微生物筛选法检测辐照食品的研究

建立一种辐照食品的微生物筛选方法.研究采用细菌内毒素/革兰氏阴性菌微生物筛选法检测不同辐照剂量的鸡肉、牛肉、羊肉、猪肉、鱼丸、虾丸、蟹棒、鱿鱼、虾仁,及进出口肉饼、糖果等食品.研究结果,表明该方法具有对多种辐照食品的初筛功能,准确性好,检测灵敏度≥1.5 kGy.细菌内毒素/革兰氏阴性菌微生物初筛法操作简便、快速,可以作为多种辐照食品的初筛鉴别检测方法.     

基于超微弱发光技术检测辐照食品的研究

基于超微弱发光检测技术,研究即食食品(麦片,藕粉)经0～12kGy剂量辐照后光子信号的变化,并探讨超微弱发光用于鉴定即食辐照食品的判定方法。试验结果表明:两种即食食品辐照前后的超微弱光子计数有明显的区别,光子计数与辐照剂量呈正相关,检测阈值可低至0.3kGy。当添加检测液后的最大光子数为本底的15倍以上时,可判定为该样品经过辐照处理。     

高效液相色谱法检测γ- 射线辐照食品中的邻酪氨酸

目的：建立含蛋白质辐照食品中邻酪氨酸的柱前衍生- 高效液相色谱检测方法。方法：样品经丙酮- 三氯甲烷溶液净化除去脂肪和糖分,在110℃经盐酸水解过夜去蛋白后,水解液与衍生剂衍生,高效液相色谱检测,外标法定量。结果：方法最低检出限为5mg/kg,样品在5、10、50mg/kg 添加水平的平均回收率为62.1%～88.3%,变异系数为3.91%～9.38%(n=6)。结论：辐照剂量在5kGy 及以上的鸡肉和猪肉可以被检测出邻酪氨酸,含量明显高于空白,且邻酪氨酸含量与辐照剂量呈线性关系。辐照剂量在5kGy 及以上的鸡肉和猪肉在－ 20℃中保存3 个月后仍可以检测出邻酪氨酸。     

辐照对新鲜肉品中革兰氏阴性菌的影响及典型菌落的初步鉴定

测定了1kGy、3kGy、5 kGy钴-60-γ射线辐照处理对白对虾、皮皮虾、梭鱼、鸽子及鲜猪肉等5种新鲜肉制品的革兰氏阴性菌的影响,结果表明,1 kGy及以上的钴-60γ射线辐照,可以有效杀灭白对虾、皮皮虾、梭鱼携带的革兰氏阴性菌;3 kGy及以上的钴-60γ射线辐照,可以有效杀灭鸽子携带的革兰氏阴性菌。对分离自样品的15株典型的革兰氏阴性菌进行了以60种生化反应为基础的初步鉴定(用VITEK-2 COMPACT全自动微生物鉴定系统进行),结果表明,其中13株与仪器数据库菌种有相似性,相似程度为86%~99%,其余2株与仪器数据库菌种无相似性,仪器无法鉴定。     

电子束辐照处理对生鲜猪肉的保鲜作用

为研究电子束辐照处理对生鲜猪肉品质的影响,该实验使用1 kGy、3 kGy、5 kGy、7 kGy、9 kGy辐照剂量对生鲜猪肉进行处理,于4 ℃环境下贮藏。在贮藏期间进行理化指标的测定,结果表明：小于3 kGy的辐照剂量,对生鲜猪肉色泽有一定促进作用。高剂量（大于7 kGy）的辐照处理,会影响生鲜肉色泽感官。辐照对生鲜肉脂肪氧化促进作用以及杀菌效果十分明显,在第12 d时空白组TBARS值最低,仅为0.446 mg/kg,9 kGy组数值最高,达到了0.650 mg/kg。空白组货架期仅为7~8 d,而7 kGy、9 kGy组第12 d时菌落值仍在合格肉标准内,延长了5 d货架期。挥发性风味物质种类方面,0 kGy、1 kGy组均检测出13种化合物,3 kGy组检测出了10种,5 kGy组检测出了16种,7 kGy组检测出了15种,9 kGy组检测出了14种化合物。高剂量（大于7 kGy）的辐照能够增加生鲜猪肉风味化合物的种类和含量,低剂量的辐照处理对生鲜猪肉风味促进作用不大。通过对各项理化指标的综合考虑,采用3 kGy的辐照处理生鲜猪肉效果最佳。     

