改进的离子色谱法测定乳制品中亚硝酸盐和硝酸盐

改进了国家标准方法GB 5009.33-2010《食品安全国家标准 食品中亚硝酸盐和硝酸盐的测定》中离子色谱法用于乳制品中亚硝酸盐(以亚硝酸根计)和硝酸盐(以硝酸根计)的测定方法。乳制品经水提取后,加入3%乙酸溶液沉淀蛋白,离心后上清液用反相固相萃取柱净化,以NaOH为淋洗液,加入乙腈作为有机改进剂分离亚硝酸根和硝酸根,外加水模式抑制,离子色谱分析柱为AS 19,柱温30 ℃,池温35 ℃,检测波长设定为225 nm,进样量200 μL。在上述条件下,亚硝酸盐和硝酸盐的质量浓度分别在0.005～0.50和0.05～1.50 mg/L时与色谱峰面积之间的线性关系良好。在电导检测模式下,亚硝酸盐的检出限为0.2 mg/kg,硝酸盐的检出限为0.04 mg/kg;在紫外检测模式下,两者检出限分别为0.02 mg/kg和0.01 mg/kg。将该方法用于乳制品的检测,加标回收率为84.0%～104.1%。该法简便、快速、准确,适用于乳制品中低含量亚硝酸盐和硝酸盐的检测。     

顶空进样-气相色谱法检测乳制品中硫氰酸盐的含量

建立了顶空进样气相色谱法测定乳制品中硫氰酸盐含量的方法。乳制品中硫氰酸盐用水提取,然后用乙酸锌溶液沉淀蛋白质,将提取液离心,取上清液加入氯胺T将硫氰酸离子衍生为氯化氰,顶空进样,经BP10(14%氰丙基苯基聚硅氧烷)气相色谱柱分离,电子捕获检测器(ECD)检测,外标法定量,同时对衍生剂用量、顶空加热时间和保温温度进行了优化。结果表明: 硫氰酸盐在0.005～0.1 mg/L内线性关系良好,相关系数(r)为0.997,定量限(以信噪比(S/N)≥10计)为0.1 mg/kg。在1.0、2.0、10.0 mg/kg 3个添加水平下进行了回收率和精密度试验,加标回收率为90.0%～110.0%,相对标准偏差(RSD, n=10)为4.98%～7.89%。该方法操作简便、快速、稳定性好,可用于乳制品中硫氰酸盐的测定,能满足日常检测要求。应用该法对市售的18种乳制品进行了检测,发现所测乳制品皆含有硫氰酸盐,含量大约在0.5～10 mg/kg。     

乳制品中胆碱及其衍生物的快速核磁共振检测

胆碱及其衍生物是一类具有重要生物功能的小分子代谢物,可部分在人体合成,但是更重要的来源是饮食.胆碱被认为是一种人体必需的营养物质,常存在于牛奶、豆类等日常饮食中,也是一种重要的婴儿食品添加剂.饮食中胆碱的长期缺乏与器官功能障碍等疾病有关,因此胆碱衍生物的快速检测分析对食品检测具有重要意义.核磁共振（NMR）技术无需样品分离就可完成相关物质的检测,是理想的食品中胆碱衍生物检测工具.但由于相关分子结构类似,化学位移接近,利用常规NMR技术检测胆碱及其衍生物较为困难.本文采用¹H-¹⁴N SOFAST-HMQC技术对乳制品中的不同胆碱衍生物进行了快速分析检测,结果发现：与1D ¹H NMR谱检测相比,该技术对胆碱衍生物的检测具有高选择性,可消除这些复杂混合体系中其它背景分子干扰;与¹H-¹⁴N HSQC谱检测技术相比,该技术具有更高的灵敏度,在单位时间内信号增强可达1.5~2.0倍.     

安培检测-离子色谱法测定乳品中的微量碘

 用安培检测 离子色谱法检测了乳品中的微量碘。以NaOH作淋洗液 ,直接进样 ,优化了碘的离子色谱分离和测定条件 ,方法的检测限达 1μg/L(3倍信噪比 )。测定了婴儿奶粉、孕产妇专用奶粉和鲜牛奶中的微量碘 ,加标回收率分别为 89 0 % ,86 0 %和 84 1%。     

Cleaning efficiency enhancement by ultrasounds for membranes used in dairy industries

Membrane cleaning is a key point for the implementation of membrane technologies in the dairy industry for proteins concentration. In this study, four ultrafiltration (UF) membranes with different molecular weight cut-offs (MWCOs) (5, 15, 30 and 50 kDa) and materials (polyethersulfone and ceramics) were fouled with three different whey model solutions: bovine serum albumin (BSA), BSA plus CaCl₂ and whey protein concentrate solution (Renylat 45). The purpose of the study was to evaluate the effect of ultrasounds (US) on the membrane cleaning efficiency. The influence of ultrasonic frequency and the US application modes (submerging the membrane module inside the US bath or applying US to the cleaning solution) were also evaluated. The experiments were performed in a laboratory plant which included the US equipment and the possibility of using two membrane modules (flat sheet and tubular). The fouling solution that caused the highest fouling degree for all the membranes was Renylat 45. Results demonstrated that membrane cleaning with US was effective and this effectiveness increased at lower frequencies. Although no significant differences were observed between the two different US applications modes tested, slightly higher cleaning efficiencies values placing the membrane module at the bottom of the tank were achieved.     

