Identification of Leuconostoc species associated with the spoilage of vacuum-packaged Vienna sausages by DNA-DNA hybridization

Approximately 36% of predominant microbiological spoilage populations from vacuum-packaged Vienna sausages consist of leuconostocs which are difficult to identify phenotypically. Seven leuconostocs selected on a pro-rata basis as representatives of three phenotypically different groups from this environment were identified by DNA-DNA hybridization as Leuconostoc mesenteroides subsp. mesenteroides (3), Leuconostoc gelidum (1) and Leuconostoc paramesenteroides (3). The presence of high proportions of Leuconostoc paramesenteroides and absence of Leuconostoc carnosum in this spoilage association was noteworthy. DNA-DNA hybridization represented a reliable identification method for meat spoilage leuconostocs.     

Bacterial populations associated with pasteurized vacuum-packed Vienna sausages

Predominant bacterial populations were isolated from vacuum-packaged Vienna sausages exposed to three in-package pasteurization treatments of increasing severity (Past1, 2 and 3) and non-pasteurized controls stored at 8°C for 128 days. The majority (>52%) of isolates from pasteurized and non-pasteurized sausages were lactic acid bacteria (LAB); the remainder includedBacillus, Gram-positive, catalase-positive cocci and enterobacteriaceae. In-package pasteurization of sausages reduced proportions of LAB from 84.4% in non- pasteurized samples, to 74.6%, 66.4% and 52.9% in Past1, 2 and 3 treated samples, respectively. In non-pasteurized sausages, leuconostocs and homofermentative lactobacilli jointly comprised the highest proportion (83.3%) of LAB isolates, whereas pediococci were isolated at a lower frequency of 16.7%. As a result of all pasteurization treatments, proportions of leuconostocs and homofermentative lactobacilli decreased toc. 40% of isolates, whereas proportions of pediococci increased to 50% or more. Although pasteurization led to a diversification of lactic spoilage populations, it did not prevent product spoilage by eliminating these bacteria. Because severe heating also increased the predominance ofBacillus, in-package pasteurization of vacuum-packaged Vienna sausages might, however, compromise product safety.     

Quantification and characterization of microbial populations associated with naturally fermented Greek dry salami

The microbial flora associated with the natural fermentation and ripening of five batches of Greek dry salami was enumerated and characterized over time. Micrococci-staphylococci increased at a level of 10⁷ cfu g^-1 during early fermentation. By day 4, lactic acid bacteria outnumbered Micrococcaceae in all batches, since they exceeded — with the exception of batch III — 10⁸ cfu g^-1. Yeasts remained below 10⁶ cfu g^-1 during the whole process, but tended to increase at a late ripening stage. Almost all colonies grown on mannitol salt agar were catalase positive cocci. Nitrate-reducing micrococci were progressively replaced by less acid-sensitive staphylococci. A high proportion (62·5%) of 112 Staphylococcus isolates grew weakly under anaerobic conditions. Typical staphylococci were less capable of reducing nitrate. Yeast populations mainly comprised Debaryomyces strains. Characterization of 348 lactic isolates indicated that the salami microflora was dominated by homofermentative lactobacilli (61·4%) and leuconostoc-like bacteria (24·9%). Most lactobacilli (51·4%) belonged to the formerly-called ‘atypical' meat streptobacteria. Typical streptobacteria (10·0%), heterofermentative lactobacilli (10·0%) and homofermentative cocci (3·1%) were mainly isolated during the first days of fermentation and failed to compete with the other two groups. The microbial interactions as reflected by the distribution and succession of different general/subgenera in each batch and their possible effect on physicochemical and sensory characteristics of the sausages were discussed.     

