Characterization of lactic acid bacteria isolated from vacuum-packed cooked ring sausages

The bacterial populations of the surface layer and the centre of 15 spoiled vacuum-packed cooked ring sausages were characterized. About 95% of the total bacterial population in the surface layer and 55% at the centre were lactic acid bacteria. Another large bacterial group at the centre consisted of Bacillus spp. The lactic acid bacteria on the surface and at the centre were quite similar. Atypical streptobacteria, i.e. homofermentative psychrotrophic lactobacilli, were a major group of lactic acid bacteria in the surface layer of the spoiled sausages. Three main homofermentative groups could be observed on the basis of different carbohydrate patterns. Heterofermentative lactic acid bacteria belonged mainly to genus Leuconostoc. The proportion of leuconostocs in the spoiled sausages was also quite large. They could be divided into three main groups on the basis of different carbohydrate fermentation patterns. The lactic acid bacteria population of spoiled cooked ring sausages thus seemed to be heterogeneous. The strains isolated resembled strains observed by other workers in meat and meat products.     

Lactic acid and pH as indicators of spoilage for vacuum-packed cooked ring sausages

Lactic acid production and pH changes of 206 vacuum-packed cooked ring sausages stored at 2, 4 and 12°C from 21 different production runs were monitored as a function of time and of microbial growth. The total lactic acid concentrations and pH values were first at a constant level, starting to increase sharply after the lactobacilli count reached about 5 × 10⁷ or 6 × 10⁷ cfu/g, respectively. The lactic acid and pH changes as a function of the lactobacilli count were similar at 4 and 12 ° C. The sharp increase at high lactobacilli counts was observed in both -lactic acid and -lactic acid. The variation was lesser and the increase greater in -lactic acid formation than in -lactic acid. Above a level of 3–4 mg lactic acid/g most of the samples were deemed unfit. The pH started to decrease from a level of approx. 6.3; below 5.8–5.9 the samples were deemed unfit. The lowest pH value observed was 4.58. Both a high lactic acid content and a low pH indicated that the sausage was spoiled. These changes, however, took place at later stages of storage, and do not give information about the early phase of spoilage.     

Lactobacillus contamination of cooked ring sausages at sausage processing plants

The contamination of Finnish cooked ring sausages with lactobacilli determined as organisms growing on Rogosa SL agar after 5 days of anaerobic incubation was studied at two sausage processing plants. After cooking, the skin of the sausages was almost free of lactobacilli and the surface of the sausages became contaminated with lactobacilli during chilling after cooking and during packing. Lactobacilli were found in the air and on the structures and equipment in the chill rooms and the packing rooms, and these areas were assumed to be sources of contamination for the sausages. The amount of lactobacilli in these areas varied between the plants examined. The number of lactobacilli in the sausage processing area apparently affected the extent of the contamination of the sausages. The lactobacilli contamination varied also during the working day. It is suggested that the extent of contamination has an effect on the shelf-life of the sausages.     

TBARS predictive models of pork sausages stored at different temperatures

2-Thiobarbituric acid reactive substances (TBARS) is an important quality index for pork sausages. To study this in pork sausages during storage, kinetic models were developed to predict TBARS content changes of pork sausages at different temperatures. The predictive models of TBARS content with respect to storage time and temperature were developed based on primary and Arrhenius equations. The regression coefficients (R² > 0.95) indicated the acceptability of the primary reaction and Arrhenius model for predicting TBARS content changes of pork sausages. The activation energy (E_A) of TBARS is 14.12 kJ mol^− 1, and the corresponding rate constant (k₀) is 9.262 × 10¹⁰. Relative errors between predicted and measured values of TBARS content are all within ± 8%. Thus, the established model could effectively predict the TBARS content of pork sausages between 5 and 35 °C during storage.     