Decomposition of DSC curves of dairy products with Gaussian functions

Summary DSC measurements have wide application in the field of biochemical/biophysical research to look into the melting behaviour of muscle proteins in different intermediate states of ATP hydrolysis cycle as well as in the field to develop dairy products. It was a demand to develop a deconvolution program to evaluate and interpret the background of DSC scans such a way that the decomposition into a proper function has to be simple and quick. There should be possible to choose the proper parameters as well as to calculate the data of decomposing curves with the simultaneous graphic representation of them including the resultant DSC scan as the sum of decomposing functions. In most cases Gaussian function is used for this purpose. Our main field of interest is the food physics where e.g. the proliferation of different probiotic bacteria follows a lognormal distribution, its first derivative is a Gaussian one, for this reason we have chosen it. The main parts of this PC program are: -the process of fitting and calculation of Gaussian functions, a multiple step correction of these function (optimal fitting), graphic representation of all functions. An example is shown for its application how to analyse the melting of butter fat.     

Trace‐level screening of dichlorophenols in processed dairy milk by headspace gas chromatography

A headspace gas chromatographic approach based on flame ionization detection has been successfully developed for the determination of parts‐per‐billion levels of 2,4‐dichlorophenol and 2,6‐dichlorophenol in processed dairy milk. Under the right environmental conditions, these compounds are produced as products of the reductive dechlorination of pentachlorophenol. Maintaining a highly inert chromatographic system and employing a recently commercialized inert capillary column permits the analysis of 2,4‐dichlorophenol and 2,6‐dichlorophenol without derivatization. Further, a detection limit improvement of more than a factor of two was achieved by adding sodium sulfate to substantially decrease the solute partition coefficient in the matrix. A detection limit of 1 ng/g and a limit of quantitation of 2 ng/g were attained, and complete analysis can be conducted in < 13 min. Reproducibility of area counts over a range from 20 to 200 ng/g and over a period of 2 days were found to be less than 6% (n = 20). A linear range from 5 to 500 ng/g with a correlation coefficient of at least 0.9992 was obtained for 2,4‐dichlorophenol and 2,6‐dichlorophenol. Spike recoveries from 10 to 500 ng/g for all the analytes range from 92 to 102%.     

基于因子分析的乳制品消费者质量安全信任研究

消费者对乳制品质量安全信心,既是重大的民生问题,也是重大的经济社会问题.乳制品安全关系到消费者的健康,近年来我国乳制品安全事件频发,极大地影响了国内消费者的信心,也使乳制品行业受到重创.以我国大部分省市的消费者为研究对象,以消费者信任、行为等相关理论为依据,采用问卷调查的方式采集数据,对回收的有效问卷,通过信度、效度、消费者特征分析和因子分析方法,对我国目前乳制品消费者质量安全信任水平进行测度与分析.研究表明:企业品牌形象、产品质量口感、产品包装、消费者对食品安全的信任、感知价值与满意度等因素对乳制品消费者质量安全信任水平的影响较大;总体来说,我国消费者对于乳制品的信心偏低.针对目前我国乳制品质量安全的实际情况,从社会各主体角度出发,提出了乳制品消费者质量安全信任提升的对策建议.     

Feasibility of biofilm production capacity by Levilactobacillus brevis isolated from motal cheese and evaluation of biofilm resistance produced in vitro and in yogurt

Traditional dairy products are a unique source which have been considered for the extraction of indigenous probiotic strains in recent years. In this study, biofilm formation power of Levilactobacillus brevis that isolated from Mutal traditional cheese were investigated. Survival was assessed during 21 days of storage time and at the presence of residues antibiotics as well as gastrointestinal conditions. The results showed after 120 min of treatment in high acidic conditions (pH 2.0), the survival rate decreased only 0.75 log CFU/mL in biofilm formed. The antibiotic susceptibility evaluated of probiotic to enrofloxacin, sulfadimidine, tetracycline, and oxytetracycline showed reducing the bacterial population in the biofilm form only 2.6 log. probiotic strain that isolated from indigenous dairy sources showed excellent resistance in the biofilm state. Therefore, extracting strong probiotic strains from indigenous resources, it can significantly improve functional products and fermentory engineering.     

Influence of acid hydrolysis,saponification and sample clean‐up on the measurement of phytosterols in dairy cattle feed using GC–MS and GC with flame ionization detection

The fortification of processed foods including dairy products is increasingly commonplace with phytosterols among many compounds used to improve the nutritional value of food products. It is also increasingly common practice for some dairy cattle feeds to be fortified for their potential to increase phytosterol levels in milk. In this study, a combined, streamlined protocol using acid hydrolysis, saponification and sample clean‐up was developed to enable the rapid and reliable measurement of phytosterols. The method was developed with focus on streamlining the overall technique to make it suitable for commercial laboratories, to reduce labor and consumable costs, while maintaining accuracy. A total of 12 different feed types commonly used in the dairy industry were analyzed with the highest and lowest sterol contents found in cotton seed oil and tannin with average phytosterol contents of 256 and <30 mg per 100 g, respectively. With a limit of reporting of 30 mg/kg for individual sterols and a correlation coefficient > 0.99, the method was validated for milk to enable feed comparison studies with respect to the total phytosterol content in raw milk.