High-pressure processing and antimicrobial biodegradable packaging to control Listeria monocytogenes during storage of cooked ham

The efficiency of combining high-pressure processing (HPP) and active packaging technologies to control Listeria monocytogenes growth during the shelf life of artificially inoculated cooked ham was assessed. Three lots of cooked ham were prepared: control, packaging with alginate films, and packaging with antimicrobial alginate films containing enterocins. After packaging, half of the samples were pressurized. Sliced cooked ham stored at 6 degrees C experienced a quick growth of L. monocytogenes. Both antimicrobial packaging and pressurization delayed the growth of the pathogen. However, at 6 degrees C the combination of antimicrobial packaging and HPP was necessary to achieve a reduction of inoculated levels without recovery during 60 days of storage. Further storage at 6 degrees C of pressurized antimicrobial packed cooked ham resulted in L. monocytogenes levels below the detection limit (day 90). On the other hand, storage at 1 degrees C controlled the growth of the pathogen until day 39 in non-pressurized ham, while antimicrobial packaging and storage at 1 degrees C exerted a bacteriostatic effect for 60 days. All HPP lots stored at 1 degrees C led to counts <100CFU/g at day 60. Similar results were observed when combining both technologies. After a cold chain break no growth of L. monocytogenes was observed in pressurized ham packed with antimicrobial films, showing the efficiency of combining both technologies.     

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.     

苏北地区冷鲜鸡加工及冷藏过程中常见微生物污染调查

本文调查了江苏省宿迁市具有代表意义的某商业屠宰企业里冷鲜鸡加工及冷藏过程中的微生物污染。分别对车间空气、接触面、刀具、预冷水及加工和冷藏过程中的鸡胴体进行取样,运用传统微生物培养方法培养和计数,找出冰鲜鸡加工工艺中存在的潜在危害。实验结果表明:生产前区(挂鸡间、放血间和烫毛脱毛间)、净膛工序、预冷水及与鸡胴体加工过程中的各类接触面是生产过程中的潜在污染源。前区与后区(去小毛间、净膛间、预冷间、分割包装间)的隔离对降低后区微生物污染起到关键作用,净膛工序加剧了鸡胴体的污染,所以应对净膛工序严格施行卫生标准操作程序。而后续的冲洗和预冷工序未能起到很好的减菌效果,造成包装后的冷鲜鸡初始微生物数量多,导致冷鲜鸡货架期短。因此应对预冷工艺进行优化,进一步降低冷鲜鸡的初始菌数。      

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.     

Antioxidant activity of Carob fruit extracts in cooked pork meat systems during chilled and frozen storage

The purpose of this study was to evaluate the effect of adding condensed tannins in the form of non-purified (Liposterine^®) or purified (Exxenterol^®) extracts obtained from Carob fruit to prevent lipid cooked pork meat systems from oxidising during chilling and frozen storage. The antioxidant activity of these extracts was compared with that of α-tocopherol. Meat lipid alteration was evaluated as thiobarbituric acid reactive substances content (TBARS) and polar material-related triglyceride compounds followed by high-performance size-exclusion chromatography (HPSEC). TBARS levels were lower (P < 0.05) in samples containing Liposterine (LM), Exxenterol (EM), and α-tocopherol (TM) than in control sample (CM) under chilled storage. TBARS formation was similar (P > 0.05) for LM and EM but lower (P < 0.05) than for TM. Polar material increased several times in all samples, but significantly less in TM and EM than in LM. Thermal oxidation compounds determined by HPSEC were lower (P < 0.05) in EM than in LM or TM. The changes in polar material were proportionally smaller after six months frozen storage than after chilled storage, with Exxenterol displaying the highest antioxidant protection. Therefore Carob fruit extracts can be successfully used to reduce fat alteration in cooked pork meat at chilled and frozen temperatures.     

High-pressure shift freezing: recrystallization during storage

High-pressure shift freezing has been proposed as a method to produce frozen food with smaller ice crystal size and, consequently, with reduced tissular damage and higher overall quality. The fate of this initially improved crystal size distribution, decisive for the long-term value of this procedure, is unclear. The recrystallization behaviour of partially frozen aqueous solutions, as food models, is here compared with that of similar classically frozen samples. A microscopic observation cell has been specially designed for this purpose. The temporal evolution of high-pressure shift frozen ice crystals has been fitted to different mechanism models and is found to be similar within experimental error to that of classically frozen samples. However, differences in the shape evolution of crystals have been detected, which can be ascribed to small differences in the initial distribution. The implications of these observations for the long-term storage of frozen food are discussed.     

Changes of bacterial diversity and main flora in chilled pork during storage using PCR-DGGE

This study was designed to explore the bacterial diversity and the main flora in chilled pork by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Longissimus muscle was removed from pork carcasses at 24 h postmortem. The muscle was tray- and vacuum-packaged at 4 degrees C for 2, 4, 7 days to extract the bacteria total DNA, respectively. The results indicated that the bacterial diversity of chilled pork decreased with storage time regardless of packaging method. Nine types of bacteria were identified, including Arthrobacter sp., Enterococcus sp., Staphylococcus sp., Moraxella sp., Pseudomonas sp., Lactobacillus sp., Aeromonas sp., Acinetobacter sp., Brochothrix thermosphacta. For tray-packaged pork, Pseudomonas sp. and B. thermosphacta were the dominant micro-organisms. The differences in the species found were related with the presence of Lactobacillus sp. in vacuum-packaged meat. The results of the present study might be useful to study the changes of the contaminating bacteria and their characteristics in chilled pork.     

