Table of Content

28 February 2012, Volume 35 Issue 1

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Basic Research

Effect of Maillard Reaction between Whey Protein and Different Sugars on the Allergenicity of β-Lactoglobulin

2012, 35(1):  1-3.  DOI: 10.15922/j.cnki.jdst.2012.01.001

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In our current study, SDS-PAGE and indirect ELISA were both used to investigate the effect of Maillard reaction between whey protein and different sugars on the allergenicity of β -lactoglobulin. It was indicated that better results were achieved when pentose instead of hexose, a monosaccharide instead of a polysaccharide or a thermo-instable polysaccharide instead of a thermostable one was used to react with whey protein. Xyololigosaccharide had less effect on the flavor of Maillard reaction products, resulted in a lower browning rate, and was more effective in reducing the allergenicity of β-lactoglobulin.

Development of an Enrichment Medium for Lactic Acid Bacteria

2012, 35(1):  4-7.  DOI: 10.15922/j.cnki.jdst.2012.01.002

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：An enrichment culture medium has been developed for the industrial mass production of lactic acid bacteria. Onefactor- at-a-time experiments were conducted to choose optimal carbon and nitrogen sources and growth factor, and their levels were optimized using an orthogonal array design. Our results demonstrated that the optimal medium composition consisted of 10% pineapple peel juice, 25% Pleurotus ostreatus soup and 20% potato juice. The enrichment culture medium was not only significantly more effective in enriching lactic acid bacteria than MRS medium but also inexpensive, thus favoring the industrial mass production of lactic acid bacteria.

Biotechnology

Effect of Methionine on Lactation Ability of Dairy Cow Mammary Epithelial Cells Cultured in vitro

2012, 35(1):  8-10.  DOI: 10.15922/j.cnki.jdst.2012.01.003

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An in vitro model of dairy cow mammary epithelial cells (DCMECs) was developed and used to study the relationship between methionine and milk protein synthesis or the lactation ability of the mammary gland. After 24 hours of in vitro culture in the presence of various concentrations (0, 0.2, 0.4, 0.8, 1.2 mmol/L and 1.6 mmol/L) of methionine, the lactation ability of DCMECs was analyzed by high performance liquid chromatography (HPLC), real-time quantitative PCR (RT-PCR), cell viability analyzer and triglyceride kit. It was found that methionine at 1.2 mmol/L had the most significant proliferationpromoting effect on DCMECs during the culture period. In addition, the highest amounts of lactose secretion, β-casein mRNA expression and triglyceride synthesis were achieved.

Application of a Cholesterol-Lowering Strain of Bifidobacterium animalis in Fat-Free Yoghurt

2012, 35(1):  11-14.  DOI: 10.15922/j.cnki.jdst.2012.01.004

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Bifidobacterium animalis strain B, a strain that is capable of lowering cholesterol levels in the body, was screened out and used in combination with the conventional fermentation starter (composed of L.bulgaricus and S.thermophilus) for the mixed-strain fermentation of fat-free yoghurt at 43 ℃. The end point of the fermentation was reached after 5.5－6 hours. The total numbers of viable Bifidobacterium animalis and lactic acid bacteria reached an average of 4.8 × 106 CFU/g and 7.4 × 107 CFU/g respectively during 28 days of storage at 4 ℃.The yoghurt obtained showed a protein content of 2.8 g/100 g, a fat content of 0.2 g/100 g, and an acidity value of 80 °T. All of these three indexes met the requirements of the National Food Safety Standard GB 19302－2010: Fermented Milk. Meanwhile, according to the Ministry of Health,s Regulation for Food Nutrition Labeling, the yoghurt product could be labeled as fat-free fermented milk. The results of sensory evaluations revealed that it had a very gentle flavor and a strong taste of fresh cream with a smooth and exquisite texture and a good consumer acceptance. Therefore, the yoghurt developed in this study has promising commercial prospects.

Fermentation Characteristics of Enterococcus hirae and Application in Yogurt Starter

2012, 35(1):  15-19.  DOI: 10.15922/j.cnki.jdst.2012.01.005

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Fermentation characteristics were assessed for Enterococcus hirae strain I-2. It was indicated that the strain had excellent fermentation characteristics. All of the tested indexes of yogurt fermented with it met the requirements of relevant national standards. Besides, the number of viable cells remained above 109 CFU/mL at the end of the fermentation and after 20 days of ripening, demonstrating that the strain has promising potential for developing dairy products and excellent health benefits.

InhibitiInhibition Effect of Skim Milk Fermented with Dominant Strains Isolated from Sayram Ketteki Yoghurt on Angiotensin-Converting Enzyme (ACE)on Effect of Skim Milk Fermented with Dominant Strains Isolated from Sayram Ketteki Yoghurt on Angiotensin-Converting Enzyme （ACE）

2012, 35(1):  20-24.  DOI: 10.15922/j.cnki.jdst.2012.01.006

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An improved ultraviolet spectrometric method was used to determine the ACE inhibitory activity of skim milk fermented by single or mixed strains of Lactobacillus helveticus mb2-1 and Streptococcus thermophilic mb5-1, both of which were isolated from Sayram Ketteki yoghurt, a home-made traditional fermented milk in Xinjiang, as well as Kluyveromycus marxianus Y6. The highest ACE inhibitory rate was observed after 48 hours of fermentation by single strains of Lactobacillus helveticus mb2-1 and Streptococcus thermophilic mb5-1 to be 70.75% and 47.17%, respectively, and the values were 75.68% and 44.85% respectively when combined with Kluyveromycus marxianus Y6.

