Table of Content

30 August 2013, Volume 36 Issue 4

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Processing Technology

Screening of Lactobacillus delbrueckii subsp.bulgaricus Strains for Use as Yoghurt Starter Cultures

GAO Shu-ran, SHAO Yu-yu, GUO Hui-ling, MENG HE Bi-li-ge, ZHANG He-ping

2013, 36(4):  1-6.  DOI: 10.15922/j.cnki.jdst.2013.04.001

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A total of 55 strains of Lactobacillus delbrueckii subsp. bulgaricus isolated from traditional fermented milk were separately used for yoghurt production to test their fermentation properties such as fermentation time, post-fermentation acidification, viscosity, syneresis and free amino nitrogen (FAN) concentration. Three strains with desired characteristics, IMAU80319, IMAU20422 and IMAU20404, were selected out of them.

Formulation and Emulsion Stability of a Composite Rice Bran Protein-Dairy Beverage

ZHANG Wei, SONG Chun-chun, XU Yu-juan, YU Lei

2013, 36(4):  7-10.  DOI: 10.15922/j.cnki.jdst.2013.04.002

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A composite beverage was developed from milk with the addition of rice bran protein. Its formulation was optimized by one-factor-at-a-time and orthogonal array design to obtain the best sensory quality and emulsion stability. Meanwhile the storage stability of the composite beverage was investigated. The optimal formulation was found to consist of 2% whole milk powder, 0.7% rice bran protein, 10% white sugar, 0.3% citric acid and 0.2% composite stabilizer. The resulting product had a delicate taste and high nutritive value, and its emulsion stability and protein content were 97.52% and 1.0%, respectively.

Formulation of a Wheat Germ-Based Dairy Beverage

LI Liang-yu, CAO Rong-an, YU Wei, JIA Peng-yu

2013, 36(4):  11-13.  DOI: 10.15922/j.cnki.jdst.2013.04.003

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Wheat germ is recognized as the treasure house and essence of nutrition, accounting for only 1.4%–3.9% of the dry weight of the grain. It is extremely rich in quality protein, fat and a variety of vitamins and minerals. In this study, CMC, citric acid, sugar and whole milk powder were used for formulating a wheat germ-based dairy beverage. By using one-factorat- a-time and orthogonal array design, the optimal formulation of the nutritional beverage was determined to consist of 0.08% CMC, 0.05% citric acid, 4% sugar and 4% whole milk powder.

Packaging & Storage

Shelf Life Prediction and Storage Stability of Bovine Colostrum Whey Powder

YU Hua-ning, GUO Ben-heng, LIU Zhen-min, HANG Feng

2013, 36(4):  14-33.  DOI: 10.15922/j.cnki.jdst.2013.04.004

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The present study aimed at understanding the storage stability of bovine colostrum whey powder. Moreover, a predictive equation to estimate its shelf life under the conditions of ambient temperature (25 ℃), 50% relative humidity (RH) and packaging in PET bags was presented. The evolution of some key physicochemical and biochemical parameters was studied over a storage period of 90 days. The results obtained in this study indicated that the contents of water and HMF and TBA value in bovine colostrum whey powder packaged in PET bags significantly increased over time during the storage period (P ＜ 0.05) and color difference also showed an increasing trend, even though with some fluctuations, while IgG level conversely exhibited a decreasing trend in the first 60 days, followed by no significant decrease. Under the storage conditions used in this study, the shelf life of bovine colostrum whey powder was 99.40 days. The findings of this study can provide basic data for industrial production of bovine colostrum whey powder.

Analysis & Detection

Establishment of PCR Method Based on the α-Lactalbumin-Encoding Gene for Detecting Milk Allergens

GUAN Xiao, CAI Qin, CHEN Qin

2013, 36(4):  19-22.  DOI: 10.15922/j.cnki.jdst.2013.04.005

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DNA was extracted from milk by collecting exfoliative cytology samples from dairy cows. A set of specific primers (α-La-F/R) was designed based on the α-Lactalbumin-encoding gene. A PCR method to detect milk allergens were established by screening the optimum experimental conditions. The results showed that the optimum PCR conditions were 56.5 ℃, 0.15 μmol/L and 35 for annealing temperature, primer concentration and number of cycles, respectively. The PCR method was highly specific and its sensitivity was 0.04 ng DNA. The PCR results of 10 types of commercial dairy products were identical to those described in the product label, suggesting this method to be accurate, reliable and thus applicable in practice.

