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.     

射频微波技术在食品与农产品灭菌杀虫中应用的研究进展

射频技术主要通过热效应对有害生物进行杀灭,具有效率高、加热均匀性好的优势。相比于微波在低含水量食品及农产品中加热效果更好。本文系统介绍谷物的射频灭菌杀虫机理、效果及应用,由于低频率电磁波用于加热处理时偶极弛豫对升温贡献所占比例降低而离子传导所占比例升高,以及低含水率食品中较低的热传导率,这些因素使得射频加热适合用于粮食等低含水量食品的灭菌杀虫操作。此外,射频频率电磁波长使得加热有较好的穿透性和内部加热均匀性。并且射频加热系统可以方便整合热风、真空、热循环等加热方式,从而达到提高加热效率、增强产品质量的目的。综上所述,射频加热相对于传统加热方式在加热效率上有很大优势,可明显降低粮食等低含水量食品由于有害生物造成的损失,对农产品保存有重大的意义。本文为粮食等低含水量农产品保存中应用射频处理技术提供依据及参考。     

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.     

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.     

发芽结合其他加工方式对全谷物的营养品质及感官特性影响

发芽全谷物在经过不同加工方式处理后,其营养品质和感官特性会发生变化,对发芽全谷物食品的开发应用产生了重要影响。本文综述了蒸煮、焙烤、挤压、发酵、酶辅助处理等五种加工方式对发芽全谷物品质特性影响的研究进展,展望了加工方式在发芽全谷物未来发展中的应用前景,旨在为生产营养型发芽全谷物类食品提供一定的参考。     

Conventional and novel peeling methods for fruits and vegetables: A review

This review explores the effects of various peeling technologies on the peeling performance of fruits and vegetables and peeled product quality. The peeling methods include conventional peeling approaches using hot-water, steam and lye and novel peeling techniques employing infrared radiation heating, ohmic heating and power ultrasound. The working principles, technology characteristics, the major factors affecting the processing efficacy, and limitations of conventional and novel peeling approaches are identified and discussed. Infrared radiation heating, ohmic heating and ultrasound-assist peeling methods have been successfully used to the peeling of tomatoes and other fruits and vegetables. The novel technologies can reduce the use of lye and can improve peeling performance and peeled product quality compared to conventional peeling. The process conditions and food properties are the major determinants affecting the processing efficacy. Future research needs are proposed to scaling-up the technology and exploring other technology used for peeling.Industrial relevance: As a key operation in the fruits and vegetables processing industry, peeling not only directly affects product quality, but also influences the processing cost and the management cost of waste generated by peeling. An unsuitable peeling process may result in low peeling efficiency and quality, high water and energy consumption, and high discharge of waste liquid, leading to the decline of economic benefits and environmental issues. The current work provides important information for selecting suitable peeling methods for high quality and safe products.     

射频解冻过程中食品加热均匀性影响因素的研究进展

射频加热(radio frequency, RF)技术作为一种新兴加热技术，是一种高效、低能耗的可替代传统加热的热处理方法。该方法在提高工业效率的同时又可保证食品的质量安全性及品质，可满足食品工业中的解冻以及其他加工需求，在食品工业中具有越来越大的应用潜力和发展前景。但解冻过程中存在的“边缘效应”等加热不均匀问题仍是制约该技术的一个瓶颈。本研究对射频解冻及其原理进行了介绍，并总结了影响解冻过程中加热均匀性等问题的因素，包括电磁场、射频功率、电极电压及间隙、食品的介电特性等，以期为射频解冻技术的研究及改善加热均匀性等未来研究发展方向提供参考。     

射频加热技术及其在果蔬干制中的研究应用进展

干制是最重要的果蔬加工技术之一,选择合适的干制技术与干燥能耗、产品品质密切相关。射频加热技术作为一种新型物理加热技术,因其加热迅速、具有体积加热效应、能量穿透深度大等优点,同时兼具微生物控制和灭酶效果,近年来备受关注。本文主要综述了射频加热技术的作用机理及特点,影响其在果蔬干制加工中应用的因素,归纳总结了射频加热技术在果蔬干制、微生物控制与灭酶中的应用现状,探讨了射频加热均匀性问题及可能的解决方案,并对未来研究方向进行了展望,为其今后在果蔬干制工业化应用提供参考。     

