Table of Content

30 December 2013, Volume 36 Issue 6

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Biotechnology

Streptomyces albulus UN2-71, an ε-Polylysine-Producing Strain: Physiological Characteristics and Optimization of Fermentation Conditions

WANG Gang, HANG Feng, XING Jia-li, TIAN Feng-wei, LIU Xiao-ming, ZHANG Qiu-xiang, ZHANG Hao, CHEN Wei

2013, 36(6):  1-5.  DOI: 10.15922/j.cnki.jdst.2013.06.001

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ε-Polylysine is widely used as a natural biological preservative in meat, dairy products and other foods for its characteristics of high safety, stability, efficiency, solublity in water and broad-spectrum antibacterial activity. In this paper, physiological and biochemical characteristics of Streptomyces albulus UN2-71, a strain capable of producing ε-polylysine, were studied. The ε-polylysine production increased from 1.64 to 2.37 g/L after optimization of fermentation conditions. The optimized conditions were defined as: 30 mL of the liquid medium in a 250 mL shake flask, inoculum size 10%, temperature 30 ℃, shaking speed 150 r/min and initial fermentation pH 7.0.

Processing Technology

Optimization of Process Parameters for Industrial Production of Mozzarella Cheese by Response Surface Methodology

GAO Yun-long, WANG Ying, ZHANG Jian-qiang, ZHANG Li-ping

2013, 36(6):  6-10.  DOI: 10.15922/j.cnki.jdst.2013.06.002

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This study used a quadratic rotation-orthogonal composite experimental design with four independent variables at five levels each to establish optimal process conditions for industrial production of Mozzarella cheese. The process conditions investigated in this study included fermentation time, clotting time, whey pH and the amount of added NaCl. A regression model to optimize these process conditions was proposed and validated for its statistical significance. The optimal process conditions that provided the maximum yield of Mozzarella cheese (24.78%) were determined as follows: fermentation time 27.5 min, clotting time 37.5 min, whey pH 6.3, and addition of 2.07% NaCl. The resulting cheese had a nice flavor, a close, smooth and flexible texture and a homogeneous color and its fiber-drawing capacity, meltability and foaming properties were good. All these parameters were comparable to those of laboratory-made cheese and met the quality requirements for use in pizza. The optimized process parameters are suitable for large-batch production of Mozzarella cheese in industrial practice.

Quality Evaluation of Whey Cheese Incorporated with Fish Protein Powder

WANG Yan, ZHAO Shuang, LIU Xiu-he, FU Mao-run

2013, 36(6):  11-34.  DOI: 10.15922/j.cnki.jdst.2013.06.003

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A whey cheese made from whey protein concentrates incorporated with fish protein powder (FPP) was evaluated. The effects of FPP concentrations including 0.4%, 0.8%, and 1.2% on the whey cheese properties were investigated by analyzing cheese yield, texture characteristics, and digestibility. The results of this study showed that the incorporation of FPP into whey cheese enhanced the yield, texture property and digestibility of whey cheese. Thus, addition of 1.2% FPP into whey cheese is useful to improve its quality.

Quality Safety

Impact of Nutritional Facts and Food Safety on Consumer Behavior toward Milk Products in Beijing

YU Ping, FAN Zhi-hong, LI Meng, LONG Fei-ping

2013, 36(6):  14-17.  DOI: 10.15922/j.cnki.jdst.2013.06.004

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Objective: To study the impact of factors including nutritional facts and food safety on consumer behavior toward milk products in Beijing. Method: Seven hundreds and thirteen consumer Beijing community residents were recruited in the questionnaire survey. Result: The consumers’ perception of health benefits of nutrients in milk was a promoting factor of milk consumption. The health-related barriers to milk purchase suppressed the purchase intention of whole-fat milk, while facilitated the choice of nutritionally modified milk products or organic products. Conclusion: The acceptability of the milk products with health claims were positively affected by consumer’s perception of nutrition and safety concerns.

Analysis & Detection

Simultaneous Analysis of Six Estrogens in Milk Powder by GC-MS-MS

LI Qiang, ZHAO Wei, CAI Li-peng, LI Hui, ZHANG Yan

2013, 36(6):  18-20.  DOI: 10.15922/j.cnki.jdst.2013.06.005

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An efficient method was developed for the simultaneous analysis of six estrogens including diethylstilbestrol, α-estradiol, β-estradiol, estriol, estrone and bisphenol A in milk powder using gas chromatography-tandem mass spectrometry (GC-MS-MS). Samples were enzymatically hydrolyzed and extracted with acetonitrile. The extract was then derivatized with pentafluoropropionic anhydride before being injected into the GC-MS-MS system. Qualitative and Quantitative analysis was carried out under the multiple reaction monitoring (MRM) mode. The results indicated that all six estrogens displayed a good linear relationship with R2 ＞ 0.999. The limits of quantification for bisphenol A and the other five estrogens were 0.03 and 0.3 μg/kg, respectively. The average recovery of six estrogens was 93.93%, with RSD of 6.05%, meeting the methodological requirements. The method developed in this study can be successfully applied in the determination of six estrogens in milk powder.

