Table of Content

01 July 2018, Volume 41 Issue 4

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Processing Technology

Preparation of Cheese Fortified with Dietary Fiber of Purple Potato and Effect of Fermentation Process on Its Quality

ZHANG Xiuxiu, LI Shaohua, CHANG Qianqian, XUE Xiuheng

2018, 41(4):  1-6.  DOI: 10.15922/j.cnki.jdst.2018.04.001

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Milk and purple sweet potato were used to produce purple potato supplemented cheese and the effect of the fermentation process on the change in dietary fiber content was investigated. Purple sweet potato, fermentation temperature and time were optimized using one-factor-at-a-time method and response surface methodology. The contents of nutrients and dietary fiber in cheese samples were measured by the national standard methods. The results indicated that the optimal process parameters were obtained as follows: 4% purple sweet potato flour, and fermentation at 42 ℃ for 8 h. The cheese prepared using the optimized conditions consisted of 19.79% protein, 15.62% fat and 46.75% moisture and contained 2.97 CFU/g of mold and its titratable acidity 78.03 °T, which met the national standards. In addition, the cheese had a dietary fiber content of 0.106 mg/100 g and its structure and texture was uniform. It was good in appearance with a light purple color and had the characteristic aroma of milk and the unique aroma and flavor of purple sweet potato.

Response Surface Methodology for the Optimization of the Formulation of a Shelf-Stable Fermented Milk Beverage

WANG Jian, SUN Yong, FENG Yuhong, WANG Xiaojun, WU Weidu, OU Kai

2018, 41(4):  7-10.  DOI: 10.15922/j.cnki.jdst.2018.04.002

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This study was an attempt to optimize the formulation of a shelf-stable fermented milk beverage using response surface methodology. The effect of whole milk powder-to-whey ratio, agar, starch, pectin, fructose and cream on the viscosity and water-holding capacity of the beverage was investigated. Whole milk powder-to-whey ratio, agar and starch were identified as the most significant factors using the Plackett-Burman design (P < 0.05). The levels of the four factors were optimized using response surface methodology with Box-Behnken design. A response surface model was developed indicating the relationship between each of the response variables and the four factors. The optimal combination obtained from the model was whole milk powder-to-whey ratio 5:1, pectin 1 g/L, starch 10 g/L and pectin 0.5 g/L.

Analysis & Detection

Determination of Nonylphenol in Liquid Milk by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

BAI Yanmei, ZHANG Lijia, LI Cuizhi, Lü Zhiyong, GAO Yujie, XIE Ruilong, DUAN Jianhua, HU Xue

2018, 41(4):  11-15.  DOI: 10.15922/j.cnki.jdst.2018.04.003

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A method for the determination of nonylphenol in liquid milk by using ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed. Samples were extracted using acetonitrile as extraction solvent and the organic phase was separated from the aqueous phase by adding saturated sodium chloride solution. The analyte was cleaned up using a ProElut PAEs Glass solid-phase extraction catridge and then separated on a Waters ACQUITY UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution with 0.1% ammonia water-methanol as mobile phase. The detection was performed by negative electrospray ionization under the multiple reaction monitoring mode and the quantitation was carried out by an internal standard method. The results showed a good linear relationship (R2 > 0.990) in then range from 1 to 200 ng/mL. The limit of detection（LOD, RS/N = 3）was 2.0 μg/kg and the limit of quantitation (LOQ, RS/N = 10）was 5 μg/kg. The recovery rate of the method for spiked samples was between 74.8% and 111.5% with relative standard deviation of 3.3%-9.0%. In general, the method was accurate, simple and reproducible and exhibited low background inference and it was thus suitable for the analysis of nonylphenol in liquid milk.

Quantitative Determination of Quaternary Ammonium Compounds in Dairy Products by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

DUAN Guoxia, ZHANG Lijia, Lü Zhiyong, MO Nan, LI Huixiu, LIU Lijun, LI Cuizhi, HU Xue

2018, 41(4):  16-20.  DOI: 10.15922/j.cnki.jdst.2018.04.004

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An ultra performance liquid chromatography-tandem mass spectrometry method for simultaneous quantitative determination of four quaternary ammonium compounds in dairy products, including milk, yogurt and milk powder, has been established. Quaternary ammonium compounds from samples were extracted with methanol and cleaned up by solid phase extraction using a weak cationic exchange reversed-phase adsorbent (WCX). The chromatographic separation was achieved using a mixture of formic acid and methanol (2:98, V/V) as the elution solvent. The eluate was evaporated to dryness under a stream of nitrogen gas and the residue was re-dissolved prior to analysis using a positive electrospray ion source in the multiple reaction monitoring mode. The limit of quantification was 10 μg/kg for dodecyl trimethyl ammonium bromide, benzylcetyldimethyl ammonium chloride, tetradecyl dimethyl benzyl ammonium chloride and didecyl dimethyl ammonium chloride in all three dairy products. The recoveries at spiked concentration levels of 10-200 μg/kg were 81.4%-105.6%, with relative standard deviations ranging from 0.97% to 6.04%. The matrix effect was in the range of 90.89%-234.94%. This method was rapid, accurate, repeatable and was suitable for the determination of quaternary ammonium compounds in various dairy products.