Extrusion processing of raw food materials and by-products: A review

ABSTRACT

Extrusion technology has rapidly transformed the food industry with its numerous advantages over other processing methods. It offers a platform for processing different products from various food groups by modifying minor or major ingredients and processing conditions. Although cereals occupy a large portion of the extruded foods market, several other types of raw materials have been used. Extrusion processing of various food groups, including cereals and pseudo cereals, roots and tubers, pulses and oilseeds, fruits and vegetables, and animal products, as well as structural and nutritional changes in these food matrices are reviewed. Value addition by extrusion to food processing wastes and by-products from fruits and vegetables, dairy, meat and seafood, cereals and residues from starch, syrup and alcohol production, and oilseed processing are also discussed. Extrusion presents an economical technology for incorporating food processing residues and by-products back into the food stream. In contemporary scenarios, rising demand for extruded products with functional ingredients, attributed to evolving lifestyles and preferences, have led to innovations in the form, texture, color and content of extruded products. Information presented in this review would be of importance to processors and researchers as they seek to enhance nutritional quality and delivery of extruded products.     

Advances in radio frequency pasteurisation equipment for liquid foods: a review

Radiofrequency (RF) heating is an alternative emerging technology to conventional thermal methods; it has been employed for food pasteurisation, providing fast and volumetric heating. However, non-uniformity in the heating pattern has been reported. RF pasteurisation has been studied in different liquid foods. This review provides information about the RF heating mechanism and equipment used to pasteurise liquid food to control deteriorative or pathogen micro-organisms and the effect of the RF treatment on the quality of liquid foods. Developing an effective RF pasteurisation for liquid foods requires knowing the food dielectric properties, which determine the heating uniformity, temperature distribution and heating rate. The efficiency of continuous RF heating systems could depend on the fluid rate, resident time and absorbed power. RF heating can pasteurise liquid food, decrease microbial population and preserve the product's nutritional and physicochemical quality.     

Effect of water,fat, and salt contents on heating uniformity and color of ground beef subjected to radio frequency thawing process

The comminuted meat products are popular and important in the global market. Radio frequency (RF) heating has been proposed as a new alternative method for thawing bulk frozen comminuted meat products with the main advantages of rapid and volumetric heating. However, the temperature non-uniformity is the main obstacle for its industrial applications. In the present study, effects of the level of added water (15–25%), fat (15–25%) and salt (0.1–1.0%) on the heating uniformity and color of ground beef were investigated using a 6 kW 27.12 MHz RF system during thawing process. The results showed that added water had a negative impact on the RF heating uniformity, and a positive impact on beef color. Fat had a major negative effect on the RF heating uniformity and a positive impact on the lightness of the beef sample. The high salt content had a positive influence on the RF heating uniformity, and a significant negative effect on L* value of beef samples. The results may provide some potential methods to improve the RF heating uniformity and quality of food during RF thawing processing.     

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.     

Nanotechnology in the food sector and potential applications for the poultry industry

BackgroundSalmonellosis and campylobacteriosis are among the most frequently reported foodborne diseases worldwide. Commercial chicken meat has been identified as one of the most important food vehicles for Salmonella and Campylobacter infection. Increased poultry consumption has forced producers to explore methods for increasing their production output, while maintaining the affordability and safety of their products. While the forecast benefits of nanotechnology have yet to be fully realised, it has potential application at many points along the food production chain and offers the opportunity to meet these challenges.Scope and approachThe commercial poultry processing environment plays a significant role in reducing foodborne pathogens and spoilage organisms from poultry products prior to being supplied to consumers. This review discusses the potential opportunities and challenges for adopting nano-enabled technologies in the poultry industry, with respect to applications in microbiological food safety and quality assurance in the processing plant.Key findings and conclusionsSeveral possibilities exist to exploit the benefits of nanotechnologies in the poultry processing plant to enhance the microbiological safety and quality of products. Those applications include the adoption of nano-enabled disinfectants, surface biocides, protective clothing, air and water filters, packaging, biosensors and rapid detection methods for contaminants, and technologies that assure the authenticity and traceability of products. Although the fate and potential toxicity of nanomaterials are not fully understood at this time and scientific risk assessments are required, it is evident that there have been significant advances in the application of novel nanotechnologies in the food industry.     