Evolution of microbial populations during traditional Feta cheese manufacture and ripening

In three different dairies (A, B and C) located in Peloponess region (Southern Greece), traditional Feta cheese trials took place February to March using mixtures of sheep's and goat's milk. Only small variations in the evolution of microbial groups were observed during the whole ripening period. The main groups, such as thermophilic cocci, mesophilic lactococci, thermophilic lactobacilli, nonstarter lactic acid bacteria (NSLAB), presumptive Leuconostoc, enterococci and micrococci, reached their highest levels during the first 16 days, and then declined approximately 1-2 log units until the end of ripening. The remaining groups investigated, comprising yeasts, coliforms and Escherichia coli, were highest at day 4. The yeasts remained constant, while coliforms and E. coli decreased sharply and were not detectable after 120 days of ripening. A number of 146 isolates (dairy A) taken from all stages of the manufacturing and ripening process were purified and studied. Lactobacillus plantarum (58/146) and isolates of related species Lactobacillus pentosus and Lactobacillus paraplantarum (16/146) were the most common microorganisms found during cheese ripening. Streptococcus thermophilus (23/146) and Lactobacillus delbrueckii subsp. bulgaricus (20/146) were detected in high levels up to 20 days, and then gradually reduced. Enterococcus faecium (29/146) was found in all manufacturing and ripening stages.     

Effect of x-ray irradiation on reducing the risk of listeriosis in ready-to-eat vacuum-packaged smoked mullet

Listeria monocytogenes can pose a serious threat in several areas of the nation's food supply including ready-to-eat seafood products. Use of irradiation processing can potentially reduce the risk of listeriosis caused by consumption of ready-to-eat seafood products. This study measured the effect of X-ray irradiation on reducing the population of L. monocytogenes on ready-to-eat, vacuum-packaged smoked mullet. Smoked mullet were inoculated with a five-strain mixture of L. monocytogenes (10(4) CFU/g), vacuum packaged, and irradiated (0, 0.5, 1.0, 1.5, and 2.0 kGy). The packaged fish were then stored at 3 and 10 degrees C for 90 and 17 days, respectively. Radiation doses of 0.5, 1.0, and 1.5 kGy reduced the initial population of L. monocytogenes by 1.1, 1.6, and 2.1 log CFU/g, respectively. The 2.0-kGy dose reduced L. monocytogenes to undetectable levels with no recovery growth at either temperature. Compared to the control, irradiation at 1.5 kGy demonstrated 1.0 and 1.7 log CFU/g less growth at 3 degrees C after 60 days and 10 degrees C after 17 days, respectively. Sensory flavor analysis was conducted to determine if a difference existed between irradiated samples. Panelists indicated that there were no differences among treated and untreated samples. An X-ray dose of 2 kGy effectively eliminated 10(4) CFU/g L. monocytogenes on smoked mullet without changing sensory quality.     

发酵剂对熏马肠脂肪氧化的影响

通过对熏马肠发酵成熟过程中的过氧化值、硫代巴比妥酸值、双烯值、脂肪氧合酶活力(LOX)、超氧化物歧化酶活力(SOD)和过氧化氢酶活力(CAT)等指标的测定,研究发酵剂对熏马肠发酵成熟过程中的脂质氧化、氧化酶和抗氧化酶活力的影响。结果表明:与对照组相比较,发酵剂可以显著抑制脂质氧化和LOX活力,且显著提高SOD和CAT活力。通过相关性分析表明,发酵剂组的LOX活力与过氧化值、硫代巴比妥酸值和双烯值这3个氧化指标呈不显著负相关,相关系数为0.089~0.427。SOD和CAT活力与3个氧化指标呈显著、极显著负相关,相关系数为0.684~0.970。     

发酵剂对熏马肠成熟过程中生物胺含量变化的影响

利用从熏马肠中分离出的具有抑菌作用并可以产生物胺氧化酶的菌株,1株表皮葡萄球菌(Staphylococcus epidermidis),3株模仿葡萄球菌(Staphylococcus simulans)作为发酵剂加入到熏马肠,在熏马肠成熟过程中采用高效液相色谱检测不同发酵剂对生物胺含量变化的影响,进而阐明发酵剂对熏马肠中生物胺累积的控制作用。从研究结果可以看出,在马肠成熟过程中,B组对色胺、苯乙胺、腐胺、组胺、酪胺都有较显著的减少作用;C组对色胺、腐胺、尸胺、组胺、酪胺减少作用显著;D组对色胺、苯乙胺、腐胺、组胺、酪胺的减少作用显著;E组对组胺、苯乙胺、色胺的减少作用显著。添加发酵剂组对精胺、亚精胺的减少作用均不显著。结果表明,上述菌种对熏马肠成熟过程中生物胺产生有较好的抑制作用,具有肉品发酵剂的良好特性,为熏马肠以及其他发酵肉制品的工业化生产和安全性奠定了基础。     

