Table of Content

01 October 2022, Volume 45 Issue 5

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Basic Research

Effects of Monascus on Physicochemical Properties, Microstructure and Flavor Compounds of Cheese during Ripening

ZHENG Yuanrong, TENG Junwei, LIU Zhenmin

2022, 45(5):  1-6.  DOI: 10.7506/rykxyjs1671-5187-20220721-044

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Mold-ripened cheese was prepared using a commercial starter culture combined with Monascus, and its physicochemical properties, free amino acids, microstructure and volatile flavor substances were evaluated. The results showed that the yield of cheese was 16.55%, and the protein, fat, calcium, water, and salt contents of the cheese were 18.03%, 33.40%, 376.67 mg/100 g, 44.47%, and 863.67 mg/100 g, respectively. During the ripening process, pH value first decreased, then increased and finally leveled off. The microstructure indicated that Monascus had a significant effect on the internal structure of mature cheese. A total of 23 free amino acids and 32 volatile compounds were identified by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). At the end of the ripening period (21 days), the content of free amino acids in mold-ripened cheese was increased by an average of 58.8 times over the beginning of ripening, and the types and contents of volatile compounds also changed significantly.

Immunoglobulin G Content and Lactoperoxidase Activity in Milk during Pasteurization and Storage

ZHANG Fenghua

2022, 45(5):  7-10.  DOI: 10.7506/rykxyjs1671-5187-20220718-042

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Immunoglobulin G (IgG) and lactoperoxidase are bioactive components with high thermal sensitivity in milk. In this study, the changes in the IgG content and lactoperoxidase activity of milk during pasteurization and shelf-life storage were investigated. The results showed that homogenization temperature below 65 °C and homogenization pressure between 15 and 25 MPa had little effect on the two bioactive substances in milk. The combination of 72–76 ℃ and 15 s better retained the bioactive substances and membrane filtration was more effective than regular pasteurization in reducing the microbial load of milk. The IgG content and lactoperoxidase activity in pasteurized milk did not decrease significantly with storage time; however, long-term exposure to light could cause partial inactivation of lactoperoxidase in products with transparent packaging.

Preparation and Storage Stability of Hypoglycemic Dairy Products

HAN Jin

2022, 45(5):  11-16.  DOI: 10.7506/rykxyjs1671-5187-20220713-041

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The in vitro hypoglycemic effect of the supernatant of fermented milk with Paenibacillus bovis BD3526 (CGMCC No.8333) was evaluated, and the supernatant was used to prepare hypoglycemic beverage, whey powder and milk powder. The storage stability of the hypoglycemic products was investigated. The results showed that the supernatant had strong (which inhibited about 90% of α-glucosidase activity) and stable hypoglycemic activity in vitro. The beverage, whey powder and milk powder inhibited 57%, 48% and 37% of α-glucosidase in vitro, and their microbial properties conformed to the national standard requirements. After storage for six months at different temperatures (8, 25 and 60 ℃), their hypoglycemic activity remained substantially unchanged, and their microbial indexes were significantly superior to those of the control group.

Processing Technology

Development and Process Optimization of Yoghurt with Muscovado Sugar and Oolong Tea

JIN Hongwei, ZHANG Judian, WANG Qingyun

2022, 45(5):  17-21.  DOI: 10.7506/rykxyjs1671-5187-20220706-039

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Yogurt was prepared from raw milk and oolong tea powder with added L-theanine and muscovado sugar using a starter culture of lactic acid bacteria. The effects of the concentration of oolong tea powder, muscovado sugar and L-theanine and inoculum size on the pH value, acidity, viscosity, water-holding capacity and sensory score of yoghurt were investigated by using a combination of one-factor-at-a-time (OFAT) method and orthogonal array design (OAD). The results showed that under the conditions of 0.3% oolong tea powder concentration, 8% muscovado sugar concentration, 0.09% L-theanine concentration and 0.010% inoculum size, the sensory score, pH value, acidity, water-holding capacity, and total viable count of the prepared yogurt were 96 points, 4.54, 72 °T, 67.34%, and 5.78 × 109 CFU/g, respectively. The product had a rich flavor, bright color, exquisite texture, prominent muscovado sugar-like flavor, strong aroma, and smooth taste without suspended particles.

Effect of Centrifugal Pump and Screw Pump at Different Temperatures on the Quality of Cream

CHEN Zhijie

2022, 45(5):  22-26.  DOI: 10.7506/rykxyjs1671-5187-20220406-019

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In this study, the effect of using centrifugal or screw pumps to deliver cream at different temperatures for ultra-high temperature (UHT) sterilization on the physicochemical quality of cream was investigated. It turned out that delivering cream at 10 ℃ by a centrifugal pump caused fat aggregation and precipitation and significantly reduced viscosity compared to delivering it at 60 ℃ or by a screw pump. The particle size of cream delivered at 10 ℃ by the centrifugal pump was the largest and most uneven, and the particle size of cream delivered at 60 ℃ by the centrifugal pump, at 10 ℃ and 60 ℃ by the screw pump were close. The particle size of cream delivered at 60 ℃ by the centrifugal pump was the most homogeneous. The whipping rate and hardness of cream delivered at 60 ℃ by the two pumps were close to each other, while cream delivered at 10 ℃ by the screw pump had the lowest whipping rate. Cream delivered at 10 ℃ by the centrifugal pump could not be whipped even after being churned for a long time. There was a significant difference in the microstructure but not the fatty acid composition of the four cream samples. Fat globules in cream delivered at 60 ℃ were small and dense while those in cream delivered at 10 ℃ were large and sparse, indicating that cream at low temperature is prone to aggregation caused by shear, resulting in fat aggregation and affecting cream quality. This finding is consistent with the particle size results.

