Proteolysis in ultra‐heat‐treated skim milk after exposure to multispecies biofilms under conditions modelling a milk tanker

Bacteria from milk tankers can form multispecies biofilms and produce heat‐stable enzymes. In this study, milk was exposed to multispecies biofilms in stainless steel vessels and was then used to produce ultra‐heat‐treated (UHT) milk, which was stored for 5 months. The UHT milks were assessed for microbial counts, free peptide concentration and pH. The free peptide concentration, which indicated proteolysis, was higher in UHT milk that had been exposed to multispecies biofilms than in untreated UHT milk. Biofilm formation may be promoted in milk tankers that are not properly cleaned, which may compromise the quality of the final dairy product.     

Near‐infrared spectroscopy and data analysis for predicting milk powder quality attributes

Near‐infrared (NIR) spectroscopy is a rapid analytical method for food products. In this study, NIR spectroscopy, data pretreatment techniques and multivariate data analysis were used to predict fine particle size fraction, dispersibility and bulk density of various milk powder samples, which are believed to have a significant impact on milk powder quality. Predictive models using partial least‐squares (PLS) regression were developed using NIR spectra and milk powder physical and functional properties, and it was concluded that the PLS models predicted milk powder quality with an accuracy of 88‐90 per cent.     

Compositional analysis of protoporphyrinogen oxidase‐inhibiting herbicide‐tolerant rice and conventional rice

Protoporphyrinogen oxidase (PPO) is a key enzyme of peroxidising herbicides. Transgenic rice event CPPO06, which overexpresses PPO gene derived from soil bacterium, Myxococcus xanthus, showed high resistance to PPO inhibitors. This study was designed to compare the compositional profile of rice event CPPO06 with that of conventional control and commercial cultivars. Field trials were carried out in the three different regions of South Korea during the 2011 and 2012 growing seasons. After harvesting, brown rice samples were analysed for their proximates, amino acids, fatty acids, minerals and vitamins. Over 2‐year field trials, statistical differences between rice event CPPO06 and its control were found for crude protein, aspartic acid, oleic acid, linoleic acid, linolenic acid, copper and potassium. However, all the tested values for these components were both within the 99% tolerance interval for the commercial cultivars and within the literature ranges. It was concluded that rice event CPPO06 is compositionally equivalent to that of the conventional rice.     

The quality of set‐style yoghurt responsible to partial lactose hydrolysis followed by protein cross‐linking of the skimmed milk

Skimmed milk used for set‐style yoghurt production was treated with lactase at 0.1 g/kg for 30 min to give partial lactose hydrolysis and then treated with horseradish peroxidase and glucose oxidase at 200 and 6 kU/kg protein to result in protein cross‐linking. Two treatments conferred higher apparent viscosity on the milk, but led to the yoghurt prepared from it with insignificantly different chemical compositions to the counterparts (P > 0.05). The prepared yoghurt also showed decreased syneresis (about 17.7%), higher apparent viscosity and viscoelastic modulus, firmer texture and finer microstructure. This ternary enzyme system is a potential approach to improving the quality of set‐style yoghurt.     

Rapid quantitative analysis of Chinese Gu‐Jing‐Gong spirit for its quality control

The rapid quantitative analysis of food systems may offer improved control of food quality. In this work, the quantitative analysis of Chinese liquor was investigated using ultraviolet (UV) spectroscopy and a similarity algorithm. The potential application of this approach was evaluated using Chinese liquors, including the same and different batches of Gu‐Jing‐Gong spirits. The effectiveness of the proposed quality control quantitative model has been demonstrated, and the method could be applied to control the quality of Gu‐Jing‐Gong spirits and to identify counterfeit products. This analytical method is simple, rapid and efficient, and has potential practical application. Copyright © 2017 The Institute of Brewing & Distilling     

偶氮染色-光谱法快速检测牛乳中组胺和酪胺含量

目的 利用偶氮染色-光谱技术,研究并设计可满足牛乳中组胺、酪胺快速检测的方法。方法 样品经盐酸溶液提取,提取后的组胺、酪胺与偶氮试剂发生染色反应后10~15 min内使用光谱法检测。结果 组胺和酪胺的定量限均为10 mg/kg,满足当前国内外标准通常规定组胺最低为50 mg/kg的限量要求,回收率在90%左右,相对标准偏差在10%左右,结果符合食品理化分析的相关要求。结论 研制的检测方法具有快速、稳定、节约成本等特点,适用于牛乳中组胺、酪胺的快速检测。     

Rheological properties of instant milk‐based puddings prepared with emulsifying salt‐containing milk powders

The present work analysed the rheological properties, water‐holding capacity (WHC) and syneresis of instant puddings prepared with the emulsifying salt‐containing milk powders (ESMPs), which contained different proportions of disodium phosphate (DSP) and tetrasodium pyrophosphate (TSPP). Rheological measurements revealed that increasing the proportion of TSPP in the ESMPs increased gel stiffness (indicated by high values of G?, G^* and consistency index) and WHC, and decreased the tan δ and syneresis of the instant puddings. It was concluded that different interactions can be assumed dependent on the proportion of DSP and TSPP in the ESMPs added to the pudding system, and a mechanism was proposed for observed changes.     