Processing Technology

Development of a Lactic Acid Bacteria-Fermented Blueberry Dairy Beverage

2012, 35(1):  25-28.  DOI: 10.15922/j.cnki.jdst.2012.01.007

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A nutritional beverage was developed by fermenting a mixture of blueberry juice and milk with mixed cultures of domesticated lactic acid bacteria. Orthogonal array design was used to determine optimal process parameters. The optimal fermentation substrate composition was composed of 60% milk, 14% blueberry juice and 6.5% sucrose. The optimal fermentation parameters were determined as 3.2% of inoculum size, 4.4 h of fermentation time and 42 ℃ of fermentation temperature.

Process Optimization for the Development of Potato Yogurt

2012, 35(1):  29-31.  DOI: 10.15922/j.cnki.jdst.2012.01.008

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The water left over from cooking potato and milk powder were used mainly for yogurt production by fermentation with mixed starter cultures of Lactobacillus bulgaria and Streptococcus thermophilus. The optimal fermentation parameters were 8% of white sugar, 6 h of fermentation time and 43 ℃ of fermentation temperature as determined using orthogonal array design for maximizing sensory evaluation score. Yogurt with a uniform color, a good texture, and a smooth taste was obtained under these parameters. Which could meet the requirements of relevant standards.

Development of a Fermented Apple Dairy Beverage

2012, 35(1):  32-35.  DOI: 10.15922/j.cnki.jdst.2012.01.009

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A highly nutritional fermented dairy beverage with a unique flavor was prepared with apple juice and milk. As determined by one-factor-at-a-time and orthogonal array design methods based on pH and sensory evaluation score, the optimal fermentation substrate composition was made up of 55% milk, 12% apple juice and 5.5% sucrose, and the optimal fermentation conditions were 3.0% of inoculum size, 5.0 h of fermentation time and 40 ℃ of fermentation temperature.

Analysis & Detection

GC-MS Determination and Uncertainty Analysis of Phthalate Acid Esters in Milk-Containing Beverages

2012, 35(1):  36-39.  DOI: 10.15922/j.cnki.jdst.2012.01.010

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Gas chromatography-mass spectrometry (GC-MS) was used to develop a method to determine phthalate acid esters in milk-containing beverages. Meanwhile, a mathematical model for uncertainty assessment for the GC-MS determination was established. The major sources of uncertainty were analyzed, and the standard, synthetic and expanded uncertainties were determined to evaluate the applicability of the method. The expanded uncertainty was found to be 0.038. Furthermore, GC-MS measurement repeatability and sample pretreatment contributed most to uncertainty.

Determination of Fructooligosaccharides in Milk and Milk Products by High Performance Ion Exchange Chromatography

2012, 35(1):  40-42.  DOI: 10.15922/j.cnki.jdst.2012.01.011

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An analytical method was established to determine fructooligosaccharides (FOS) in milk and milk products by high performance ion exchange chromatography method with pulsed amperometric detection. The column was a CarboPac PA1 (4 mm × 250 mm) anion exchange column. Fructooligosaccharides were separated under gradient elution mode. The mobile phase A was 150 mmol/L NaOH and the mobile phased B was composed of 150 mmol/L NaOH and 100 mmol/L sodium acetate. The relative standard derivations for 6 replicate determinations of four fructooligosaccharides in liquid milk were less than 9%. The average spike recovery rates for three fructooligosaccharides in liquid milk varied between 94.8% and 103.6%. The method was simple, fast and suitable for determining FOS in milk and milk products.

Machinery and Equipment

Design and Application of Direct Sterilization in Falling-Film Evaporator

2012, 35(1):  43-45.  DOI: 10.15922/j.cnki.jdst.2012.01.012

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In the production of milk power, direct sterilization offers many advantages over indirect sterilization such as more stable and more evenly distributed sterilization temperature, better sterilization effect, being less easy to cause fouling and coking, and longer time intervals for cleaning. Its disadvantage lies in its high requirements for the quality of steam as the material fluid is moistened as a result of direct mixing of steam during the sterilization process and the absorbed moisture has to be removed by flash evaporation after the sterilization. Therefore, steam must be strictly filtrated or be generated by a specialized generator before coming into contact with the material fluid. In this study, a three-effect falling film evaporator RNJM03-8000, manufactured by Huayu Dairy Machinery Manufacturing Co. Ltd., was used to evaluate its application for the production of milk powder. The design of direct sterilization for producing milk powder using the device and points for attention were elaborated.

Reviews

Recent Progress on Analytical Techniques for Free Biotin

2012, 35(1):  46-49.  DOI: 10.15922/j.cnki.jdst.2012.01.013

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Biotin is one of the essential vitamins for maintaining normal physiological functions of the animal organism. This paper provides a review on microbiological, chromatographic and mass spectrometric assays for free biotin in dairy products. Their advantages and disadvantages as well as points for attent2ion during the operation are compared. Guidelines on how to select the appropriate assay in the industrial production and future trends in the analysis of biotin are put forward.