Microbiological and enzymatic activity of bovine whole milk treated by pulsed electric fields

Pulsed Electric Fields Effects on Proteins: Extraction, Structural Modification, and Enhancing Enzymatic Activity

Pulsed electric field (PEF) is an innovative physical method for food processing characterized by low energy consumption and short processing time. This technology represents a sustainable procedure to extend food shelf-life, enhance mass transfer, or modify food structure. The main mechanism of action of PEF for food processing is the increment of the permeability of the cell membranes by electroporation. However, it has also been shown that PEF may modify the technological and functional properties of proteins. Generating a high-intensity electric field necessitates the flow of an electric current that may have side effects such as electrochemical reactions and temperature increments due to the Joule effect that may affect food components such as proteins. This article presents a critical review of the knowledge on the extraction of proteins assisted by PEF and the impact of these treatments on protein composition, structure, and functionality. The required research for understanding what happens to a protein when it is under the action of a high-intensity electric field and to know if the mechanism of action of PEF on proteins is different from thermal or electrochemical effects is underlying.

Impact of pulsed electric field intensity on the cream separation efficiency from bovine milk and physico-chemical properties of the cream

Low-temperature (9-12 °C) pulsed electric field (PEF) was investigated in milk before cream separation at different intensities (9-27 kV/cm, 66 μs, 16-28 kJ/L) regarding its potential to render processing more sustainable, retain a high physico-chemical quality, enhance functional properties, and gently modify the structure of the milk fat globule membrane (MFGM). Cream volume per L milk were most efficiently increased by 31 % at the lowest PEF intensity in comparison to untreated milk and cream (P < 0.05). Untreated and PEF-treated milk and obtained cream were assessed with compositional (fat, protein, casein, lactose, and total solids content) and particle size distribution analyses, showing no significant differences (P ≥ 0.05) and, thus, indicating retention of 'native-like' product quality. Overrun and stability of cream, whipped for 20 and 60 s at 15000 rpm using a high-shear mixer, were improved most notably by the lowest and the highest PEF intensities, achieving up to 69 % enlarged overrun and up to 22 % higher stability, respectively (P < 0.05), than in untreated whipped cream. Protein component analyses for milk and cream were carried out by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Noticeable differences between untreated and PEF-treated milk were not observed, but the SDS-PAGE results for cream showed noticeably different bands for some of the protein components, indicating structural changes in MFGM-, whey-, and phospho-proteins due to PEF and/or separator processing effects. More intense bands of xanthine oxidase, xanthine dehydrogenase, butyrophilin, bovine serum albumine, adipophilin (ADPH), and glycoproteins PAS6/7 were observed specifically at 21 kV/cm. Gentle electroporation of both MFGM layers by PEF was determined based on the changes in MFGM monolayer components, such as ADPH and PAS 6/7, exhibiting intensified bands. PEF intensity-dependent impact on the structure of MFGM and casein, leading to a reconfiguration of the cream matrix due to different structuring interactions among proteins, among milk fat globules, and between fat and protein components, was suggested. Overall, low-temperature PEF applied at different intensities showed great potential for gentle, efficient, and functional properties-tailored dairy processing and may also enable effective extraction of highly bioactive ingredients from dairy sources.

Implications of Pulsed Electric Field Pre-Treatment on Goat Milk Pasteurization

Goat milk is an interesting product from a nutritional and health standpoint, although its physico-chemical composition presents some technological challenges, mainly for being less stable than cow's milk at high temperatures. As pasteurization and ultra-high temperature processing are universally employed to ensure milk quality and safety, non-thermal methods, such as pulsed electric fields (PEFs), reduce the microbial load and eliminate pathogens, representing an interesting alternative for processing this product. This study demonstrates how the combined use of a PEF with short thermal processing and moderate temperature can be effective and energy-efficient in goat milk processing. A combination of thermal treatment at 63 °C after a low-intensity PEF (50 µs pulses, 3 Hz, and 10 kV·cm-1) caused the same reduction effect on the population of Listeria monocytogenes (goat's raw milk artificially spiked), as compared to a thermal treatment at 72 °C without a PEF. However, z values are significantly higher when PEF is used as a pre-treatment, suggesting that it may induce heat resistance in the survival population of L. monocytogenes. The sensitivity of L. monocytogenes to high temperatures is less pronounced in goat's milk than cow's milk, with a more pronounced impact of a PEF on lethality when combined with lower temperatures in goat's milk. The effect of a PEF on Escherichia coli viability was even more pronounced. It was also observed that thermal treatment energy needs with a PEF as a pre-treatment can be reduced by at least 50% of the total energy requirements.

The Impact of Pulsed Electric Fields on Milk's Macro- and Micronutrient Profile: A Comprehensive Review

Consumers around the world are attracted to products with beneficial effects on health. The stability, functionality, and integrity of milk constituents are crucial determinants of product quality in the dairy industry. Milk contains macronutrients and micronutrients that aid in a wide range of physiological functions in the human body. Deficiencies of these two types of nutrients can confine growth in children and increase the risk of several diseases in adults. The influence of pulsed electric fields (PEF) on milk has been extensively reviewed, mostly concentrating on the inactivation of microbes and enzymes for preservation purposes. Therefore, the information on the variations of milk macro- and micronutrients treated by PEF has yet to be elucidated and it is imperative as it may affect the functionality, stability, and integrity of the milk and dairy products. In this review, we describe in detail the introduction, types, and components of PEF, the inactivation mechanism of biological cells by PEF, as well as the effects of PEF on macro- and micronutrients in milk. In addition, we also cover the limitations that hinder the commercialization and integration of PEF in the food industry and the future outlook for PEF. The present review consolidates the latest research findings investigating the impact of PEF on the nutritional composition of milk. The assimilation of this valuable information aims to empower both industry professionals and consumers, facilitating a thorough understanding and meticulous assessment of the prospective adoption of PEF as an alternative technique for milk pasteurization.

