Ohmic heating in dairy processing: Relevant aspects for safety and quality

doi:10.1016/j.tifs.2017.01.010

Trends in Food Science & Technology

Volume 62, April 2017, Pages 104-112

https://doi.org/10.1016/j.tifs.2017.01.010 Get rights and content

Highlights

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Relevance of Ohmic heating for dairy processing is presented.
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Safety and quality of dairy foods using ohmic heating are described.
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Electroporaction effect and fouling is also explained.

Abstract

Background

Ohmic Heating (OH) technology is a heating process wherein electric current is passed through the food acting as an electrical resistor, converting the electrical energy into thermal energy. This fact results in shorter heating times compared to the conventional process, which promotes some advantages, such as, the maintenance highest levels of nutritional compounds, the uniformness in heating system and the reduction in fouling formation. The success of the process depends on the parameters related to the food and process itself, such as, frequency, electrical field strength, residence time and electrical conductivity.

Scope and approach

This review aims to describe the main factors and parameters involved in this technology, highlighting its effects on quality, microbial inactivation, and fouling during processing of dairy products.

Key findings and conclusions

Due to the more rapid and uniform heating, the OH technology has advantages over the conventional processes, such as maintenance of nutritional compounds and reduction of fouling, which are important factors in the dairy products processing. In addition, there are additional effects of electroporation on microbial cells, which promotes further microorganisms inactivation which are problematic for safety of dairy foods.

Introduction

The conventional thermal processing (HTST pasteurization and UHT sterilization) stands out as the most used technique to ensure microbiological safety of processed foods (Goullieux & Pain, 2005). However, due to the heat transfer mechanisms involved (conduction and convection), such processes have certain disadvantages, including overheating, loss of nutritional compounds, and sensory changes; moreover, the combustion of fossil fuels to generate heat causes economic and energy losses (Sakr & Liu, 2014). These drawbacks can be avoided with emerging technologies, such Ohmic Heating (OH) (Goullieux and Pain, 2005, Kaur and Singh, 2016, Sudhir, 2004, Varghese et al., 2014).

Despite being considered a new thermal technology, the concept of OH applied to foods is known since the 19th century, being first applied to milk pasteurization (De Alwis & Fryer, 1990). The process fell into disuse because of the high cost of the electricity, lack of suitable inert materials to make the electrodes and difficulties to control the process parameters (Allali et al., 2008, Fryer et al., 1993). However, over the years this technology has been studied by many scientists, and lots of improvements were made. Nowadays, it is applied in different fields, including blanching, evaporation, dehydration, fermentation, extraction, thawing foods, sterilization and pasteurization (Duygu and Ümit, 2015, Guida et al., 2013, Stancl and Zitny, 2010, Varghese et al., 2014).

OH is defined as a process wherein electric current is passed through materials with the primary purpose of heating them through the conversion of electrical into thermal energy, resulting generally in a rapid and uniform temperature increase within the food (Leizerson and Shimoni, 2005, Mercali et al., 2014). This phenomenon is the greatest advantage of this technique as it allows the development of faster and more effective processes, ensuring greater nutrient retention capacity and sensory attributes (Guida et al., 2013, Pereira et al., 2008, Pereira et al., 2015).

The knowledge of the mechanisms during OH is an important factor for the correct application of this technology for thermal processing (Pellegrino, De Noni, & Resmini, 1995). Although the main mechanism involved in the OH microbial inactivation is based on thermal effects, several studies reported the existence of an additional non-thermal effect, which consists of pore formation in the microorganism cell membrane (Jaeger et al., 2016). This phenomenon, known as electroporation, changes the cell permeability and can disrupt the membrane, leading to cell death (Loghavi et al., 2009, Park and Kang, 2013, USA-FDA, 2000, Yoon et al., 2002). However, electroporation is still not fully understood and more research is necessary to elucidate it.

Few studies have reported the effect of OH on the intrinsic quality parameters and microbiological stability in dairy products. Jermann, Kuchma, Margas, Leadley, & Ros-Polski (2015) have reported the trends of using emerging technologies for food processing, involving researchers and CEOs (Chief Executive Officer) of large companies, and found that the OH is a promising technology for the dairy sector, with great commercial interest in the next five years. In this context, this paper aims to describe the main factors and parameters necessary for the application of this technology during processing of dairy products, considering its effects on products quality, microbial inactivation and fouling.

Section snippets

Fundamentals and process parameters

The basic principle of OH is given by the passage of alternating electric current (AC) via two electrodes inserted in the food, as shown in Fig. 1. The electrical energy conducted through the food is converted into thermal energy due to the electrical resistance of the food (phenomenon known as Joule effect), leading to a volumetric and instantaneous heating. Power generation is directly proportional to the square of the electric field applied (E, V/cm) and the electrical conductivity of the

General aspects

As with conventional process, non-uniformity heating could be observed in products, although the heating is generated directly in the product through the conversion of electric energy into thermal (Goullieux & Pain, 2005). This fact results in regions of high temperatures (hot spots) and low temperatures (cold spots), which has been the Knowledge of the distribution of the temperature profile as a critical point for food quality and food safety (Jaeger et al., 2016). From the safety aspects, it

Ohmic heating and intrinsic quality parameters in dairy processing

The physicochemical and sensory characteristics of dairy products are important for their quality and preservation assessment, being influenced by different factors, such as the type and the intensity of the treatment applied (Esmerino et al., 2015, Gaze et al., 2015, Morais et al., 2014). In order to evaluate the benefits of OH and to define the optimum process parameters, it is essential to evaluate the influence of this technique on quality and sensory factors of the product. The same

Ohmic heating and fouling in dairy processing

Fouling is a major problem in thermal processes of milk products, especially in those involving indirect heating, where the heat transfer is carried out from the fluid (generally steam or heated pressurized water) to the product, separated by the equipment wall (Bansal & Chen, 2006a). Two basic mechanisms are responsible for fouling in dairy processing plants: type A fouling, derived from the aggregates formed by the presence of whey protein (mostly β-Lg and α-La) at 75 and 110 °C; and type B

Ohmic heating and allergenicity of dairy foods

Food allergy is any adverse reaction involving food or to a specific component capable of sensitizing the immune system, where after repeated contact, it can trigger a severe allergic reaction (EAACI, 2014). Due to the presence of various types of allergic reactions, the diagnosis can be difficult to identify, while in some cases such as “immediate hypersensitivity” allergies, which are rapidly detected due to reactions that occurs right after the food intake (Huang, Hsu, Yang, & Wang, 2014).

Advantages and disadvantages of ohmic heating

The application of OH has several advantages over conventional processing, due to the possibility to promote fast and even heating in the product. Due to the rapid heating rate in the processing caused by internal energy generation, which make possible to reduce the impact of the treatment on food quality (C value) (Jaeger et al., 2016). Moreover, this treatment presented the same effectiveness to reduce microbial counts (same Fo value). Thus, OH process results in a better product quality with

Perspectives

The growing global demand for dairy products has driven the major industries and research centers to develop new technologies to minimize the deleterious effects of processing, ensuring the microbiological safety and increasing products shelf life. However, the cost and difficulties to control the process parameters, as well as lack of appropriate legislation, are the main issues for the implementation of these technologies. Therefore, several aspects need to be investigated in OH processing: