Effect of NaCl on lipid peroxidation-derived aldehyde, 4-hydroxy-2-nonenal formation in minced pork and beef

Pork and beef containing NaCl were stored at 0 °C and changes in 4-hydroxynonenal (HNE) content were analyzed after 0, 3, 7 and 10 days. As an index of the lipid peroxidation level, malonaldehyde (MA) content was also analyzed. In pork, HNE content in samples with 2% NaCl increased (P<0.05) after 7 and 10 days of storage. In beef, HNE content in all samples increased during storage. The HNE content in samples with NaCl was higher than those of the control, after 7 and 10 days of storage, although the difference was not always significant. Judging from MA content, NaCl may act as a pro-oxidant in pork and beef. HNE may accumulate in pork and beef in which lipid peroxidation is progress.     

Lipid peroxidation-derived cytotoxic aldehyde, 4-hydroxy-2-nonenal in smoked pork

The contents of 4-Hydroxy-2-nonenal (HNE), cytotoxic aldehyde, in smoked meat products (ham, bacon and sausage) were analyzed. All the samples analyzed contained HNE, although large differences in the contents between the different samples were observed. In one lot of ham (H1) and wiener sausage (WS1) a high level in HNE was observed. The changes of HNE contents of pork meats containing 0, 0.1, 0.5 and 1% Sugi wood vinegar (SWV) stored at 0?°C were also analyzed for 7 days. As an index of lipid peroxidation level, malonaldehyde (MA) contents were also analyzed in these samples. After 7 days of storage, HNE was detected only in pork meats containing 1% SWV and the level was similar to those of H1 and WS1. Judging from MA contents, SWV may act as a pro-oxidant in pork meats and HNE may accumulate in pork in which lipid peroxidation is in progress.     

PCR方法快速鉴别食品中肉的种类

本文针对食品中肉成分种类鉴别开发了一种快速灵敏的PCR检测方法,可检测食品中是否存在猪肉、牛肉、羊肉以及鸡肉等成分。采用微波助提法提取样品中DNA,简化了前处理步骤,可在短时间内完成从多种不同类型肉与肉制品中提取肉成分DNA。为了评价方法的可靠性与灵敏度,猪肉以及掺入了不同比例浓度猪肉成分的食品样品采用本方法进行了核酸提取与PCR分析。检测结果表明,方法可检测出低至含有0.5%浓度的猪肉成分的混合样品。随机抽取50份不同类型的市面食品样品,检测出5份食品含有猪肉成分,7份食品中含有牛肉成分,5份食品中含有羊肉成分。该样品前处理方法、DNA提取方法以及PCR检测方法可广泛应用于食品中肉成分种类的检测鉴别。     

DETECTION OF SPECIES ADULTERATION IN PORK PRODUCTS USING AGAR-GEL IMMUNODIFFUSION AND ENZYME-LINKED IMMUNOSORBENT ASSAY

Mixing undeclared species in meat products is illegal under food labeling regulations. This study compared the conventional agar-gel immunodiffusion (AGID) with the Enzyme-Linked Immunosorbent Assay (ELISA) for detecting species adulteration and assessed the species adulteration problem in raw ground pork products in Alabama retail markets. Forty-two ground pork and 87 fresh pork sausage samples collected throughout Alabama were examined by AGID and ELISA for four species: pork, beef, poultry and sheep. Using ELISA, 91 % of the ground pork samples were found to contain other meats while 71 % were found to be contaminated using AGID. Using ELISA, 54% of the sausage samples were found to contain undeclared species while none were found to be contaminated using AGID. The major adulterating species in the pork products was beef followed by poultry and sheep. Reliable analytical methods, such as ELISA, must be used as a regulatory tool to discourage the meat species adulteration problem in retail markets.     