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.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Research trends and emerging physical processing technologies in mitigation of pesticide residues on various food products

The application of pesticides enhances food production vastly, and it cannot be prevented; longer fresh produce is contaminated with health-threatening pesticides even though traditional processing methods can remove these pesticides from food surfaces to a certain extent; novel emerging technologies such as cold plasma, ultrasound, electrolyzed water, and pulsed electric field could more effectively dissipate the pesticide content in food without the release of toxic residual on the food surface. The present review focuses on applying emerging technologies to degrade pesticide residues in great utility in the food processing industries. This review also discusses the pesticide removal efficacy and its mechanism involved in these technologies. The oxidation principle in cold plasma is recently gaining more importance for the degradation of pesticide residue in the food processing industries. Analysis of the emerging physical processing methods indicated greater efficacy in eradicating pesticide residues during agriculture processing. Even though the technologies such as EO (99% reduction in dimethoate), ultrasound (98.96% for chlorpyrifos), and irradiation (99.8% for pesticide in aqueous solution) can achieve promising results in pesticide degradation level, the rate and inactivation highly depend on the type of equipment and processing parameters involved in different techniques, surface characteristics of produce, treatment conditions, and nature of the pesticide. Therefore, to effectively remove these health-threatening pesticides from food surfaces, it is necessary to know the process parameters and efficacy of the applied technology on various pesticides.

Current insights into non-thermal preservation technologies alternative to conventional high-temperature short-time pasteurization of drinking milk

Milk is an important nutritional food source characterized by a perishable nature and conventionally thermally treated to guarantee its safety. In recent years, an increasing focus on competing non-thermal food processing technologies has been driven mainly by consumers' expectations for minimally processed products. Due to the heat sensitivity of milk, much research interest has been addressed to mild non-thermal pasteurization processing to keep safety, 'fresh-like' taste and to maintain the organoleptic qualities of raw milk. This review provides an overview of the current literature on non-thermal treatments as standalone alternative technologies to high-temperature short-time (HTST) pasteurization of drinking milk. Results of lab-scale experimentations suggest the feasibility of most emerging non-thermal processing technologies, including high hydrostatic pressure, pulsed electric field, cold plasma, cavitation and light-based technologies, as alternative to thermal treatment of drinking milk with premium in shelf life duration. Nevertheless, a series of regulatory, technological and economical hurdles hinder the industrial scaling-up for most of these substitutes. To date, only high hydrostatic pressure treatments are applied as alone alternative to HTSH pasteurization for processing of "cold pasteurized" drinking milk. Milk submitted to HTST treatment combined to ultraviolet light is currently accepted in EU countries as novel food.

The application of PEF technology in food processing and human nutrition

During the last decades, many novel techniques of food processing have been developed in response to growing demand for safe and high quality food products. Nowadays, consumers have high expectations regarding the sensory quality, functionality and nutritional value of products. They also attach great importance to the use of environmentally-friendly technologies of food production. The aim of this review is to summarize the applications of PEF in food technology and, potentially, in production of functional food. The examples of process parameters and obtained effects for each application have been presented.

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

Milk oxidases are an integral part of milk immune system, and good indicators for milk thermal history. Current assay methods for milk oxidases are either insensitive, tedious or not cost-effective. In this study, a high-throughput fluorescence assay method for determination of xanthine oxidase (XO) and polyamine oxidase (PAO) activities in milk samples was developed. The hydrogen peroxide generated by XO catalysed oxidation of hypoxanthine, and PAO catalysed oxidation of spermine, was coupled to horseradish peroxidase conversion of Amplex® Red (1-(3,7-dihydroxyphenoxazin-10-yl)ethanone) to the fluorescent product resorufin. The assay was highly sensitive, with limits of detection of activity in milk being 3 × 10^-7 and 7 × 10^-7 U/mL for XO and PAO, respectively. Intra-run and inter-run results showed good assay repeatability and reproducibility. The assay was successfully applied to survey the XO and PAO activities in human, bovine, goat and camel milk samples, and it can be readily adapted for measurements of other oxidase activities.

Strategies to Extend Bread and GF Bread Shelf-Life: From Sourdough to Antimicrobial Active Packaging and Nanotechnology

Bread is a staple food worldwide. It commonly undergoes physico-chemical and microbiological changes which impair its quality and shelf-life. Staling determines organoleptic impairment, whereas microbiological spoilage causes visible mould growth and invisible production of mycotoxins. To tackle this economic and safety issue, the bakery industry has been working to identify treatments which allow bread safety and extended shelf-life. Physical methods and chemical preservatives have long been used. However, new frontiers have been recently explored. Sourdough turned out an ancient but novel technology to preserve standard and gluten-free bread. Promising results have also been obtained by application of alternative bio-preservation techniques, including antifungal peptides and plant extracts. Active packaging, with absorbing and/or releasing compounds effective against bread staling and/or with antimicrobials preventing growth of undesirable microorganisms, showed up an emerging area of food technology which can confer many preservation benefits. Nanotechnologies are also opening up a whole universe of new possibilities for the food industry and the consumers. This work thus aims to provide an overview of opportunities and challenges that traditional and innovative anti-staling and anti-spoilage methods can offer to extend bread shelf-life and to provide a basis for driving further research on nanotechnology applications into the bakery industry.