Table of Content

30 April 2012, Volume 35 Issue 2

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Basic Research

Effect of Soluble Dietary Fiber from Wheat Bran on Yoghurt Quality

2012, 35(2):  1-3.  DOI: 10.15922/j.cnki.jdst.2012.02.001

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Soluble dietary fiber (SDF) was prepared by hydrolyzing wheat bran with a mixture of amylase, alkaline protease and cellulase at ratio of 2:1:2 and added to fresh milk together with other auxiliary materials for yoghurt fermentation. The results showed that the presence of wheat bran SDF in yoghurt resulted in an obvious increase in the contents of calcium and essential amino acids. In terms of the quality and nutritional composition of yoghurt, the optimal fermentation substrate composition for SDF-supplemented yoghurt was 80.0% raw milk, 3.0% whole milk power, 1.0% SDF, 3.0% sucrose, 10.0% water, 2.5% fermentation starter (a mixture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, 1:1), 0.5% stabilizer.

Effect of Different Milk-Clotting Enzymes on Properties of Cheese Curds

2012, 35(2):  4-6.  DOI: 10.15922/j.cnki.jdst.2012.02.002

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To understand the effect of different milk-clotting enzymes on the quality of cheese curds, calf rennet, chymopapain, and Mucor pusillus rennin were individually used for milk clotting. Meanwhile, the feasibility of partially replacing rennets of animal origin with those of non-animal origin for cost reduction was explored. The results demonstrated that Mucor pusillus rennin could partially replace calf rennet when added in a proportion not exceeding 25% with no obvious adverse effect on the flavor and taste of cheese curds.

Application of Whey in Cheese Production

2012, 35(2):  7-11.  DOI: 10.15922/j.cnki.jdst.2012.02.003

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One-factor-at-a-time design coupled with response surface methodology based on Box-Behnken experimental design was applied to explore the effects of different amounts of whey and glutamine transaminase (TG) added to raw milk and enzymatic reaction time on cheese yield. A corresponding mathematic model was established. In the production process of cheese, whey and TG were concurrently added at levels of 30% and 1.4048 g/100 mL, respectively and allowed to react for 89.955 min before milk clotting. Under these conditions, the maximum theoretical cheese yield was 14.8463%, which did not significantly differ from the actual average value, 13.875% (P＞ 0.05). A difference in texture characteristics, protein hydrolysis and color was observed during the early stages of ripening compared to control samples. After 50 days of ripening, all other tested indexes showed no significant difference (P＞0.05) except springiness and chewingness, both of which had significant difference (P＜0.05).

Biotechnology

Preparation of Antimicrobial Peptides Powder Derived from Bovine Casein Hydrolysates

2012, 35(2):  12-16.  DOI: 10.15922/j.cnki.jdst.2012.02.004

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In order to prepare highly active antibacterial peptides power, casein was extracted from fresh milk and then hydrolyzed with one of four different proteases (neutral protease, alcalase, trypsin and papain). Casein hydrolysates prepared with papain exhited stronger inhibitory effects on Escherichia coli, Salmonella and Staphylococcus aureus than those prepared with neutral protease, alcalase or trypsin. Using one-factor-at-a-time and orthogonal array design methods, the optimal hydrolysis conditions for the preparation of highly active antibacterial casein hydrolysates with papain were determined as following: 50 ℃ of hydrolysis temperature, 4.5 h of hydrolysis time, 4500 U/g of enzyme amount, pH 5.5, and 6 g/100 mL of substrate concentration. Moreover, we found that both the prepared casein hydrolysates and their lyophilized powder had stable antimicrobial activity. Meanwhile, the lyophilized powder showed slightly stronger antimicrobial activity.

Optimal Carbon and Nitrogen Sources for Lactic Acid Production by Lactobacillus rhamnosus and Fermentation Dynamics

2012, 35(2):  17-20.  DOI: 10.15922/j.cnki.jdst.2012.02.005

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The abilities of Lactobacillus rhamnosus to utilize various carbon and nitrogen sources were examined with the aim of finding optimal carbon and nitrogen sources for lactic acid production by Lactobacillus rhamnosus. It was indicated that glucose was the best carbon source although it at high concentrations had a certain inhibitory effect on Lactobacillus rhamnosus growth and lactic acid production. Yeast extract was the best nitrogen carbon for Lactobacillus rhamnosus growth and lactic acid production. Basically the same lactic acid production was obtained when yeast extract was replaced with other cheap nitrogen carbons such as soybean meal or ammonium sulfate. The lactic acid yield and productivity were 48.25 mg/mL and 80.53%, respectively after 48 h of culture in a medium containing yeast extract as the nitrogen source and glucose as the carbon nitrogen at an initial concentration of 60 mg/mL under thermostatic anaerobic conditions.