辐照灭菌处理对中式酱牛肉理化性能的影响

目的：对比分析辐照灭菌和高温釜式灭菌对酱牛肉理化性能、质构变化和脂质氧化情况的影响。方法：选择辐照剂量2,4,6,8 kGy对酱牛肉进行辐照处理,高温釜式选择121 ℃、20 min灭菌。结果：辐照处理剂量为6,8 kGy时,辐照处理具有与高温釜式相同的灭菌效果,可延长酱牛肉的保质期;辐照剂量的增加可使得酱牛肉的L*(亮度值)整体呈下降趋势,且辐照组样品L*值高于未经灭菌处理的酱牛肉,a*值先上升后逐渐降低,当辐照剂量＜6 kGy时,随着辐照剂量的增加样品的b*值逐渐升高,当辐照剂量＞6 kGy时,样品的b*值又减小,且辐照组处理的酱牛肉b*值均显著高于对照组(P＜0.05);辐照处理组对酱牛肉硬度与弹性的维持性优于高温釜式灭菌;而辐照处理的酱牛肉过氧化值与酸价值随着辐照剂量的增加显著增高(P＜0.05),高温釜式灭菌对酱牛肉过氧化值影响不显著,8 kGy辐照剂量组与高温釜式灭菌组酸价值均显著高于其他组(P＜0.05),辐照使得样品的初始丙二醛值增加。结论：6 kGy辐照剂量组的酱牛肉货架期相较于对照组延长且该剂量辐照处理更容易被消费者接受。     

基于正交偏最小二乘判别分析探究60Co-γ辐照对羊肚菌采后低温贮藏品质的影响

目的：探究60Co-γ辐照处理对采后低温贮藏期间羊肚菌保鲜效果的影响。方法：以黑脉羊肚菌为试材,分别用实际吸收剂量1.64、2.18、2.43 kGy和2.93 kGy进行辐照处理,测定低温贮藏期间其感官品质和理化指标的变化。采用正交偏最小二乘判别分析（orthogonal partial least squares-discriminant analysis,OPLS-DA）建立基于羊肚菌理化品质指标的辐照处理判别模型,并采用变异权重参数值（variable importance in the projection,VIP）筛选差异显著指标。结果：经不同辐照剂量处理后,羊肚菌在4 ℃贮藏条件下其感官品质和理化特性呈现不同的变化规律。贮藏5 d后,与对照组相比,1.64 kGy和2.18 kGy辐照处理能提高过氧化氢酶活力、总酚含量和类黄酮含量,降低丙二醛含量、多酚氧化酶活力和过氧化物酶活力,有效延缓褐变和软化现象,其中1.64 kGy剂量处理保鲜效果最好（P＜0.05）,而2.43 kGy和2.93 kGy辐照处理样品则在贮藏末期品质劣变加剧。通过构建辐照处理判别模型,有效区分样品因辐照处理所造成的差异,并筛选出过氧化氢酶和过氧化物酶活力为相应的差异显著指标。结论：1.64 kGy和2.18 kGy辐照处理可明显延缓羊肚菌采后品质的劣变,且1.64 kGy处理组和对照组差异最大;OPLS-DA法能有效区分不同处理的样品组。     

