Table of Content

01 March 2018, Volume 41 Issue 2

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Basic Research

Antimicrobial Resistance Profiles of Staphylococcus aureus from Dairy Cows with Mastitis in Shanghai

ZHANG Hui, DAI Chunfeng, HAN Yiyi

2018, 41(2):  1-4.  DOI: 10.15922/j.cnki.jdst.2018.02.001

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Sixty milk samples were collected from dairy cows with mastitis in Shanghai to study the antimicrobial resistance of Staphylococcus aureus. Staphylococcus aureus isolation, identification and antimicrobial resistance were investigated. Eight Staphylococcus aureus isolates (8/60, 13.33%) were obtained from the collected samples. The antimicrobial resistance test revealed that 100.00% of the isolates were resistant to penicillin G and ampicillin as well as cefalotin, cefmetazole and cefuroxime sodium, 50.00% were resistant to sulfamethoxazole, 37.50% were resistant to cefaclor, ceftizoxime, lomefloxacin, norfloxacin, tetracycline, gentamicin, erythromycin, clindamycin and chloramphenicol, 25.00% were resistant to ciprofloxacin and ofloxacin, and 12.50% were resistant to cefotaxime, ceftazidime and enoxacin. Four Staphylococcus aureus isolates had multi-resistance abilities.

Screening and Growth Characteristics of Lactic Acid Bacteria from Kombucha

GAO Xi, HUANG Yanhua, WANG Qianqian, HAN Mengfei, FENG Meiqin

2018, 41(2):  5-10.  DOI: 10.15922/j.cnki.jdst.2018.02.002

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Kombucha, also known as Haibao, is a traditional acidic tea beverage fermented by a symbiotic culture of lactic acid bacteria, acetic acid bacteria and yeast. Lactic acid bacteria (LAB) were isolated and purified from kombucha and the purified strains were identified. The results showed that a total of 4 LAB strains (XC, XD, XL and XQ) were isolated and they were all identified as Lactobacillus plantarum. These strains entered the stationary growth phase after 14 h. For all four strains, both the pH value and titratable acidity declined during their growth. The optimal inoculum size for XC, XD and XQ was 4%, while that for XL was 6%. The optimal growth temperature for these strains was 30 ℃ and none of them was resistant to salts. All these strains had different tolerance to bile salts and acidity and XQ was the most tolerant among them.

Taste Characteristics of Edam Cheese

WANG Lei, MO Beihong, LIU Zhenmin

2018, 41(2):  11-15.  DOI: 10.15922/j.cnki.jdst.2018.02.003

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The four taste-active compounds in Edam cheese, i.e., lactic acid, sodium chloride, free amino acids and free fatty acids were determined. Changes in the contents of lactic acid, sodium chloride and free amino acids were examined after being treated with human saliva, simulated saliva and deionized water were examined. The contribution of these compounds to cheese taste was identified by taste active value (TAV). The results showed that lactic acid had no contribution to cheese taste after three treatments. Sodium chloride mainly contributed to the salty taste and there was no significant difference of sodium chloride content between human saliva and deionized water treatments. Free fatty acids were primarily responsible for the acid taste with a mellow mouth feeling. The glutamic acid content of cheese was below the threshold value after human saliva treatment and no umami taste was perceived. Sensory evaluation indicated that the salty taste of cheese was strong and retained well.

Isolation and Biological Characterization of Lactic Acid Bacteria from Kombucha

HUANG Yanhua, GAO Xi, REN Yun, CHEN Yixiao, FENG Meiqin

2018, 41(2):  16-21.  DOI: 10.15922/j.cnki.jdst.2018.02.004

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Kombucha is a?symbiotic?culture?of?lactic acid bacteria, acetic acid bacteria and yeast. Four strains (HC, HD, HQ and HL) of lactic acid bacteria (LAB) were isolated and purified from kombucha and their biological characteristics were evaluated by morphological and physicochemical identification, acid production, growth performance, and salt, acid and bile salt tolerance. The results showed that all of the LAB strains were identified as Lactobacillus plantarum. The optimal growth temperature for these four strains was 30 ℃, and the strains entered the stationary phase of growth after 14 h. The optimal inoculum amount for HC, HD, HQ and HL was 4%, 4%, 6% and 6%, respectively. All these strains could tolerate salts and had good tolerance to acid and bile salt, and HQ was the best among them.