Moisture sorption properties of smoked chicken sausages from spent hen meat

Moisture sorption characteristics of smoked chicken sausages from spent hen meat were investigated at 5, 25 and 50°C over a water activity (a_w) range of 0.11–0.87. Sigmoidal (type-II) desorption isotherms were observed for these samples. The sorption data were analysed using mathematical equations of Caurie, Halsey, GAB and Oswin. The Halsey equation gave the best fit over the entire temperature range. GAB model also described the isotherms fairly well. The GAB and BET monolayer moisture values were not significantly different (P>0.01) and decreased with increasing temperature. The number of adsorbed monolayers, density and amount of bound water and surface area of adsorption also decreased as the sorption temperature increased. The pores, in general, enlarged with rising temperature.     

Acid treatment and pasteurization affect the shelf life and spoilage ecology of vacuum-packaged Vienna sausages

Vacuum-packaged Vienna sausages, treated by a combination of in-package pasteurization and surface application of an organic-acid cocktail, were compared with untreated controls and samples that were only pasteurized or acid treated. Total aerobic bacteria, lactic acid bacteria, Enterobacteriaceae and yeasts were quantified by replicate plate counting of duplicate samples stored at 8°C, and 425 predominant colonies were isolated and characterized. Microbiological shelf life was set at 5×10⁶cfu g⁻¹. Acid treatment decreased shelf life 1.8-fold while ac. four-fold increase in shelf life was noted for pasteurized and combined pasteurized and acid-treated samples. Populations of non-lactic acid bacteria consisted predominantly ofBacillusisolates, especially in pasteurized samples. The relative predominance of non-lactic acid bacteria increased to >44% of isolates in pasteurized samples. Lactic acid bacteria were the predominant group in samples of all treatments and populations consisted predominantly of homofermentative lactobacilli in control and acid-treated samples, whereas pediococci and leuconostocs showed increased predominance in pasteurized samples.     

Hygienic evaluation of smoked sausages produced by traditional and improved technologies]

The results of the physico-chemical and hygienic investigations of smoked sausages produced according to the improved technology were compared to those of routine products. The changes in the content of smoking substances in uncooked smoked sausage depend on the duration of smoking and drying. Microstructural and microbiological data, as well as carcinogenic compounds detected in the samples studied have been presented. It has been shown that the use of vacuum evaporation improves the product structure and significantly decreases the content of carcinogenic substances in smoked sausages, as well as makes better their taste and scent, that leads to the improvement of consumer's properties of the product.     

发酵剂对熏马肠成熟过程中蛋白质降解的影响

对熏马肠发酵成熟过程中蛋白质的降解变化进行了研究。结果表明,非蛋白氮含量在加工过程中持续增加,并且发酵剂组的非蛋白氮值上升较快;通过SDS-PAGE图谱分析,肌浆蛋白和肌原纤维蛋白均发生了降解,发酵剂组的蛋白降解程度明显高于空白组,尤其是肌浆蛋白,分子质量在14.4 ku、27～35 ku、66～90 ku附近的蛋白条带均降解消失;通过对组织蛋白酶B和L活力测定,得出空白组的酶活力高于发酵剂组。     

Influence of cooking on benzo(a)pyrene content in smoked sausages

The changes in benzo(a)pyrene (BaP) content of smoked sausages were monitored during 1 h cooking. During this time, the BaP content decreased from 4·80 to 1·87 μg/kg. The maximum drop in BaP content was reached in the first 20 min of cooking. Two factors affected the course of BaP changes, viz. water-holding capacity and the fat content. After excluding these factors, there was a high correlation coefficient of 0·996 between time of cooking and BaP content, which confirmed an inverse relationship between the decrease in BaP content and time of cooking.

