Table of Content

01 March 2020, Volume 43 Issue 2

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Basic Research

Effect of Polymerized Whey Protein on Physicochemical Properties of Low-Fat Cheddar Cheese

CHI Tao, WANG Huan, JIANG Nan, LIU Liyu, WANG Yifan, ZHANG Tiehua, LIU Peng

2020, 43(2):  1-7.  DOI: 10.15922/j.cnki.jdst.2020.02.001

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In this study, a low-fat Cheddar cheese was developed using polymerized whey protein (PWP) as a fat replacer and Lactobacillus helveticus as an auxiliary culture, and the effects of PWP on the physicochemical properties of cheese were studied. Results showed that addition of PWP and Lactobacillus helveticus increased the contents of moisture, protein, free amino acids and volatile compounds and lactic acid bacterial population, and markedly improved sensory characteristics and acceptance of cheese. Addition of PWP reduced the fat ripening period, and increased pH 4.6-soluble nitrogen (SN) fraction by 9.45% and 12 g/100 mL trichloracetic acid (TCA)-SN fraction by 11.74% after ripening. Cheese yield was not affected by adding PWP or the auxiliary culture. All the data indicated that polymerized whey protein can be used as a promising fat replacer for developing low-fat Cheddar cheese with good texture and sensory properties.

Processing Technology

Screening of Lactobacillus for Probiotic Potential

XU Xianrui, LI Cuifeng, YANG Honglai, SUI Yongjun, LI Daohe, ZHANG Zongbo, CHEN Zhengyan, ZHANG Lanwei

2020, 43(2):  8-12.  DOI: 10.15922/j.cnki.jdst.2020.02.002

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A total of 30 food-grade Lactobacillus strains isolated from naturally fermented products from Tibetan, Xinjiang and Qinghai regions including Lactobacillus rhamnosus LGG (as a control) were evaluated for acid and bile salt tolerance, hydrophobicity, surface charge and auto-aggregation ability. Out of these, 16 strains were selected and further evaluated for tolerance to artificial gastric and intestinal fluids. The results showed that the survival rates of 4 of the 16 strains were greater than 14.44% after 60 min of incubation in artificial gastric fluid and were 3.91%–100.00% after 30 min. For all 16 selected strains, the survival rate was 31.73%–112.83% after 5 h, and Z-1 had the strongest tolerance to artificial gastric fluid of these strains with a 93.07% survival rate after 60 min. The survival rate of Z-1 was 106.5% after 5 h of incubation in artificial intestinal fluid, hydrophobicity 97.52%, surface charge 97.35% and 24.67% in the presence of chloroform and ethyl acetate, respectively, and auto-aggregation ability 11.26%.

Optimized Manufacture and Functional Characteristics of Tibetan Kefir Fermented Milk

ZHANG Feifei, MU Guangqing, XU Yunpeng, JIANG Shan, LI Xinling, ZHAO Fujunzhu, QIAN Fang

2020, 43(2):  13-18.  DOI: 10.15922/j.cnki.jdst.2020.02.003

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In order to evaluate the functional characteristics of Tibetan kefir, the conditions for the fermentation of skim milk with Tibetan kefir were preliminarily optimized by one-factor-at-a-time method based on titratable acidity and sensory evaluation, and the antioxidant capacity and cholesterol-lowering ability of the fermented milk were studied in vitro. It was found that the optimal fermentation conditions were as follows: inoculum size 6%, fermentation time 7.5 h, and temperature 37 ℃. The fermented milk produced under the optimized conditions had a medium acidity, delicate taste, uniform texture and unique flavor, and its lactic acid bacterial population was 1.48 × 108 CFU/mL. The hardness of the fermented milk was 178.43 g, higher than that of traditional fermented milk, the adhesion was -103.52 g·s and the non-fat solid content, protein content and titratable acidity all conformed to the national standard for fermented milk. The quality of the fermented milk was good overall. Compared with traditional fermented milk, its antioxidant activity was not particularly prominent, but the cholesterol-lowering ability was particularly considerable, with removal rate of as high as 37.98% (fermented skim milk) and 40.68% (fermented whole milk).

