasts. Chemical data revealed that pH, ammonia, glucose and lactate examinations might not be useful for monitoring eel quality differences.     

Shelf life extension of lamb meat using thyme or oregano essential oils and modified atmosphere packaging

The effect of thyme (TEO) and oregano (OEO) essential oils as well as modified atmosphere packaging (MAP) in extending the shelf life of fresh lamb meat stored at 4 °C was investigated. In a preliminary experiment TEO and OEO were used at concentrations 0.1 and 0.3% v/w while MAP tested included MAP1 (60% CO(2)/40% N(2)) and MAP2 (80% CO(2)/20% N(2)). Microbiological, physicochemical and sensory properties of lamb meat were monitored over a 20 day period. Sensory analysis showed that at the higher concentration both essential oils gave a strong objectionable odour and taste and were not further used. Of the two essential oils TEO was more effective as was MAP2 over MAP1 for lamb meat preservation. In a second experiment the combined effect of TEO (0.1%) and MAP2 (80/20) on shelf life extension of lamb meat was evaluated over a 25 day storage period. Microbial populations were reduced up to 2.8 log cfu/g on day 9 of storage with the most pronounced effect being achieved by the combination MAP2 plus TEO (0.1%). TBA values varied for all treatments and remained lower than 4 mg MDA/kg throughout storage. pH values varied between 6.4 and 6.0 during storage. Color parameters (L and b) increased with storage time while parameter (a) remained unaffected. Based primarily on sensory analysis (odour) but also on microbiological data, shelf life of lamb meat was 7 days for air packaged samples, 9-10 days for samples containing 0.1% of TEO and 21-22 days for MAP packaged samples containing 0.1% TEO.     

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.     

The effect of treatment with buffered lactic acid on microbial decontamination and on shelf life of poultry

The use of buffered lactic acid systems compared with unbuffered lactic acid solutions enhances the decontaminating effect and increases shelf life of chicken legs. A reduction of about 2 pH units of the chicken skin is obtained by treatment with 10% lactic acid buffer. The buffer keeps the pH of the skin lower than that of untreated legs. Legs treated with 10% lactic acid buffer have a shelf life of 12 days at 6 degrees C, which means an increase of 6 days compared with the shelf life of untreated legs.     

Effects of three preservative agents on the shelf life of vacuum packaged Chinese-style sausage stored at 20°C

The influence of 3% sorbitol, 3% sodium lactate and 100 mg/kg nisin on the shelf life of vacuum packaged Chinese-style sausage stored at 20°C was studied. Growth of microbiological populations (aerobe, anaerobe, lactic acid bacteria, leuconostocs) and slime formation on the sausage were not retarded during storage by addition of nisin. Sorbitol lowered the initial water activity of the sausage, however, microbiological spoilage accompanied with pH decline, increase in volatile basic nitrogen compounds and a sour odour defect were observed after 10 days storage. Sodium lactate was bacteriostatic as it inhibited microbial as well as chemical changes during storage so that the shelf life was 25 days at 20°C. The dextran content of the vacuum packaged Chinese-style sausage indicated the spoilage 2-3 days earlier than that seen by other chemical assays or sensory evaluation.     

Sodium lactate addition on the quality and shelf life of refrigerated sliced poultry sausage packaged in air or nitrogen atmosphere

The aim of this study was to determine the effect of sodium lactate addition on shelf-life extension of sliced poultry sausage packaged both in air and nitrogen atmospheres and stored in refrigerated conditions. Basic chemical composition, pH, and malonaldehyde content were assayed and color measurement using the reflection method was carried out. Microbiological examination consisted of determination of total number of aerobic psychrotrophic bacteria and number of lactic acid bacteria. Sensory evaluation of products was performed. Microbiological and sensory quality of sliced poultry meat sausage was dependent on the addition during production of sodium lactate and the composition of gases (air or nitrogen) used in packaging. Slices of poultry sausage with 1% as well as 2% of sodium lactate maintained their initial quality of evaluated sensory attributes longer, irrespective of the applied gases. Sodium lactate inhibited growth of aerobic psychrotrophic bacteria and lactic acid bacteria during refrigerated storage. Sodium lactate also inhibited the formation of malonaldehyde in sliced poultry sausage during refrigerated storage. The effectiveness of this process depended on the concentration of sodium lactate addition. It was concluded that 1% as well as 2% addition of sodium lactate could extend the shelf life of sliced poultry sausage packaged in air atmosphere and stored at 5 to 7 degrees C by 3 or 4 times, respectively. Sliced poultry sausage treated with 2% sodium lactate packed in nitrogen had the longest (35-day) shelf life. This was a sevenfold increase in the shelf life of sliced poultry sausage compared with the control.     