Microbiological safety of retail vacuum-packed and modified-atmosphere-packed cooked meats at end of shelf life

A study of retail modified-atmosphere-packed and vacuum-packed cooked ready-to-eat meats was undertaken from September through mid-November 2003 to determine the microbiological quality at the end of shelf life and to establish any risk factors in the production, storage, and display of this product. Examination of 2,981 samples using Microbiological Guidelines criteria revealed that 66% were of satisfactory or acceptable microbiology quality, 33% were of unsatisfactory quality mainly due to high aerobic colony counts and Enterobacteriaceae concentrations, and 1% were of unacceptable quality due to the presence of Listeria monocytogenes at 100 CFU/g or higher (27 samples; range of 10(2) to 106 CFU/g) and Campylobacter jejuni (1 sample), indicating a risk to health. All samples at the end of the shelf life had satisfactory (<20 CFU/g) and/or acceptable (<102 CFU/g) levels of Staphylococcus aureus and Clostridium perfringens, four samples (<1%) had unsatisfactory levels of Escherichia coli (range of 102 to 106 CFU/g) and 5.5% of the samples contained L. monocytogenes at <20 CFU/g (4.8%) or between 20 and 100 CFU/g (0.7%). More samples of chicken (45%; 224 of 495 samples), beef (43%; 160 of 371 samples), and turkey (41%; 219 of 523 samples) were of unsatisfactory or unacceptable quality compared with ham (23%; 317 of 1,351 samples) or pork (32%; 67 of 206 samples). Twelve different L. monocytogenes typing characters (serotype-amplified fragment length polymorphism type-phage type) were evaluated for isolates recovered from samples of unacceptable quality, and the 1/2-IX-NT type was recovered from almost half (48%) of these samples. Salmonella was not detected in any samples examined. Risk factors identified for cooked meats that were microbiologically contaminated more frequently included vacuum packaging, packaging on retail premises, slicing, temperature not monitored in display units, and no hazard analysis system in place. Results from this study also suggest that the shelf life assigned to some modified-atmosphere-packed and vacuum-packed meats may not be appropriate.     

Biogenic amines in vacuum-packed and non-vacuum-packed flesh of carp (Cyprinus carpio) stored at different temperatures

Samples of carp flesh (Cyprinus carpio), vacuum-and non-vacuum-packed were stored at 3 and 15 °C. Chemical, sensory and microbial qualities were measured throughout the storage time to determine the changes that took place and to evaluate the effects of both storage temperature and the means of packaging. Seven biogenic amines (putrescine, cadaverine, spermidine, spermine, histamine, tyramine and tryptamine) were determined. Putrescine and cadaverine showed the best correspondence with the sensory and microbial states of the samples. Low storage temperature had a dominant effect, resulting in low biogenic amine content and better quality of samples. The effect of vacuum-packaging was less obvious, especially in samples kept at 15 °C. Application of vacuum-packaging at 3 °C prolonged the shelf life by about 4–5 days.     

The ecology of bacterial spoilage of fresh meat at chill temperatures

At chill temperatures the spoilage flora of meat is composed of psychrotrophs originating largely from the hides of slaughtered animals. Under humid conditions, aerobic floras are usually dominated by pseudomonads while anaerobic floras are dominated by lactobacilli. In both cases growth occurs on low molecular weight soluble components of meat which are attacked in the order glucose, glucose-6-phosphate (Enterobacteriaceae only) and amino acids. Under aerobic conditions spoilage becomes detectable when the bacteria begin to degrade amino acids which remain abundant at the meat surface when growth ceases, probably because of limited availability of oxygen. Under anaerobic conditions growth ceases because the diffusion of fermentable substrates to the surface is not rapid enough to support further growth. Aerobically, there is no interaction between different bacterial species until the maximum cell density is approached; anaerobically, however, lactobacilli produce an antimicrobial agent which inhibits growth of competing species. The composition of spoilage floras can be affected by changes in water activity and the storage atmosphere.     

