A sensitive, high-throughput fluorescent method for the determination of lactoperoxidase activities in milk and comparison in human, bovine, goat and camel milk

Nanosecond pulsed electric field treatment of human milk: Effects on microbiological inactivation, whey proteome and bioactive protein

In the current study, nanosecond pulsed electric field (nsPEF) was investigated at lab-scale to optimise processing conditions of donor human milk to reduce bacterial counts, and to evaluate its effect on the bioactive proteins in human milk. Response surface methodology was utilized to optimise critical processing parameters. Two optimal nsPEF processing conditions were validated: 15 kV voltage, 6000 pulses at 20 Hz frequency, and 15 kV voltage, 6000 pulses at 50 Hz frequency. Compared to raw human milk, nsPEF processed milk had over 60 % retention of lysozyme, lactoperoxidase and lactoferrin, and 100 % retention of xanthine oxidase and immunoglobulin A. The contents of the five proteins were significantly higher after nsPEF processing when compared with Holder pasteurization. Liquid chromatography-mass spectrometry analysis showed that loss of milk proteins was smaller for samples treated with nsPEF than Holder pasteurization. These results indicated that nsPEF is a promising novel pasteurization method.

Three recombinant peroxidases as a degradation agent of aflatoxin M1 applied in milk and beer

The aim of this work was to estimate the effects of three recombinant peroxidases (rPODs) on the degradation of aflatoxin M₁ (AFM₁) in a model solution and were applied in milk and beer to study the AFM₁ degradation. Besides, the contents of AFM₁ in model solution, milk and beer were evaluated, and the kinetic parameters of rPODs were determined (Michaelis-Menten constant - K_m and maximal velocity - V_max). The optimized reaction conditions (The degradation was over 60 %) for these three rPODs in the model solution were, respectively as follows: pH were 9, 9, and 10; hydrogen peroxide concentrations were 60, 50, and 60 mmol/L; at an ionic strength of 75 mmol/L and reaction temperature of 30 °C with 1 mmol/L K⁺ or 1 mmol/L Na⁺. These three rPODs (1 U /mL) presented the maximum activity for degradation of AFM₁ of 22.4 %, 25.6 %, and 24.3 % in milk, while 14.5 %, 16.9 %, and 18.2 % in beer, respectively. Meanwhile, the survival rate of Hep-G2 cells raised about 1.4 times after treated with peroxidase-generated AFM₁ degradation products. Therefore, POD may be a promising alternative to reduce the pollution of AFM₁ in model solution, milk, beer, and minimize their impact on the environment in humans.

Effects of different heat treatments on Maillard reaction products and volatile substances of camel milk

Camel milk has unique compositional, functional and therapeutic properties compared to cow's milk and also contains many protective proteins with anti-cancer, anti-diabetic and anti-bacterial properties. In this experiment, fresh camel milk was heat-treated at different temperatures and times, and the changes in Millard reaction products were analyzed. Meanwhile, headspace-gas chromatography-ion migration spectrometry (HS-GC-IMS), electronic nose and electronic tongue were used to analyze the changes of volatile components in camel milk after different heat treatments. The results showed that the Maillard reaction was more severe with the increase of heat treatment, and the contents of furosine and 5-hydroxymethylfurfural increased significantly when the heat treatment temperature was higher than 120°C. HS-GC-IMS results showed that the contents of aldehydes and ketones increased obviously with the increase of heat treatment degree. The study clarifies the effects of different heat treatment degrees on Maillard reaction degree and flavor of camel milk, which has practical production guidance significance for the research and industrialization of liquid camel milk products.

The Results of Different Heating Temperatures on Activities of Bioactive Proteins in Human Milk

BACKGROUND

The most utilized pasteurization method in donor human milk banks is Holder pasteurization (heating 62.5 °C for 30 min). However, many bioactive proteins are heat sensitive and are inactivated.

RESEARCH AIM

To determine the results of a range of heating regimes on the activities of xanthine oxidase, lactoperoxidase and lysozyme, the concentrations of immunoglobulin A and lactoferrin, as well as bacterial inactivation.

METHOD

This prospective, cross-sectional, intervention study was designed to measure the influence of heating temperatures on bioactive components in donor human milk. Milk samples were processed at 40, 50, 55, 62.5, 75, 127 °C and the activities of the enzymes, and the concentration of immune proteins, were measured.