Botulism challenge studies of a modified atmosphere package for fresh mussels: inoculated pack studies

A series of botulism challenge studies were performed to determine the possibility of production of botulinum toxin in mussels (Mytilus edulis) held under a commercial high-oxygen (60 to 65% O(2)), modified atmosphere packaging (MAP) condition. Spore mixtures of six strains of nonproteolytic Clostridium botulinum were introduced into mussel MAP packages receiving different packaging buffers with or without the addition of lactic acid bacteria. Dye studies and package flipping trials were conducted to ensure internalization of spores by packed mussels. Inoculated mussel packages were stored at normal (4°C) and abusive (12°C) temperatures for 21 and 13 days, respectively, which were beyond the packaged mussels' intended shelf life. Microbiological and chemical analyses were conducted at predetermined intervals (a total of five sampling times at each temperature), including total aerobic plate counts, C. botulinum counts, lactic acid bacterial counts, package headspace gas composition, pH of packaging buffer and mussel meat, and botulinum toxin assays of packaging buffer and mussel meat. Results revealed that C. botulinum inoculated in fresh mussels packed under MAP packaging did not produce toxin, even at an abusive storage temperature and when held beyond their shelf life. No evidence was found that packaging buffers or gas composition influenced the lack of botulinum toxin production in packed mussels.     

Influence of modified atmosphere packaging on the shelf life of prebaked pizza dough with and without preservative added

The possible effect of different modified atmospheres on the shelf life of prebaked pizza dough, with and without added calcium propionate, was investigated. Three packaging atmospheres were tested: 20% CO2: 80% N2, 50% CO2: 50% N2, 100% CO2, and air (control). Samples were examined daily for visible mold growth and analysed after 2, 8, 17 and 31 days throughout storage (15-20 degrees C and 54-65% relative humidity, RH) for changes in gaseous composition, pH and microbial populations (mesophilic aerobic and anaerobic bacteria, lactic acid bacteria (LAB), and yeasts and molds). Microbiological results showed that molds had a greater sensitivity to CO2 than bacteria and yeasts. Products containing calcium propionate did not show mold growth throughout storage (31 days) when packaged in air or in CO2-enriched atmospheres (20, 50 and 100%). However, in pizza dough without preservative (calcium propionate), mold growth was evident after 7 days, except under 100% CO2 atmosphere (13 days) regardless of the packaging atmosphere. From these results we conclude that the addition of calcium propionate had more and decisive influence on the shelf life extension of prebaked pizza dough.     

不同气调包装结合冰温贮藏对羊肉保鲜效果的影响

为延长鲜羊肉的保鲜时间,研究不同气体组分的气调包装对羊肉冰温贮藏过程中品质的影响。以真空包装为对照,比较75% O2＋25% CO2、75% N2＋25% CO2气调包装羊肉在－1 ℃冰温条件下贮藏过程中感官品质、色泽、汁液流失率、嫩度、挥发性盐基氮、pH值、微生物等品质指标的变化。结果表明：真空包装羊肉的汁液流失率显著高于2 种气调包装,而75% N2＋25% CO2气调包装羊肉的色泽和感官评分最差。75% O2＋25% CO2气调包装的保鲜效果最好,其色泽和感官评分最高,汁液流失率较小,pH值最低,－1 ℃冰温条件下贮藏42 d时,羊肉的菌落总数、假单胞菌菌数、乳酸菌菌数的对数值分别为5.91、5.95、5.23 （lg（CFU/g））,其中菌落总数指标符合国家二级鲜肉标准。因此,－1 ℃冰温条件下结合75% O2＋25% CO2气调包装可以使羊肉有效保鲜42 d,是较好的鲜羊肉保鲜方法。     

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.     

微冻及冰温结合气调包装对羊肉的保鲜效果

比较微冻、冰温结合气调包装对羊肉品质的影响,确定适合于羊肉保鲜新方法。以羊肉为原料,比较-3℃微冻、-1℃冰温气调包装(75%O2+25%CO2)与两个温度条件下普通包装的羊肉在贮藏过程中p H值、挥发性盐基氮(total volatile base-nitrogen,TVB-N)值、微生物菌落总数、汁液流失率等品质等指标的变化。结果表明,与-1℃冰温相比,-3℃微冻能很好地控制羊肉微生物菌落总数和TVB-N值,延缓p H值的升高,但汁液流失率为-1℃冰温贮藏的4~5倍。相同温度条件下,与普通包装相比,气调包装能使羊肉保持良好的色泽,抑制微生物菌落总数的增加,延长羊肉的保鲜期10 d。综合来看,-3℃微冻气调包装对于宰后羊肉品质的保持效果最好,可以使羊肉有效保鲜时间达40 d,此时羊肉微生物菌落总数为5.79(lg(CFU/g)),符合国家安全鲜肉标准(≤6(lg(CFU/g));TVB-N值为14.47 mg/100 g,符合国家一级鲜肉的标准(≤15 mg/100 g);p H值为5.84,符合国家一级鲜肉的标准(p H 5.18~6.12)。     