Analysis & Detection

Comparison of Micellar Electrokinetic Capillary Chromatography with Diode Array Detector (MECC-DAD) and High Performance Liquid Chromatography with Fluorescence Detector (HPLC-FLD) for Detecting Five Aflatoxins in Raw Milk

XU Mingfang, GENG Mengmeng, WANG Yang, LI Ming, CHEN Gengnan

2020, 43(2):  19-25.  DOI: 10.15922/j.cnki.jdst.2020.02.004

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A new method for detecting five aflatoxin residues in raw milk was presented using micellar electrokinetic capillary chromatography with a diode array detector (MECC-DAD). The specificity of MECC-DAD was evaluated in comparison with that of high-performance liquid chromatography with a fluorescence detector (HPLC-FLD). In the MECC-DAD method, samples were cleaned up by immunoaffinity column chromatography before separation on an uncoated fused-silica capillary column using 7.5 mmol/L borate buffer with 30 mmol/L sodium dodecyl sulfonate (pH 8.5) and 5% acetonitrile and the detection wavelength was set at 214 nm. In the HPLC-FLD method, samples were separated on a C18 column (150 mm × 4.6 mm, 5 μm) by gradient elution using a mobile phase consisting of acetonitrile and water after being cleaned up by immunoaffinity column chromatography. The analytes were detected by a fluorescence detector at 360 nm excitation wavelength and 440 nm emission wavelength. Results showed that MECC-DAD gave smoother and sharper peaks that were more symmetrical without tailing. The limits of detection of MECC-DAD and HPLC-FLD were 0.182–1.669 and 0.014–0.058 μg/L, both meeting the requirements for the determination of aflatoxin residues in raw milk. The precision of HPLC-FLD was somewhat higher than that of MECC-DAD. The recoveries of MECC-DAD and HPLC-FLD were 80.3%–137.0% and 79.6%–134.0%, respectively. When the two methods were applied to the same commercial milk samples, the P value for the deviation between the quantitative results obtained was 0.900, greater than 0.05, indicating no significant difference. In conclusion, MECC-DAD was simple, efficient and inexpensive, making it more suitable for the simultaneous determination of five aflatoxins in milk than HPLC-FLD.

Determination of 4 Steroid Hormones in Milk and Milk Power by Filtration Solid Phase Extraction Coupled to High Performance Liquid Chromatography-Tandem Mass Spectrometry

LIU Dong, LI Qiang, FAN Sufang, ZHANG Yan

2020, 43(2):  26-30.  DOI: 10.15922/j.cnki.jdst.2020.02.005

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An analytical method for the determination of 4 steroid hormones in milk and milk power was developed by filtration solid phase extraction combined with ultra performance liquid chromatography-tandem mass spectrometry. Samples were extracted with acetonitrile, and purified on a PRiME HLB cartridge. Then the chromatographic separation was achieved using an Acquity BEH C18 column (2.1 mm × 100 mm, 2.5 μm) with a mobile phase consisting of water and acetonitrile. The compounds were ionized using an electrospray ionization source in the negative ion mode and quantitated by the internal standard method. The results showed that the calibration curves of all analytes had a good linear relationship in the concentration range of 0.2–100.0 ng/mL. The limits of detection and limits of quantitation were 0.4–2.0 and 0.8–4.0 μg/kg, respectively. The recoveries of the method were in range of 87.7%–110.8% with relative standard deviations (RSDs) of 0.85%–4.56% in milk and in range of 89.2%–107.4% with RSDs of 0.85%–4.56% in milk power. This method was proved to be rapid, sensitive, and useful for the quantification of 4 steroid hormones in milk and milk power samples.