Storage stability of cooked sausages containing vegetable oils

Comminuted cooked sausages were produced using standard industrial practices, by substituting corn oil, sunflower oil, cotton seed oil, soybean oil and hydrogenated vegetable fat for animal fat. When processed, products were assessed for their stability with respect to autoxidation and change in organoleptic properties during vacuum-packed storage in a domestic refrigerator at 4 °C. Data obtained indicated that changes in thiobarbituric acid (TBA) values and organoleptic properties of products produced using corn oil, sunflower oil and hydrogenated vegetable fat were similar to those observed for reference material produced using lard. In the case of samples produced using soybean and cotton seed oil, TBA value changes were more pronounced, but did not exceed acceptable limits. A more rapid deterioration of organoleptic characteristics was also observed for the same samples, which showed flavour problems after 3 months of storage at 4 °C. Substitution of plant oils for lard considerably reduced the cholesterol content and increased the ratio of unsaturated to saturated fatty acids of cooked sausages.

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Lagerungsstabilität von Brühwürsten, die mit verschiedenen pflanzlichen Ölen hergestellt wurden

Zusammenfassung Es wurden feinzerkleinerte Brühwürste unter Praxisbedingungen gefertigt, die anstelle des tierischen Fettes (Schweinespeck), pflanzliche Öle, wie Sonnenblumenöl, Maiskornöl, Sojabohnenöl, Baumwollsamenöl und Kokosnußsfett enthielten. Die Untersuchungen der fertigen Produkte erstreckten sich vor allem auf sensorische Eigenschaften und autoxidative Stabilität während der Kühllagerung bei 4 °C unter Vakuum. Die Ergebnisse haben gezeigt, daß die Änderungen der TBA-Werte und der organoleptischen Eigenschaften der Chargen mit Maiskornöl, Sonnenblumenöl und Kokosnußfett fast ähnlich wie die der Kontrollcharge (Schweinespeck) waren. Bei der Verwendung von Sojabohnenöl und Baumwoll-samenöl waren die Änderungen der TBA-Werte dagegen intensiver, ohne jedoch die obersterlaubte Grenze zu überschreiten. Hier wurde ebenfalls, nach einer dreimonatigen Lagerung bei 4 °C, eine unerwünschte Änderung ihrer organoleptischen Eigenschaften, vor allem des Aromas, beobachtet.

     

Fish silage prepared from different cooked and uncooked raw materials: chemical changes during storage at different temperatures

Four silage types were prepared from raw and cooked whole herring, whole mackerel, by‐products from the filleting‐line of cod and saithe, and from the viscera of cod. Each silage type was stored at 4, 20 and 50°C for 48 days. The raw materials were analysed fresh and after 2, 4, 8, 16, 32 and 48 days of storage. Dry matter, crude protein and total fat were not affected by the different storage temperatures or the length of the storage period. Neither was there any change in amino acid contents. Chemical composition in different silage types reflected the amounts in the raw materials used for silage production. Hydrolysis, on the other hand, varied with the type of raw material used for silage production as well as with the temperature under which the silages were stored. Cooked raw materials did not show any change in hydrolysis during storage. © 1999 Society of Chemical Industry     

真空包装低温熟制鸽子货架期预测模型的建立

为了研究低温熟鸽货架期模型,对真空包装低温熟制鸽子在不同温度条件下贮藏的品质变化进行了评价：贮藏在4℃,10℃,15℃,20℃,25℃样品的菌数总数、总挥发性盐基氮均随着贮藏天数增加有不同程度的增加,在10～25℃条件下,贮藏后期菌落总数变化趋势高于贮藏初期;与 4 ℃和10℃的样品相比,其它3组温度下的感官变化更加明显。此外,所有样品的总大肠菌群平板计数均小于10 CFU/g,且不同贮藏温度下没有差异。利用熟制鸽子菌落总数指标,通过Gompertz方程和平方根方程进行拟合,建立低温熟鸽货架期模型。该模型的预测的数值与实践测定值的相对误差在±10%以下。表明该模型是可靠的。     

Dried sausages fermented with Staphylococcus xylosus at different temperatures and with different ingredient levels - Part II. Volatile components

