Table of Content

28 February 2015, Volume 38 Issue 1

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Basic Research

Dipeptidyl Peptidase-Ⅳ Inhibitory Activity and Physicochemical Properties of Yak Milk Casein Hydrolysates

SONG Jiajia, BAI Hanyu, WANG Qian, SONG Jue, MAO Xueying

2015, 38(1):  1-4.  DOI: 10.15922/j.cnki.jdst.2015.01.001

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The dipeptidyl peptidase-Ⅳ (DPP-Ⅳ) inhibitory activity and physicochemical properties of yak milk casein hydrolysates produced with alcalase, papain and trypsin were investigated. The effect of hydrolysis periods and different proteases on the DPP-Ⅳ inhibitory activity of yak milk casein hydrolysates was assessed by DPP-Ⅳ inhibitory rate. The physicochemical properties of yak milk casein hydrolysates were evaluated by degree of hydrolysis, trichloroacetic acidnitrogen soluble index (TCA-NSI), solubility and ash content. Results showed that the DPP-Ⅳ inhibitory activity of yak milk casein hydrolysate obtained with papain was significantly higher than that of those obtained with alcalase or trypsin at the same hydrolysis period (P < 0.05). The yak milk casein hydrolysate obtained after 0.50 h hydrolysis with papain displayed the highest DPP-Ⅳ inhibitory activity (with inhibitory rate of (53.95 ± 1.57) %), higher extent of hydrolysis degree, and the lowest ash content. The results suggest that peptides with DPP-Ⅳ inhibitory activity can be generated from yak milk casein. The yak milk casein hydrolysate produced by papain may be used as a functional dairy ingredient to develop functional foods.

Coagulation Properties of Milk from Beijing and Surrounding Areas

ZHENG Zhe, SUN Yuchen, YANG Zhennai

2015, 38(1):  5-8.  DOI: 10.15922/j.cnki.jdst.2015.01.002

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The coagulation properties of milk from dairy farms of different scales in Beijing and its surrounding areas such as Shandong were investigated in this study. Analyses were carried out with physiological factors (age, parity and lactation stage) and environmental factors (season, raising condition) affecting milk coagulation. The results showed that milk coagulation properties induced by fermentation or rennet were strongly related to milk source. Milk coagulation properties decreased with the extension of cow’s age and parity and were poorer during middle lactation stage. Coagulation properties reached the peak point in fall and winter among the four seasons. Large-scaled and modernized raising conditions were helpful in improving milk coagulation properties.

Isolation and Identification of Thermostable Lipase Produced by Pseudomonas fluorescens from Fresh Milk

SHI Pujie, LI Lin, LIU Meng, WANG Yun, TU Maolin, YANG Jian, FAN Fengjiao, DU Ming, ZHANG Lanwei

2015, 38(1):  9-12.  DOI: 10.15922/j.cnki.jdst.2015.01.003

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In the present study, a preliminary purification was carried out to obtain heat-resistant lipase secreted by Pseudomonas fluorescens separated from fresh milk. Moreover, the effects of temperature, pH, and Ca2+ concentration on the activity of this lipase were determined. Results showed that the lipase from Pseudomonas fluorescens had a molecular weight 55 kD and a purity of 91.5% after the purification, and its relative activity was 75.02%, 86.21%, 73.25%, 17.62% and 13.63% after heat treatment at 50 ℃ for 30 min, 63 ℃ for 30 min, 72 ℃ for 20 s, 90 ℃ for 10 min, and 121℃, 0.1 MPa for 20 min, respectively. The optimum reaction pH and temperature for this enzyme were 8.0 and 63 ℃, respectively. The lipase activity was not significantly affected by Ca2+ concentration.

Effect of Ultrasonic Treatment on the Solubility of Milk Protein Concentrate

FAN Fengjiao, LIU Meng, WANG Yun, YANG Jian, TU Maolin, SHI Pujie, DU Ming, ZHANG Lanwei

2015, 38(1):  13-17.  DOI: 10.15922/j.cnki.jdst.2015.01.004

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The solubility of milk protein concentrate (MPC), which has a direct impact on its application value, may be reduced during storage. The effect of ultrasonic treatment with different powers for different durations on the solubility of fresh and stored MPC was studied. The results showed when stored MPC85, a commercial product, was treated with ultrasonic (at 50, 300 or 600 W for 5 min, or at 300 W for 3, 5 or 10 min), its solubility decreased sharply. As for fresh MPC70 stored for 30 d after treated with ultrasonic (at 300 or 600 W for 3, 5 and 10 min, respectively), its solubility decreased slowly and the smallest decrease was observed upon ultrasonic treatment for 300 W, 10 min. Ultrasonic treatment is useful to retard the decrease in the solubility during storage of MPC.