The BaP decrease was directly proportional to the decrease of fat content during cooking, when the relatively high BaP content of 7·71 μg/kg was found in the cooked-out fat.     

Relationships between ultimate pH and microbial, chemical, and physical characteristics of vacuum-packaged pork loins

ABSTRACT:  This study evaluated the effect of ultimate pH (pHu) of pork on shelf life based upon microbial growth, drip loss, and oxidative rancidity (2-thiobarbituric acid [TBA] procedure) in vacuum-packaged loins stored at 4 °C. Glucose and lactate concentrations of the pork loins were also measured. Thirty-six pork loins (pH = 5.56 to 6.57) were collected at a commercial slaughter facility 1-d postslaughter. All pigs were from the same genetic line. Loins were grouped by pH (group: pH range): A: 5.55 to 5.70, B: 5.71 to 5.85, C: 5.86 to 6.00, D: 6.01 to 6.15, and E: > 6.16. They were analyzed at days 0, 6, 14, 24, and 34. For aerobic plate counts, groups A and B were significantly lower than C through E, while psychrotrophic or Enterobacteriaceae counts of groups A and A through C were significantly lower than groups B through E and D and E, respectively. Lactic acid bacteria counts were not significantly influenced by pHu. Group A had higher glucose concentrations than groups C through E and higher lactate concentrations than groups D through E on most sampling days. Group A had a higher TBA value than group E at days 0 and 34. Group A displayed greater drip loss than groups D and E at day 6 and groups B through D on days 24 and 34. Based on the microbial and drip loss results, a pork loin pHu of 5.8 to 5.9 appears to be optimum to provide a vacuum-packaged shelf life of at least 24 d with minimum drip loss.     

The microbial flora of vacuum packed smoked herring fillets

The quantitative and qualitative changes in the microbial flora of vacuum packed smoked herring fillets, held at 10°C over a period of 18 weeks, were examined. Samples were periodically tested by a sensory panel for taste and smell. Initial total counts were in the order of 10⁴/g. After 7 weeks' storage the counts reached 10⁸/g. No significant changes were recorded thereafter. Initially, the incidence of yeasts was high (64%). After 9 weeks of storage these were no longer detected. Homofermentative Lactobacillus sp(p). increased during the keeping period, reaching 84% of the total flora after 12 weeks' storage. Sensory data indicated a keeping quality of at least 3 months at 10°C. No correlation was observed between sensory scores and total microbial counts. It appears that total plate counts have a minor significance in quality assessment of vacuum packed smoked herring fillets.     

Changes in volatile, sensory and microbial profiles during preparation of smoked ewe cheese

BACKGROUND: Oscypek is a special type of Polish smoked ewe cheese with a unique flavour described as slightly sour, piquant, salted and smoked. In this study the volatile, sensory and microbial profiles of Oscypek cheese were analysed during its various preparation stages of curding, scalding, brining and smoking. RESULTS: The smoked ewe cheese was characterised by 54 volatile compounds belonging to nine different chemical groups (free fatty acids, esters, ketones, alcohols, aldehydes, furans/furanones, phenols, sulfur compounds, terpenes). The sensory aroma profile analysis of unsmoked and smoked cheese showed an important correlation with the analysis of volatile compounds. The microbial profile data indicated that in smoked cheese such as Oscypek the levels of selected bacteria diminished after the curding stage as a result of the subsequent scalding, brining and smoking stages. CONCLUSION: From the results it can be concluded that, although the analysed smoked cheese consisted of three groups of compounds, the first derived from biochemical reactions (free fatty acids, esters, ketones, alcohols, aldehydes, sulfur compounds), the second from smoking (furans and furanones, phenols) and the third from milk flavour (terpenes), it is the smoking process that mainly influences its typical flavour. Copyright © 2011 Society of Chemical Industry     

Observations on the succession dynamics of lactic acid bacteria populations in chill-stored vacuum-packaged beef

Drip samples were collected at 4-week intervals from 10 vacuum-packaged beef striploins stored for 16 weeks at −1.5 °C and assayed for populations of lactic-acid bacteria (LAB), pH and spoilage-causing fermentation products. A total of 15 LAB species were identified using pulsed-field gel electrophoresis and biochemical analysis. A pattern of succession was observed during storage between strains of Carnobacterium, Lactobacillus, Leuconostoc and Pediococcus. Acetic acid production was associated with increasing LAB populations generally and butyric acid production was associated with the development of a particular strain of Leuconostoc. Changes in pH is postulated as a driver of succession.     

