Table of Content

01 March 2017, Volume 40 Issue 2

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Basic Research

Effect of pH on the Rheological Properties of Propylene Glycol Alginate Aqueous Solution

WU Weidu, ZHU Hui, WANG Yaqiong, LI Yanjun

2017, 40(2):  1-4.  DOI: 10.15922/j.cnki.jdst.2017.02.001

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Propylene glycol alginate is widely used in dairy products or milk-based beverages as a thickener.The aim of the work was to study the influence of pH on the rheological properties of propylene glycol alginate solution.For this purpose,steady-state flow sweep,strain sweep,frequency sweep,dynamic viscoelasticity temperature sweep and dynamic viscosity temperature sweep experiments were carried out with an AR-G 2 rheometer.The experimental results showed that the viscosity,viscoelasticity,and complex viscosity of propylene glycol alginate solution decreased as pH increased,while the loss tangent increased.Meanwhile,at pH below 7 the degree of shear thinning decreased while it increased at pH above 7.In addition,pH influenced the effect of temperature on the viscosity and viscoelasticity of propylene glycol alginate solution.

Investigation of Proteolytic Activity of Psychotrophic Pseudomonas Species Isolated From Refrigerated Raw Milk

XU Yu

2017, 40(2):  5-9.  DOI: 10.15922/j.cnki.jdst.2017.02.002

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Pseudomonas frequently occur in refrigerated raw milk as the predominant bacteria,which secret heat-resistant enzymes that can cause milk spoilage.A total of 102 strains of Pseudomonas isolated from raw milk were identified by rpoB gene sequencing at the species level,and azocasein was used to quantify the proteolytic activity and heat resistance of their extracellular peptidases under two sets of cultivation conditions (30 ℃ for 2 days or 6 ℃ for 8 days).Pseudomonas fluorescens was the most dominant Pseudomonas species in the samples,followed by Pseudomonasfragi and Pseudomonas sp1.A significant variation in the proteolytic activity of different Pseudomonas species was observed.Most isolates of Pseudomonasfluorescens (23/41) showed proteolytic activity after cultivation at two temperatures (30 or 6 ℃),while most isolates of Pseudomonas sp1 did not.In addition,all isolates of Pseudomonasfragi (13/13) showed proteolytic activity only after cultivation at 6 ℃.Temperature stability of their extracellular peptidases was determined.After cultivation at 6 ℃,P.fluorescens M02 had the highest peptidase activity (11.78 ΔA/(h·mL)).The peptidase showed maximum activity at pH 6.5 and 40 ℃.The addition of 103 CFU/mL P.fluorescens M02 resulted in destabilization of skim milk during 5 days of culture at 6 ℃.Monitoring the predominant psychrotrophic bacteria at species level will be useful in designing effective monitoring methods and tools to improve the quality and safety of raw milk or dairy products.

Processing Technology

Response Surface Methodology for Optimization of the Formulation of Donkey Hide Glue Containing Aqueous Extract from Edible Flowers and Skim Goat Milk

ZHANG Xuexi, WANG Cunfang

2017, 40(2):  10-16.  DOI: 10.15922/j.cnki.jdst.2017.02.003

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The formulation of donkey hide glue containing aqueous from edible flowers and skim goat milk was optimized using combination of one-factor-at-a-time method and response surface methodology with Box-Behnken design.The response variables were sensory evaluation scores and gel strength.The results showed that the optimum formulation was composed of 62.4％ skim goat milk,6.2％ donkey hide glue,aqueous flower extract 14.9％,and 0.075％ composite gelling agent.The resultant product showed a sensory score of 9.6 and a gel strength of 35.8 g.Physicochemical analysis indicated that the product contained ≥ 6.80 g of protein and ≤4.00 g of fat per 100 g of sample and thus could nourish blood and maintain beauty as a high-protein,low-fat product.

