Table of Content

30 October 2013, Volume 36 Issue 5

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Basic Research

Effect of Addition of Plant Proteins on Cheese Properties

WANG Ying, ZHANG Jian-qiang, CAO Yan, JING Xue-lian, ZHANG Li-ping

2013, 36(5):  1-4.  DOI: 10.15922/j.cnki.jdst.2013.05.001

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This study investigated the effect of addition of protein isolates from three different plants (pea, mung and soybean) on cheese properties to find the most suitable plant protein for application in cheese. Milk coagulation properties (coagulation time, curd strength and whey OD value) and textural properties (elasticity, cohesiveness and chewiness) were comparatively tested on the three cheese samples. Moreover, sensory evaluation was carried out fuzzy judgment as well. Results showed that pea protein isolate provided better quality of cheese than the other two protein isolates.

Comparative Analysis of Textural and Rheological Properties among Different Kinds of Cheeses

YU Hua-ning, WANG Jia-yue, GUO Ben-heng, LIU Zhen-min, HOU Jian-ping, HANG Feng

2013, 36(5):  5-10.  DOI: 10.15922/j.cnki.jdst.2013.05.002

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The textural properties of cheese samples with different hardness, including three kinds of hard cheeses and two kinds of soft cheeses, were measured by using a texture analyzer and the rheological parameters of the same samples were evaluated by using a rheometer to compare the rheological and textural properties of all the cheeses. Result showed that there was a significant difference in physicochemical properties (P ＜ 0.05), including pH, moisture content and water activity, between hard and soft cheeses. Hardness was significantly higher in hard cheeses than in soft cheeses. Hardness of all the cheeses obtained by TPA analysis correlated well with viscoelastic moduli. The dynamic analysis showed that all these cheeses manifested a more solid-like form. The rheological parameters were dependent on the oscillatory frequency. The differences of viscoelastic moduli between soft and hard cheeses were probably attributed to different amounts of moisture content and different levels of proteolysis. Hard and soft cheeses were significantly different through texture and rheology analysis. Viscoelastic moduli in the frequency range of 0.1 to 75 Hz could be used as a measure to distinguish among five kinds of cheeses.

Influence of NaCl on Rheological Properties and Structural Change of Sodium Caseinate Solution

ZHAO Zheng-tao, WANG Xiu-ju

2013, 36(5):  11-15.  DOI: 10.15922/j.cnki.jdst.2013.05.003

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Sodium caseinate is commonly used in the food industry. In its many applications as a food ingredient, significant quantities of salts are simultaneously used. Previous studies have shown that co-existing salts can change physiochemical properties of sodium caseinate, especially rheological properties. NaCl has been shown to be able to dramatically increase viscosity of sodium caseinate solution; however, the mechanism is still debatable. In order to further probe the influence of NaCl on rheological properties of sodium caseinate solution and clarify the mechanism. A rheometer, diffusing wave spectroscopy (DWS) and FTIR were combined to investigate the effect of NaCl on properties of sodium caseinate solution. The results showed that the shape and peak positions of FTIR spectra did not change after addition of NaCl, but the intensity changed. Preliminary analysis suggested that NaCl molecules could compete with sodium caseinate for water and indirectly increased protein concentration, while decreasing diffusion properties of the system, as indicated by the increased characteristic decay time τ. It also indicated that NaCl did not influence the secondary structure of sodium caseinate molecules. Rheological characterization indicated that 3% and 7.5% sodium caseinate solutions were Newtonian fluid while 15% sodium caseinate solution was non-newtonian fluid. Addition of NaCl significantly increased protein solution viscosity, and this phenomenon was more obvious at higher protein concentration. To further investigate the rheological properties of 15% sodium caseinate solutions, time dependence and thixotropy measurements were performed. The results showed that viscosity of all these samples increased in a linear manner with increasing time as thixotropic fluid. Collectively, we concluded that high concentrations of sodium caseinate solutions are negative rheopecticity fluid. All these results could help us better understand interactions of NaCl with sodium caseinate and provide theoretical guidance for using sodium caseinate in the food industry.

Processing Technology

Effect of Perilla Oil Microcapsule on the Texture of Quark Cheese

HU Ying, JANG Wei, XU Qian, ZHU Qiu-jin

2013, 36(5):  16-37.  DOI: 10.15922/j.cnki.jdst.2013.05.004

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The effect of addition of perilla oil microcapsule to quark cheese on its texture properties was investigated. Results showed that addition of perilla oil microcapsule affected various texture parameters of quark. Quark hardness increased followed by a decrease with increasing addition of perilla oil microcapsule, and springiness dramatically rebounded, showing statistical significance (P ＜ 0.05) when the addition level was 2%. Perilla oil did not significantly affect the cohesiveness of quark regardless of its being microencapsulated or not, while the resilience was significantly changed (P ＜ 0.05) by addition of perilla oil microcapsule. Native and microencapsulated perilla oil had similar effects on the adhesiveness of quark.

