Effect of thermal and non‐thermal pasteurisation on the microbial inactivation and phenolic degradation in fruit juice: a mini‐review

Fruit juice has been traditionally preserved by thermal pasteurisation. However, the applied heat can cause detrimental effects on health‐promoting components such as phenolic compounds. Several non‐thermal technologies such as membrane filtration, pulsed electric field (PEF) and ultraviolet (UV) exposure are promising methods developed for liquid food preservation. In particular, the combination of UV and PEF has proven to be more effective for microbial inactivation and maintaining nutritional quality of fruit juice compared with individual applications. © 2012 Society of Chemical Industry     

Inactivation of Escherichia coli K-12 and Listeria innocua in milk using radio frequency (RF) heating

Using a 2 kW, 27.12 MHz RF heater, studies were conducted to evaluate the effectiveness of RF heating in inactivating surrogates of both Listeria and Escherichia coli cells in milk under continuous flow conditions. Depending on product residence time and RF power level, RF heating was found to be capable of inactivating both Listeria and E. coli in milk, with E. coli being the more heat sensitive of the two. For a total residence time of 55.5 s (i.e., 29.5 and 26 s in the applicator and holding tube, respectively), up to 5- and 7-log reductions were found for heating Listeria and E. coli, respectively at 1200 W, and an applicator tube exit temperature of approximately 65 °C. This study demonstrates that RF heating could be used to effectively pasteurize milk by manipulating incident power levels and flow rate. While these studies have been conducted under mild fluid flow (laminar) conditions, further studies are necessary to justify its industrial application using more realistic flow conditions.

Industrial relevance

Radio frequency (RF) heating can provide rapid heating. Compared to the microwave, RF has the added advantage of higher penetration depth. These advantages could be harnessed for pasteurizing large volume liquid foods and, most importantly, RF heating could potentially replace traditional heat exchangers that are easily fouled by products such as milk. This study demonstrates the effectiveness of using RF heating under mild flow conditions to inactivate microorganisms that could contaminate milk.     

Recent developments in pasteurising seeds and their products using radio frequency heating: a review

Food-borne or plant diseases mainly rely on the spread of seeds with pathogens. It is vital to eliminate food/seed-borne pathogens of seeds and their products before commercial import/export or circulation. Radio frequency (RF) heating is identified as an effective method with lack of chemical residues, rapid or volumetric heating and large penetration depth, and also validated as a potential physical method to eliminate pests or pathogens in agricultural products or foods. Although, many reviews have summarised the applications of RF treatment during the process of foods, little comprehensive review has been focused on seeds and their products pasteurised by the RF energy. Comprehensive summary about principles and main applications of RF energy for pasteurising seeds and their products was reported in this review. This review also introduced some typical RF heating systems, thermal death kinetics of pathogens, influences of RF heating on germination rate of seeds and some ways for improving uniformity of RF heating. Furthermore, this review recommended the future research directions about treatment of seeds and their products using RF energy, especially for seed industry to control the pathogens in seeds without reducing their quality after RF treatments.     

Effect of dispersion and ion concentration on radio frequency heating

Radio frequency (RF) heating has been applied to process foods due to its unique advantages like volumetric heating. To investigate the interaction between dispersed liquid food and electromagnetic field, four dispersion structures, formed by polypropylene pellets dispersed in the samples, and six solutions with different ion concentrations were analyzed. The Results showed that 4 mm dispersion structure and 0.01 mol/L ion concentration involved in the highest heating rate and made the heating rate increase from 1.23 °C/min to 5.53 °C/min. For materials with different ion concentrations, the maximum heating rate corresponded to the dispersion structure of different sizes. But the dispersion structure would reduce the heating uniformity of the horizontal surface of materials. It suggested that dispersion structure and an proper ion concentration could change the material into a dispersed status, further improve RF heating rate, and ensure the efficiency of sterilization as well as retain the nutrition of foodstuffs.     