High number of Yersinia enterocolitica 4/O:3 in cold-stored modified atmosphere-packed pig cheek meat

Yersinia enterocolitica is a psychrotrophic, facultative anaerobic zoonotic bacterium belonging to family Enterobacteriaceae and it can be transmitted from pigs to humans through pork. The growth of bacteria belonging to Enterobacteriaceae and aerobic spoilage bacteria is usually effectively restricted by 20% or more CO(2) enriched atmosphere at refrigerated temperatures. In this study, 40 samples of meat strips from pig cheek (musculus masseter) and 40 samples from hind leg (m. semimembranosus) muscles were packaged in modified atmosphere (MA) (30% CO(2)/70% O(2)) and stored at 6°C for 12d. Twenty naturally contaminated samples per muscle type were studied on days 1 and 13. Violet red bile glucose (VRBG) and de Man Rogosa Sharpe (MRS) agar plates were used for enumeration of Enterobacteriaceae including Y. enterocolitica and lactic acid bacteria, respectively. During the 12-d storage at 6°C in MA, the mean number of bacteria on pork strips of cheek meat was increasing from 1.6 to 4.5 log cfu/g and from 3.1 to 7.2 log cfu/g on VRBG and MRS agar plates, respectively. Most of the oxidase-negative isolates on VRBG plates, which were isolated from the cheek meat samples after 12-d cold storage in MA, were identified as Y. enterocolitica 4/O:3. The mean number of this pathogen was 4.1 log cfu/g varying between 2.3 and 5.4 log cfu/g. The pH of the cheek meat and leg meat was measured on days 1 and 13, and it remained high (pH>6) in most cheek meat samples during the storage. No Y. enterocolitica 4/O:3 was isolated from meat strips of hind leg. This study shows that cheek meat of slaughter pigs is contaminated with Y. enterocolitica 4/O:3 and that this pathogen can grow well on raw pork packaged in MA at 6°C even in the presence of high number of lactic acid bacteria.     

Isolation of Yersinia enterocolitica from ready-to-eat foods and pork by a simple two step procedure

Out of 119 ready-to-eat food samples and pork processed for isolation of Yersinia enterocolitica, 15 samples (12·6%) were positive for the presence of Y. enterocolitica by a two step procedure in a modified trypticase soy broth containing 0·25% yeast extract, 0·2% bile salts and 4 μg ml^-1 Irgasan at pH 7·6 and upon incubating at 10°C and 22°C for 6 days. Only five samples (4·2%) were positive by cold enrichment in trypticase soy broth containing 0·2% yeast extract, incubated at 4°C for 14 days. Four strains of Y. enterocolitica and one strain of Y. intermedia were isolated from pork samples processed by cold enrichment. Out of 15 strains of Y. enterocolitica isolated from pork (four strains) and ready-to-eat food samples (10 strains) by two step procedure only three strains belonged to pathogenic serotype O:3 and which were isolated only from pork samples. Overall recovery of Y. enterocolitica was much better by the two step procedure as compared to cold enrichment (P < 0·05).     

两种方式加工鱼香肉丝的SDE-GC-MS挥发性风味成分对比

采用同时蒸馏萃取法结合气相色谱-质谱联用技术分别对鱼香肉丝市售菜肴和料理包中的挥发性风味成分进行提取与分离。结果共鉴定出136 种成分,市售菜肴鉴定出化合物79 种,料理包鉴定出化合物104 种,两种样品中均检测到的化合物有47 种,两者在酯类及含硫含氮及其他杂环化合物检出上存在较大差异。可能造成风味差异影响的化合物有：β-水芹烯、石竹烯、倍半水芹烯、苯甲酸甲酯、苯甲酸乙酯、桉树脑、2,3,5,6-四甲基吡嗪、二烯丙基三硫醚。     

