Table of Content

01 January 2024, Volume 47 Issue 1

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Basic Research

Differences in Steroid Hormone Contents between Goat and Cow Milk at Different Lactation Stages

SHARI Akang, REN Xinyang, QU Yingxin, WANG Guang, YU Mengqi, CHEN Lu, YUAN Yuxin, LI Guang

2024, 47(1):  1-7.  DOI: 10.7506/rykxyjs1671-5187-20240207-007

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Purpose: To understand the differences in steroid hormone contents between goat and cow milk at different lactation stages. Methods: The contents of steroid hormones in goat and cow milk at different lactation stages were investigated using ultra-high liquid chromatography-mass spectrometry (UPLC-MS). Gradient elution was performed using 0.5 mmol/L ammonium fluoride aqueous solution as mobile phase A and methanol as mobile phase B at a flow rate of 0.3 mL/min, and the target analytes were qualitatively and quantitatively detected using an electrospray ionization (ESI) source in the multiple reactions monitoring (MRM) mode. Results: A total of 11 steroid hormones, 17α-hydroxyprogesterone, 17α-pregnenolone, epi-testosterone, pregnenolone, progesterone, androstenedione, testosterone, estradiol, estrogen, cortisol, and cortisone, were detected from goat and cow milk samples. At the early lactation stage, the contents of 17α-hydroxyprogesterone, estrogen and cortisol showed significant differences between goat and cow milk (P < 0.05), and the contents of progesterone and progesterone showed extremely significant differences (P < 0.01); at the full lactation stage, significant differences in the contents 17α-hydroxyprogesterone, 17α-pregnenolone, androstenedione, and cortisone (P < 0.05), and extremely significant differences in the contents of progesterone and pregnenolone were found (P < 0.01); at the late lactation stage, significant differences in the contents of 17α-hydroxyprogesterone, androstenedione, estrogen, and cortisol (P < 0.05) were observed as well as extremely significant differences in the content of 17α-hydroxypregnenolone, pregnenolone, and progesterone (P < 0.01). Conclusion: The differences in steroid hormone contents between goat and cow milk may be due to different pregnancy status.

Impact of Interaction with Docosahexaenoic Acid on the Allergenicity of β-Lactoglobulin

ZHOU Weini, WANG Jing, WU Ting, WO Yuxin, DU Yaxuan, JI Yaya, SHA Yicheng, CHEN Daichang, ZHAO Qian, LIANG Xiaona

2024, 47(1):  8-13.  DOI: 10.7506/rykxyjs1671-5187-20240207-006

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β-lactoglobulin (β-LG) is a major allergen in cow’s milk. In this study, synchronous fluorescence spectroscopy, three-dimensional fluorescence spectroscopy, circular dichroism (CD) spectroscopy, molecular docking, and indirect competitive enzyme-linked immunosorbent assay were used to explore the interaction of docosahexaenoic acid (DHA) with β-LG and its influence on the allergenicity of β-LG. The results showed that the binding of DHA to β-LG significantly changed the microenvironment of the aromatic residues of β-LG and increased its polarity. DHA bound to β-LG to form a stable complex through hydrophobic interactions, changing the secondary structure of β-LG and resulting in folding of its backbone. The relative content of β-sheet increased and then decreased with increasing concentration of DHA, while the relative content of α-helix showed an opposite trend. However, the relative contents of β-turn and random coil showed irregular changes. In addition, the antigenicity of β-LG decreased after combination with DHA, and the immunoglobulin E (IgE) binding ability inhibition rate was about 29% by 3 mmol/L DHA.

Analysis & Detection

Determination of Nitrite and Nitrate in Milk Products by Ion Chromatography

YIN Jie, ZHENG Guojian, YE Yinying

2024, 47(1):  14-18.  DOI: 10.7506/rykxyjs1671-5187-20240401-014

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An ion chromatography with conductivity detector (IC-CD) method was developed for the determination of nitrite and nitrate in milk products. Samples were dissolved in water and added with potassium ferrocyanide and zinc sulphate solutions for protein precipitation. The supernatant was cleaned up on C18, Ag, and Na solid-phase extraction (SPE) columns, and analyzed by IC-CD. An external standard method was used for quantification. The IC-CD method was validated. Good linearity between the concentrations of nitrite (NaNO2) and nitrate (NaNO3) in the range of 0.01–0.20 mg/L and 0.1–2.0 mg/L, respectively and peak area was observed with correlation coefficient equal to or higher than 0.99. The limits of quantitation for nitrite and nitrate were 0.2 and 0.4 mg/kg, respectively. The spiked recoveries ranged from 92.5% to 102.0%, and the relative standard deviation (RSD) for precision from 1.5% to 6.6%. This method is accurate, repeatable, simple and applicable to the determination of nitrite and nitrate in milk products.