Ohmic heating: A promising technology to reduce furan formation in sterilized vegetable and vegetable/meat baby foods

Occurrence of furan, classified as carcinogen 2B by the International Agency for Research on Cancer, in heat-processed foods, especially sterilized baby foods, is of a health concern. On this account, innovative processing practices ensuring microbial safety, acceptable sensorial features, and, at the same time, minimizing furan formation have to be searched. In this study, the potential of ohmic heating to mitigate furan formation was demonstrated. Compared to conventional retort sterilization, significant mitigation (70–90%) of furan was achieved, assumingly due to reduced degradation of furan precursor under faster terms heating conditions. In purees containing meat, approx. two times less furan was formed, regardless of the processing technology. In addition to furan, also other headspace volatiles were measured and statistically evaluated. Compounds originated through fatty acids oxidation and Maillard reaction products were more abundant in conventionally sterilized samples compared to those treated by ohmic heating.Industrial relevanceOhmic heating is an emerging technology being employed in the field of food processing which applies a direct electric current to food products, providing rapid and uniform heating throughout the product. Shorter heating times used in ohmic heating, as compared to conventional retort sterilization, reduce potential losses of valuable nutrients and as well as reduce the formation of undesirable processing contaminants, in particular furan.The presented work examines furan concentrations across various stages of baby food production, in order to compare ohmic heating and retort sterilization processes. Volatile compound fingerprints for baby food purees processed via both sterilization methods, both prior and post sterilization were assessed. The results presented in this work are of high potential interest to the baby food industry to reduce both heat induced chemical changes and exposure of infants and babies to hazardous processing contaminants such as furan.     

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.     

A novel strategy for improving radio frequency heating uniformity of dry food products using computational modeling

This study attempted to quantify effects of dielectric properties (DPs) and densities of a surrounding container and treated food products on heating uniformity in a 6 kW, 27.12 MHz parallel plate radio frequency (RF) system. A computer simulation model was established with finite element-based commercial software, COMSOL Multiphysics®, and experiments with 1.5 kg soybean flour packed in a rectangular polystyrene container were performed to validate the developed model. Surface temperature distributions of soybean flour in three different horizontal layers were obtained with an infrared camera, and temperature–time histories at two representative locations inside the container were monitored with two optical fiber sensors. The uniformity index (UI) was used as a criterion to evaluate the RF heating uniformity within food products. Results showed that the RF heating uniformity in food samples was clearly influenced by DPs and density of the surrounding container. UI was the lowest when the surrounding container dielectric constant was in a comparable range of the sample's, with the loss factor values of surrounding container lying between 0.01–0.1% of the sample's. The optimum RF heating uniformity in food products could be achieved with a smaller density value of the surrounding container. The correlations of DPs and density between surrounding container and food products derived from the validated simulation model could provide valuable information and strategy to improve the RF heating uniformity in low moisture foods for insect or microbial control. Thus, the established strategy can further be used for developing effective industrial-scale RF treatment protocols after optimization of this process by the food industry.Industrial relevanceAlthough the most important characteristic of radio frequency (RF) treatments is fast and volumetric heating generated by dipole rotation and ionic conduction, edge over-heating is still a major problem for foods heated in rectangular containers. The validated model was used to study the effects of dielectric properties and density of sample and surrounding container on sample uniformity index. Simulated results illustrated that the RF heating uniformity could be improved when the dielectric constant and density of surrounding container and sample were in accordance with the established relationships. The established strategy may provide valuable optimized methods to ensure RF heating uniformity in industrial applications.     

