Spectroscopic techniques coupled with chemometric tools for structure and texture determinations in dairy products

Structure conditions both textural and flavour properties of cheeses and dairy products. Until recently, delineating the structure of the food matrices and the interactions between components in dairy products has been impaired by the lack of techniques. More and more evidence shows that front face fluorescence spectroscopy and attenuated total reflection infrared spectroscopies may be valuable techniques. These spectroscopic techniques remove methodological locks and allow the structure at molecular level and the dynamics of “real dairy products” to be investigated.Over the last few years, we gave most of our interest to the delineation of the molecular structure of dairy products and to the understanding of the relationships between structure and texture in cheese. The analysis of large spectral collections recorded for dairy products using multivariate analysis techniques such as principal component analysis, factorial discriminant analysis and canonical correlation analysis makes it possible to extract relevant information related to the molecular structure of proteins and fats in semi-hard cheeses, the interactions between dairy product components and the relation between structure and texture of soft and semi-hard cheeses. The presented data show that the texture of a dairy product is a reflection of its structure at the molecular level.     

魔芋葡甘露聚糖通过肠道菌群-胆汁酸途径发挥降脂作用

建立高脂饮食诱导金黄地鼠血脂紊乱模型,从肠道菌群和胆汁酸代谢关系角度探究魔芋葡甘露聚糖（konjac glucomannan,KGM）降脂机理。5 周龄地鼠随机分为Control组、高脂饮食（high fat diet,HFD）组、2%（质量分数,下同）KGM组、6% KGM组和10% KGM组,干预5 周后测定血清和肝脏脂质水平,并分析KGM对肠道菌群及其代谢物胆汁酸代谢的影响。结果表明,6%和10% KGM干预可显著降低血清中总胆固醇（total cholesterol,TC）、甘油三酯（triglyceride,TG）、低密度脂蛋白胆固醇（low density lipoprotein cholesterol,LDL-C）浓度以及肝脏中TC浓度。HFD组分别与Control组、KGM组比较后共筛选出51 种差异代谢物,经类别富集分析后发现,胆汁酸类物质种类在所有代谢物类别中占比最高（24%）。此外,京都基因与基因组百科全书代谢物通路富集分析显示初级胆汁酸合成代谢途径存在差异。盲肠内容物肠道菌群分析及胆汁酸测定结果表明,6%和10% KGM干预后嗜胆菌属（Bilophila）以及具有胆盐水解酶（bile salt hydrolase,BSH）活力的双歧杆菌属（Bifidobacterium）和乳杆菌属（Lactobacillus）相对丰度显著下降,且脱氧胆酸（deoxycholic acid,DCA）和石胆酸（lithocholic acid,LCA）含量降低。此外,在6% KGM干预组中,肝脏中胆汁酸合成关键酶胆固醇7α-羟化酶（cholesterol 7α-hydroxylase,CYP7A1）的基因表达上调。综上,KGM可通过降低具有BSH活力的肠道菌群和嗜胆菌属相对丰度及上调CYP7A1基因表达调节机体胆汁酸水平,从而改善机体脂质代谢紊乱。     

抗孔雀石绿单链抗体-碱性磷酸酶融合表达和活性鉴定

采用重叠延伸的方法成功将抗孔雀石绿（malachite green,MG）单克隆细胞的轻链VL和重链VH用连接肽(Gly4Ser)3连接,形成单链抗体（single chain variable fragment,scFv）基因,并将其酶切连接进入含有碱性磷酸酶（alkaline phosphatase,PhoA）基因的载体plip6/GN中,成功构建重组质粒plip6/GN-MG-scFv。随后重组质粒转入大肠杆菌BL21,经诱导表达后,十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和Western blotting鉴定结果表明所获得的融合蛋白scFv-PhoA大小约72 kD。利用scFv与MG特异性结合的活性和PhoA催化对硝基苯磷酸二钠的显色机制,经过直接竞争酶联免疫吸附法测定融合蛋白scFv-PhoA的IC50为9.81 ng/mL。本方法操作简单、灵敏度高且检测时间短,这为进一步进行MG免疫法快速检测提供了参考。     

辐照处理对魔芋葡甘聚糖肠道益生作用的影响

为探究辐照改性技术对魔芋葡甘聚糖（konjac glucomannan,KGM）肠道益生性的影响,以60Co为辐射 源制备0、10、20、30 kGy辐照剂量的KGM样品,采用健康志愿者粪便体外厌氧发酵,比较不同辐照剂量KGM 体外发酵液pH值、短链脂肪酸含量、有益菌及有害菌数目、双歧杆菌数量/大肠杆菌数量（B/E值）、益生元指数 （prebiotic index,PI）的差异。结果表明：相对于葡萄糖阳性对照,不同辐照剂量KGM均能有效降低发酵液pH 值,维持酸性环境,促进短链脂肪酸生成,同时改善发酵液微生物构成,提高B/E值及PI。在0～30 kGy辐照范围 内,随辐照剂量增大,KGM发酵液短链脂肪酸生成量增加,PI升高,0、10、20、30 kGy KGM的PI分别为0.48、 0.61、0.76、0.78。综上,KGM具有良好的肠道益生元作用,γ-辐照改性有助于进一步提高KGM的肠道益生性,综 合考虑辐照效率及KGM肠道PI,推荐20 kGy作为制备KGM低聚糖的适宜辐射剂量。     