Processing Technology

Optimization of Medium Composition and Culture Conditions for Lactobacillus paraplantarum L-ZS9

WANG Shibo, WANG Danting, ZHANG Jinlan, LI Pinglan

2018, 41(2):  22-29.  DOI: 10.15922/j.cnki.jdst.2018.02.005

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Lactobacillus paraplantarum L-ZS9, isolated from fermented meat foods, as a probiotic strain and a fermentation starter has a great application potential in the dairy industry. In order to achieve high-density culture of strain L-ZS9, the modified MRS medium and culture conditions were optimized. The optimal carbon and nitrogen sources were selected by one-factor-at-a-time method. The Plackett-Burman experimental design was used to recognize the most significant medium components and culture conditions. The steepest ascent method was used to determine the levels for these variables. A central composite rotary design (CCRD) was used to fit cell density as a function of the independent variables and response surface methodology was employed to determine optimal culture conditions. The results showed that sucrose and yeast powder were used as carbon and nitrogen sources, respectively. The optimized medium formulation consisted of sucrose 3%, yeast extract 7.26%, sodium acetate 0.5%, dipotassium phosphate 0.2%, magnesium sulfate 0.02%, triammonium citrate 0.2%, and Tween-80 0.1%; the optimized culture conditions were as follows: the initial pH value of the medium was 9.53, the volume of inoculum was 1.74%, and the culture temperature was 37 ℃. It was verified that after 14 hours of cultivation under the optimized conditions, the optical density at wavelength of 600 nm of the broth was 1.214, and the viable count was 4.53 × 109 CFU/mL at this time, which was 6 times higher than that before optimization.

Application of Modified Mung Bean Starch and Maltodextrin as Fat Substitute in Low-Fat Ice Cream Production

DONG Yanfu, CHEN Bingyu, ZHAO Wenting, WANG Dawei

2018, 41(2):  30-36.  DOI: 10.15922/j.cnki.jdst.2018.02.006

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Modified mung bean starch and maltodextrin were used as a fat substitute in low-fat ice cream. The formulation of low-fat ice cream was optimized using response surface methodology (RSM) based on central composite design (CCD). The responses were overrun, melting rate, first dripping time and slurry viscosity. The results showed that incorporation of 1.5% modified mung bean starch and 2.0% maltodextrin gave a better product, whose overrun, melting rate, initial melting time and slurry viscosity of 61.7%, 20.0%, 1 249 s and 1 243 mPa·s, respectively. Texture profile analysis (TPA) showed that the hardness, adhesiveness, gumminess and chewiness of the ice cream were (811.4 ± 4.4) g, (215.7 ± 2.5) g·s, 1.091 ± 0.025 and (168.2 ± 5.6) g, respectively. The use of fat substitute significantly improved texture characteristics of ice cream. The results of size distribution showed that the D (4,3), D (10), D (50) and D (90) of low-fat ice cream increased to (3.36 ± 0.39), (0.14 ± 0.00), (0.51 ± 0.00) and (9.84 ± 1.07) μm as compared with the blank sample. This fat substitute could increase fat instability in ice cream, facilitating the formation of ice crystals. Stereo microscope showed that low-fat ice cream contained a large number of air bubbles uniform in size and evenly distributed.

Analysis & Detection

Determination of Three Glycopeptide Antibiotics in Milk by High Performance Liquid Chromatography-Tandem Mass Spectrometry

FAN Sufang, WANG Liming, LI Qiang, ZHANG Dongsheng, SUN Wenyi, ZHANG Yan

2018, 41(2):  37-41.  DOI: 10.15922/j.cnki.jdst.2018.02.007

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A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of vancomycin, norvancomycin and teicoplanin in milk samples. Selective reaction monitoring was performed and the external standard method was used for quantification. Among various solvents tested, 0.1% formic acid-acetonitrile (85:15, V/V) was selected. Samples were ultrasonically extracted and vancomycin and norvancomycin were cleaned up by cation exchange column chromatography, while teicoplanin was purified using a C18 solid-phase extraction (SPE) cartridge. Acetonitrile-0.1% formic acid solution was chosen as mobile phase for gradient elution. The analytes were separated on a reversed-phase C18 column before being analyzed by mass spectrometry. The limits of detection (LOD) for vancomycin, norvancomycin and teicoplanin were 2, 1 and 2 μg/kg, and the limits of quantitation (LOQ) were 4, 2 and 4 μg/kg, respectively. The recoveries of the method ranged from 77.3% to 84.5% at spiked levels equal to LOQ, 5 × LOQ and 10 × LOQ, with relative standard deviations (RSD) of 4.7%–7.2%. The method could be used in the qualitative and quantitative detection of vancomycin, norvancomycin and teicoplanin in milk samples.

Reviews

Characteristics of Lactoperoxidase and Its Application in Ewe Milk Industry

CHEN Di, WANG Cunfang

2018, 41(2):  42-46.  DOI: 10.15922/j.cnki.jdst.2018.02.008

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Ewe milk is rich in nutrients such as vitamins and protein, which is easy to be digested and absorbed by the human but simultaneously is very conducive to the growth of microorganisms. How to use safe, convenient and low-cost preservation methods to promote the development of ewe milk industry is a realistic problem that must be solved. In this paper, the structure, composition, antibacterial mechanism, thermodynamic characteristics, stability, and other characteristics of lactoperoxidase are discussed in details, and its application in milk preservation and detection and its influence on fermented milk products and cheese are reviewed. The purpose of this review is to provide insights into the development and application of lactoperoxidase in ewe milk industry.