直接荧光过滤/平板计数法检测辐照食品

研究建立一种适用于我国香辛料及脱水蔬菜辐照鉴别初筛方法,对11种调味料及5种脱水蔬菜样品在4、5、10 kGy剂量下进行辐照,同时以未辐照样品作为对照。试验结果表明:辐照后4组样品之间Dc值差异显著,4、5、10、0 kGy下辐照处理样品的Dc均值分别为3.1~5.1、3.6~5.7、5.6~7.5和1.3~3.0。随辐照剂量增加,DEFT值基本不变,APC值逐渐降低;当阈值设定为3.0时,可检测出5.0 kGy及5.0 kGy以上辐照处理样品,假阳性率为3.1%。     

多元法分析高能电子束辐照对白芷挥发性成分的影响

为探究高能电子束辐照对白芷挥发性成分的影响,设置不同辐照剂量处理白芷样品,采用电子鼻结合顶空固相微萃取-气相色谱-质谱技术分析其辐照前后主要成分的变化。结果表明,白芷经高能电子束1、3、5、7、10 kGy剂量辐照处理后,分别鉴定出54、64、59、53、58 种化合物,对照组（0 kGy处理）样品检测出17 种化合物。辐照处理使样品挥发性成分增多,主要贡献风味的物质为醛类、酯烃类,同时辐照后样品产生了酮类化合物,且随着辐照剂量的增大,醛、酮类物质相对含量增加。利用主成分分析、线性判别分析、聚类分析和偏最小二乘法统计分析数据,将辐照样品分为0～3 kGy和5～10 kGy两类,即不高于3 kGy剂量的辐照处理对白芷气味无明显影响,高能电子束不同辐照剂量对白芷挥发性成分影响不相同。为高能电子束辐照处理白芷样品对其品质所产生的影响提供理论依据和参考,也为高能电子束在食药两用资源方面的辐照应用提供一定的基础。     

电子束辐照对泥蚶杀菌保鲜效果的影响

目的：研究电子束辐照对泥蚶微生物数量及其感官质量的影响。方法：泥蚶经不同剂量电子束处理,测定辐照后及冷藏期间菌落总数、大肠菌群及其感官评分。结果：电子束辐照能有效地杀灭泥蚶中的微生物,经过0、1、3、5、7、9kGy 不同剂量处理,泥蚶的菌落总数逐步下降,当泥蚶的初始菌落总数为3.10 × 105CFU/g时, D10=3.12kGy;泥蚶的感官质量与辐照剂量有关,经过7、9kGy 剂量处理后样品产生令人不愉快的异味。结论：结合辐照后及冷藏期泥蚶的微生物和感官指标,泥蚶电子束冷杀菌的适宜剂量为3～5kGy,经3～5kGy 处理后,泥蚶的货架期由对照组的5d 延长至15～19d。     

Evaluation of a gas chromatographic method for detection of irradiation of chicken and a chicken meat product

A method was developed for the detection of irradiation of chicken and chicken meat products. The method consists of the extraction of fat from chicken skin or a chicken meat product, separation of hydrocarbons with an alumina column and gas chromatography (GC) and GC-mass spectrometry analyses of the hydrocarbons 16:2, 16:3, 17:1 and 17:2 formed from oleic, linoleic and stearic acids during irradiation. These hydrocarbons were only detected in irradiated samples at doses of 5 and 10 kGy. The mean concentrations of the hydrocarbons were linearly related to the dose levels of irradiation in the case of chicken fat. The concentrations of two of the hydrocarbons (16:2 and 17:1) gave the best correlation with dose. When a dose of 10 kGy was used, the concentrations of major degradation products were 1.5-5.0 mg/kg fat. The same relationship was not found in the case of chicken meat products because the amounts of hydrocarbons detected after irradiation with the same doses were similar. On the basis of this study it was clearly demonstrated that it is possible to judge analytically whether or not a chicken sample or a chicken meat product has been irradiated at doses of 5 or 10 kGy. It should also be possible to recognise samples irradiated with doses below 5 kGy.     

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.     