Analysis of Fatty Acids in White Yak's Milk from Pastoral Areas in Gansu's Tianzhu

TUO Yan-feng, GAN Bo-zhong, HANG Feng, SONG Xin

2013, 36(4):  23-27.  DOI: 10.15922/j.cnki.jdst.2013.04.006

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In this study, white yak’s milk samples from three pastoral areas in Tianzhu county, Gansu province, collected at four different growth stages (withering, the final stage of withering, reviving and green) of forage grasses as well as from female yaks of different parity were analyzed by GC–MS for fatty acid composition. The results showed no significant difference in fatty acid content of yak’s milk among three pastoral areas or among 5 parities (P ＞ 0.05). The SFA:USFA ratio of yak’s milk at the withering stage, the final part of withering, the reviving stage and the green stage was 1.86, 1.75, 1.62 and 1.32, respectively. Lower amounts of SFAs but higher amounts of USFAs were found in white yak’s milk as the temperature increased and forage became more mature.

A Validated Method for the Determination of Dicyandiamide in Milk and Dairy Products

GU Ye, WANG Qin, ZHAN Sheng, FENG Yong-wei

2013, 36(4):  28-31.  DOI: 10.15922/j.cnki.jdst.2013.04.007

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An HPLC method to determine dicyandiamide in milk and dairy products was proposed and validated in the present study. A comparative investigation of gradient and isocratic elution was carried out for the chromatographic separation of dicyandiamide. The results of this study indicated a good linear relationship for dicyandiamide over the concentration range of 0.1002 to 10.0200 μg/mL under gradient elution conditions (r = 0.9996). The average recovery of dicyandiamide was 92.8%, and the limit of detection was 0.01 μg/mL. This method proved to be applicable for the determination of dicyandiamide in milk and dairy products.

Reviews

Recent Advances in Analytical Techniques for the Determination of Melamine in Dairy Products

YU Chao, MA Jun-qiu, BAI Su-qin

2013, 36(4):  32-35.  DOI: 10.15922/j.cnki.jdst.2013.04.008

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This review describes recent progress in the development of sample pretreatment methods and instrumental detection systems for the determination of melamine in dairy products. Currently there are three popular methods used to extract and purify melamine from sample matrices, solid phase extraction (SPE), dispersed solid phase extraction (DSPE) and liquid-liquid extraction (LLE). Data from various studies indicate that DSPE and LLE are easier and faster to use with recoveries above 90% than SPE. Several popular techniques are currently used to determine melamine, including HPLC, LC–MS, GC–MS and ELISA. Among them, HPLC is easier to use, more sensitive and time saving, while LC–MS is more effective for qualitative analysis and has lower detection limit and GC–MS is highly uncertain under varying conditions despite higher sensitivity. Moreover, ELISA is generally used for large-scale determination and primary screening of melamine in milk and dairy products.

Origins and Risk Assessment of Thiocyanate in Dairy Products

LIU Yuan, ZOU Jie

2013, 36(4):  36-38.  DOI: 10.15922/j.cnki.jdst.2013.04.009

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The lactoperoxidase–thiocyanate–hydrogen peroxide system is widely used as a feasible method for temporary preservation of raw milk in China. Nevertheless, due to its toxic and harmful nature, thiocyanate has been listed as an illegal food additive in raw milk and dairy products. In this study, various amounts of thiocyanate less than 10 mg/kg were found in 852 samples of dairy products marketed in China, of which 25.9% were less than 1 mg/kg and only 6.24% were 5–10 mg/kg. Furthermore, our analysis showed that the possible origin of thiocyanate might be raw milk but not illegal addition. Finally a risk assessment was performed on its potential health hazards.

A Review of Recent Applications of Microecologics in Dairy Products

WANG Fang, QU Xiao-yuan, REN Chun-guang

2013, 36(4):  39-42.  DOI: 10.15922/j.cnki.jdst.2013.04.010

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Miroecologics have a variety of functions such as regulating human intestinal microecology, immune enhancement, antitumor, anti-aging, etc and are important elements of functional dairy products. Application of probiotics in dairy products has very important significance in enriching the functions of dairy products, guiding the healthy diet and promoting the development of the dairy industry. Research and development of dairy products rich in probiotics, prebiotics and/or synbiotics will become the dominant direction of the development of dairy products. This paper introduces recent applications of microecologics in dairy products with emphasis on key technologies.