Compositional factors associated with calcium lactate crystallization in smoked Cheddar cheese

Previous researchers have observed that surface crystals of calcium lactate sometimes develop on some Cheddar cheese samples but not on other samples produced from the same vat of milk. The causes of within-vat variation in crystallization behavior have not been identified. This study compared the compositions of naturally smoked Cheddar cheese samples that contained surface crystals with those of samples originating from the same vat that were crystal-free. Six pairs of retail samples (crystallized and noncrystallized) produced at the same cheese plant on different days were obtained from a commercial source. Cheese samples were 5 to 6 mo old at the time of collection. They were then stored for an additional 5 to 13 mo at 4°C to ensure that the noncrystallized samples remained crystal-free. Then, the crystalline material was removed and collected from the surfaces of crystallized samples, weighed, and analyzed for total lactic acid, l(+) and d(−) lactic acid, Ca, P, NaCl, moisture, and crude protein. Crystallized and noncrystallized samples were then sectioned into 3 concentric subsamples (0 to 5 mm, 6 to 10 mm, and greater than 10 mm depth from the surface) and analyzed for moisture, NaCl, titratable acidity, l(+) and d(−) lactic acid, pH, and total and water-soluble calcium. The data were analyzed by ANOVA according to a repeated measures design with 2 within-subjects variables. The crystalline material contained 52.1% lactate, 8.1% Ca, 0.17% P, 28.5% water, and 8.9% crude protein on average. Both crystallized and noncrystallized cheese samples contained significant gradients of decreasing moisture from center to surface. Compared with noncrystallized samples, crystallized samples possessed significantly higher moisture, titratable acidity, l(+) lactate, and water soluble calcium, and significantly lower pH and NaCl content. The data suggest that formation of calcium lactate crystals may have been influenced by within-vat variation in salting efficacy in the following manner. Lower salt uptake by some of the cheese curd during salting may have created pockets of higher moisture and thus higher lactose within the final cheese. When cut into retail-sized chunks, the lower salt, higher moisture samples contained more lactic acid and thus lower cheese pH, which shifted calcium from the insoluble to the soluble state. Lactate and soluble calcium contents in these samples became further elevated at the cheese surface because of dehydration during smoking, possibly triggering the formation of calcium lactate crystals.     

自然发酵中式香肠加工成熟过程中乳酸菌菌群研究

研究自然发酵川味、广味香肠加工成熟过程中乳酸菌菌群,旨在探明乳酸菌在香肠加工成熟过程中菌群分布及其变化规律。结果表明:(1)发酵初期两种香肠中乳酸菌数量均在104cfu/g水平,2d后不断增加,广味香肠中乳酸菌数量增加更快,第12天两者趋于一致,达到106cfu/g,第21天数量均跃升至107cfu/g,第30天达最大值,接近108cfu/g,40d后数量开始下降。(2)香肠中水分含量和pH值在加工成熟过程中总体呈下降的趋势,其乳酸菌数量变化与pH值和水分含量变化具有一定的相关性。(3)分离出的115株菌株经初步鉴定,杆菌80株,球菌35株,均为G ;从3个不同时期选出14株有代表性的菌株进行生理生化鉴定,拟确定S1-4、S3-2为清酒乳杆菌(Lactobacillus sakei),G21-10、C50-6、G50-4为戊糖乳杆菌(L.Pentosus),C21-6、C50-8、G50-9为植物乳杆菌(L.plantarum),其他的仅能鉴定到属,有乳杆菌、乳球菌。