Thermal behavior of CMC solutions under simulation of radio frequency pasteurization

Pasteurization and enzyme-inactivation are an economical and convenient way to provide safety and shelf-life stability. However, long heating time and non-uniform temperature distribution are the main issues of traditional thermal processing for enzyme-inactivation. Because of the volumetric heating and high heating rate, radio frequency (RF) treatment is considered as one of the most promising physical enzyme-inactivating methods. A 6 kW, 27.12 MHz RF heating system was applied to explore the effect of cylindrical container dimension and solution concentration on the thermal behavior of high-viscosity liquid food. Carboxymethylcellulose (CMC) solution as a non-Newtonian fluid was selected as a model liquid food in this study. The target temperature for enzyme inactivation was 70 °C. The experimental results showed that the electrode gap, container length, and container diameter affected the heating rate and uniformity of the liquid food. Furthermore, when the concentration of CMC solution increased from 0.5% to 2.0%, the heating rate of the solution firstly increased and then decreased, while the heating uniformity index of the solution increased from 0.008 ± 0.001 to 0.056 ± 0.002. The simulation results showed that the higher electric field strength led to a higher heating rate, temperature, and velocity of natural convection of the solution at the ends of the container. Then, the recirculation zones from the ends to the center of the container were formed, which was diminished with the increasing concentration solution, resulting in the increased maximum temperature difference of solution. The results of this research may provide useful data for subsequent continuous flow studies and information on potential RF enzyme-inactivation in high-viscosity liquid foods.     

On-line local thermal pulse analysis sensor to monitor fouling and cleaning: Application to dairy product pasteurisation with an ohmic cell jet heater

In the process industry, fouling is considered as a complex (sometimes partially known and identified) phenomenon. In this paper, a fouling sensor (FS) based on local differential thermal analysis is scrutinized and we report the comparison of two operating modes, steady (STR) and periodic (PTR) thermal regimes. Moreover, the development of alternating technologies like direct Joule effect (ohmic) heating to pasteurise and sterilise liquid food products in a continuous process is of great scientific and industrial interest. Heat treatment by direct Joule effect exhibits numerous advantages because rapid heating kinetics or homogeneous heat treatment is required. However, fouling of electrode surfaces in this kind of apparatus is much more problematic than in conventional heat exchangers. In the present study, a new continuous ohmic heating apparatus (Emmepiemme®, Piacenza, Italy) in which an alternating electrical current is applied directly to a jet falling between two stainless steel electrodes is investigated during pasteurisation of a dairy product. Conventional fouling measurements (pressure drop, heat transfer or electrical parameters) cannot be used in such a heater. Fouling and cleaning phases are monitored with fouling sensor and fouling quantified.     

Computer simulation for improving radio frequency (RF) heating uniformity of food products: A review

Radio frequency (RF) heating has great potential for achieving rapid and volumetric heating in foods, providing safe and high-quality food products due to deep penetration depth, moisture self-balance effects, and leaving no chemical residues. However, the nonuniform heating problem (usually resulting in hot and cold spots in the heated product) needs to be resolved. The inhomogeneous temperature distribution not only affects the quality of the food but also raises the issue of food safety when the microorganisms or insects may not be controlled in the cold spots. The mathematical modeling for RF heating processes has been extensively studied in a wide variety of agricultural products recently. This paper presents a comprehensive review of recent progresses in computer simulation for RF heating uniformity improvement and the offered solutions to reduce the heating nonuniformity. It provides a brief introduction on the basic principle of RF heating technology, analyzes the applications of numerical simulation, and discusses the factors influencing the RF heating uniformity and the possible methods to improve heating uniformity. Mathematical modeling improves the understanding of RF heating of food and is essential to optimize the RF treatment protocol for pasteurization and disinfestation applications. Recommendations for future research have been proposed to further improve the accuracy of numerical models, by covering both heat and mass transfers in the model, validating these models with sample movement and mixing, and identifying the important model parameters by sensitivity analysis.     

