Recent Studies Related to Microwave Processing of Fluid Foods

Microwave Treatment vs. Conventional Pasteurization: The Effect on Phytochemical and Microbiological Quality for Citrus-Maqui Beverages

This study uncovered the impacts of microwave (MW) treatments compared to conventional pasteurization (TP) on the quality of functional citrus-maqui beverages, with added sucrose or stevia. The influence of these thermal treatments on the microbiological burden and phytochemical composition was determined by processing under two MW power levels (600 W and 800 W) and TP at 85 °C for 15 s for 60 days at room temperature (20 °C). The results indicated that, beyond the microbiological quality achieved in the juices treated by both MW and TP technology, there were no differences among the treatments regarding the stability of vitamin C, anthocyanin, and flavanone concentrations. However, anthocyanins were more stable in those beverages with sucrose added, rendering a better red color. Besides, all treatments ensured microbiological stability throughout the entire storage time. In conclusion, MW treatment could be considered as an alternative to TP, which ensures microbial safety, protecting functional compounds associated with health effects.

Validation of Pasteurisation Temperatures for a Tomato-Oil Homogenate (salmorejo) Processed by Radiofrequency or Conventional Continuous Heating

Salmorejo is a viscous homogenate based on tomato, olive oil and breadcrumbs commercialised as a "fresh-like" pasteurised-chilled purée. Due to its penetration, dielectric heating by radiofrequency (RF) might improve pasteurisation results of conventional heating (CH). The objective was to validate the pasteurisation temperature (70-100 °C, at 5 °C intervals) for salmorejo processed by RF (operating at 27.12 MHz for 9.08 s) or conventional (for 10.9 s) continuous heating. The main heat-induced changes include: orangeness, flavour homogenisation, loss of freshness, thickening, loss of vitamin C and lipid oxidation. Both CH and RF equivalent treatments allowed a strong reduction of total and sporulated mesophilic microorganisms and an adequate inhibition of the pectin methylesterase, peroxidase and, to a lesser extent, polyphenol oxidase but did not inhibit the polygalacturonase enzyme. Pasteurisation at 80 °C provided a good equilibrium in levels of microbiological and enzymatic inhibition and thermal damage to the product. Increasing this temperature does not improve enzyme inactivation levels and salmorejo may become overheated. A "fresh-like" good-quality salmorejo can be obtained using either conventional or radiofrequency pasteurisers.

Starch Modification with Molecular Transformation, Physicochemical Characteristics, and Industrial Usability: A State-of-the-Art Review

Starch is a readily available and abundant source of biological raw materials and is widely used in the food, medical, and textile industries. However, native starch with insufficient functionality limits its utilization in the above applications; therefore, it is modified through various physical, chemical, enzymatic, genetic and multiple modifications. This review summarized the relationship between structural changes and functional properties of starch subjected to different modified methods, including hydrothermal treatment, microwave, pre-gelatinization, ball milling, ultrasonication, radiation, high hydrostatic pressure, supercritical CO₂, oxidation, etherification, esterification, acid hydrolysis, enzymatic modification, genetic modification, and their combined modifications. A better understanding of these features has the potential to lead to starch-based products with targeted structures and optimized properties for specific applications.

The Application of Non-Thermal Technologies for Wine Processing, Preservation, and Quality Enhancement

Recently, non-thermal wine processing technologies have been proposed as alternatives to conventional winemaking processes, mostly with the aims to improve wine quality, safety, and shelf-life. Winemakers typically rely on sulfites (SO2) to prevent wine oxidation and microbial spoilage, as these processes can negatively affect wine quality and aging potential. However, SO2 can trigger allergic reactions, asthma, and headaches in sensitive consumers, so limitations on their use are needed. In red winemaking, prolonged maceration on skins is required to extract enough phenolic compounds from the wine, which is time-consuming. Consequently, the wine industry is looking for new ways to lower SO2 levels, shorten maceration times, and extend shelf life while retaining wine quality. This review aggregates the information about the novel processing techniques proposed for winemaking, such as high-pressure processing, pulsed electric field, ultrasound, microwave, and irradiation. In general, non-thermal processing techniques have been shown to lead to improvements in wine color characteristics (phenolic and anthocyanin content), wine stability, and wine sensory properties while reducing the need for SO2 additions, shortening the maceration time, and lowering the microbial load, thereby improving the overall quality, safety, and shelf life of the wines.

Microwave bag cooking affects the quality, glucosinolates content and hydrolysate production of broccoli florets

Appropriate processing and cooking technologies can effectively improve the content of bioactive compounds in vegetables. The effects of microwave bag cooking on broccoli floret quality attributes, glucosinolates (GLSs) content and hydrolysate production were investigated in this study. Microwave bag cooking not only preserved the color of the florets, but also enhanced the total phenolic and flavonoid content, as well as total chlorophyll and ascorbic acid content. Furthermore, the majority of the microorganisms were inactivated, and the structure of the florets was greatly destroyed, thereby increasing antioxidant capacity and promoting the release of GLSs and myrosinase activity in the florets. Moreover, microwave bag cooking significantly enriched the sulforaphane (SFN) and indole-3-carbinol (I3C) production of broccoli florets in the meantime, demonstrating that it was a convenient and quick cooking option to satisfy the requirements of modern consumers.