RESULTS

No bacterial colonies were detectable, using standard culture methods, after heating above 50 ºC. All proteins studied retained over 60% concentrations or activities when the pasteurization temperature was 50 ºC or lower, while their concentrations or activities were lost at higher temperatures. For lactoferrin, the residual concentration was above 80% when heating temperature was under 55 °C, while only 20% remained after Holder pasteurization. Both xanthine oxidase and lactoperoxidase had little residual activity when temperatures were above Holder pasteurization. Lysozyme retained a greater proportion of residual activity than other proteins, following heating at all temperatures.

CONCLUSIONS

The concentrations or activities of immune proteins and bioactive enzymes decreased when heated above 50 °C. The results of this study can be used to design temperature control guidance during alternative methods of pasteurization.

Comprehensive biochemical and proteomic characterization of seasonal Australian camel milk

Although camel milk is increasingly becoming a popular alternative to bovine milk around the world including Australia, studies of Australian camel milk are still lacking. A comprehensive and systematic analysis of major nutritional components, physical properties, antimicrobial enzymes and whey proteomes of Australian camel milk obtained over four seasons was conducted, for the first time in present study. The composition and physical properties of Australian camel milk varied with season, milking frequency and yield. The highest lactoperoxidase and polyamine oxidase activity was observed in summer and winter, respectively. A total of 97 proteins were quantified, on a relative basis, across all the seasonal bulk milk samples. Summer camel milk contained higher amounts of functional whey proteins, such as lactotransferrin, peptidoglycan recognition protein 1, osteopontin and lactoperoxidase. These results contribute to a better understanding of the Australian camel milk and provide insights into processing of dairy products from this milk.

Comparing the effects of hydrostatic high-pressure processing vs holder pasteurisation on the microbial, biochemical and digestion properties of donor human milk

In this study, hydrostatic high-pressure processing (HHP), a non-thermal pasteurisation method, was used to achieve the microbiological safety of donor human milk. After HHP, no bacteria were detected in human milk processed at 400 MPa for 5 min. Activities of a selection of bioactive components, including lysozyme, xanthine oxidase, lactoperoxidase, immunoglobulin A, lactoferrin, lipoprotein lipase and bile salt-stimulated lipase, did not decrease significantly. This study further investigated the gastrointestinal digestion kinetics of HoP and HHP milk compared with raw human milk, using an in vitro static infant digestion model. After 60 min of 'gastric digestion', the microstructure and protein profile of HHP milk samples were more similar to raw milk samples than HoP milk samples. Overall, HPP showed a better retention in milk nutrients and closer digestion behavior than that of HoP.

Physicochemical Properties and Whey Proteomes of Camel Milk Powders Produced by Different Concentration and Dehydration Processes

Camel milk powder production is an alternative to preserve the perishable milk for later-date consumption. However, the impacts of dehydration processes on bioactive compounds in camel milk are largely unknown. Hence, the present study attempted to compare the physicochemical properties and protein profiles of camel milk powders produced by different concentration and dehydration processes. Six camel milk powders were produced by freeze- and spray-drying methods in conjunction with two liquid concentration techniques, namely spray dewatering and reverse osmosis. The results of proteomic analysis showed that direct freeze-dried camel milk powder had the least changes in protein profile, followed by direct spray-dried powder. The camel milk powders that underwent concentration processes had more profound changes in their protein profiles. Among the bioactive proteins identified, lactotransferrin and oxidase/peroxidase had the most significant decreases in concentration following processing. On the contrary, glycosylation-dependent cell adhesion molecule 1, peptidoglycan recognition protein 1, and osteopontin increased in concentration. The results revealed that direct freeze drying was the most ideal method for preserving the bioactive proteins during camel milk powder production. However, the freeze-drying technique has cost and scalability constraints, and the current spray-drying technique needs improvement to better retain the bioactivity of camel milk during powder processing.