Comparative Analysis of Sugars in Infant Formula Milk Powder by Ion Chromatography and High Performance Liquid Chromatography Specified in Chinese National Standard

CAO Wenjun, LI Li, XUE Weifeng, LIU Ming

2020, 43(2):  31-37.  DOI: 10.15922/j.cnki.jdst.2020.02.006

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A high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was established to analyze glucose, sucrose, lactose, galactooligotrisaccharide, 1-kestose, galactooligopentosaccharide, nystose and 1F-fructofuranosyl nystose in four commercial brands of infant formula. The spiked recoveries of HPAEC-PAD ranged from 78.0% to 96.8% with relative standard deviation (RSD) of 4% (n = 5). Its limits of detection were between 3.0 and 12.0 mg/100 g. When HPAEC-PAD and the high-performance liquid chromatography (HPLC) specified in the Chinese national standard were applied to detect sucrose, lactose and 1-kestose in real samples, consistent results were obtained. However, the five other sugars were detected by HPAEC-PAD but not by HPLC. Accordingly, compared with HPLC, HPAEC-PAD was more sensitive and useful for the simultaneous determination of multiple sugars in infant formula.

Reviews

Functional Characteristics and Application in Infant Formula of β-Casein: A Review

CHEN Wenliang, SU Miya, JIA Hongxin, QI Xiaoyan

2020, 43(2):  38-43.  DOI: 10.15922/j.cnki.jdst.2020.02.007

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β-casein is the major casein component in human milk. Adjusting the content of β-casein in infant formula can make the protein and amino acid composition closer to that of human milk. In this paper the amino acid composition and spatial structure of β-casein are described, and the differences in some characteristics between human and cow milk β-casein are compared. Moreover, the functional characteristics of β-casein and its application in infant formula are also discussed. This review is expected to provide useful information for the development of new infant formula products.

Recent Advances in the Mechanism of Action and Application of Enzymes in Dairy Production

HUANG Mengyao, FAN Xiaoxue, WANG Cunfang

2020, 43(2):  44-48.  DOI: 10.15922/j.cnki.jdst.2020.02.008

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Enzymes are characterized by many advantages, including being needed only in micro-amounts, highly efficient, environmentally friendly and nontoxic, energy saving, highly specific, and able to react under mild conditions. Based on the reactions between enzymes and their specific substrates in milk, desirable results can be obtained safely and efficiently to improve the quality of dairy products. Thus, enzymes are widely used in dairy products. This article reviews the mechanisms of action of lactase, transglutaminase, rennet and lactoperoxidase and their applications in dairy processing and preservation, together with the application of enzyme-linked immunoassay to detect in the detection of dairy products. The aim of this review is to provide a theoretical basis for the application of enzymes in the processing, preservation and detection of dairy products.

Progress in Research on Lactic Acid Bacterial Metabolism

JIAO Jingkai

2020, 43(2):  49-55.  DOI: 10.15922/j.cnki.jdst.2020.02.009

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Research on lactic acid bacterial metabolism has already stepped into a new era. This review summarizes the current research on sugar, citric acid and protein metabolism in lactic acid bacteria, as well as the application of genomics, comparative genomics and metagenomics based on next-generation sequencing technology in studies of lactic acid bacterial metabolism. It is expected that this review will provide theoretical support for further research of lactic acid bacterial metabolism.

Recent Progress in Lactobacillus-Fermented Fruits and Vegetables

WANG Sixuan, FU Xue, ZHU Xuemei, TUO Yanfeng, MU Guangqing, QIAN Fang

2020, 43(2):  56-59.  DOI: 10.15922/j.cnki.jdst.2020.02.010

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Fruits and vegetables have a high nutritional value, and they, apart from still being nutritious, has a good flavor after being fermented with Lactobacillus. The present article summarizes the Lactobacillus strains used for fermenting fruits and vegetables, the probiotic effect of fruits and vegetables fermented with Lactobacillus, the quality improvements of fruits and vegetables after Lactobacillus fermentation, and reviews the current global status of Lactobacillus-fermented fruits and vegetables. In addition, the main problems existing in this field and future research directions are discussed.