A Review and Perspective of Environmental Disinfection Technology Based on Microwave Irradiation

PURPOSE OF REVIEW

In the context of COVID-19 sweeping the world, the development of microbial disinfection methods in gas, liquid, and solid media has received widespread attention from researchers. As a disinfection technology that can adapt to different environmental media, microwave-assisted disinfection has the advantages of strong permeability, no secondary pollution, etc. The purpose of this review is to put forward new development requirements for future microwave disinfection strategies by summarizing current microwave disinfection methods and effects. From the perspective of the interaction mechanism of microwave and microorganisms, this review provides a development direction for more accurate and microscopic disinfection mechanism research.

RECENT FINDINGS

Compared to other traditional environmental disinfection techniques, microwave-assisted disinfection means have the advantages of being more destructive, free of secondary contamination, and thorough. Currently, researchers generally agree that the efficiency of microwave disinfection is the result of a combination of thermal and non-thermal effects. However, the performance of microwave disinfection shows the differences in the face of different environmental media as well as different types of microorganisms.

SUMMARY

This review highlights the inactivation mechanism of microwave-assisted disinfection techniques used in different scenarios. Suggestions for promoting the efficiency and overcoming the limitations of low energy utilization, complex reactor design, and inaccurate monitoring methods are proposed.

Recent Insights on the Role of Various Food Processing Operations Towards the Development of Sustainable Food Systems

Chronic hunger and malnutrition will eventually result from the population's rapid growth. It is unlikely to succeed in tackling the rising challenges of delivering sustainable food for all people unless high attention is paid on the function of food processing to ensure the supply of stable food. It is impossible to overstate the importance of developing food processing and preservation technologies that can reduce food losses and wastage during surplus seasons. Therefore, sustainable food systems must be developed to provide healthy diets without damaging our world and its resources. The goal is to use various perspectives to confirm why food processing is crucial to future food supply. It is important to show the appropriate utilization of sustainability factors and effect assessments to construct for feeding the globe while staying within planetary limits. There has never been a better time to assure a plentiful food supply to feed the people than right now, when the population is expanding at a worrying rate. The sustainable food project seeks to move the food systems in a long-term, more equitable direction. Food processing, or the conversion of raw materials into functional, edible, and consumer acceptable food, is a critical link in the food value chain between consumption and production. This review looked at various existing and emerging food processing followed by preservation techniques. Food systems must also attempt to reduce food waste and losses, as well as the current and future impacts on the environment and society, to be sustainable.

Effects of Container Design on the Temperature and Moisture Content Distribution in Pork Patties during Microwave Heating: Experiment and Numerical Simulation

Effects of the container design on the heat transfer rate and food quality during microwave heating were explored and validated with numerical simulations and experiments. The uniformity of moisture content and temperature was investigated, and to describe microwave heating patterns, a simulation model was created. Pork patties with different moisture and salt contents were heated in three different containers (center and edge-perforated lid as well as without lid) to achieve 80 °C using a domestic microwave oven. Compared to the center or mid-way positions, the temperatures at the edge of the patties rose quickly. By containing the evaporated vapor from the heated pork patties inside the container, the container with a center-perforated lid decreased the heating rate and non-uniformity in temperature and moisture content. A simplified numerical model for the electromagnetics, heat, and momentum transfer coupling simulation was developed to understand the moisture and temperature distribution of the pork patties after microwave heating. Heating uniformity and the final quality of the pork patties could be improved by a container with a center-perforated lid. The proposed model was able to describe the microwave warming process for ready-to-eat products; thus, it is a useful tool for designing microwavable ready meals.

Continuous flow microwave heating and sterilization for liquid food

Continuous flow microwave sterilization for liquid food has advantages of a short time and high retention rate of nutrients. However, uneven microwave heating is the critical factor restricting the industrialization of microwave sterilization. This paper reviews the up-to-date research on the continuous flow microwave heating and the continuous flow microwave sterilization system for liquid food. The causes of the non-uniformity of continuous flow microwave heating are thoroughly discussed and the methods of improving the uniformity are proposed. Finally, the recommendations for future research of continuous flow microwave sterilization for liquid food are presented.