Extent of microbial contamination in United States pork retail products

To determine the extent of microbiological contamination of U.S. pork, 384 samples of retail pork were collected from 24 stores in six cities, including (i) whole-muscle, store-packaged pork; (ii) fresh, store-packaged ground pork and/or pork sausage; (iii) prepackaged ground pork and/or pork sausage; and (iv) whole-muscle, enhanced (injected or marinated; 60% store-packaged, 40% prepackaged) pork. Additional samples (n = 120) of freshly ground pork and/or pork sausage were collected from two hot-boning sow/boar sausage plants, two slaughter and fabrication plants, and two further-processing plants. Samples were analyzed for aerobic plate counts (APC), total coliform counts (TCC), Escherichia coli counts (ECC), and incidences of Salmonella spp., Listeria monocytogenes, Campylobacter jejuni, Campylobacter coli, and Yersinia enterocolitica. Mean log APC and TCC were highest (P < 0.05) for store-ground pork, while whole-muscle, enhanced products and prepackaged ground products had the lowest (P < 0.05) APC. Mean log APC and TCC were higher (P < 0.05) in samples from the slaughter and fabrication plants than in samples from hot-boning and further processing plants. Mean log ECC were lower (P < 0.05) in samples from further-processing plants compared to slaughter and fabrication plants and hot-boning, sow and boar sausage plants. L. monocytogenes was detected in 26.7% of plant samples and 19.8% of retail samples and was present more frequently in ground products. Y. enterocolitica was detected most often in whole-muscle, store-packaged cuts (19.8%) and in store-ground product (11.5%). Salmonella spp. were found in 9.6% of retail samples and 5.8% of plant samples, while C. jejuni and C. coli were found in 1.3% of retail samples and 6.7% of plant samples. Pork products exposed to the most handling and processing appeared to be of the poorest microbiological quality. These results should be useful in risk assessments that are directed at the identification of actions that could enhance food safety.     

ANALYSIS OF PORK PRODUCTS FOR CHEMICAL RESIDUES

Ham (n=29), pork sausage (n=27), and pork subcutaneous adipose tissue (n=71) samples were analyzed for a maximum of 25 different chlorinated hydrocarbon/organophosphate pesticide/metabolite residues by gas chromatography. Furthermore, 13 samples each of adipose tissue, kidney, liver and muscle (total, n=52) were collected from commercial hog slaughter facilities and analyzed for diethylstilbestrol, zeranol, trenbolone acetate, azaperone and propiopromazine (tranquilizers), clenbuterol, and carazolol. Results showed that none of the adipose tissue samples contained pesticide residue levels greater than the detection threshold of 0.05 ppm. Five ham samples contained detectable (>0.003ppm), but nonviolative residue levels of dichloro-diphenylchloroethane (DDE) and alpha-benzene hexachloride (α-BHC). Six sausage samples contained detectable (> 0.05ppm) but nonviolative levels of diazinon, dichlorodiphenyltri-chloroethane (DDT), tetrachlorodiphenylethane (DDD), DDE, lindane or alpha, beta and delta isomers of BHC. None of the pork tissue samples contained tranquilizers or other drug residues at levels higher than the detection threshold of 1 ppb.     

2010年泰州市餐饮业食品安全监测结果分析

目的了解泰州市餐饮业食品安全动态,及时发现餐饮服务食品安全隐患,为监管部门有效监管提供参考。方法按照《关于委托开展江苏省2010年餐饮服务食品安全监督抽检工作的函》检测技术要求提供的检测方法和食品检验工作规范进行监测抽样,采高风险食品、餐饮具及食品原料3大类样品312份,对大肠菌群、菌落总数、沙门菌等7个微生物指标及防腐剂、色素、重金属、兽药残留等28个理化指标进行监测。结果 312份样品总体合格率为50.3%,其中食物原料大米、小麦粉、食用油全部合格;生活饮用水合格率为75.0%;猪肉(猪肝)合格率为56.2%;高风险食品合格率仅为17.3%,熟肉制品、鲜榨果蔬汁、非发酵豆制品、沙拉、凉拌菜、生食水产品、盒饭合格率分别为20.0%、15.0%、6.25%、25.0%、0、12.5%、37.5%。合格率偏低主要受菌落总数、大肠菌群两个卫生学指标的影响,7类样品合格率差异无显著性;餐饮具合格率为75.6%。结论猪肉污染严重;熟肉制品、沙拉等直接入口食品卫生状况较差,提示相关监管部门应加强加工场所卫生管理,从业人员卫生意识宣导以及原料选控、加工过程及餐具消毒等关键环节的监督管理。     

Evaluation of a combined culture and PCR method (NMKL-163A) for detection of presumptive pathogenic Yersinia enterocolitica in pork products