雌二醇间接竞争酶联免疫吸附方法的建立

建立食品中雌二醇免疫分析方法。将雌二醇进行结构改造合成半抗原并经过核磁氢谱和红外光谱验证,再采用活泼酯法与载体BSA和OVA偶联制备人工抗原,免疫兔子制备多克隆抗体,经过反应条件优化建立间接竞争酶联免疫吸附检测方法。结果表明：IC50为3.9ng/mL,检测限为0.3ng/mL,交叉反应率均小于1.21%。检测方法具有高灵敏度和特异性,可应用于食品中雌二醇检测试剂盒的研制。     

QuEChERS-酶联免疫快速检测法测定茶叶中 黄曲霉毒素B1

目的建立QuEChERS-酶联免疫快速检测茶叶中黄曲霉毒素B1的方法,并对样品前处理条件进行优化。方法茶叶样品用70%乙腈水提取溶液进行提取目标物,离心后取上清液并用PSA+MgSO4进行净化处理后,采用酶联免疫快速检测方法进行分析测定。结果本方法的检出限为0.078μg/kg,线性范围为0.125~0.854μg/kg,IC50值为0.327 ng/m L。在三个不同添加水平下,样品的平均回收率为87.66%~97.17%,相对标准偏差为4.89%~7.16%。检测结果与高效液相色谱法(high performance liquid chromatography,HPLC)方法的相关系r2=0.9854,线性相关性良好。结论该方法更加简便、快速、高效,能够用于茶叶中黄曲霉毒素B1的检测。     

基于食品安全指数法的台山市蔬菜和水果农药残留风险评估

该研究监测了2019~2021年台山市10个类蔬果中16种农药的残留量,采用食品安全指数法（Index of Food Safety,IFS）和危害物风险系数法（Hazard Risk Coefficient,R）对其进行安全水平评估。结果表明,1 928份蔬果样品中,34份不合格,总体合格率为98.24%,芽菜类等3类蔬菜合格率低于总体水平,毒死蜱和克百威超标占比达35.90%。食品安全指数法显示,叶菜类蔬菜 为2.59,安全状态不可接受,豆类蔬菜等5类 为0.066~0.38,安全状态可以接受,其余4类安全状态良好;氟虫腈等3种农药IFS为0.68~14.05,对安全性影响不可接受,其余13种农药IFS为0.005 8~0.76,对安全性影响可以接受。危害物风险系数法显示,毒死蜱等5种农药风险系数R为2.67~6.10,处于高风险,丙溴磷等4种风险系数R为1.91~2.22,处于中风险,其余7种均为低风险。建议监管部门应采取多种评价方法综合评估农药残留风险,加大风险品种蔬果、中高风险以及对安全影响较高的农药残留监测,同时提高快检技术在监管工作的覆盖面,加大植物生长调节剂和新型农药快检技术研发。     

Application of an indirect ELISA and a PCR technique for detection of cows’ milk in sheep's and goats’ milk cheeses

We have applied a polymerase chain reaction (PCR) procedure and an indirect enzyme-linked immunosorbent assay (ELISA) for detecting the presence of cows’ milk in sheeps’ and goats’ milk cheeses. The PCR used a cattle-specific primer set targeting a 223 bp fragment from the mitochondrial 12S rRNA gene. This technique was applied to experimental cheese mixtures, industrial cheeses produced with known amounts of cow's milk, and several commercial cheeses, enabling the detection of low percentages of cows’ milk (1%). An indirect ELISA using a monoclonal antibody (AH4) against bovine β-casein was also assayed in this study for the specific detection of bovine milk in cheese. Results suggested that both ELISA and PCR may provide specific and reliable tools for detection of low percentages of undeclared cows’ milk in sheeps’ and/or goats’ milk cheeses and other dairy products.     

Biogenic amines in Chinese soy sauce

The biogenic amine contents in 40 samples of Chinese soy sauce from different manufactures were determined using HPLC after pre-column derivatization with dansyl chloride. Also, the amino nitrogen levels and pH values of these samples were analyzed. Of the five biogenic amines under study, tyramine was the most prevailing amine and was detected in 97.5% of the samples, followed by spermidine (95%), histamine (92.5%), cadaverine (82.5%) and spermine (80%). The total content for the five biogenic amines in these samples was 497 mg/l with a range from 41.7 to 1357 mg/l. The pH and amino nitrogen levels in soy sauce samples were between 3.86 and 4.98 and between 0.25 and 1.26 mg/100 g, respectively. In general, total content for the five biogenic amines was high in samples that had high amino nitrogen levels.     

基于MnO2纳米片类氧化酶特性的有机磷农药荧光分析方法建立

利用MnO2纳米片类氧化酶特性并结合有机磷农药的酶抑制原理,构建一种快速、简便、高灵敏有机磷农药荧光分析方法。通过测定反应体系荧光强度前后的变化,可以检测样品中有机磷农药的含量。通过优化酶浓度、底物浓度和反应时间,发现乙酰胆碱酯酶浓度为9.375 U/L,底物浓度为10 mmol/L,反应时间为11 min时,该荧光分析方法检测性能最佳,对氧磷的动态检测范围为1.56～200 ng/mL,检出限达到0.5 ng/mL（RSN=3）,运用该方法测定标准添加的自来水、卷心菜、燕麦样品的回收率在83.4%～105.9%之间,表明该方法具有很高的灵敏度与准确性,为快速高灵敏测定有机磷农药提供一种新的可能。