Table of Content

01 November 2023, Volume 46 Issue 6

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Basic Research

Effect of Exogenous Addition of Lactobacillus paracasei LZ9077 on Properties of Set-type Yogurt

TANG Jiaqi, TANG Xia, ZHANG Feng, LUO Jie, LIU Chengguo, ZHOU Hui

2023, 46(6):  1-6.  DOI: 10.7506/rykxyjs1671-5187-20231224-063

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In this study, Lactobacillus paracasei LZ9077 was used as a test strain to investigate the application of this bacterium and commercial fermenter agents in fermented milk. The acid production ability, the number of live bacteria, sensory evaluation and other evaluation indexes were used for process optimization. The optimal fermentation conditions were obtained by single factor test and orthogonal test, and the changes of yogurt during fermentation were determined. The results showed that the optimal fermentation conditions were as follows: the inoculum amounts of L. paracasei LZ9077 and commercial fermenter were 4% (V/V) and 0.1% (m/V), respectively, and the fermentation time was 6 h. The addition of L. paracasei LZ9077 increased the number of viable bacteria and the acid-producing efficiency of the fermented milk, and the number of viable bacteria was up to 9.22 (lg (CFU/mL)) at the end of the fermentation, and the titration acidity was (99.94 ± 0.36) °T, and the viscosity and stability of yoghurt were significantly improved.

Key Factors for Nutritional Quality Evaluation of Raw Milk in Shanghai

DENG Bo, YANG Xiaojun, MA Yingqing, CHEN Rouhan, ZHANG Weiyi

2023, 46(6):  7-12.  DOI: 10.7506/rykxyjs1671-5187-20231205-060

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In order to explore the key factors for the nutritional quality evaluation of raw milk in Shanghai, a total of 167 batches of raw milk were collected from 11 large-scale dairy farms in Shanghai from July 2022 to March 2023, and their amino acid composition, fatty acid composition, vitamins, lactoferrin and trace elements were detected. The amino acid composition data were analyzed by means of principal component analysis (PCA) and the proportions of various fatty acids were compared. The results showed that 16 amino acids, 26 fatty acids, active factors including lactoferrin, α-lactalbumin and β-lactoglobulin, and 9 essential trace elements were detected in raw milk. On this basis, we selected 13 key factors for the nutritional quality evaluation of raw milk, which could provide an important reference for the further screening and utilization of raw milk sources in Shanghai.

Processing Technology

Influence of Dry Process on the Quality of Infant Formula Milk Powder

LI Linyao, CHU Xiaojun, HUA Jiacai, GAO Chao

2023, 46(6):  13-19.  DOI: 10.7506/rykxyjs1671-5187-20231229-066

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The production and storage process are closely related to the quality of infant formula milk powder. This study examined nutrient mixing homogeneity, the decay rate of nutrients and the changes in safety indicators during accelerated storage of infant formula milk powder. The results showed that among the 15 nutrients selected, the mixing uniformity of lactoferrin was above 90%, while the mixing uniformity of the other nutrients was above 95%. Under the accelerated storage conditions, macronutrients and fatty acids were relatively stable, and vitamins and minerals did not show significant attenuation. The decay rate of taurine as an optional ingredient was relatively high, being 8.06%, 8.40%, and 8.08% at the end of the accelerated storage for milk formulae for younger and older infants and young children, respectively. After accelerated storage for 186 days, the safety indicators (Tin, nitrate, nitrite, aflatoxin M1, and melamine) remained basically unchanged.

Analysis & Detection

Establishment of a Fluorescence-Based Quantitative Real-Time PCR Method for Detection for Caprine-Derived Ingredients in Milk Powder

CHEN Chen, ZHANG Rui, WANG Yuxin, ZHANG Tonghe, ZHANG Zilun, JIA Wenshen, ZHOU Wei

2023, 46(6):  20-24.  DOI: 10.7506/rykxyjs1671-5187-20231224-062

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This study established a fluorescence-based quantitative real-time polymerase chain reaction method for the detection of caprine-derived ingredients in milk powder. The specificity, sensitivity, and stability of the caprine-specific primers were evaluated. By linear fitting of the difference in cycle threshold (ΔCt) as a function of the mixing proportion between goat and horse milk powder, a calibration curve for the relative quantitation of caprine-derived ingredients in milk powder was established as follows: y = 0.720 9x + 5.651 9 (R2 = 0.987 5), and the minimum detection limit of this method was 0.000 1 ng/μL. The recoveries of the proposed method were 96.22%-112.00%, and the inter- and intra-group coefficient of variation was ≤ 0.79% and ≤ 1.77%, respectively.