Radio frequency heating of foods: principles, applications and related properties--a review

Radio frequency (RF) heating is a promising technology for food applications because of the associated rapid and uniform heat distribution, large penetration depth and lower energy consumption. Radio frequency heating has been successfully applied for drying, baking and thawing of frozen meat and in meat processing. However, its use in continuous pasteurization and sterilization of foods is rather limited. During RF heating, heat is generated within the product due to molecular friction resulting from oscillating molecules and ions caused by the applied alternating electric field. RF heating is influenced principally by the dielectric properties of the product when other conditions are kept constant. This review deals with the current status of RF heating applications in food processing, as well as product and system specific factors that influence the RF heating. It is evident that frequency level, temperature and properties of food, such as viscosity, water content and chemical composition affect the dielectric properties and thus the RF heating of foods. Therefore, these parameters should be taken into account when designing a radio frequency heating system for foods.     

Dielectric properties of foods: Reported data in the 21st Century and their potential applications

Dielectric properties (DP) are the main parameters that provide information about how materials interact with electromagnetic energy during dielectric heating. These properties have gained great importance and applications for foods that are subjected to novel microwave (MW) or radio frequency (RF) heating treatments. The knowledge of the DP of a determined foodstuff is fundamental in order to understand and model the response of the material to the electromagnetic field, at certain desired frequencies and temperatures. Through the last years, many potential applications of electromagnetic heating for foods have emerged and been published in the literature; however, new uses or research in food products to be treated with MW or RF may be limited due to lack of DP data. This review provides an overall introduction and definition of the DP, factors that affect them, methods for their determination, as it also includes reported DP data for foods after the year 2000. DP values were grouped depending on the nature of foods, such as: 1) fruits and vegetables, 2) flour, dough and bread, 3) nuts, 4) coffee grains, 5) meats, fish and seafood, 6) dairy products, 7) eggs and egg products and 8) liquid fluids. We consider that this paper is a useful reference that contains current and valuable information on the DP of foods, which can be available and used for further developments employing MW or RF heating food technologies.     

Review of Dense Phase CO2 Technology: Microbial and Enzyme Inactivation, and Effects on Food Quality

ABSTRACT Dense phase CO₂ (DPCD) is a non‐thermal technology that can inactivate certain microorganisms and enzymes at temperatures low enough to avoid the thermal effects of traditional pasteurization. This technology has been investigated over the past 50 y, particularly in the past 2 decades, and its effects on vegetative cells and spores of various microorganisms including pathogens, spoilage bacteria, yeasts, and molds, and various enzymes of importance to foods have been demonstrated. Many liquid foods retained freshlike sensory, nutritional, and physical properties after DPCD treatment. This article is a review of mechanisms of microbial reduction, enzyme inactivation, DPCD treatment systems, both experimental and commercial, and examples of applications with effects on quality attributes.     

Advances in Ultraviolet Light Technology for Non-thermal Processing of Liquid Foods

A negative, public reaction is growing over the addition of chemical preservatives to liquid foods and beverages to extend their shelf life and to protect against foodborne pathogens. As a physical method, ultraviolet light (UV) irradiation has a positive consumer image and is of interest to the food industry as a low cost non-thermal method of preservation. Recent advances in the science and engineering of UV light irradiation have demonstrated that this technology holds considerable promise as an alternative to traditional thermal pasteurization for liquid foods and ingredients, fresh juices, soft drinks, and beverages. However, its use for treating foods is still limited due to low UV transmittance of liquid foods. The goal of this review is to provide a summary of the basic principles of UV light generation and propagation with emphasis on its applications for liquid food processing. The review includes information on critical product and process factors that affect UV light inactivation and consequently the delivery of a required scheduled process in liquids foods; measuring and modeling of UV inactivation, and the important effects of UV light on overall quality and nutritional value of liquid foods. The commercially available UV light sources and UV reactor designs that were used for liquid foods treatment are reviewed. The research priorities and challenges that need to be addressed for the successful development of UV technology for liquid foods treatment are discussed.     