A combined culture and PCR method for detection of pathogenic Yersinia enterocolitica in food (NMKL-163A) was evaluated by testing samples of artificially and naturally contaminated pork. The performance of the pre-PCR sample treatment, buoyant density centrifugation, was first compared with two commercially available methods (DNeasy tissue kit and PrepMan). We found that similar sensitivity was reached (i.e., 25 CFU/g of food was detected by single PCR) with the buoyant density centrifugation and the DNeasy Tissue kit when tested on overnight enrichments. However, the DNeasy tissue kit was superior when tested on nonenriched homogenates; the detection limit was 25 CFU/g in minced beef by single PCR and 25 CFU/g in sausage by nested PCR. We then analyzed 100 raw minced pork samples. Thirty-five tested positive for presumptive pathogenic Y. enterocolitica when analyzed by the NMKL-163A method, whereas none tested positive when analyzed in parallel by a standard culture method (ISO 10273). We also analyzed 97 samples of cold-smoked pork sausage, of which approximately 11% tested positive by the NMKL-163A method. This study showed that sensitivities such as those obtained by nested PCR were required for detection of the pathogen in naturally contaminated samples, and therefore the nested PCR primers, which are included in the NMKL-163A method only as an option, need to be validated and applied routinely.     

EVALUATION OF FLUORESCENT IN SITU HYBRIDIZATION (FISH) AS A RAPID SCREENING METHOD FOR DETECTION OF SALMONELLA IN TONSILS OF SLAUGHTERED PIGS FOR CONSUMPTION: A COMPARISON WITH CONVENTIONAL CULTURE METHOD

The pork tonsils are an important carrier of Salmonella, which could be involved in the contamination of pork products during the slaughter process. This paper reports a 23S rRNA fluorescent in situ hybridization (FISH) method used as a rapid screening tool for Salmonella detection in tonsils of slaughtered pigs and its comparison with the conventional culture method. As a rapid screening method, the FISH technique would reduce the high volume of negative samples that are routinely analyzed, indicating presumptive positive samples in a real and practical time. The use of a Sal3 probe allowed the rapid (7 h) Salmonella detection in 16 (34%) of 47 naturally contaminated tonsils, without pre‐enrichment. Salmonella was isolated by the culture method in six samples that were also FISH‐positive samples, and FISH failed to identify only one of the culture‐positive samples. The results indicate the potential of this technique as a rapid screening method for detecting Salmonella in tonsils from pork slaughtered for consumption.     

On-Site NIR Spectroscopy to Control the Shelf Life of Pork Meat

Control of meat shelf-life includes the time that it remains in the exhibitor of sale (such as the supermarket) until its rejection for the consumer, or withdrawal due to expiry date. Near infrared spectroscopy (NIRS) is one of the most promising techniques for large-scale meat quality control. This study investigated the potential of on-site NIRS portable instrumentation-based models to predict three microbiological parameters to establish if pork meat is acceptable or not for consumption (aerobic Mesophilous microorganisms, Enterobacteriaceae, and lactic acid bacteria) and pH to quality control food preservation and shelf-life extension on intact slices of pork meat packaged under two different modified atmospheres. NIR calibrations were developed by using an on-site Phazir instrument (Polychromix, Wilmington, MA, USA) in the range 1,600–2,400 nm. A total of 252 samples of pork meat slices were directly scanned twice in reflectance mode on trays, once before and another one after removing the film cover at 1, 3, 5, 7, 9, 12, and 15 days of storage. Results showed that spectra of meat acceptable or not for consumption have marked differences around 1,660 nm. NIRS quantitative prediction models showed r ² values between 0.19 and 0.65 for the microbiological parameters assayed. The developed NIRS methodology makes possible on-site prediction of microbiological status of pork meat with a standard error of cross-validation around 1 log cfu/g. Results have shown that modified atmosphere packaging has no influence on calibration statistics.     