Self‐segmenting of rennet‐induced milk gel in cheesemaking tank

The phenomenon of self‐segmenting of milk gel in an open‐type cheesemaking tank is described. It is shown that the self‐segmenting of the gel is caused by the thermo‐gravitational convection of Rayleigh–Bénard and the thermo‐capillary convection of Bénard–Marangoni. A mechanism for the self‐segmenting of milk gel, in which the important role of fat globules in this process has been noted, is proposed. It is noted that the self‐segmenting of the milk gel can cause some defects in the finished cheese: uneven texture and colour disorder.     

A survey of the physicochemical and microbiological quality of ultra‐heat‐treated whole milk in Brazil during their shelf life

The objective was to evaluate the quality of important brands of ultra‐heat‐treated (UHT) milk marketed in the northern of Parana State, Brazil, during the shelf life of the product. Five brands were analysed at 30, 60, 90 and 120 days after UHT milk production. The physicochemical quality of the milk was assessed in terms of fat content, titratable acidity, density, freezing point depression, total solids, solids‐not‐fat, proteolysis and alcohol stability. Microbiological quality was assessed by the enumeration of aerobic mesophilic micro‐organisms. None of the brands complied with all the physicochemical standards. Two brands met all applicable microbiological requirements. Gelation was observed from 90 days of storage onwards in all brands.     

Development and application of a new multiplex real‐time PCR assay for simultaneous identification of Brucella melitensis,Cronobacter sakazakii and Listeria monocytogenes in raw milk and cheese

Brucella melitensis, Cronobacter sakazakii and Listeria monocytogenes are important foodborne pathogens in milk and milk products, which are responsible for a variety of diseases that pose serious hazards to public health and food safety. The objective of this study was to develop a novel multiplex RTi‐PCR for the detection of B. melitensis, C. sakazakii and L. monocytogenes and to characterise the potential risk of these pathogens in raw milk and cheese. The raw milk (n = 25) and cheese samples (n = 20) were analysed by multiplex RTi‐PCR assay and detected for quantification of the three pathogens. In this study, B. melitensis, C. sakazakii and L. monocytogenes were simultaneously identified using BMEII0466, mms operon and hly as target genes, respectively. The multiplex RTi‐PCR assay that was developed showed good sensitivity and selectivity for the pathogenic microorganisms (r² = 0.986–0.997). Multiplex RTi‐PCR results showed that most of the samples were contaminated with the pathogens screened.     

Effects of dietary rumen‐protected lysine on milk yield and composition in lactating cows fed diets containing double‐low rapeseed meal

This study investigated the effects of dietary rumen‐protected lysine (RPLys) on milk yield and composition in lactating cows fed diets containing double‐low rapeseed meal. Twenty‐four cows were divided into three groups and fed one of three dietary treatments: 10% soya bean meal (SBM) diet (control), 15% double‐low rapeseed meal (DLRSM) diet and 15% DLRSM + 32 g/d RPLys (DLRSML) diet. The results showed that no differences (P > 0.05) were observed in milk yield, 4% fat correction milk (FCM), energy correction milk (ECM), protein yield, milk fat yield, milk fat, lactose yield and lactose between control and DLRSM. Supplementation with DLRSML increased (P < 0.05) milk yield, 4% FCM, ECM, and protein yield compared with the SBM. The results indicated that DLRSM and DLRSML might be used to substitute for SBM as a protein source in lactating cows, and the latter might be more beneficial to improve the performance.     

The influence of enzymatic cross‐linking of proteins on the Maillard reaction in milk

The influence of transglutaminase (TGase) on the Maillard reaction was investigated in skimmed milk samples during heat treatment. TGase‐treated and control samples were heated at 80, 120 and 140 °C for 1, 5, 15, 30, 40 and 60 min. Compared with the TGase‐treated samples heated at 80 and 120 °C, the sample heated at 140 °C showed a larger decrease in furosine concentration. It was also found that TGase did not affect the formation of hydroxymethylfurfural and lactulose at 120 °C, whereas their concentrations increased in the presence of TGase at 140 °C. It was concluded that blockage of lysine residues via enzymatic cross‐linking of milk proteins had a limited effect on the Maillard reaction.     