Effects of microfiltration combined with ultrasonication on shelf life and bioactive protein of skim milk

To extend the shelf life and retain bioactive proteins in milk, this study utilized microfiltration (MF) combined with ultrasonication to treat skim milk and investigated its efficiency in removing bacteria and retaining bioactive proteins compared with HTST pasteurization and microfiltration alone. Results showed that microfiltration combined with ultrasonication at 1296 J/mL could completely remove the bacteria in skim milk. Ultrasonication further extended the shelf life (4 °C) of microfiltered skim milk, which could reach at least 40 days when MF was combined with ˃1296 J/mL ultrasonication. In addition, ELISA showed that HTST pasteurization significantly decreased the levels of IgG by ~30%, IgA by ~ 50%, IgM by ~60%, and lactoferrin by ~40%, whereas the activity of the enzymes lactoperoxidase and xanthine oxidase were also decreased by ~ 20%. Compared with HTST, MF alone or combined with ultrasonication retained these bioactive proteins to a larger degree. On the other hand, proteomics indicated both damage to casein micelle and fat globule structures in milk when ultrasonication at >1296 J/mL was applied, as shown by increases in caseins and milk fat globular proteins. Simultaneously, this ultrasound intensity also decreased levels of bioactive proteins, such as complement factors. Taken together, this study provided new insights that may help to implement this novel combination of non-thermal technologies for the dairy industry aimed at improving milk quality and functionality.

Changes in Native Whey Protein Content, Gel Formation, and Endogenous Enzyme Activities Induced by Flow-Through Heat Treatments of Goat and Sheep Milk

The aim of the present study was to assess the effects of different flow-through heat treatments—68, 73, 78, 85, 100 °C for 16 s—applied to in-line homogenized goat and sheep milk. Alkaline phosphatase (ALP) activity in raw goat milk was 324.5 ± 47.3 μg phenol/mL, and that of lactoperoxidase (LPO) was 199.3 ± 6.7 U/L. The respective activities in raw sheep milk were 7615 ± 141 μg phenol/mL and 319 ± 38.6 U/L. LPO activity was not detected in both milk kinds treated at 85 °C for 16 s. Residual enzyme activities at 73 °C for 16 s with respect to the initial levels in raw milk were higher in goat than in sheep milk. The whey protein fraction of sheep milk was more heat sensitive compared to goat counterpart. Sheep milk rennet clotting time (RCT) was not affected by the treatments, while curd firmness decreased significantly (p < 0.05) at 100 °C for 16 s. Treatments more intense than 73 °C for 16 s increased the RCT of goat milk significantly but inconsistently and decreased curd firmness significantly, while yoghurt-type gels made from 73 °C or 78 °C for 16 s treated goat milk exhibited the highest water-holding capacity.

Transmission of Major and Minor Serum Proteins during Microfiltration of Skim Milk: Effects of Pore Diameters, Concentration Factors and Processing Stages

Effects of pore diameters (100, 50, and 20 nm), concentration factors (1-8) and processing stages (1-5) on the transmission of major serum proteins (β-lactoglobulin and α-lactalbumin) and minor serum proteins (immunoglobulin (Ig) G, IgA, IgM, lactoferrin (LF), lactoperoxidase (LPO), xanthine oxidase (XO)) during ceramic microfiltration (MF) of skim milk were studied. Holstein skim milk was microfiltered at a temperature of 50 °C, a transmembrane pressure of 110 kPa and a crossflow velocity of 6.7 m/s, using a tubular single stainless steel module that consisted of three ceramic tubes, each with 19 channels (3.5 mm inner diameter) and a length of 0.5 m. For MF with 100 nm and 50 nm pore diameters, the recovery yield of major serum proteins in permeate was 44.3% and 44.1%, while the recovery yield of minor serum proteins was slightly less by 0%-8% than 50 nm MF. MF with 20 nm pore diameters showed a markedly lower (by 12%-45%) recovery yield for both major and minor serum proteins, corresponding with its lower membrane flux. Flux sharply decreased with an increasing concentration factor (CF) up to four, and thereafter remained almost unchanged. Compared to the decrease (88%) of flux, the transmission of major and minor serum proteins was decreased by 4%-15% from CF = one to CF = eight. With increasing processing stages, the flux gradually increased, and the recovery yield of both major and minor proteins in the permeate gradually decreased and reached a considerably low value at stage five. After four stages of MF with 100 nm pore diameter and a CF of four for each stage, the cumulative recovery yield of major serum proteins, IgG, IgA, IgM, LF, LPO, and XO reached 95.7%, 90.8%, 68.5%, 34.1%, 15.3%, 39.1% and 81.2% respectively.