Review
Cold plasma processing of milk and dairy products

https://doi.org/10.1016/j.tifs.2018.02.008Get rights and content

Highlights

  • Cold plasma as non-thermal technology is reviewed.

  • Diversity of systems, operational parameters and mechanisms are revised.

  • Effects of cold plasma on the quality and safety of dairy foods are reported.

Abstract

Background

Thermal pasteurization and sterilization are predominantly used in the dairy industry due to their efficacy in improving the product safety and shelf life. However, heat treatment can cause undesirable protein denaturation, non-enzymatic browning, loss of vitamins and volatile flavor compounds, freezing point depression, and flavour changes. Cold plasma is a non-thermal technology that has gained attention in recent years as a potential alternative method for chemical and thermal disinfection in foods using ambient or moderate temperatures and short treatment times.

Scope and approach

This review aims to describe the fundamentals, parameters, and technology on cold plasma, discussing the critical processing factors involved in this technology. Also, it describes the mechanisms of microbial inactivation and provides an overview of the effects of non-thermal plasma on the quality of dairy products, considering a physicochemical, sensory and microbiology perspective.

Key findings and conclusions

Cold plasma uses less aggressive mechanisms of action to the milk matrix when compared to the techniques currently used, and has shown an excellent performance on the elimination of pathogenic and spoilage microorganisms besides maintaining, in many cases, the nutritional, functional, and sensory characteristics of the product.

Introduction

Milk contains carbohydrates (lactose), fatty acids, high-quality protein, and various micronutrients, such as vitamins, minerals, and trace elements (European Milk Forum, 2017). According to the Food and Agriculture Organization (FAO), global per capita dairy consumption will increase 12.5% by 2025 (IDFA, 2016, pp. 1–6). In addition to the nutritional value, dairy products are considered health-promoting foods for the prevention or amelioration of osteoporosis, sarcopenia, metabolic syndrome, cardiovascular disease, cognitive decline, and digestive disorders (Hess, Jonnalagadda, & Slavin, 2016).

To prevent pathogenic bacteria, toxic substances, and off flavours in dairy products, fresh whole milk should be submitted to thermal processing before commercialization (Amaral et al., 2017). This step eliminates pathogenic microorganisms, and provides low counts of spoilage microorganisms, acceptable aroma and flavour and adequate physicochemical characteristics (Barba, Koubaa, Prado-Silva, Orlien, & Sant’Ana, 2017).

Consumers have searched for dairy products that are safe, nutritious, practical, minimally processed, environmentally friendly, healthy, appetizing, economical, and personalized but that also have a long shelf life (Mir, Shah, & Mir, 2016). Thermal processing improves the microbiological safety (Misra et al., 2017), but they extensively damage sensory, nutritional, and physicochemical properties (Barba et al., 2012, Mosqueda-Melgar et al., 2008), resulting in non-enzymatic browning, loss of vitamins and volatile flavour compounds, freezing point depression, and flavour changes in dairy products (Gurol, Ekinci, Aslan, & Korachi, 2012). In addition, they require high-energy consumption, which compromises with the final product value to guarantee the profitability of the industry (Barba et al., 2017).

Non-thermal processes can meet microbial food safety standards and improve the physical, nutritional and sensory characteristics of the products, preserving unstable bioactive compounds and modulating enzyme activity (Amaral et al., 2017). These methods include ohmic heating (Cappato et al., 2017), high hydrostatic pressure (Barba et al., 2012), pulsed electric field (Cruz et al., 2010), pulsed-light technology (Abida, Rayees, & Masoodi, 2014), ultrasound (Ashokkumar et al., 2010), supercritical carbon dioxide technology (Amaral et al., 2017), and irradiation (Odueke, Farag, Baines, & Chadd, 2016). However, scientific knowledge on the utilization of cold plasma as an emerging non-thermal technology for dairy products is scattered and none of the previous studies reviewed these aspects.

This review aims to describe the fundamentals, process parameters, and technology involved in cold plasma. It also describes the mechanisms of microbial inactivation and provides an overview of the effects of non-thermal plasma on the quality of dairy products, considering the physicochemical, sensory and microbial characteristics.

Section snippets

Fundamentals

Plasma is known as the fourth state of matter, and is an electrically energized matter in a gaseous state composed of charged particles, free radicals, and some radiation. It is obtained by an electrical discharge (Fernández & Thompson, 2012), in which a partially or completely ionized gas is formed that is composed of photons (essentially), ions, free electrons, and atoms in their fundamental or excited states. These species are designated light species (photons and electrons) or “heavy”

Microbiological aspects

Infectious diseases caused by the ingestion of pathogenic bacteria in contaminated milk are still a major health concern, especially for children. The most predominant infectious diseases caused by contaminated milk include campylobacteriosis, salmonellosis, yersiniosis, listeriosis, tuberculosis, brucellosis, staphylococcal enterotoxin poisoning, streptococcal infections and Escherichia coli 0157: H7 (Gurol et al., 2012, Ranadheera et al., 2017).

Although many studies have focused on the

Advantages, disadvantages, and limitations of cold plasma

Cold plasma is a newcomer to the food technology field. Like all techniques, it presents advantages and disadvantages. Table 4 shows the main advantages, disadvantages, and limitations of cold plasma treatment for food preservation.

The advantages of plasma processes include high microbial inactivation efficiency at low temperatures; low impact on the internal product matrix; on-demand production of the acting agent; precise generation of plasmas suitable for the intended use; and the absence of

Perspectives

Cold plasma technology can be utilized as a novel antimicrobial intervention for the inactivation of pathogens and improvement of dairy product safety. The technique is classified as environmentally safe, fits all ecological standards, has high microbial inactivation efficiency at low temperatures, and a low impact on the product matrix. It creates on-demand production of the acting agent and precise generation of plasma suitable for the intended use, and importantly, requires no water or

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