Processing Technology

Effect of Different Factors on Water Vapor Permeability and Transparency of Whey Protein Isolate Film

2012, 35(2):  21-25.  DOI: 10.15922/j.cnki.jdst.2012.02.006

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This study focused on the effect of different factors such as whey protein isolate (WPI) concentration, glycerol concentration, sodium chloride concentration, carboxymethyl cellulose sodium (CMC) concentration, transglutaminase (TG) reaction time on the water vapor permeability and transparency of WPI film. The results indicated that under the conditions: 10.0 g/100 mL WPI, 5.00 g/100 mL glycerol, 1.0g/100 mL sodium chloride, 0.25 g/100 mL CMC, and 45 min of TG reaction time, the lowest water vapor permeability was found in WPI film. By contrast, the concentrations of WPI, glycerol, sodium chloride, CMC, and TG reaction time resulting in the lowest transparency of WPI film were 15.0 g/100 mL, 1.50 g/100 mL, 2.5 g/100 mL, 0.50 g/100 mL, and 15 min, respectively. According to the results of response surface optimization, 5.0 g/100 mL WPI, 1.27834 g/100 mL sodium chloride and 20 min TG reaction resulted in the lowest water vapor permeability, 3.9428 g/(h·m2), and while the lowest transparency of 0.0381 was obtained by using 15.0 g/100 mL WPI, 1.5 g/100 mL sodium chloride and 10 min of TG reaction time.

Development of a Fermented Mango Dairy Beverage

2012, 35(2):  26-28.  DOI: 10.15922/j.cnki.jdst.2012.02.007

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A novel health-care fermented beverage was developed from mango juice and raw milk. The optimal fermentation substrate composition consisted of 65% fresh milk, 10% mango juice and 7.0% sucrose, and the optimal inoculum size, fermentation time and temperature were 2.5%, 3.5 h and 40 ℃, respectively, as optimized by orthogonal array design.

Development of Clarified Beverage Based on Lactic Acid Fermentation of Apple Juice and Milk

2012, 35(2):  29-33.  DOI: 10.15922/j.cnki.jdst.2012.02.008

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In this study, a clarified beverage was developed based on lactic acid fermentation of apple juice and raw milk. The production process was optimized by one-factor-at-a-time and orthogonal array desigh methods. The optimal fermentation conditiions were a blend of Lactobacillus delbruechii subsp. bugaricus, S. thermophilus and Lactobacillus acidophilus at a ratio of 2:1:2 inoculated at an inoculum size of 6%, 38 ℃ of fermentation temperature, 11 mL/100 mL of milk concentration, and 11 d of fermentation time, yielding a lactic acid concentration of 13.85 g/L. The optimal clarification conditions were 2 h treatment with chitosan added at 0.3 g/L at 40 ℃, resulting in a transparency of 96.167%. The optimal beverage formula was composed of 0.5 g of lactic acid, 6 g of sucrose, 60 mg of sodium chloride and 0.05 g of honey per 100 mL. The trolox equivalent total antioxidant capacity of the fermentation broth was 42.68 mg/mL, and the DPPH radical scavenging rate was as high as 52.186% at a dose of 100 μL.

Analysis & Detection

Discrimination of Milk by FTIR and Soft Independent Modeling of Class Analogy

2012, 35(2):  34-37.  DOI: 10.15922/j.cnki.jdst.2012.02.009

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Fourier transform infrared spectroscopy (FTIR) combined with soft independent modeling of class analogy (SIMCA) method was employed to the identification of different varieties of milk. The optimized PCA model was built by leave-one-out cross-validation (LOOCV) method after series of pre-treatments such as baseline correction and Savitzky-Golay smoothing in the region of 3100 — 850 cm-1. Under the α ＝5% significance level, the identification rates of this model for pure milk, low lactose milk, low fat milk and high protein milk were 80%, 80%, 100% and 80%, respectively, and the rejection rates were 93%, 100%, 100% and 93%, respectively. This indicates that FTIR combined with SIMCA is a valid method for rapid identification of different varieties of milk.

Optimization of Ninhydrin Reaction Conditions for Determination of Amino Acid Content in Sterilized Milk

2012, 35(2):  38-40.  DOI: 10.15922/j.cnki.jdst.2012.02.010

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One-factor-at-a-time and orthogonal array design methods were used to optimize the major reaction conditions affecting the determination of amino acid content in sterilized milk by ninhydrin colorimetric method. Water-bath heating time influenced significantly determination results so that it required strict control. The optimal determination conditions were 1.2 mL of ninhydrin solution and heating for 30 min in 70 ℃ water-bath. Under these conditions, the amino acid content in sterilized milk was determined to be 1.62 g/100 mL.

Determination of Choline in Formula Milk Powder for Infants and Young Children

2012, 35(2):  41-43.  DOI: 10.15922/j.cnki.jdst.2012.02.011

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This paper describes a Reinecke,s salt colorimetric method for the determination of choline in formula milk powder for infants and young children. The detection limit of the method was 5 mg/100 g. It was easy to operate, sensitive, stable and overcame some disadvantages of traditional methods such as tediousenss and expensive instrumnets. Thus, this method can provide a new approach for determining choline in formula milk powder for infants and young children as well as other similar products.

Reviews

Research on the CAC Standards System Concerning Milk and Milk Products

2012, 35(2):  44-47.  DOI: 10.15922/j.cnki.jdst.2012.02.012

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The main task of Food Codex Alimentarius Commission (CAC) is to formulate worldwide coordinated standards, the structure of which system is clear, including horizontally general principle and vertically specific commodity standards. The milk and milk-related CAC standards, as well as their current situation and characteristics, were analyzed in this study. They are widely covered, highly used, well arranged and established referring to the most scientific risk analysis methods. They are also rigorously and professionally formulated and fast revised and updated according to the latest international situation.