High pressure processing applied to cooked sausage manufacture: physical properties and sensory analysis

Vacuum-packaged cooked sausages were treated at 500 MPa for 5 or 15 min at mild temperature (65?°C). Colour, texture and yield of pressure-treated sausages were evaluated, and compared to those of sausages treated with a conventional heat pasteurisation (80-85?°C for 40 min). Colour attributes did not change. Pressurised sausages were more cohesive and less firm than heat-treated sausages. Pressure treatment induced higher yield than heat treatment. Sensory analysis was also carried out. In some cases, the sensory panel did not detect differences between both types of sausages; and when there were differences, pressurised samples were preferred in more occasions because of their better appearance, taste and, especially, texture. High pressure processing can replace the second industrial heat treatment of cooked sausages.     

Biogenic amines in pressurized vacuum-packaged cooked sliced ham under different chilled storage conditions

This work was undertaken to study how storage conditions (at constant temperatures of 2±1 and 12±1°C and temperature fluctuations at 7±5°C) affect microbial development and the production of biogenic amines in vacuum-packaged cooked sliced ham subjected to high pressure (400MPa/10min/30°C). Initially, the product exhibited low levels of contamination. Microbiological changes during storage depend on the processing (non-pressure and pressure treatment) and the chilled storage conditions. Generally, microbial growth in pressurized samples was similar to that in the non-pressurized samples, although the total viable count and lactic flora were lower and growth was delayed. Processing and storage conditions affected the formation of each amine differently. The most important changes were in tyramine, which formed more quickly in non-pressurized products stored at 12°C and with temperature fluctuations. The formation of biogenic amines in these products can be prevented not only by ensuring good manufacturing practices and applying high pressure but also by ensuring the right chilled storage conditions.     

Changes in sugars during storage of sausages

The shelf-life of fresh British sausages is determined by the production of off-odours and colour changes due to microflora in the sausage. From work on meat, and in pure culture, it is known that the carbon source of the principal spoilage microorganism (Brochothrix thermosphacta) can affect its metabolism and change the nature of the secondary metabolic products. The sugar content of sausages was determined immediately after manufacture and during storage at 4°C. Reducing-sugar content (measured by dinitrophenol phenolate, or DNP) increased in the first few days after manufacture, then decreased. The apparent increase in reducing sugar was due to hydrolysis of rusk components (oligo- or polysaccharides) either by meat or microbial enzymes. Thus, the amounts and types of sugar available for microbial growth change during storage. The effect of sulphite on the sugar assay and on sugar utilisation was also measured. Sulphite affected the DNP reducing sugar assay and caused a small increase in the absorbance at 510 nm. Addition of sulphite to the sausage formulation also caused some changes in the reducing-sugar content during storage at 4°C.     

Vacuum-packed ripened sausages: evolution of volatile compounds during storage

BACKGROUND: Various studies have shown the ability of volatile compounds to influence the quality of charcuterie products because of their effect on sensorial properties. To the best of our knowledge, there are no data in the scientific literature concerning the evolution of volatile compounds of vacuum‐packed ripened sausages over time. The aim of this work was to evaluate the evolution of volatile compounds in vacuum‐packed ripened sausages over time, considering that this kind of packaging is the most commonly used to prolong the shelf‐life of these products. RESULTS: Sixty‐nine volatile compounds were identified. Those derived from spices represented the prevailing compounds at the beginning of storage and significantly decreased (P < 0.001) during 5 months of storage, as a result of the well‐known antioxidant activity. Conversely, compounds derived from the autoxidation of lipids, which are among those chiefly responsible of sensorial properties of meat products, significantly increased (P < 0.001). CONCLUSION: The research demonstrated that vacuum packaging influenced the evolution of volatile compounds during storage of ripened sausages. In particular, the increase of volatile compounds derived from autoxidation of the lipid fraction indicated that oxidative processes involved the fatty fraction of ripened sausages also in the scarcity of oxygen. Copyright © 2011 Society of Chemical Industry     

Biogenic amines in dry sausages during shelf-life storage

 Supercritical fluid extraction (SFE) with subsequent HPLC analysis was performed in order to determine the amount of capsaicinoids in paprika and chillie powder samples. The extraction yields obtained by SFE were compared to those obtained by organic solvent extraction and were found to be comparable or slightly lower. The advantages of SFE are shorter extraction times, less sample preparation needed prior to HPLC analysis and fewer interfering peaks in the chromatograms. In addition, the SFE method developed (extraction temperature=80 ^°C, density= 0.75 g/ml, modifier=20 μl water) was shown to be suitable for analysis of capsaicinoids (capsaicin, dihydrocapsaicin, nordihydrocapsaicin) that are present over a wide range of concentrations (10–1400 μg/g) in the samples. Received: 12 July 1996/Revised version: 26 August 1996     