Sausages, with added Staphylococcus xylosus, were fermented at different temperatures and with different added levels of salt, glucose, nitrite, nitrate and Pediococcus pentosaceus in accordance with a six factor fractional design. The volatile compounds from the sausages were collected by dynamic headspace sampling and quantified and identified by gas chromatography and gas chromatography-mass spectrometry. The effects of temperature and different ingredients on the levels of individual volatiles were tested using multiple linear regression and analysis of variance. The study showed that sausages fermented under modern production conditions (high temperature, addition of glucose, nitrite, Pediococcus pentosaceus) in contrast to 'old-fashioned' sausages (added nitrate and fermented at low temperature) are likely to contain higher amounts of volatile acids, but lower levels of ethyl esters, certain short chain aldehydes as well as lipid autoxidation products. Several nitriles, nitro-alkanes and one organic nitrate were identified for the first time in fermented sausages. Reaction mechanisms for those compounds and other classes of compounds are proposed and discussed in detail.     

Determination of vitamins A and E in cooked sausages

A reliable and sensitive reverse-phase HPLC method is described for the separation and quantification of all-trans-retinol and dl-α-tocopherol in cooked sausages. Samples were chromatographed with UV and fluorescence detection on a 15 cm × 0.4 cm i.d. Spherisorb ODS-2, 5 μm column, using as mobile phase a mixture of 90% acetonitrile and 10% tetrahydrofuran. Sample preparation included saponification and extraction by n-hexane. Addition of pyrogallol and oxygen-free conditions avoided oxidation of both vitamins, increasing recovery percentages, which ranged from 90.0 to 95.0%. Precision was 1.0% (within a day) and 3.4% (between days) for all-trans-retinol and 1.1% (within a day) and 2.6% (between days) for dl-α-tocopherol. Detection limits were 10 μg/100 g for all-trans-retinol and 0.1 mg/100 g for dl-α-tocopherol with a signal-to-noise ratio of 3. Twenty samples of six different products were analyzed in duplicate. Average for all-trans-retinol in “enriched chopped” was 108 mg/100 g fresh weight, and the mean value for dl-α-tocopherol in “enriched chopped” was 2.3 mg/100 g fresh weight.     

低温猪肉火腿肠加工工艺

为探究低温猪肉火腿肠的最佳生产工艺,研究在传统高温火腿肠加工工艺的基础上,结合低温肉制品加工原理制备低温猪肉火腿肠,以感官评价为指标,探究影响产品质量的主要因素。结果表明,原料肥瘦比、肥肉预处理方式、腌制剂配方、斩拌工艺与烘烤条件是影响低温猪肉火腿肠的主要因素,产品制备的最佳工艺条件为:原料肉肥瘦比2∶8(质量比),用出肉板孔径为8 mm的绞肉机对肥肉进行初步的绞制,腌制液配料(质量分数)为食盐2. 5%,亚硝酸盐0. 003%,D-异抗坏血酸钠0. 3%,复合磷酸盐0. 5%(m(六偏磷酸钠)∶m(三聚磷酸钠)∶m(焦磷酸钠)=10∶30∶17)在4℃环境下腌制24 h,最佳斩拌条件为低速(1 000 r/min)与高速(2 000 r/min)结合斩拌330 s,肉糜灌肠后60℃烘烤30 min再蒸煮杀菌,低温保藏。该条件下制备的产品在气味、外观、组织结构、风味等方面均最佳。     

Dried sausages fermented with staphylococcus xylosus at different temperatures and with different ingredient levels. Part IV. Amino acid profile

Sausages with added Staphylococcus xylosus were fermented at different temperatures and with different added levels of salt, glucose, nitrite, nitrate and Pediococcus pentosaceus in accordance with a six-factor fractional design. The amounts of individual amino acids were measured and the effects of temperature and different ingredients on the amino acid profile were tested using multiple linear regression and analysis of variance. Also, the amino acid profile was correlated to the level of volatile compounds by partial least squares analysis. The study showed that the level of free amino acids was significantly affected by the different factors. High fermentation temperature and nitrite content increased the amount, while high contents of salt, nitrate, glucose and P. pentosaceus lowered the amount of free amino acids. In general, temperature and nitrate had the greatest influence. It was shown that the amounts of the volatile compounds, 2-methyl propanal, 2- and 3-methyl butanal, were inversely correlated with the amounts of valine, isoleucine and leucine, respectively, indicating that those volatiles were degradation products of the latter.     

