Table of Content

01 May 2019, Volume 42 Issue 3

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Basic Research

Effects of Adjuvant Starter Cultures on the Quality of Fermented Milk

LUO Tianqi, CAI Miao, ZHANG Min, LI Xiaowan, WANG Shijie, ZHU Hong, YANG Zhennai

2019, 42(3):  1-7.  DOI: 10.15922/j.cnki.jdst.2019.03.001

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The purpose of this investigation was to study the influence of adjuvant starter cultures on the quality of fermented milk. Seven strains of common lactic acid bacteria, including Lactococcus lactis subsp. cremoris (Lcr), Lactococcus lactis subsp. lactis (Ll), Lactobacillus casei (Lca), Lactobacillus fermentum (Lf), Lactobacillus rhamnosus (Lr), and two Lactobacillus plantarum strains (Lp1 and Lp2), were used separately as adjuvants to a commercial starter culture for fermented milk. The results showed that addition of adjuvant starter cultures could shorten the fermentation time and affect the pH value of fermented milk during storage. Moreover, Lcr and Ll could cause significant changes in the oxidationreduction potential during fermentation. Rheological measurements indicated that these strains could increase the viscosity, and reduce the elasticity and fluidity of fermented milk. The texture analysis showed that all the strains could increase the water-holding capacity, and Lr, Lf and Lp1 could enhance the cohesiveness and adhesiveness of fermented milk. Gas chromatography-mass spectrometry (GC-MS) analysis and principal component analysis showed that Lr, Lp1, Lp2 had little effect on the flavor of fermented milk, while Lca could promote the formation of heptanol, benzaldehyde and 2-tridecanone, and Lf, Ll and Lcr could increase the content of flavor substances such as short-chain and medium-chain fatty acids in fermented milk.

Effect of Heat Treatment on the Structure and Digestibility of Milk Protein

WU Xiangyi, LIU Zepeng, MAO Xueying

2019, 42(3):  8-12.  DOI: 10.15922/j.cnki.jdst.2019.03.002

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In this study, the effect of thermal modifications (25, 75, 85 and 95 ℃ for 15 min) on the structure and digestibility of milk protein concentrate (MPC70) was evaluated. Results shows that the free sulfhydryl content and surface hydrophobicity increased significantly with temperature up to 95 ℃, reaching the highest value of 42 μmol/L and 1 008, respectively. The contents of α-helix and β-turns decreased, while the contents of β-sheet and random coil increased. sodium dodecyl sulfate polyacrylamide gel electrophoresis after simulating gastrointestinal revealed that a certain degree of heat treatment enhanced the digestibility of milk proteins, which may be attributed to structural changes.

Functional Properties of Yak Whey Powder

GAO Ruiping, LIANG Qi, BAI Lili, SHI Yongqi

2019, 42(3):  13-18.  DOI: 10.15922/j.cnki.jdst.2019.03.003

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To provide insights into the chemical composition and functional properties of yak whey powder, in this experiment, native yak whey powder (NYW) from the supernatant of acid precipitated yak milk and sweet yak whey powder (SYW) from waste cheese whey (resulting from enzymatic milk coagulation) for measurement of their total protein, lactose and ash contents, pH values and functional properties such as solubility, water-holding capacity, oil-holding property, foaming capacity, emulsifying capacity and thermal stability. The results showed that the difference between the total protein contents of SYW and NYW was 3.433% which was significant (P < 0.05) while the difference in lactose content was not significant (P > 0.05). The ash content of NYW was 11.188%, which was 3.156% higher than that of SYW, with a significant difference being found between them (P < 0.05). The pH values of NYW and SYW solutions were 4.837 and 5.410, respectively, with the difference being significant (P < 0.05). The difference in solubility was significant (P < 0.05), 34.207% for SYW versus 27.079% for NYW. The water-holding capacity of NYW was significantly higher than that of SYW, but the oil-holding capacity was significantly lower than that of SYW (P < 0.05). The foaming ability, foam stability, emulsifying activity and emulsion stability of SYW were significantly higher than those of NYW (P < 0.05). When NYW and SYW were heat treated at 60 ℃, precipitation began to occur. When the temperature exceeded 75 ℃, the amount of precipitation increased significantly (P < 0.05), and the maximum value occurred at 85 ℃, indicating yak whey powder to be the least stable at 85 ℃. On the other hand, yak whey powder was more thermos-stable commercial Holstein whey powder (HW), the most unstable at 80 ℃. The findings from this study show that the main components and functional properties of the yak whey powders obtained by acid precipitation and enzymatic coagulation are different.

Analysis & Detection

A Quadrupole-Time of Flight Mass Spectrometry Method for the Discrimination of Ultra-High Temperature Milk from Reconstituted Milk

CUI Jing, SU Meicheng, TAN Dongfei, ZHANG Xia, JIA Man

2019, 42(3):  19-23.  DOI: 10.15922/j.cnki.jdst.2019.03.004

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In this study, ultra-high temperature (UHT) milk and reconstituted milk were discriminated by high resolution quadrupole-time of flight mass spectrometry (LC-Q-TOF-MS) combined with chemometrics based on non-targeted metabolomic approaches. Sample pretreatment was performed prior to chromatographic separation on a C18 column, and the mass spectrometer was operated in the full scan mode. The obtained data were preprocessed before being imported into SIMCA-P 14.1 for principal component analysis (PCA) and partial least squares-discrimination analysis (PLS-DA). A total of 14 characterization factors were selected in both positive and negative ion modes to establish a discriminant model. The results showed that this model could be used as a robust approach to discriminate between UHT and reconstituted milk and provide a theoretical basis for the identification of reconstituted milk.