Analysis & Detection

Determination of Naringin in Milk and Dairy Products by High Performance Liquid Chromatography

GONG Huili, DUAN Guoxia, LIU Lijun, CHEN Sumin, XIE Ruilong, LIU Chunxia, CHEN Jing, WU Lunwei, LIU Wang, TANG Shuo, LI Cuizhi, LÜ Zhiyong

2022, 45(5):  27-31.  DOI: 10.7506/rykxyjs1671-5187-20220621-038

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A high performance liquid chromatographic (HPLC) method was developed for the determination of naringin in milk and dairy products. Samples were extracted with methanol, and the analytes were separated on a C18 column using a mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile (75:25, V/V), detected by a diode array detector at 284 nm and quantified by an external standard method. The results showed that the linearity of this method was good in the concentration range of 5–500 μg/mL with a correlation coefficient of 0.999 9. The recoveries of powdered and liquid milk power and yogurt spiked at 0.02, 0.04, and 0.08 g/100 g were 96.2%–103.2%, 96.3%–103.7%, and 99.7%–104.1%, respectively, with relative standard deviations (n = 6) of 1.12%–2.31%, 1.25%–1.85%, and 1.24%–1.66%, respectively. The reported method is simple, rapid, accurate, repeatable, and suitable for the determination of naringin in milk and dairy products.

Reviews

Recent Development in Research on Lactic Acid Bacterial DNA Methylation

JIAO Yangbo, ZHAO Jie

2022, 45(5):  32-37.  DOI: 10.7506/rykxyjs1671-5187-20220516-032

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In recent years, with the rapid innovation and development of sequencing technology, researchers have tended to focus on DNA methylation research. DNA methylation is a way of regulating bacterial gene expression and altering the genetic performance without altering the DNA sequence. While a great deal of research has been conducted to understand the effect of eukaryotic DNA methylation on disease occurrence and plant growth, prokaryotic DNA methylation has barely been researched so far. For a better understanding of the current status of research on bacterial DNA methylation, herein, we briefly summarize recent developments in research on DNA methyltransferase and methylome in pathogenic bacteria and lactic acid bacteria and the techniques used to detect DNA methylation in order to provide a theoretical basis for the application of DNA methylation in lactic acid bacteria.

Research Progress on Vitamin A in Human Milk and Its Health Effects on Infants and Young Children

JIA Hongxin, SU Miya, CHEN Wenliang, LIU Haian

2022, 45(5):  38-43.  DOI: 10.7506/rykxyjs1671-5187-20220510-031

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Human milk contains various types of vitamin A (VA), such as retinol, β-carotene, β- cryptoxanthin, α-carotene, lycopene and lutein. The content of VA is different among colostrum, transitional milk and mature milk, but it generally decreases with the duration of lactation. For instance, the content of retinol, the most abundant type of VA in human milk, is 478–1 920, 440–1 270 and 178–825 mg/L in colostrum, transition milk and mature milk, respectively. The VA content in human milk is not only affected by lactation time, but also related to regions, the diet of lactating mothers, the fat content of human milk, etc. This paper summarizes the types, contents, influential factors and health effects (visual health, immune health, growth and development, etc.) of VA in breast milk from different countries and regions, in order to provide a basis for the development of infant formula milk powder.

Research Progress on Fungal Polysaccharides and Their Application in Lactic Acid Bacteria Fermented Products

YANG Yang

2022, 45(5):  44-52.  DOI: 10.7506/rykxyjs1671-5187-20220804-047

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Fungal polysaccharides are a group of high polymers extracted from the fruiting body, mycelium or fermentation broth of fungi, and are one of the main bioactive substances in edible fungi. They are composed of a variety of monosaccharides and form a complex structure through the connection of chemical bonds, which makes them have a variety of biological activities such as anti-tumor, antioxidant, hypoglycemic, and hypolipidemic effects. They are often added to foods as prebiotics. In recent years, with the continuous exploration of fungal polysaccharides, rapid progress has been made in the extraction, purification, structure analysis, biological activities and product development of fungal polysaccharides. In this paper, the chemical composition, structure analysis and biological activities of fungal polysaccharides are summarized, and the development status and future prospects of lactic acid bacteria fermented foods incorporated with fungal polysaccharides are discussed, so as to provide reference for functional exploration of fungal polysaccharides and for future research to enrich the variety of lactic acid bacteria fermented products.

Research Progress on Yak Milk and Its Flavor Substances

LIU Qingxue, XIAO Zijun

2022, 45(5):  53-58.  DOI: 10.7506/rykxyjs1671-5187-20220706-040

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The yak is a species mainly distributed in and around the Qinghai-Tibet Plateau in China, and its special living environment makes yak milk unique in terms of nutritional value and flavor substances compared to cow’s milk, so that more and more consumers pay attention to yak milk. This paper summarizes the annual milk yield of yaks and the factors influencing it, and the nutritional composition, flavor substances, and flavor substance concentration and identification of yak milk from the perspective of the industrial chain of yak milk commercialization. This review can help to develop and utilize raw yak milk as high-quality commercial aseptic milk.