Radio frequency pasteurization and disinfestation techniques applied on low-moisture foods

Abstract

The shelf life of foods is usually limited due to the frequent contamination by pests and microorganisms. Although low risk of pathogen contamination and no growth potential compared to those in high water activity animal- or vegetal-derived products, the low-moisture food has still significantly contributed to the total number of foodborne infections and outbreaks. Radio frequency (RF) treatments can be classified as a dielectric heating, which is a promising technology for achieving effective food pasteurization and disinfestations because of the associated rapid and volumetric heating with large penetration depth. The RF technique could be applied at low-moisture food as both the dipole dispersion and ionic conductivity may play effective roles. It can selectively heat and kill the microorganisms/pests without damaging the agricultural product because of the large difference of dielectric loss factors between target microorganisms/pests and host foods. In this article, the low-moisture foods sterilized and disinfested by RF energy are reviewed through basic theories, dielectric properties, heating effect, and uniformity. The potential research directions for further RF heating applications are finally recommended in low-moisture foods.     

Critical Issues Pertaining to Application of Pulsed Electric Fields in Microbial Control and Quality of Processed Fruit Juices

Pasteurisation of fruit juices is normally carried out by thermal means. Heat treatment is an efficient technology for pasteurisation, but may also cause impairment of nutritive and sensory attributes. High-voltage pulsed electric field (PEF) treatment is a promising non-thermal processing method for pasteurisation of liquid foods. Sensory quality of fruit juices is important for consumers. PEF lends itself to be employed as an alternative to produce fruit juices of high quality and safe for consumption, and yet its practical application has been really limited. This paper reviews research carried out recently about the potential use of PEF to different fruit juices, aimed at employing the technology at industrial scale in order to search for wider commercialisation.     

Radio-frequency heating of heterogeneous food - Meat lasagna

This research studied feasibility of using radio-frequency (RF) energy to thermally process highly heterogeneous foods in large containers as shelf-stable products. Meat lasagna was selected as the food for the study. Dielectric properties of beef, mozzarella cheese, noodles, and sauce were determined between 1 and 1800 MHz and from 20 to 121 °C. A 6-kW 27-MHz RF system was used to sterilize packaged meat lasagna in large polymeric containers (295 × 253 × 42 mm) during which the temperature of different components were monitored. Computer simulations were also conducted to evaluate the influence of the dielectric properties of each food component on the electric field distribution and heating pattern during RF heating. The measurements indicated small temperature differences in beef meatballs, mozzarella cheese and sauce when they were properly distributed between layers of noodles. Simulation results suggested that in spite of large differences in electric field intensities in different food components, adequate heat transfer reduced differential heating. Thus, RF heating can be used to process pre-packaged heterogeneous foods and retain product quality.     

Enhancement of diffusion through foods using alternating electric fields

This work describes a procedure and equipment to study molecular diffusion in model foods under conditions of elevated temperatures and in the presence of alternating electrical fields by the uptake of indicator dyes. A series of experimental rigs have been built which allow diffusion to be studied over a range of temperatures. A technique, based on image analysis and optical microscopy, has been developed to visualise diffusion into solids on a micron scale. Diffusion between potato, alginate and agar gels and a series of dyes (rhodamine, methylene blue and fluorescein) has been quantified using this equipment; the development and accuracy of standard curves is discussed. The enhancement of diffusion is proven for rhodamine infusion into potato at 100 °C, where electric fields enhance infusion by ca. 70%. Enhancement of diffusion is also shown for diffusion of the three dyes into alginate–potato mix and agar gels.Industrial relevanceA range of effects have been shown to occur when electric fields are applied to foods. Ohmic (electrical resistance) heating has been used commercially as a way of rapidly providing volumetric heating for sterilisation or pasteurisation of foods. This paper demonstrates that similar electric field strengths significantly enhance diffusion processes between real and model foods and the surrounding liquid.     