Determination of Quinoxyfen in Milk by QuEChERS Dispersive Solid Phase Extraction Combined with Gas Chromatography-Mass Spectrometry

QI Xiaoru, SU Yuncong, LI Fei, LI Xingjia, ZHANG Yaoguang, CHAI Yanbing

2019, 42(3):  24-28.  DOI: 10.15922/j.cnki.jdst.2019.03.005

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A gas chromatography-mass spectrometry (GC-MS) method was developed for the determination of quinoxyfen in milk. The sample was extracted with acetronitrile, and then the extract was cleaned up by dispersive solid-phase extraction (dSPE) with C18 and N-propyl ethylenediamine (PSA) as sorbent materials. The analyte was separate on an Agilent HP- 5MS column, detected by GC-MS, and quantified by matrix-matched external standard method. The results showed that good linearity was obtained within the concentration range of 0.00–1.00 μg/mL with a correlation coefficients (R2) > 0.998 7. The average recoveries at three spiked levels (5, 10 and 20 μg/kg) ranged from 83.2% to 100.8% with relative standard deviations (RSDs) of 2.1%–4.3%. The limit of quantitation was 5 μg/kg. The proposed method was simple, sensitive and reliable, and could be applied to the determination of quinoxyfen in milk. The content of quinoxyfen in milk samples from 75 dairy households was detected to be less than the national limit value by this method.

Quantitative Determination of Salicylic Acid in Milk and Dairy Products by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

HU Xue, ZHANG Yue, ZHANG Lijia, MO Nan, DUAN Guoxia, LIU Lijun, LI Cuizhi

2019, 42(3):  29-32.  DOI: 10.15922/j.cnki.jdst.2019.03.006

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An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the quantitative determination of salicylic acid in milk and dairy products was developed. The sample was extracted with 1% acidified acetonitrile, and then the extract was purified by solid-phase extraction (SPE) with an HLB cartridge. The separation was performed on an Acquity UPLC BEH C18 chromatographic column (50 mm × 2.1 mm, 1.7 μm）with gradient elution using 0.1% aqueous formic acid-acetonitrile as the mobile phase. The target compound was monitored under the negative ion mode with an electrospray ionization (ESI) source and quantified by external standard method. The results demonstrated that the linear range of the proposed method was from 0.5 to 50.0 ng/mL with a correlation coefficient (R2) > 0.999. The average recovery of salicylic acid in different matrixes spiked at low, medium and high levels varied from 68.3% to 111.7%, and the relative standard deviations (RSDs) of precision were between 3.3% and 15.2%. The limits of detection (LODs) were 5.0 and 10.0 μg/kg in milk and milk powder, respectively. This method can meet the requirements for the determination of different salicylic acid levels in milk and dairy products.

Reviews

A Reviews of Lipids in Milk Fat Globule Membrane and Their Application in Infant Formula

ZHENG Shan, YU Jinghua, LIU Xiaohui, LUO Zhigang

2019, 42(3):  33-37.  DOI: 10.15922/j.cnki.jdst.2019.03.007

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Breast milk is the golden standard of nutrition for newborn infants. The best way to improve infant formula is not only by simulating the composition of breast milk, but also by focusing on the structure of milk fat globule membrane (MFGM). New knowledge on MFGM has been steadily acquired. This article reviews the structure and composition of MFGM, and recent progress in understanding the effect of supplementation of MFGM in infant formula on infant growth and development, which is supported by recent clinical trials. Research in rodents has shown that adding MFGM to infant formula has benefits for intestinal digestion, physiology, and protection against pathogens and inflammation. However, there is still uncertainty about the amount and safety of MFGM added to infant formula.

Recent Progress in Functional Activities of Probiotics in Prevention and Treatment of Organ Diseases

XU Yu

2019, 42(3):  38-43.  DOI: 10.15922/j.cnki.jdst.2019.03.008

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Nowadays, probiotics are a hot concern in the health market. In this paper, the functional activities of the two main probiotics, Lactobacillus and Bifidobacterium, in the prevention and treatment of skin, oral, respiratory, liver, gastrointestinal and female genital tract diseases are summarized including the activities in animal experiment and clinical trials and the related mechanisms. This review will provide important theoretical support for further scientific research and product development of probiotics.

Recent Progress in Milk Fat Globule Membrane

LIU Tingting, ZHANG Guofang, LIU Libo

2019, 42(3):  44-49.  DOI: 10.15922/j.cnki.jdst.2019.03.009

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Milk fat globule membrane (MFGM), the membrane surrounding fat globules in milk, is particularly interesting due to its specific composition of proteins and polar lipids which makes it an excellent candidate to develop a wide range of innovative applications such as emulsifiers, stabilizers, and health promoters in both food and non-food fields. In addition, MFGM has been proven to be rich in nutrients. This review focuses on current studies on the structure, composition, preparation and nutritional aspects of MFGM. Furthermore, new technologies for preparing MFGM-derived phospholipids liposomes entrapping bioactive compounds are described. We hope that this review can provide a rationale for the application of MFGM.

Advances in Application of Ultra High Performance Liquid Chromatography in Food Safety Detection

ZHANG Minmin

2019, 42(3):  50-56.  DOI: 10.15922/j.cnki.jdst.2019.03.010

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Ultra high performance liquid chromatography (UPLC) is a stable, easy-to-use, and selective analytical technology with variable sensitivity which is superior to high performance liquid chromatography in many aspects such as better chromatographic separation, more sensitive analysis, shorter analysis time and reduced solvent consumption. The application of UPLC in the rapid detection of dairy additives, food additives, contaminants, mycotoxins and illegal chemical additives is reviewed in this article.