凝胶渗透色谱净化系统与气相色谱-串联质谱法检测5种食品中14种有机磷和7种拟除虫菊酯类农药残留

建立GPC与GC-MS/MS测定5种食品中14种有机磷和7种拟除虫菊酯类农药残留的方法,初步分析GPC净化技术及MS/MS分析技术在食品农药多残留分析的优势。方法 用GPC作为样品前处理方法,处理韭菜、大白菜、辣椒、猪肉、鱼肉五种食品,用 GC-MS/MS检测并进行定性、定量分析。结果 GPC与GC-MS-MS检测食品中14种有机磷和7种拟除虫菊酯类农药方法的线性相关系数r＞0.995,定量限为0.002～0.034 mg/kg,对韭菜、猪肉样品按0.05、0.10、0.20 mg/kg三组水平加标测试,方法精密度RSD%为2.9～10.2%,回收率为78.6～108.3%。结论 本方法检测样品范围广、灵敏度高、定性可靠、定量准确,适合多种类食品中农药多残留分析。     

Detection of irradiated food using 2-alkylcyclobutanones as markers: verification of the european committee standardization method EN1785 for the detection of irradiated food containing lipids

2-Alkylcyclobutanones (ACBs) are specific radiolytic products in irradiated lipid-containing food and can be used to detect irradiation of foodstuffs. EN1785, a European Committee Standardization Method, can detect 2-dodecylcyclobutanone (DCB) and 2-tetradecylcyclobutanone (TCB), which are ACBs, using GC/MS, thereby allowing judgement as to whether foodstuffs have been irradiated. In this study, the performance of EN1785 as a qualitative test in a single laboratory was evaluated and its applicability to beef, pork, chicken and salmon was verified. In the performance evaluation test, lipids extracted from unirradiated food using the Soxhlet extraction method were used as negative samples. Further, negative samples, to which DCB and TCB were added at 0.05 μg/g lipid (equivalent to the amount generated in food when irradiated at 0.5 kGy or more), were used as positive samples. For each food type examined, 4 negative and 16 positive samples were analyzed by EN1785 to verify the method's ability to detect irradiation. All of the negative samples were judged negative and all of the positive samples were judged positive. Thus, the method should be able to detect irradiation in beef, pork chicken and salmon irradiated at 0.5 kGy or higher. Next, to confirm that this is the case, the same types of food examined above, both unirradiated and irradiated at doses of 0.5-4 kGy, were analyzed by the method. All of the unirradiated samples were judged negative and all of the irradiated samples were judged positive. In a laboratory different from the one where the aforementioned evaluation was conducted, a performance evaluation test was carried out. Blind coded samples, including unirradiated and irradiated samples, were then analyzed in the laboratory according to EN178S. Ten samples (2 unirradiated and 8 irradiated samples) were analyzed for each type of food and the verified method was found to be 100% accurate. Even after the irradiated foodstuffs had been frozen for 6-9 months, it was still possible to judge whether the foodstuffs had been irradiated or not using the EN1785 method.     

2013年苏州地区肉及其制品掺假情况调查

了解苏州地区肉及其制品的掺假情况,通过对肉类种源与标签明示肉源进行比对,鉴别摻假食品,为加强食品标签管理提供依据。方法 运用自建的动物源性食品种源判定Taqman实时荧光PCR检测体系对苏州地区的肉及其制品进行种源判定,与标签明示肉源进行比对,鉴别摻假食品。结果 本次调查共检验涉及32个生产单位的90份样品,总不符合率为25.6%(23/90)。检测的44份牛肉及其制品中有12份与标签不符,8份用猪肉部分替代牛肉,1份以鸭肉部分代替牛肉进行销售;此外有3份不含有牛肉成分,存在猪、鸡、鸭源性肉类之外的肉类成分。共检测羊肉及其制品16份,有2份用鸭肉代替羊肉出售,3份羊肉样品中掺入了部分猪成分,其中1份样品还存在单个样品掺杂两种外源肉类的现象(猪源性和鸭源性)。检测猪肉及其制品19份,其中2份样品含有标签未注明的鸡肉成分。在所检测的11份混合肉类样品中有4份成分与标签不符,主要是以廉价的鸡肉取代/部分取代相对高价的牛肉和猪肉。结论 肉制品掺假情况明显,用猪肉、鸭肉部分代替牛肉和羊肉仍是主要的掺假手段,牛肉掺假样品主要是熟制牛肉制品,而火锅食用羊肉卷样品则是羊肉掺假高危品,开展肉制品摻假检测对规范肉制品市场具有积极意义。此外,3份未知种源成分的牛肉样品提示在现有检测基础上还需扩大检测范围,防患于未然。     