Detection of irradiated frozen food with the DNA comet assay: interlaboratory test

Ionising radiation induces DNA damage in the cells of the foodstuff. This fact was used to analyse DNA from single cells by agarose gel electrophoresis (DNA comet assay). The pattern formed by the DNA after electrophoresis (DNA comet) was visualised in a microscope, where hundreds of cells could be observed in a short time. Irradiated cells showed comets with long tails, while unirradiated cells showed no tail or very short ones. An estimation of the dose was made based on the shape of the comets. Nine laboratories, from Berlin, Berne, Chipping Campden, Karlsruhe, Copenhagen, Strasbourg, Uppsala and Warsaw, participated in a test to assess the validity of the method. The test material consisted of code-labelled cell suspensions made of irradiated and unirradiated chicken bone marrow, chicken and pork muscle tissue. The doses varied between 0 and 5 kGy. Samples of chicken bone marrow were used as references. A total of 162 test samples were sent for analysis. Results of analysis from 148 samples were reported. Of these, 138 were correctly identified. Six laboratories succeeded in identifying all the samples. In the group of 106 irradiated samples, 99 were correctly detected, while 39 out of 42 unirradiated samples were correctly detected. It is concluded that the comet assay can be used to detect frozen irradiated food. © 1998 SCI.     

Quality and Microbial Population of Cornish Game Hen Carcasses as Affected by Electron Beam Irradiation

ABSTRACT:  We evaluated the chemical and microbiological quality of Cornish game hen carcasses irradiated up to 7 kGy with a 10 MeV linear accelerator (dual beam configuration). Eighty frozen and vacuum packaged (approximately 0.45 kg) Cornish game hens ( Gallus domesticus ) were irradiated and stored in low-density polyethylene bags at 4 ± 1 °C for 21 d; nonirradiated chickens served as controls. Fat oxidation (in terms of malonaldehyde content) increased with storage time and dose for all chicken parts analyzed (breast, thigh, and skin). As expected, the skin had the highest level of fat oxidation while the breast samples had the lowest. Oxidation level in all samples exposed to 2 kGy reached a maximum on day 14. Sensory evaluation showed that irradiation caused significant textural toughening, and increased the redness of raw chicken meat. In terms of overall quality and aroma, lipid oxidation was not a major problem since it was not detected by the panelists. Irradiation significantly reduced the total viable microbial counts (TVC) in the breast and thigh samples. Exposure to 3-kGy dose decreased the TVC by 0.3-log cycles on the surface of the skin. In less than 14 d, the nonirradiated chicken carcasses had counts greater than 6 log CFU/50 cm², while the 2 and 3 kGy irradiated samples reached these numbers only after 21 d of storage. Samples irradiated at 7 kGy had consistently the lowest counts (2.5 log CFU/50 cm²) throughout storage time.This study shows that irradiation up to 7 kGy and refrigerated storage (4 °C) inhibits microbial growth and extends shelf life of Cornish game hens without affecting consumers' acceptability.     

Migration of dioctyladipate plasticizer from food-grade PVC film into chicken meat products: effect of γ-radiation

Food-grade PVC film containing 28.3% dioctyladipate (DOA) plasticizer was used to wrap chicken meat samples, with and without skin, contained in a polystyrene tray. Samples were then irradiated with γ-radiation [⁶⁰Co] at doses equal to 4 kGy and 9 kGy corresponding to “cold pasteurization”. Irradiation was carried out at 8–10 °C and samples were subsequently stored at 4–5 °C. Contaminated chicken meat samples were analysed for DOA at intervals between 7 h and 240 h of contact, using an indirect GC method. Identical non-irradiated (control) samples were also analysed for their DOA content. Results showed no statistically significant differences in migrated amounts of DOA between irradiated and non-irradiated samples. Neither were differences observed between samples irradiated at 4 kGy and 9 kGy. This was supported by identical IR spectra recorded for irradiated and non-irradiated samples and leads to the conclusion that, at such intermediate radiation doses (?kGy), the migration characteristics of PVC film are not affected. DOA migration was found to be time dependent, approaching equilibrium after approximately 170 h for the chicken flesh plus skin samples and 120 h for the chicken flesh samples. The amount of DOA migrated into chicken flesh plus skin samples was significantly greater (3.2–22.3 mg/dm²) than that for chicken flesh samples (0.9–8.9 mg/dm²). After 240 h of sample/ film contact under refrigeration, loss of DOA was approximately 35.6% for chicken flesh plus skin samples and 14.3% for chicken flesh samples. Sample spoilage, as demonstrated by off-odour development, occurred after approximately 120 h of refrigerated storage. Diffusion coefficients for DOA were calculated and were found to be lower for chicken flesh (1×10^?13) than for flesh plus skin (4.4×10^?13) samples.     