High-pressure liquid chromatographic determination of ascorbic acid in cooked sausages

The purpose of this paper was to study and optimize both extraction and high-pressure liquid chromatography (HPLC)-UV detection procedures to develop a proper method for the determination of ascorbic acid content in cooked sausages. A simple and sensitive reversed-phase HPLC method for the NH2-bonded phase has been described for the determination of ascorbic acid content in cooked sausages. Various extracting agents were tested to solubilize the vitamin, with 5% (wt/vol) metaphosphoric acid giving the best results. Samples were chromatographed with UV detection at 248 nm on a 25-cm Spherisorb NH2 cartridge with a 0.4-cm inside diameter with a mixture of 0.02 M potassium phosphate buffer solution (pH 3.6) and acetonitrile (40:60, vol/vol) for the mobile phase. The method's precision within a day was 1.2%, and its precision between days was 3.8%. The detection limit was 1.6 mg/100 g. Recovery ranged from 91.4 to 96.2% for ascorbic acid added to meat samples. Twenty samples of six different products were analyzed in duplicate. For the samples analyzed, the mean value for ascorbic acid ranged between 21.555 and 24.899 mg/100 g of fresh weight.     

Dried sausages fermented with Staphylococcus xylosus at different temperatures and with different ingredient levels - Part I. Chemical and bacteriological data

Sausages with added Staphylococcus xylosus were fermented at different temperatures and with different added levels of salt, glucose, nitrite, nitrate and Pediococcus pentosaceus in accordance with a six factor fractional design. The numbers of surviving Staphylococcus xylosus, lactic acid bacteria, pH, free fatty acids and residual amounts of nitrite and nitrate were measured. The effects of temperature and different ingredients on the chemical and bacterial data were tested using multiple linear regression and analysis of variance. The study showed that numbers of surviving Staphylococcus xylosus were reduced by high fermentation temperature, especially when salt concentration was low and glucose concentration high. High levels of nitrite and addition of Pediococcus pentosaceus had adverse effects as well. pH was lowered by high fermentation temperature, low salt concentration and addition of glucose and Pediococcus pentosaceus. On the other hand p H was increased by addition of nitrate. The pH-lowering effect of glucose was small when temperature was low. The residual levels of nitrite and nitrate were increased by addition of nitrate, but then increased and decreased, respectively, by increasing temperature. Addition of glucose and Pedio coccus pentosaceus lowered the residual amount of nitrite. The level of free fatty acids was reduced by salt and increased by higher temperature. Of the individual acids, the amount of linoleic acid was also increased by addition of Pediococcus pentosaceus and decreased by nitrate.     

Effect of high pressure treatment on microbial populations of sliced vacuum-packed cooked ham

In this study, culture-dependent and culture-independent approaches were used to reveal the microbial diversity and dynamic changes occurring in sliced vacuum-packed cooked ham after high pressure processing (HPP, 400MPa or 600MPa for 10min at 22°C) during refrigerated storage over 90days. Direct extraction of genome DNA and total RNA from meat samples, followed by PCR-denaturing gradient gel electrophoresis (DGGE) and RT-PCR-DGGE on 16S rDNA V3 region, was performed to define the structure of the bacterial populations and active species in pressurized cooked ham. Results showed that HPP affected differently the various species detected. The predominant spoilage organisms of cooked ham, such as Lactobacillus sakei and Lactobacillus curvatus, were found to be very sensitive to pressure as they were unable to be detected in HPP samples at any time during refrigerated storage. Weissella viridescens and Leuconostoc mesenteroides survived HPP at 600MPa for 10min at 22°C and were responsible for the final spoilage. An RNA-based DGGE approach clearly has potential for the analysis of active species that have survived in pressurized cooked ham. High pressure processing at 400 or 600MPa for 10min at room temperature (22°C) has a powerful inhibitory effect on the major spoilage bacteria of sliced vacuum-packed cooked ham. High pressure treatment may lead to reduced microbial diversity and improve the products' safety.