Inhibition of cholesterol oxidation in marinated foods as affected by antioxidants during heating

Chinese marinated foods rich in cholesterol, such as eggs and pork, can be susceptible to formation of carcinogenic cholesterol oxidation products (COPs) during prolonged heating. The objectives of this study were to compare the effects of various antioxidants on the inhibition of COPs in marinated eggs, pork and juice. The various COPs in marinated food samples were analyzed by a GC–MS technique. The incorporation of antioxidants, vitamin C, vitamin E, BHA and trolox were all effective in inhibiting COPs formation, with vitamin C being the most pronounced in marinated eggs, and BHA in marinated pork and juice. The inhibition effect increased with increasing levels of BHA and trolox. However, vitamin E was more effective at a low level (0.02%) than at a high level (0.1%), probably because of prooxidant activity of the latter. The same phenomenon also occurred for 0.1% vitamin C in marinated eggs, but a reversed trend was observed in marinated pork and juice. The residual amounts of each antioxidant in marinated eggs, pork and juice were also determined by HPLC.     

Mastication efforts on block and finely cut foods studied by electromyography

To quantify the mastication effort for finely cut foods, mastication patterns were analyzed by electromyography (EMG) while normal subjects ate a mouthful size (7 g block, the same weight cut, and the same volume cut) of raw carrot, cucumber, roast pork, and surimi gels. Instrumental compression test revealed that raw carrot and cucumber exhibited high fracture stress and small relative deformation for fracture, while roast pork and surimi gels fracture at low stress and large deformation. For raw carrot and cucumber, the number of chews, masticatory time, total duration of mastication, and total muscle activities evaluated by EMGs were greater for cut samples than for same weight block samples. For roast pork and surimi gel, these factors were the same for equal-weight cut and block samples. Cut samples with the same volume, but of smaller weight, were often eaten with less total mastication effort until swallowing than a block sample. These results revealed that cutting food does not help reduce mastication effort for the same weight as a mouthful size block, although it may make easier mastication by decreasing the weight of one mouthful.     

EFFECT OF PARTICLE SIZE AND HEAT ON ABSORPTIVE PROPERTIES OF SOY HULLS1,2

Given the potential contribution of soy hulls to the human diet, a methodology was developed to determine their moisture and lipid absorptive properties under conditions simulating those within a restructured pork product during thermal processing. Laboratory procedures were developed to determine the interactive effects of particle size, heat (25, 50, 75, and 95°C), and varying levels of available water, pork lipids, and water/pork lipids emulsion upon absorption abilities. Absorption of all media was influenced by particle size; as particle size increased, media absorption generally increased. Higher temperatures tended to increase water and water/pork lipid emulsion absorption, but had no effect on pork lipid absorption. Water was found to be preferentially absorbed over lipids. These results can be used by food processors in developing a restructured pork/soy hull product for human consumption.     

FLAVOR ENHANCEMENT OF RESTRUCTURED PORK

Restructured pork chops were formulated using boneless pork shoulders, 1% NaCl and .25% sodium tripolyphosphate (STP). Experimental treatment included (1) 90% pork—10% dried apples (A), (2) 100% pork (C), (3) 90% pork—10% corn crumbs (CC), and (4) 90% pork—10% mushrooms (M). All samples were stored at —20°C until evaluation at 10 or 70d. Corn crumbs appeared to have less potential as an enhancer due to their adverse effect on color, overall appearance, texture, tenderness and flavor. Dried apples appeared to impair product cohesion more than overall product and color stability. Mushrooms appeared to be a viable source for flavor and appearance enhancement. Among nonmeat ingredients evaluated, none enhanced texture. Storage time had minimal effect on product tenderness.