Validation of an alternative method for the identification of 2-dodecylcyclebutanone (2-DCB) of irradiated meats by solid-phase microextraction (SPME) gas chromatography–mass spectrometry (GC-MS)

A rapid and simple procedure to detect irradiated food containing fat is proposed. This method is based on HS-SPME coupled with GC-MS to determine the presence of a radiolytic product in irradiated meats: 2-dodecylcyclobutanone (2-DCB) and is proposed as an alternative to EN 1785:2003, which is a long and complex procedure. The qualitative confirmation method is validated on different type of meats: chicken, turkey, duck, beef, pork on both nonirradiated and irradiated samples at different dose levels (0.05, 0.12, 0.5, 1.0 and 3.0 kGy) with a biological X-ray irradiator. The validation parameters investigated are selectivity, minimum dose level (MDL), limit of detection (LOD), sensitivity and specificity. The MDL and LOD values were 0.5 kGy and 5.0 ng mL⁻¹, respectively, for all matrices. No false positives or false negatives occurred, and 100% of samples were correctly identified. The results show that HS-SPME GC-MS is suitable for routine analysis.     

肉鸡屠宰过程中沙门氏菌的监控方法及其应用实验

通过肉鸡屠宰加工过程中沙门氏菌抽样方法、样品处理、检测方法的建立和使用,确立一套可行的沙门氏菌监控模型,为评价肉鸡屠宰加工过程的卫生状态提供科学手段,以改进卫生管理水平。采用该模型对3家肉鸡加工企业的屠宰过程进行了沙门氏菌监控,共计检测样品4 987个,检出阳性样品314个,阳性率为6.36%,监控数据表明工厂的卫生状态处于较高水平。     

Detection of 2-dodecylcyclobutanone in radiation-sterilized chicken meat stored for several years

Results are presented indicating a linear relationship between irradiation dose (10–60 kGy) and the quantity of 2-dodecylcyclobutanone produced in irradiated frozen (-46°C) chicken meat. 2-Dodecylcyclobutanone was found in chicken meat sterilized (at -40°C) by gamma and electron beam irradiation 12 years previously and used for toxicity clearance. After freeze-drying the irradiated chicken samples still contained 2-dodecylcyclobutanone indicating that it was present in the diets tested. The compound was not detected in chicken meat sterilized by thermal processing 13 years ago. In addition, there was evidence that 2-tetradecylcyclobutanone was also present in the irradiation sterilized samples.     

电子束辐照对冷鲜鸡相关品质的影响研究

为研究经过电子束辐照后的冷鲜鸡微生物与相关品质的变化,将冷鲜鸡于2.5 kGy电子束辐照后在4、15℃下贮存,分别进行菌落总数、大肠菌群、TVB-N值、系水力、pH、嫩度、色度检测和辐照后氨基酸的测定,并与4℃下贮存的未辐照冷鲜鸡进行比较。结果表明:电子束辐照使冷鲜鸡的起始菌数量显著(p<0.05)降低、大肠菌群未检出,氨基酸总量比未辐照增加62.75%,pH不同处理均在新鲜肉要求范围内;电子束辐照冷鲜鸡4℃贮存时TVB-N值、系水力、嫩度、色度均显著(p<0.05)好于未辐照4℃贮存冷鲜鸡,其中TVB-N值在第7 d时,电子束辐照冷鲜鸡4℃贮存为7.1 mg/100 g,电子束辐照15℃贮存、未辐照4℃贮存冷鲜鸡均接近食品安全标准规定限值15 mg/100 g。