Detection of Lactoferrin in Formulas for Special Medical Purposes Intended for Infants

GUAN Yue, DAI Jianghua, JIANG Xing, ZHANG Zhaomin

2018, 41(4):  21-24.  DOI: 10.15922/j.cnki.jdst.2018.04.005

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In this study, a high performance liquid chromatography (HPLC) method was developed for the determination of lactoferrin in formulas for special medical purposes intended for infants. Lactoferrin from samples was extracted with phosphate buffer. After being purified on a heparin affinity column, the analyte was separated by reversed-phase HPLC using gradient elution with 0.1% trifluoroacetic acid and acetonitrile mixture as the mobile phase, detected by a UV detector and quantitated by the external standard method. Results showed that good linearity was observed for lactoferrin in the concentration range of 50–500 μg/mL. The detection limit of the method was 5 mg/100 g, and the quantitation limit was 15 mg/100 g. The average recovery was 93.9%. The precision expressed as relative standard deviation (RSD) was 0.12%, and the stability RSD was 0.96%. Proficiency testing confirmed the reliability of the method. This method was convenient, fast, accurate, reliable and reproducible, and could effectively detect lactoferrin in formulas for special medical purposes intended for infants.

Proficiency Testing for Determination of Aflatoxin M1 in Milk Powder

HAN Yiyi, CHEN Meilian, YANG Xiaojun, LU Zhongfei

2018, 41(4):  25-28.  DOI: 10.15922/j.cnki.jdst.2018.04.006

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A proficiency testing (PT) program for the determination of aflatoxin M1 (AFM1) in milk powder was designed and conducted so as to identify the interlaboratory differences and to understand, assess and improve the proficiency of the participant laboratories. Split-level test samples were prepared according to the Guidance on Statistical Treatment of Proficiency Testing Results and Proficiency Evaluation (CNAS?CL002), and the uniformity and stability of the samples were analyzed by one-way analysis of variance and t test, respectively. Robust statistical analysis of the proficiency testing results was conducted to evaluate laboratory proficiency through Z score. The homogeneity and stability of the samples met the requirements of proficiency testing. Of 49 laboratories that reported results for AFM1 in milk powder, 45 (91.8%) performed satisfactorily. The majority of the participant laboratories passed the proficiency testing with satisfactory results, indicating that the laboratory performance for the determination of AFM1 in milk powder was generally good. The outlier results found in a few laboratories was largely ascribed to experimental operation and data processing errors.

Quantitative Determination of Cephalosporin Residues in Dairy Products by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry Coupled with PRIME HLB Solid Phase Extraction

MO Nan, ZHANG Lijia, Lü Zhiyong, DUAN Guoxia, LIU Lijun, LI Cuizhi, ZHAO Jing, HU Xue

2018, 41(4):  29-33.  DOI: 10.15922/j.cnki.jdst.2018.04.007

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An ultra performance liquid chromatography-tandem mass spectrometry method for the simultaneous quantitative determination of four cephalosporin residues in dairy products, including milk, yogurt and milk powder, has been established. The samples were extracted with 5% formic acid acetonitrile. After being purified by solid-phase microextraction using an Oasis PRIME HLB cartridge, the extract was blown to dryness under a stream of nitrogen gas and then re-dissolved. The analysis was carried out using a positive electrospray ion source in the multiple reaction monitoring mode. The limit of quantification was 32 μg/kg for cefalexin, cefapirin, cefalonium and cefquinome?in milk powder; the limit of quantification was 4 μg/kg in milk and yogurt. The recoveries at spiked concentration levels of 4-150 μg/kg were 63.3%-112.1%, with relative standard deviations of 1.6%-10.5%. The matrix effects were 108.77%-379.91%. This method was characterized by short analysis time and was suitable for the determination of cephalosporin residues in different dairy products.

Quantitative Determination of Fipronil and Its Metabolites in Whole Egg Powder, Egg Yolk Powder and Dairy Products by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

ZHANG Lijia, BAI Yanmei, Lü Zhiyong, LI Huixiu, LIU Lijun, LI Cuizhi, HU Xue

2018, 41(4):  34-38.  DOI: 10.15922/j.cnki.jdst.2018.04.008

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An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous quantitative determination of fipronil and its metabolites in whole egg powder, egg yolk powder and dairy products was developed. Samples were extracted with acetonitrile and saturated sodium chloride solution was added to separate the organic and aqueous phases. The supernatant after low-temperature precipitation of protein was applied onto an HLB solid-phase extraction cartridge for purification. The chromatographic separation was accomplished with an Acquity UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution with a mobile phase consisting of a mixture of acetonitrile and water. The analytes were detected using a negative electrospray ion source under the multiple reaction monitoring mode and quantitated by the external standard method. The results demonstrated that the linear ranges were from 0.5 to 20.0 μg/L with good correlation coefficients (R2 > 0.990). The limit of detection and the limit of quantitation were 0.2 and 1.0 μg/kg for all analytes, respectively. The recoveries of fipronil and its metabolites in different matrixes at spiked concentration levels of 1, 2, 4 and 20 μg/kg varied from 63.4% to 118.7%, with relative standard deviations between 0.7% and 10.3%. The method proved to besensitive, accurate and suitable for the rapid quantification of fipronil, fipronil sulfide, fipronil sulfone and fipronil desulfinyl in protein-rich foods.