Evaluation of the Measurement Systems for Chromium Determination in Milk Powder by ICP-MS and GF-AAS

FENG Hao, SU Ying, GENG Yawen, GUO Qingqing, LIN Jin, ZHOU Taohong

2024, 47(1):  19-25.  DOI: 10.7506/rykxyjs1671-5187-20240409-017

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Chromium is an important analytical item in food quality and safety monitoring. Two common methods to detect chromium in food: graphite furnace atomic absorption spectrometry (GF-AAS) and inductively coupled plasma mass spectrometry (ICP-MS) are specified in the National Food Safety Standard Determination of Chromium in Foods (GB 5009.123-2023). This study systematically evaluated the stability, bias, linearity, repeatability, and reproducibility of the two methods using Minitab statistical tools by control chart, independent sample, t test and analysis of variance (ANOVA) methods. The results showed that no outliers were found in the range or mean plots for each method, with within-group errors under statistical control and good stability; the results of gauge linearity and bias analysis showed no significant bias or significant linear error; the gauge repeatability and reproducibility (R&R) analysis showed good repeatability and reproducibility. Two-way ANOVA showed that the sample was the only factor that significantly affected the measurement error. Research variation analysis showed that the measurement system error was acceptable. ICP-MS and GF-AAS can effectively ensure the reliability and repeatability of the detected data of chromium content in milk powder. The findings of this study can not only provide a scientific basis for laboratory analysis and control of measurement system errors, but also provide a reference for the evaluation of measurement systems for the determination of other heavy metals in dairy products and other foods.

Analysis of Volatile Compounds in Three Milks with Different Fat Contents by GC × GC-TOFMS

WANG Haitao, SHEN Xiao, YAO Lingyun, SUN Min, WANG Huatian, FENG Tao

2024, 47(1):  26-32.  DOI: 10.7506/rykxyjs1671-5187-20240415-021

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In this study, headspace solid phase microextraction in combination with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (HS-SPME-GC × GC-TOFMS) was used to analyze the volatile compounds in whole (WM), low-fat milk (LFM) and non-fat milk (NFM). Altogether 49 volatile compounds were detected, among which methyl ketones with odd-numbered carbon chain lengths such as 2-nonanone and 2-undecanone constituted the main flavor compounds of WM. Using partial least squares discriminant analysis (PLS-DA), a model which could well differentiate among the 3 milks was developed and it was found to have good variance and cross-validation predictive ability. Nine differential key aroma compounds were identified using variable importance in the projection (VIP) > 1, P ≤ 0.05 and their contents ≥ 1% as criteria, which may be the main factors contributing to the differences in flavor profiles among the 3 milks. The heatmap from clustering analysis indicated that NFM had poor sensory performance due to the presence of off-flavor compounds (e.g., hexadecanal), whereas WM and LFM contained more aroma compounds, having a full and rich sensory aroma profile. The HS-SPME-GC × GC-TOFMS method can provide theoretical guidance for dairy flavor improvement and dairy flavoring formulation.

Uncertainty Evaluation for the Determination of Nicotinamide in Milk Powder by Ultra-High Performance Liquid Chromatography

CUI Suxia

2024, 47(1):  33-37.  DOI: 10.7506/rykxyjs1671-5187-20240401-013

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The uncertainty in the determination of nicotinamide in milk powder by ultra-high performance liquid chromatography was evaluated. According to the technical normal “Evaluation and Expression of Uncertainty in Measurement” (JJF 1059.1-2012), a mathematical model was established, and the source of each uncertainty component in the mathematical model was analyzed and calculated. The results showed that the uncertainty in nicotinamide determination mainly came from the dilution of the standard solution. In addition, the average content of nicotinamide in milk powder was 5 007 μg/100 g with an expanded uncertainty of about 197 μg/100 g (k = 2).

Packaging & Storage

Comparative Analysis of Nutrient Decay Rates of Infant Formula Milk Powder in Accelerated and Long-Term Storage Tests

LI Linyao, CHU Xiaojun, HUA Jiacai, YAN Yali, GUAN Xueqing

2024, 47(1):  38-41.  DOI: 10.7506/rykxyjs1671-5187-20240305-008

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According to the relevant requirements and methods specified in the Guidelines for Stability Study of Powdered Milk Formulae for Infants and Young Children (on Trial), nutrient decay in infant formula milk powder was investigated in accelerated and long-term tests. The results showed that the macronutrients and fatty acids in infant formula milk powder were relatively stable in both tests, with a decay rate of less than 5%. Vitamins did not significantly decay with a decay rate of less than 10%. The mineral iodine decayed evidently in the accelerated test, with a maximum decay rate of 11.37%. Other minerals did not significantly lose. The optional components were relatively stable in the accelerated and long-term tests, with a decay rate of less than 5%.

Reviews

Progress in the Study of Microplastics Contamination in Dairy Products

TANG Qi, MENG Deshang, ZHANG Yan

2024, 47(1):  42-46.  DOI: 10.7506/rykxyjs1671-5187-20240326-012

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Microplastics (MPs) in food have aroused widespread concern, and it has been clarified that MPs have toxic effects on cells, animals and human organoids, and that the cytotoxicity is inversely proportional to the particle size of MPs, and positively proportional to the concentration of MPs and the time of exposure; in experimental animal models, the toxic effects of MPs mainly occur in the digestive, nervous, respiratory, reproductive, and cardiovascular systems; the hazardous effects of MPs have also been identified in the human organoids of liver, intestine, heart and brain. The contamination of MPs in dairy products may occur at different stages of the production process. This paper reviews the sources, toxicological effects and detection methods of MPs contamination in dairy products, with the aim of providing a reference for the risk prevention and control of MPs in dairy products and for future research.