Determination of 20 Phthatic Acid Esters in Milk and Dairy Products by GC-MS

XU Wei-ping, HU Xue, LI Cui-zhi, SHAO Jian-bo, GAO Yu-jie

2013, 36(6):  21-23.  DOI: 10.15922/j.cnki.jdst.2013.06.006

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A method was developed for the determination of 20 phthatic acid esters in milk and dairy products by gas chromatography-mass spectrometry (GC-MS). Samples were extracted with n-hexane and separated on a DB-5MS capillary column (30 m × 0.25 mm, 0.25 μm). The injector temperature was 280 ℃,the interface temperature was 280 ℃, and the ion source temperature was 230 ℃. Under optimized conditions, the linear range was 0-10 μg/mL with a correlation coefficient greater than 0.9990. The average spike recovery rates were in the range of 80%-109%. The detection limits were respectively 1.0 and 0.5 mg/kg for DINP and DIDP and 0.05 mg/kg for 18 others. This method proved to be simple, rapid, sensitive, specific and accurate.

Detection of Clostridium botulinum in Food by Real-Time Fluorescent Quantitative PCR

SUN Li-hua, WANG Yun-xia, DU Xiao-hua, LI Cui-zhi, LIU Li-jun, SHAO Jian-bo

2013, 36(6):  24-26.  DOI: 10.15922/j.cnki.jdst.2013.06.007

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This paper is about the detection the four serotypes A, B, E and F of Clostridium botulinum from milk powder and whey powder by using real-time fluorescent quantitative PCR method (RT-PCR). The standard curves for blends of serotypes A and B as well as of E and F were established using the original positive control from a commercial RT-PCR kit and its 10, 102, 103 and 104-fold dilutions. The cycle threshold (Ct) values exhibited excellent specificity, repeatability and accuracy. By using the method, none of these four serotypes was detected in 82 samples milk power and whey power with suspected strains as confirmed by the Chinese national standard and the industry standard of entry-exit inspection and quarantine.

Packaging & Storage

Changes in Nutrient Contents in Milk-Based Food Products for Infants and Young Children during Shelf-Life Storage

HU Jun-rong, FENG Yu-hong, XUE Yu-qing, LIU Xiao-jie

2013, 36(6):  27-29.  DOI: 10.15922/j.cnki.jdst.2013.06.008

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The stability of macronutrients such as protein, fat, calcium, iron and zinc as well as micronutrients such as vitamin B1, vitamin A, nicotinic acid in formulas for infants and young children from different production processes was tested during shelflife storage. Results showed that the contents of unsaturated fatty acids, vitamin B1 and iodine were reduced, while the moisture content was increased with no obvious change in protein, fat, calcium, iron or zinc. In general, a combination of wet and dry methods is more beneficial for the preservation of nutrients in milk powder products during shelf-life storage.

Reviews

Relationship between Key Genes for Milk Secretion and Milk Quality

YU Cui-ping, GAO Xue-jun, LUO Chao-chao, ZHANG Na, LI Qing-zhang

2013, 36(6):  30-33.  DOI: 10.15922/j.cnki.jdst.2013.06.009

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Recent years have seen rapid progress in dairy cattle genomics with many achievements having been made up to now. For the synthesis of protein and fat, the key positive regulatory genes STAT5, mTOR and SREBP and the key negative genes SOCS3 and GSK3Beta have been established; however, their mechanisms of action need further research. Additional regulatory genes for milk secretion are needed to elucidate the mechanism responsible for controlling milk quality.

China's Supervisory System and Legal Framework for Dairy Product Safety

WANG Wen-zhi, JIANG Ping-ping, WANG Bo, FENG Feng, CHU Xiao-gang

2013, 36(6):  34-38.  DOI: 10.15922/j.cnki.jdst.2013.06.010

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China’s dairy industry has seen rapid development over the last three decades, but at the same time some problems have emerged. Since the melamine incident in 2008, the country has accelerated its efforts to formulate and revise food safety laws and regulations. It should be especially mentioned that dairy management practices are being gradually improved. This article elucidates the current situation of quality supervision of exported and imported dairy products in China with respect to its supervisory system and legal framework. However, there are still many problems under the current supervision mechanism regarding the supervision of milk sources. The governmental departments and social organizations should play a greater role in this regard, providing relevant suggestions for facilitating the healthy development of the dairy industry. In this article, we also point out that the supervisory work still faces a great challenge in the current complex and volatile situation of food safety. In addition, gradually establishing a multiple supervisory system that is dominated by the government and complemented by the participation of social forces may be an important idea for reform of our food safety system.