Determination of Three Aldehydes in Infant Formula Milk Powder by High Performance Liquid Chromatography

DENG Xiaoqing, ZHENG Lijun, TANG Wanli, WEN Xin, TANG Wenjie, CHEN Tongqiang

2023, 46(6):  25-28.  DOI: 10.7506/rykxyjs1671-5187-20231205-059

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A high performance liquid chromatography (HPLC) method was established to determine the contents of three aldehydes (malondialdehyde, acrolein, and 4-hydroxyhexenal) in infant formula milk powder, and the effect of storage temperature on the content of three aldehydes in infant formula milk powder was studied. The analytical figures of merit including linearity, accuracy, recovery, detection limit and quantitation limit were determined. The external standard method was used to quantify the analytes. The results indicated that this method exhibited good linearity in the range between 0 and 40 μg with a correlation coefficient (R2) greater than 0.999, and the detection limits for malondialdehyde, acrolein, and 4-hydroxyhexenal were 0.3, 0.4, and 0.3 mg/kg, respectively. The quantitation limits were 0.8, 1.0 and 0.8 mg/kg, respectively. The average recoveries for spiked samples were in the range of 88.29%–96.87%, with relative standard deviation (RSD) less than 10%. With increasing storage temperature above 40 ℃, the contents of the three aldehydes showed an upward trend, and a significant increase was observed in the contents of malondialdehyde and acrolein. This method has the characteristics of rapidity, high accuracy, and good reproducibility, which is suitable for the determination of the three aldehydes in infant formula milk powder.

Simultaneous Determination of Niacin, Nicotinamide, and Vitamin B6 in Formula Milk Powder by Ultra Performance Liquid Chromatography

CUI Suxia, MENG Genhua, LIN Tingjuan, LI Xiaoyan

2023, 46(6):  29-33.  DOI: 10.7506/rykxyjs1671-5187-20240116-003

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To establish an ultra performance liquid chromatography (UPLC) analysis method that can simultaneously determine niacin, niacinamide, and vitamin B6 in formula milk powder. Gradient elution was performed with 10 mmol/L ammonium acetate solution (containing 0.1% formic acid) as mobile phase A and methanol as mobile phase B. The analytes were separated by Poroshell 120 EC-C18 in tandem with ACQUITY? UPLC HSS T3 column, detected with the UV detector and fluorescence detector, and quantified by an external standard method. Good linearity was observed for niacin concentrations in the range of 0.0-0.8 μg/mL，nicotinamide concentrations in the range of 0.0-20.0 μg/mL, pyridoxamine concentrations in the range of 0.0-0.2 μg/mL, pyridoxal concentrations in the range of 0.0-0.6 μg/mL and pyridoxine concentrations in the range of 0.0-4.0 μg/mL, and the correlation coefficients of standard curves were all greater than 0.999. The limits of detection and quantification met the requirements. The average recoveries of the method were all in the range of 80.5%-104.1% with relative standard deviation (RSD) were 0.37%-2.99%. This method is simple, accurate, can be used for batch detection of niacin, niacinamide, and vitamin B6 in formula milk powder.

Quantitative Determination of Fumonisin Residues in Milk and Milk Powder by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry

MO Nan, ZHANG Lijia, GAO Yujie, BAI Yanmei, WANG Yang, LIU Lijun, LI Cuizhi

2023, 46(6):  34-39.  DOI: 10.7506/rykxyjs1671-5187-20231201-058

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An ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous quantitative determination of fumonisin B1 (FB1), fumonisin B2 (FB2) and fumonisin B3 (FB3) residues in milk powder and milk has been established. The samples were extracted with methanol-acetic acid (98:2, V/V), diluted, cleaned up by immunoaffinity chromatography (IAC), and blown to dryness under nitrogen. The residue was re-dissolved and detected using an electrospray ionization source (EIS) in the positive ion mode with multiple reaction monitoring (MRM) and quantitative analysis was performed by the isotope-labeled internal standard method. The limit of quantification was 10 μg/kg for FB1, FB2 and FB3 in milk powder and milk. The recoveries at spiked concentration levels of 10–400 μg/kg were 92.8%–107.5%, with relative standard deviations (RSD) of 2.0%–4.3%. The matrix effects were 96.25%–122.84%. This method was characterized by short analysis time and was suitable for the determination of fumonisin residues in different dairy products.

Reviews

Determination of the Content of Citric Acid in Milk and Dairy Products by Ultra-High Performance Liquid Chromatography

XU Hong, TANG Zhenxin*, ZHANG Xuejiao, JI Helian, ZHAO Shuli, WANG Chen, GAO Wandong, WU Xiaoli, ZHANG Caixia

2023, 46(6):  40-43.  DOI: 10.7506/rykxyjs1671-5187-20231011-052

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An ultra-high performance liquid chromatography (HPLC) method was established for the determination of the content of citric acid in dairy products. The samples were precipitated by K3Fe(CN)6 and (CH3COO)2Zn, extracted ultrasonically, and cryogenically centrifuged to precipitate protein and fat. The chromatographic separation was accomplished on a Poroshell 120 Aq-C18 column (4.6 mm × 100 mm, 2.7 μm) using gradient elution with a mobile phase consisting of a mixture of methanol and ammonium dihydrogen phosphate solution. The analyte was detected by an ultraviolet (UV) detector and quantified by the external standard method. The results showed that the calibration curve was linear with a correlation coefficient above 0.999 9. The average recovery from spiked samples was 95.3%–104.8%, the detection limit was 100 mg/kg, and the relative standard deviation (RSD) for precision was 0.16%–2.41%. The method is simple and rapid and has good separation effect. It is suitable for the quantitative analysis of citric acid in milk and dairy products.