Sterilization of Foodstuffs Using Radio Frequency Heating

ABSTRACT: A study was conducted with a pilot-scale sterilization system based on 27-MHz radio frequency (RF) energy to investigate the effectiveness in shortening process time and in improving quality for foods sealed in 6-pound military-ration polymeric trays. Chemical marker M-1 was used to evaluate heating uniformity in 20% whey protein gels as a model food, and macaroni and cheese was processed to assess the influence of RF process on product quality. With the RF system, a lethality ( F ₀= 10 min) was achieved in both model food and macaroni and cheese within 30 min with relative uniform heating, compared to a 90 min conventional retort process that delivered a similar lethality.     

USING CAPACITIVE (RADIO FREQUENCY) DIELECTRIC HEATING IN FOOD PROCESSING AND PRESERVATION – A REVIEW

Capacitive (Radio Frequency) dielectric heating has great potential for achieving rapid and uniform heating patterns in foods, providing safe, high quality food products. This review describes and discusses the major technology behind capacitive (RF) dielectric heating in food processing and preservation, the current applications of the technology in the industry, the potential use of mathematical modeling for heating system design, and the major challenges facing the use of this technology in food processing. A vast amount of work is still necessary to further understand the dielectric properties of both food and packaging materials in order to refine system design and maximize performance of this technology in the field of packaged food products. Various economic studies will also play an important role in understanding the overall cost and viability of commercial application of this technology in food processing.     

紫外发光二极管（UV-LED）技术对食品微生物灭活应用的研究进展

紫外辐照是一种非热杀菌技术,汞蒸气紫外灯是现阶段用于食品卫生处理的主要设备,但受某些因素影响,汞灯的生产使用将逐渐变少,被环保节能的紫外发光二极管（UV-LED）取代是一种不可避免的趋势。本文根据UV-LED发光原理和多波长耦合应用的特点,综述了对微生物灭活的机理、探究了影响灭活效果的因素（波长、紫外剂量和物料特性）、处理食品的灭菌效果以及对部分食品品质的影响,为UV-LED在食品领域的杀菌处理工艺和设备参数优化提供参考。     

Recent developments in applications of radio frequency heating for improving safety and quality of food grains and their products: A review

Abstract

Food grains constitute a vital part of the daily diet of the population worldwide, and are generally considered as safe products with high storage stability due to their low moisture contents. However, post-harvest losses (PHL) caused by insects, fungi, food-borne pathogens, and undesirable enzymes remain a major concern for the grain industry. Thermal treatments are commonly used to reduce the PHL of grains and their products without any chemical residues. Among which, radio frequency (RF) technology has been regarded as a promising alternative to traditional heating methods for improving safety and quality of food grains due to its fast, volumetric, and deep penetration heating characteristics. This review provided comprehensive information about principles of RF technology and its main applications including disinfestation, pasteurization, enzyme inactivation, drying, and roasting for processing food grains and their products. The methods to improve the RF heating uniformity and effects of RF heating on product quality were also reviewed. Finally, the current problems and recommendations for future work related to RF processing of grains and their products were discussed. This review would improve the understanding of RF heating for food grains and their products and promote the application of RF technology in the food grain industry.     

Use of ultrasounds in the food industry–Methods and effects on quality,safety, and organoleptic characteristics of foods: A review

The use of ultrasounds has recently gained significant interest in the food industry mainly due to the new trends of consumers toward functional foods. Offering several advantages, this form of energy can be applied for the improvement of qualitative characteristics of high-quality foods as well as for assuring safety of a vast variety of foodstuffs, and at the same time minimizing any negative effects of the sensory characteristics of foods. Furthermore, the non-destructive nature of this technology offers several opportunities for the compositional analysis of foods. However, further research is required for the improvement of related techniques and the reduction of application costs in order to render this technology efficient for industrial use. This review paper covers the main applications of ultrasounds as well as several advantages of the use of the technology in combination with conventional techniques. The effects of ultrasounds on the characteristics, microbial safety, and quality of several foods are also detailed