Feasibility of Nutrients Fortified in Milk Porridge Dessert

GUO Xiu-feng, LIU Xiao-jie

2013, 36(5):  21-24.  DOI: 10.15922/j.cnki.jdst.2013.05.005

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The feasibility of fortifying milk porridge dessert with vitamins, taurine and β-carotene was evaluated in the present study. The manufacturing principle and process were described, and the stability of the nutrients fortified in milk porridge dessert was investigated during storage at room temperature, 37 ℃ or 55 ℃. The results showed that all these nutrients had good stability at each temperature, and milk porridge dessert provided a good carrier for them. According to our market survey, milk porridge dessert showed good overall taste acceptability and could be consumed by children and teenagers for dietary balance and energy supplementation.

Analysis & Detection

Application of Real-Time Optoelectronic Microbiological Assays in Quality Control of Dairy Products

FAN Yun-xiu, LI Min, ZHENG Jun, GAO Lei

2013, 36(5):  25-28.  DOI: 10.15922/j.cnki.jdst.2013.05.006

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A real-time (RT) optoelectronic microbiological assay for rapid detection of moulds and yeasts in yogurt was reported and validated by comparing its results with those obtained by applying the Chinese national standard method plate counting. Rapid detection of moulds and yeasts in commercialized yoghurt and spiked positive samples was successfully achieved by a semi-quantitative analytical procedure using the method, which makes it possible to pre-alert their presence or absence. The RT microbiological assay allowed detection of 10–3.5×105 CFU/mL of moulds and yeasts in 1.8–33 h. The time spent in this method for detecting microbial numbers below 10 CFU/mL as determined by conventional plate counting was over 33 h, without pre-alert during 48 h running. In addition, the results obtained closely agreed with those obtained by the plate counting method. The proposed method in this study provided a sensitive, simple and convenient approach for rapid screening of moulds and yeasts in yogurt in factories and laboratories and hence monitoring of critical control points.

Detection of Bacillus cereus in Yogurt by Loop-Mediated Isothermal Amplification Assay

ZHOU Wei， ZHANG Wei，LIU Liang，LIU Dong，WANG Zan，QIN Li1，ZHAO Yong，ZHANG Yan

2013, 36(5):  29-31.  DOI: 10.15922/j.cnki.jdst.2013.05.007

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Objective: A loop-mediated isothermal amplification (LAMP) assay was designed for rapid and accurate detection of Bacillus cereus in yogurt. Methods: Two pairs of oligonucleotide primers exclusively amplifying the hblA gene of Bacillus cereus were designed and Bacillus cereus could be directly detected by LAMP in yogurt, and the amplification products were detected by electrophoresis. Results: Detection of Bacillus cereus in yogurt by the LAMP assay was highly specific, the sensitivity was 6.4 CFU/mL, and the detection limit was 21 CFU/mL. Conclusion: The LAMP was fast, sensitive and useful for the detection of Bacillus cereus in yogurt.

Determination of Conjugated Linoleic Acid in Milk and Milk Powder by Gas Chromatography

LIU Li-jun, LI Cui-zhi, LIANG Yan, YU Hai-jing, HU Xue

2013, 36(5):  32-34.  DOI: 10.15922/j.cnki.jdst.2013.05.008

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A gas chromatographic (GC) method was developed and applied to determine conjugated linoleic acid (CLA) in milk and milk powder. Fat extraction from samples and methylation were made before GC analysis. Excellent separation of c9,t11-CLA was achieved. The developed method proved to be simple, safe, accurate, reliable and reproducible.

Reviews

Progress in Applications of Magnetic Solid Phase Extraction in Detection of Veterinary Drugs Residuals in Milk

LI Long-fei, SU Min, SHI Xiao-lei, WANG Ya-na, WANG Min-min, HE Jin-xing

2013, 36(5):  35-38.  DOI: 10.15922/j.cnki.jdst.2013.05.009

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Milk occupies an important position in the human diet structure, while some studies indicated residues of various veterinary drugs in commercial milk. Meanwhile, detection of veterinary drug residues is difficult due to the complexity of milk matrix. As development of separation techniques based on magnetic materials has become a hot topic for international researchers, magnetic solid-phase extraction (MSPE) as a new mode of solid-phase extraction (SPE) has powerful advantages in the field of separation science due to its superparamagnetic character and adsorption selectivity. This paper describes the new SPE technique and reviews its current applications in the detection of veterinary drug residues in milk.