Chopping temperature effects on the characteristics and chilled storage of low- and high-fat pork Bologna sausages

The object of this study was to investigate the influence of chilled storage (2 °C) and final chopping temperatures (8, 15 and 22 °C) on the characteristics and stability of Bologna sausage containing two levels of fat (8.5 and 23%). When the fat level was reduced there was a significant decrease in penetration force and an increase in both cooking and purge loss. A lower chopping temperature reduced purge loss during chilled storage. In general, an inverse relationship was found between chopping temperature and penetration force. Chopping temperature did not influence total aerobic count, but during chilled storage counts were significantly higher in the low fat sausages.     

Identification of extracellular DNase-producing bacterial populations on catfish fillets during refrigerated storage

Food spoilage is a major problem faced by consumers across the globe. As an enzyme that degrades DNA, DNase production on fish tissue seemed likely to aid in fish spoilage. Based on physical characteristics, bacteria producing extracellular DNase were isolated on selective media. 16S rDNA sequences were obtained identifying isolates as bacteria belonging to Aeromonas spp., Serratia spp., Shewanella spp., and Rahnella spp. Aeromonas spp. were the predominant bacteria isolated in this study; this statistically suggests that Aeromonas spp. are dominant in DNase-producing bacterial populations on catfish tissue. Results obtained in this study suggest that extracellular DNase-producing bacteria play a large role in catfish spoilage and support the need for further research on the role of Aeromonas spp. in fish spoilage. Rahnella spp. was isolated from catfish fillets in this study and identified, for the first time, as DNase producing bacteria.     

熟制小龙虾冷冻贮藏期间的品质变化研究

目的研究熟制小龙虾冷冻贮藏期间的品质变化。方法以熟制的带壳和去壳小龙虾为原料,将其在-18℃下贮藏1个月,通过检测虾肉的脂肪氧化程度、pH值、挥发性盐基氮(total volatile base nitrogen,TVB-N)值、盐溶性蛋白含量、色泽、质构特性等指标,考察小龙虾在冷冻贮藏期间的品质变化。结果在贮藏期间,带壳和去壳小龙虾虾肉的脂质氧化程度、pH值、TVB-N均呈上升趋势,总巯基含量和盐溶性蛋白含量持续下降,去壳虾肉颜色变化不显著,而带壳虾肉的色泽参数L*值和白度值W显著降低,硬度、弹性、咀嚼度和回复力在贮藏前期下降显著,之后下降趋势较为平缓。结论带壳和去壳的虾肉在贮藏前期(0～2周)的各指标无显著差异,而冷冻贮藏3周之后,带壳虾肉的品质优于去壳虾肉,冷冻贮藏一个月后,带壳虾肉和去壳虾肉均可正常食用。     

Effects of high-pressure processing on the volatile compounds of sliced cooked pork shoulder during refrigerated storage

The effect of high-pressure processing (pressure levels of 400, 500 and 600 MPa, and exposure times of 5 and 10 min) on the volatile profile of vacuum-packaged sliced cooked pork shoulder held for 28 days at 4 °C was assessed. The volatile fraction of pressurized samples scarcely changed immediately after treatment and remained stable for 14 days, regardless the pressure and time of exposure. After 21 days of storage, significant differences were observed in the profile of volatile compounds in pressurized samples as compared with control samples, these differences being treatment dependent. At the end of the storage period, control and 400 MPa samples showed higher levels of acetic and fatty acids, ethanol and ethyl esters, whereas 500 and 600 MPa samples contained higher levels of ethanal, branched-chain aldehydes, diacetyl, acetoin, and 2,3-butanediol among other compounds. These results suggest that the high-pressure treatment had a discriminant effect on the microbiota of cooked pork shoulder, which led to the accumulation of different volatile compounds during the refrigerated storage of control and pressurized samples.     

槟榔贮藏及加工过程中细菌群落结构变化

目的：确保槟榔产品细菌指标合格。方法：采用Illumina Miseq高通量测序技术对槟榔由原料到成品全过程关键工序样品进行测序分析。结果：7个样品共获得191 456条有效序列,隶属于239科790属,优势菌属包括Bacillus（芽孢杆菌属）、Pseudomonas（假单胞菌属）、Hydrogenophaga（氢噬胞菌属）、Leuconostoc（明串珠菌属）和Chryseobacterium（金黄杆菌属）。槟榔原籽贮藏前后细菌的群落结构存在显著差异,贮藏前（新籽）的物种丰富度要高于贮藏后（老籽）的,而老籽则拥有更高的物种多样性。槟榔加工过程中煮籽及切籽后的工序能有效减菌,两阶段消亡细菌属数量分别为216和227,煮籽到闷香之间的工序易受到环境中细菌污染,新增细菌属数量为126。结论：槟榔加工过程中污染细菌多样性变化的研究指示细菌污染应重点防控发制闷香中的细菌增殖及各工序中的环境污染,而用好煮籽工序及成品前工序是减菌的关键。