包装材料对高氧气调包装冷鲜肉品质变化的影响

气调包装能有效延长冷却肉的货架期,但是不同阻隔性的包装材料对冷却肉的保质期影响差异显著,因此选用3种不同阻隔性的包装材料,对冷鲜肉进行高氧气调包装(35% CO2、65% O2),测定冷鲜肉在贮藏期的菌落总数、大肠菌群、色泽、挥发性盐基态氮、汁液流失率和pH值等指标,观察不同阻隔性的材料对冷却肉货架期品质的影响。结果表明：高氧包装条件下,高阻隔材料包装的冷却肉在贮存10d菌落总数已经超标,pH值在贮存期内处于二级鲜肉的范围内;中阻隔包装材料包装的冷却肉菌落总数对数值在保质期内未超过6(lg(CFU/g)),但是肉色保持的较好,感官评价相对较好,但是汁液流失较大;低阻隔包装材料低阻隔性的包装材料菌落变化最大,13d时菌落总数对数值达到6.46(lg(CFU/g)),肉的色泽相对较差,气味和总体可接受性也较差,因此,中阻隔性包装材料效果较好。     

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。     

Centralized packaging of retail meat cuts: a review.

Centralized packaging of retail meat cuts is growing more popular because of its economies and potential to maintain quality, enhance safety, and extend the shelf life of fresh meat. Requirements for optimizing shelf life of centrally prepared retail cuts for periods up to 15 weeks are slightly different from those needed to extend the shelf life of fresh, chilled meat. Chilled meat primarily deteriorate at the cut or uncut muscle surface. In long-term storage, primal cuts are placed in an atmosphere saturated with carbon dioxide and containing very low residual oxygen. These cuts are held at -1.5+/-0.5 degrees C. When the meat is removed, it is fabricated into retail or food service cuts. New fresh surfaces are created in the process, revitalizing the meat's appearance. After being prepared for retail display, the meat normally has four more days of shelf life. Depending on the meat species, shelf life is usually limited by development of undesirable organoleptic changes, usually defects in color, which are independent of microbial presence. The microbes consist of a lactic acid bacterial population that maximizes under storage conditions at about 10(8) CFU/cm2 well before shelf life ends. Circumstances are different with centralized distribution of retail-ready fresh meat. The wholesale storage period following initial packaging of the retail cuts is about 20 to 30 days. Prepared products must withstand retail display for up to 2 days without further manipulation of package contents. Retail packages are simply moved from their storage container (usually a unit or overwrap containing a modified atmosphere) to retail display, where desirable meat color develops upon exposure to air. Three gas atmospheres have some potential to satisfy storage needs for centralized distribution of retail-ready packages: 100% CO2, 100% N2, or 70% N2 + 30% CO2. Shelf life is limited by undesirable changes in surfaces exposed at initial packaging, caused by growth of psychrotrophic bacteria. If 100% CO2 is used, these are all lactic acid bacteria (LAB). Therefore, initial bacterial numbers on the meat and storage temperature become critical to success. The most attractive storage option is 100% CO2 used at - 1.5 +/-0.5 degrees C. This review presents the reason for that recommendation, along with basic concepts of meat chemistry, a discussion of modified atmosphere packaging, meat microbiology, and current results with simulated centralized packaging of retail-ready meats.     

不同含氧气调包装方式对调理鸭肉制品的保鲜效果

为延长调理鸭肉制品货架期,将调理后的鸭肉分别以托盘包装为对照,用不同含氧气调包装方式（MAP1（20% CO2＋80% N2）、MAP2（20% CO2＋40% O2＋40% N2）、MAP3（20% CO2＋80% O2））对调理鸭肉制品进行保鲜处理（0～4 ℃）,测定调理鸭肉贮藏期间微生物指标和生理生化指标。结果表明：与托盘包装组相比,3 种气调包装方式均能有效抑制调理鸭肉中微生物生长,减少挥发性盐基氮产生;含氧组（MAP2和MPA3）的保鲜效果显著优于MAP1组和对照组（P＜0.05）,含氧组的保质期均为12 d;在贮藏12 d时,MAP2组的TBARS值和肠杆菌数显著低于MAP3组（P＜0.05）,MAP3组的菌落总数显著低于MAP2组（P＜0.05）,且这两组的TVB-N含量和L*值均无显著差异（P＞0.05）。综合分析,MAP2包装对调理鸭肉制品保鲜效果最好。     