Production and Stability Evaluation of a Dairy Beverage Supplemented with Mung Bean Protein

WU Yuying, LIU Yang, REN Huahua, LI Guijie, LIU Tingting, ZHANG Xu

2017, 40(2):  17-22.  DOI: 10.15922/j.cnki.jdst.2017.02.004

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A beverage stabilizer consisting of a mixture of xanthan gum,carboxy methyl cellulose (CMC) and propylene glycol alginate (PGA) at a ratio of 1 ∶ 1.5 ∶ 6.25 was developed by one-factor-at-a-time method and used in a dairy beverage supplemented taking mung bean protein as one of the ingredients.The formulation of the beverage was optimized by orthogonal array design for improved sensory evaluation and emulsion stability.Meanwhile,the thermal stability of the product was evaluated.The optimal formulation was found to consist of 8.0％ whole milk powder,1.0％ mung bean protein,10.0％ white sugar,0.4％ stabilizer and 0.3％ citric acid.The resulting product had a rich milky aroma and delicate taste with moderate sweetness,and its emulsion stability was 98.60％.The milk protein content was 1.95％,which was in line with the national standard requirements of GB/T 21732-2008 for milk beverages.

Analysis & Detection

Determination of Fructose, Glucose, Sucrose, Maltose and Lactose in Fermented Milk Drink by High Performance Liquid Chromatography

YUE Hong, ZHAO Zhen, LIU Lijun, LI Cuizhi, SHAO Jianbo

2017, 40(2):  23-26.  DOI: 10.15922/j.cnki.jdst.2017.02.005

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A method for the determination of fructose,glucose,sucrose,maltose and lactose in fermented milk drink by high performance liquid chromatography (HPLC) with refractive index detector was developed.The samples were extracted with water.The method was performed on a carbonhydrate column using acetonitdle-water as mobile phase.The average spiked recoveries of fructose,glucose,sucrose,maltose and lactose spiked in the concentration range of 0.2％-10.0％ were between 92.6％ and 102.0％ with relative standard deviation (RSD,n =6) less than 3.00％.The limit of quantitation was 0.2％.The results indicated that this method is accurate,simple,reproducible and suitable for the analysis of fructose,glucose,sucrose,maltose and lactose in fermented milk drink.

Determination of Hippuric Acid and Benzoic Acid in Dairy Products by High Performance Liquid Chromatography

ZHAO Zhen, LIU Chunxia, LIU Lijun, YUE Hong, WAN Peng, LI Cuizhi

2017, 40(2):  27-29.  DOI: 10.15922/j.cnki.jdst.2017.02.006

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A method for determination of hippuric acid and benzoic acid in dairy products by high performance liquid chromatography (HPLC) is described.The protein samples was precipitated by adding lead acetate and centrifuged,and then the analytes were separated on a C18 column with a mobile phase consisting of ammonium acetate and methanol solution and detected with a UV detector at 230 nm.The results showed that hippuric acid and benzoic acid displayed a good linearity relationship in the concentration range of 1-100 mg/kg.The recovery rate was 95.3％-103.6％.The method proved to be simple,accurate and repeatable.

Detection of Gluconacetobacter in Yogurt by Helicase-Dependent Isothermal DNA Amplification

TANG Xinyi, LIU Bo, ZHANG Tao, LI Yongyan, ZHANG Cuixia, WANG Zan, ZHANG Jingjing, ZHOU Wei

2017, 40(2):  30-33.  DOI: 10.15922/j.cnki.jdst.2017.02.007

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A helicase-dependent isothermal DNA amplification (HDA) assay was developed for the rapid and accurate detection of Gluconacetobacter in yogurt.A pair of specific oligonucleotide primers according to the 16S ribosomal RNA gene (GenBank accession number:HQ677466.1) of Gluconacetobacter was designed,and the optimal concentration of UvrD helicase and T4 gp32 in the reaction system were determined.The HAD method enabled direct detection of Gluconacetobacter in yogurt.The specificity of the method was tested by amplification and electrophoresis of various strains in yoghurt using the HAD system.The amplification product by HDA was the same as the designed gene fragment (101 bp).The sensitivity of HDA was 102 CFU/g.The optimal reaction system was established by the use of 0.1 μg of UvrD helicase and 5.0 μg of T4 gp32.In conclusion,the method was sensitive and time saving.

Reviews

Analysis of Infant Formula Labeling Standardization and Management

LONG Jihong

2017, 40(2):  34-37.  DOI: 10.15922/j.cnki.jdst.2017.02.008

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At present,there are numerous problems with respect to infant formula labeling such as confused product names,non-standard labeling of ingredients and nutritional information,unreasonable functional claims,confused source claims,and redundant information unrelated to the product,which can easily mislead consumers.With this in mind,it is recommended that infant formula labeling be standardized and managed by clearly defining the primary responsibilities in order to ensure the safety of infant formula and promote the healthy development of this industry.