Innovative food processing technologies on the transglutaminase functionality in protein-based food products: Trends,opportunities and drawbacks

BackgroundConsumption of protein-based food products has a key role in the improvement of human health. The crosslinking agent microbial transglutaminase (mTGase) is an effective and promising tool to modify animal proteins used in the food industry. Improvement in the gelation process, physicochemical and textural quality, and consumer's demand of protein-based food products could be attained by combining mTGase and some non-conventional food processing technologies.Scope and approachNew perspectives and key areas for future research in the development of high-quality food proteins and protein-based products as a function of interaction effect of mTGase and some new processing techniques (e.g. high pressure processing (HPP), ultrasound, microwave (MW) and ultraviolet (UV) irradiation) are reviewed. The effect of conventional thermal and emerging processing methods on the mTGase crosslinking activity and protein gel functionality are also compared.Key findings and conclusionsThe crosslinking density and functional properties of protein gels can be strongly promoted by the synergistic action of mTGase and innovative processing methods. Compared to the conventional heating, HPP with further increase of mTGase affinity to proteins can result in products with better physicochemical quality and more complex and firmer gel structure. The yield, water holding capacity, surface hydrophobicity, strength, and viscoelastic characteristics of mTGase-catalyzed protein gels can be significantly increased by ultrasonication treatments. mTGase-crosslinked hydrogels subjected to high-intensity ultrasonic pretreatment have potential to be used as delivery vehicles for a wide spectrum of bioactive compounds. The application of MW and UV light can substantially improve the surface, textural and structural features of gels generated by mTGase-technology.     

A Tool for Predicting Heating Uniformity in Industrial Radio Frequency Processing

Radio frequency energy is utilised for heating in a wide range of applications, particularly in the food industry. A major challenge of RF processing is non-uniform heating in loads of variable and angular geometry, leading to reduced quality and product damage. In this study, the specific effects of geometry on the heating profiles of a range of geometrically variable loads in an industrial scale RF system are analysed, and the understanding used to derive a general tool to predict heating uniformity. Potato was selected as a test material for experimental work; dielectric properties were measured using a 44-mm coaxial probe. Analysis of simulated and experimental surface temperature profiles and simulated power uniformity indices indicates the presence of vertices and edges on angular particles, and their proximity to faces perpendicular to the RF electrodes increases localised heating; faces parallel to the electrodes heated less than those faces perpendicular to them. Comparison of the same geometrical shape in different orientations indicates that overall power absorption uniformity can be better even when localised heating of edges is greater. It is suggested, for the first time, that the rotation of angular shapes within a parallel plate electric field can improve heating uniformity, and that this can be achieved through the design of bespoke electrode systems. A Euler characteristic-based shape factor is proposed, again for the first time, that can predict heating uniformity for solid, dielectrically homogeneous shapes. This gives industry a tool to quickly determine the feasibility for uniform RF heating of different three-dimensional shapes based on geometry alone. This provides a screening method for food technologists developing new products, allowing rapid assessment of potential heating uniformity, and reducing the need for early-stage specialist computational modelling.     

萌芽全谷物的研究现状、问题与机遇

近年来,伴随人们对全谷物健康关注度逐年提高,全谷物食品呈快速发展趋势.萌芽全谷物作为全谷物食品的重要配料,其关注度也在不断提高.萌芽技术可以进一步提高全谷物制品的营养价值和生物有效利用率,改善烘培类产品感官品质,并对慢性代谢综合症预防和控制具有积极作用.从萌芽全谷物定义、全谷物萌发分子机制、功能性成分及生理功效、抗营养...     

挤压处理对全谷物理化和功能特性影响研究进展

全谷物富含多种生物活性成分,但其适口性差、消费者接受度低。挤压是一种高效、低耗及功能多样化的加工技术,通常用于开发具有高营养和感官质量的食品。本文综述了国内外挤压技术在全谷物方向的研究进展。介绍了全谷物、挤压技术,并分析总结了挤压技术对其物理化学性质的影响。挤压全谷物制品还体现出抑制糖尿病和肥胖症等慢性疾病的潜力。