Lactic acid‐mediated isolation of alpha‐, beta‐ and kappa‐casein fractions by isoelectric precipitation coupled with cold extraction from defatted cow milk

The present study focused on the isolation of individual caseins (α, β and κ) from defatted cow's milk using lactic acid‐mediated isoelectric precipitation coupled with cold extraction technique, followed by purification using sucrose‐based density gradient centrifugation method. In vitro characterisation of the isolated casein fractions confirmed preservation of micellar morphology throughout the experimental conditions with anionic surface charge and wider particle size range. The RP‐HPLC analysis showed a peak at retention time of 25.13 min and 27.84 min for α‐casein and β‐casein, respectively. Results confirmed isolation of pure casein fractions from cow's milk which could serve as a rich source of bioactive peptides for nutraceutical/pharmaceutical applications.     

Development of a method employing reversed‐phase thin‐layer chromatography for establishing milk fat purity with respect to adulteration with vegetable oils

A systematic study was conducted using reversed‐phase thin‐layer chromatography wherein unsaponifiable matter of samples namely, pure cow and buffalo milk fats, vegetable oils (groundnut oil, soya bean oil and sunflower oil) and milk fats adulterated with vegetable oils (≥1%) were run along with the reference standards using two new solvent systems to detect adulteration in milk fat. The results of the study revealed that adulteration at even a 1% level could easily be detected using this rapid, reliable and reproducible method based on the presence of β‐sitosterol as a marker and some additional spots ascribable to their occurrence in vegetable oils only.     

The physicochemical and sensory properties of milk supplemented with ascorbic acid‐soluble nano‐chitosan during storage

This study was carried out to assess the feasibility of adding the ascorbic acid‐soluble nano‐chitosan (AANC) into the milk for improving the functionality of milk and to determine the effects of such addition on the physicochemical and sensory properties of the product during storage. The pH and titratable acidity of the AANC milks were not changed significantly when stored at 4°C for 15 days. The addition of the nano‐chitosan solution (1～9%, v/v) into the milk samples led to an increase in the amounts of L‐ascorbic acid, thereby indicating an enhancement in health benefits. The sensory test revealed that astringency scores increased and colour scores decreased when the highest concentration of the nano‐chitosan solution (9%, w/w) was added into the milk samples The colour values, L‐ and a‐, in the milks were not significantly influenced by adding the nano‐chitosan solution (1～9%, v/v); whereas the b‐values significantly increased with the addition of the nano‐chitosan solution (5～9%, v/v). Based on the data obtained from this study, it is concluded that the low concentrations (1～3%, v/v) of the nano‐chitosan solution could be used to produce a nanopowdered chitosan‐added milk without the significantly adverse effects on the physicochemical and sensory properties.     

Effect of distillers dried grains with solubles diet supplemented with rumen‐protected lysine and methionine on milk production and milk amino acids in the lactating cow

This study was to quantify the milk protein and amino acids (AA) in response to rumen‐protected lysine (Lys) and methionine (Met) supplementation in dairy cows fed distillers dried grains with solubles (DDGS) diet. Forty cows were divided into five dietary treatments: soybean meal diet (SM), DDGS diet and DDGS diets with 40 g/day Lys (DL), 20 g/ day Met dry matter (DM) and 20 g/ day Met plus 40 g/ day Lys (DLM), separately. Compared with SM, DL and DM groups, DLM group increased milk yield, 4% fat‐corrected milk, energy‐corrected milk yield and protein in milk. DDGS treatments increased total AA and the essential AA in milk. Results indicated that dietary DDGS increased intestinal supplies of Lys and Met.     

Comparative analysis of the fermentation performance of high‐quality milk beer strains (Kluyveromyces marxianus) and optimisation of medium formula for high‐density fermentation

Milk beer is a new type of dairy beverage in China and increasingly popular with consumers. The strain FXJ1 isolated in our laboratory was an excellent strain for the production of milk beer with alcohol content of 0.48%. Our research verified that the strain FXJ1 was superior to the commercial strain MJ for milk beer production and got the optimal medium formula (67.37 g/L sucrose, 29.7 g/L yeast extract, 15.61 g/L corn steep liquor, 4.13 g/L KH₂PO₄ and 0.3 g/L MgSO₄) which allowed the biomass production of strain FXJ1 to achieve 8.88 ± 0.08 g/L and increase 2.94‐fold as compared with yeast extract peptone dextrose base medium.     

Effect of lactose on cross‐linking of milk proteins during heat treatments

The major types of nondisulphide cross‐linking which cause milk protein aggregation were investigated in milk, with and without lactose, heated at 95 °C for up to 8 h. Compared with the milk containing no lactose, the milk containing lactose showed a smaller increase in pH, a larger increase in pH 4.6 soluble nitrogen, much smaller increase in lysinoalanine (LAL) and a much higher percentage of cross‐linked proteins. It was concluded that cross‐linking in milk products containing lactose occurs mainly via Maillard reaction products, and in milk products with no lactose, it occurs mainly via isopeptide linkages such as in LAL.