Analysis & Detection

Surface Plasmon Resonance for Rapid Determination of Melamine in Milk

DENG Shaoli, CUI Dafu, LIAN Shuangqiu

2015, 38(1):  18-21.  DOI: 10.15922/j.cnki.jdst.2015.01.005

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The residual melamine in milk is one of the important risk factors for human health. A method for the rapid quantitative detection of melamine (MEL) in milk has been designed based on surface plasmon resonance (SPR) technique. As a vector, nano-gold was used to connect MEL to the surface of SPR biosensor chip. The antibody quantity and regeneration conditions were optimized. The designed chip was tested regarding its stability and the accuracy of the proposed method was checked. Using pollution-free milk added with serial concentrations of MEL, the competitive inhibition curve was developed and used to detect real samples. The results showed that the chip exhibited a good reproducibility, with a relative standard deviation (RSD) of 5.05% for 60 replicate determinations. The detection limit of this method was 3.24 ng/mL, much lower than the maximum residue limits adopted by the Codex Alimentarius Commission and by relevant state authorities. The whole analytical procedure including sample preparation could be completed within 30 min and is suitable for rapid in-situ quantitative detection of milk.

Determination of β-Sitosterol in Milk by GC-MS

ZHAO Jing, SHI Xin, HU Meijie, LIU Bo

2015, 38(1):  22-25.  DOI: 10.15922/j.cnki.jdst.2015.01.006

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A gas chromatography-mass spectrometry (GC-MS) method was developed for determining β-sitosterol in milk by optimizing important sample pretreatment parameters such as saponification temperature, extraction solvent, extraction number, shaking method during extraction and rotary evaporation temperature. The feasibility of the developed method was examined. This method exhibited a wide linear range and could meet the requirements for routine quantitative analysis of β-sitosterol in milk samples with high precision, good repeatability, accurate results and high reliability.

Reviews

Risk Assessment of Staphylococcus aureus in Raw Milk: A Review of Worldwide Research

LI Jiao, DONG Qingli, LU Baiyi, YE Xingqian, LIU Donghong, DING Tian

2015, 38(1):  26-31.  DOI: 10.15922/j.cnki.jdst.2015.01.007

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In recent years, with the growth of dairy consumption, dairy quality and safety have become a matter concerning people’s health and safety. However, poisoning incidents often occurred because of dairy products contaminated by enterotoxin-producing strains of Staphylococcus aureus. Thus risk assessment of Staphylococcus aureus is important for raw milk as the source of dairy products. Based on the principles and guidelines of the Codex Alimentarius Commission for microbial risk assessment, this paper reviews the studies in the field of risk assessment of Staphylococcus aureus in raw milk, including hazard identification, hazard characterization, exposure assessment and risk characterization. Through the mature cases of quantitative risk assessment, we introduce the basic framework for quantitative risk assessment of Staphylococcus aureus in raw milk and propose that more intensive studies are needed to construct a prediction model of enterotoxin and that systematic monitoring and microbial risk assessment of raw milk from pasture to table is necessary for providing basic information for safety monitoring and early warning security system of raw milk and dairy products.

Advances in Detection Methods for Lactoferrin

TU Maolin, YANG Jian , LIU Meng, SHI Pujie , WANG Yun , FAN Fengjiao , DU Ming, ZHANG Lanwei

2015, 38(1):  32-37.  DOI: 10.15922/j.cnki.jdst.2015.01.008

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Lactoferrin is an important multifunctional protein that has a variety of biological activities, such as anti-bacterial, anti-tumor, anti-allergy, immunoregulatory and so on. The related basic research and application development of lactoferrin have attracted wide attention. Therefore, the detection methods for lactoferrin have drawn increasing attention. Especially the advantages, sensitivity, accuracy and stability of different methods vary to different extents, which directly affects their applicable scope. The present paper has described the detection methods which have been reported to be suitable for different types of biological samples, mainly including spectrophotometry, high performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA), high affinity chromatography (HPAC), efficient capillary electrophoresis (HPCE) and surface plasmon resonance (SPR). The advantages and disadvantages of these different detection technologies also have been analyzed and compared. This review is expected to provide reference for selection of the suitable detection method for lactoferrin in research and development practices.

Current Status and Development Trends of Functional Dairy Products

WANG Yun, YANG Jian, FAN Fengjiao, LIU Meng, DU Ming, ZHANG Lanwei

2015, 38(1):  38-43.  DOI: 10.15922/j.cnki.jdst.2015.01.009

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Nowadays, the Chinese dairy industry is developing fast. Dairy products have become an important part in people’s dietary structure. Functional dairy products are an emerging type of dairy products which exerts physiological effects through added probiotics and bioactive molecules. The present article presents an overview of China’s dairy products market and analyzes the classification, market and consumption conditions, current status and limitations of functional dairy products. Moreover, some suggestions regarding the development trends of functional dairy products in China are given based on the development of related products and technologies worldwide. This paper can provide useful references for the research and development of functional dairy products.