Shelf life characteristics of enhanced modified atmosphere packaged pork

The objective of these studies was to identify a chemical indicator for predicting performance of enhanced pork during storage, then select raw materials with the potential for color and shelf life instability and enhance them with antimicrobial solutions in an attempt to overcome their initial deficits. The purpose of Study 1 was to evaluate the use of pH, glycolytic potential, and glucose levels in the drip to assess shelf life characteristics of modified atmosphere packaged (MAP), enhanced pork loin chops during display. Chops from higher pH carcasses had higher color scores and aerobic plate counts, and less discoloration. Study 2 evaluated shelf life characteristics of chops derived from high pH (>5.75) raw materials enhanced with solutions containing salt and phosphate, and/or lactate and/or acetate. Overall, pH was the best indicator of color and microbiological stability. Raw materials with high ultimate pH were least stable. MAP chops derived from high pH raw materials and enhanced with a sodium acetate-containing solutions had better color and microbiological shelf life than those enhanced with other solutions.     

Effect of packaging conditions on shelf-life of fresh foal meat

The objective was to determine the shelf life of foal meat (Longissimus dorsi) stored in four different packages: (i) vacuum, (ii) overwrap and (iii) two modified atmospheres (MAP): high O(2) MAP (80% O(2)+20% CO(2)) and low O(2) MAP (30% O(2)+70% CO(2)) stored at 2 °C during 14 days. Shelf life evaluation was based on pH, colour, lipid and protein oxidation, microbial counts and sensory assessment of odour, colour and appearance. Based on aerobic bacterial counts, the shelf life of foal meat samples in overwrap and high O(2) MAP packages would be 10 days at most, almost 14 days in low O(2) MAP and more than 14 days in vacuum packaging. Scores for sensorial evaluation were unacceptable after 10 days of storage in samples in overwrap and MAP packs, but they were still acceptable in vacuum ones. Moreover, for all packaging conditions except vacuum, which remained constant, a decrease in redness (a*) and an increase in carbonyl content and TBAR'S values was observed with storage time. High O(2) levels negatively affected foal meat quality, while anaerobic conditions extended shelf life to 14 days.     

Effect of potassium lactate and a potassium lactate-sodium diacetate blend on Listeria monocytogenes growth in modified atmosphere packaged sliced ham

Two commercially available organic acid salts, potassium lactate (PURASAL HiPure P) and a potassium lactate-sodium diacetate blend (PURASAL Opti.Form PD 4), were assessed as potential inhibitors of Listeria monocytogenes growth in modified atmosphere packaged (MAP) sliced ham in challenge studies. The influence of the initial inoculation level of L. monocytogenes (10(1) or 10(3) CFU g(-1)) and storage temperature (4 or 8 degrees C) was also examined. The addition of either organic acid salt to MAP sliced ham strongly inhibited the growth of L. monocytogenes during the normal shelf life of the product under ideal refrigeration conditions (4 degrees C) and even under abusive temperature conditions (i.e., 8 degrees C). During the challenge studies and in the absence of either organic acid salt, L. monocytogenes numbers increased by 1000-fold after 20 days at 8 degrees C and 10-fold after 42 days at 4 degrees C. Both organic acid salt treatments were found to be listeriostatic rather than listericidal. The addition of either organic acid salt to the MAP ham also reduced the growth of indigenous microflora, i.e., aerobic microflora and lactic acid bacteria. The influence of these compounds on the risk of listeriosis in relation to product shelf life is discussed.     

Combined effects of modified atmosphere packaging and thymol for prolonging the shelf life of caprese salad

The aim of this study was to investigate the influence of packaging atmosphere and a thymol dipping solution on the shelf life of caprese salad. Caprese salad was prepared with sliced tomatoes and mozzarella cheese. The samples were pretreated by dipping in a 400-ppm thymol solution and then packaged under air or under a modified atmosphere (65% N2, 30% CO2, and 5% O2). Changes in natural microflora of mozzarella and tomato, the O2 and CO2 in the head space, pH, and sensory characteristics were monitored during storage. The combination of the thymol dip and the modified atmosphere decreased the coliform populations in caprese salad from 5.65 to 4.23 log CFU x g(-1) and extended the shelf life from 3.77 to 12 days. A decrease in the concentration of Pseudomonadaceae from 7.03 to 5.09 log CFU x g(-1) was observed, and the lag phase was prolonged to approximately 3 days. The combination of the modified atmosphere and thymol did not affect the growth kinetics of lactic acid bacteria and enterococci, thus preserving the function of mozzarella cheese in the salad.