A process optimization approach for microwave vacuum drying of concentrated skim milk

Microwave vacuum drying (MVD) of concentrated skim milk and its resulting powder properties have been studied to a very limited extent. To explore the potential of this technology for the manufacture of milk powder, MVD of concentrated skim milk (37.5% total solids) was evaluated with respect to product properties and drying efficiency. A custom factorial design was used to optimize drying parameters, which enabled us to find optimal drying conditions with a minimal number of drying experiments (16). Vacuum level (3.3-13.3 kPa), specific power input (0.86-1.72 W·g^-1), and product layer thickness (1-4 mm) were studied as factors. Total drying time, product foaming at the beginning of the process, product temperature in the last drying interval, browning, insolubility index, and calculated product yield were used as responses to identify optimal MVD processing parameters. Optimal drying of concentrated skim milk that maximized yield and minimized drying time while maintaining good product quality was achieved at a layer thickness of 2 mm, pressure of 6.0 kPa, and a specific power input of 1.29 W·g^-1. Under constant power output, layer thickness was found to be the most important processing parameter to control product temperature during the final drying stage. Maximum product temperatures below 55°C yielded powder with good solubility. The findings of this exploratory study for MVD of concentrated skim milk yield important information and guidelines for production of good quality milk powders or preservation of starter cultures in a dairy matrix such as infant formula.

Amelioration for oxidative stability and bioavailability of N-3 PUFA enriched microalgae oil: an overview

Technological improvements in dietary supplements and nutraceuticals have highlighted the significance of bioactive molecules in a healthy lifestyle. Eicosapentaenoic acid and Cervonic acid (DHA), omega-3 polyunsaturated fatty acids seem to be famed for their ability to prevent diverse physiological abnormalities. Selection of appropriate pretreatments and extraction techniques for extraction of lipids from robust microalgae cell wall are very important to retain their stability and bioactivity. Therefore, extraction techniques with optimized extraction parameters offer an excellent approach for obtaining quality oil with a high yield. Oils enriched in omega-3 are particularly imperiled to oxidation which ultimately affects customer acceptance. Bio active encapsulation could be one of the effective approaches to overcome this dilemma. This review paper aims to give insight into the cultivation methods, and downstream processes, various lipid extraction approaches, techniques for retaining oxidative stability, bioavailability and food applications based on extracted or encapsulated omega-3.

Non-conventional Stabilization for Fruit and Vegetable Juices: Overview, Technological Constraints, and Energy Cost Comparison

This study will provide an overview and a description of the most promising alternatives to conventional thermal treatments for juice stabilization, as well as a review of the literature data on fruit and vegetable juice processing in terms of three key parameters in juice production, which are microbial reduction, enzyme inactivation, and nutrient-compound retention. The alternatives taken into consideration in this work can be divided, according to the action mechanism upon which these are based, in non-conventional thermal treatments, among which microwave heating (MWH) and ohmic heating (OH), and non-thermal treatments, among which electrical treatments, i.e., pulsed electric fields (PEF), high-pressure processing (HPP), radiation treatments such as ultraviolet light (UVL) and high-intensity pulsed light (PL), and sonication (HIUS) treatment, and inert-gas treatments, i.e., the pressure change technology (PCT) and supercritical carbon dioxide (SC-CO2) treatments. For each technology, a list of the main critical process parameters (CPP), advantages (PROS), and disadvantages (CONS) will be provided. In addition, for the non-thermal technologies, a summary of the most relevant published result of their application on fruit and vegetable juices will be presented. On top of that, a comparison of typical specific working energy costs for the main effective and considered technologies will be reported in terms of KJ per kilograms of processed product.

Enhancing the Efficacy of Microwave Blanching-cum-black Mould Inactivation of Whole Garlic (Allium sativum L.) Bulbs Using Ultrasound: Higher Inactivation of Peroxidase, Polyphenol Oxidase, and Aspergillus niger at Lower Processing Temperatures

The freshly harvested whole garlic bulbs require the inactivation of peroxidase (POD), polyphenol oxidase (PPO), and Aspergillus niger. However, the conventional hot water blanching and modern pretreatment like ultrasound (US) and microwave (MW) cannot individually inactivate both the enzymes and Aspergillus niger to the desired levels without compromising the quality of the garlic due to either of the higher process temperatures (> 85 °C) or prolonged treatment times. Therefore, a two-stage sequential US followed by MW pretreatment for garlic bulbs was developed for simultaneous inactivation of POD, PPO, and Aspergillus niger to the desired levels and overcome the individual pretreatment drawbacks. The separate experiments were conducted for US and MW pretreatment using central composite design, and optimization was carried out using response surface methodology. When temperature constraint was considered during optimization, the US was able to reduce POD, PPO, and Aspergillus niger by 80.87%, 93.80%, and 2.60 logs, respectively, whereas MW reduced POD, PPO, and Aspergillus niger by 77.84%, 77.04%, and 1.90 logs, respectively. The US treatment (58.43 WL⁻¹ ultrasound power density for 40 min with an initial bath temperature of 60 °C) followed by MW treatment (3 Wg⁻¹ MW power density for 120 s) resulted in 90.37% POD and 92.38% PPO inactivation with 2.62 log reduction in Aspergillus niger. The maximum temperature reached in US + MW process was 83 °C which ensured no severe thermal damage to the garlic bulbs. The scanning electron microscopic images indicated that ultrasonication induced the porous structure in garlic and helped microwaves increase the product temperature rapidly and achieve the higher inactivation of enzymes and Aspergillus niger. Thus, the US was found to be enhancing the efficacy of the MW heating process.

Mild processing of seafood-A review

Recent years have shown a tremendous increase in consumer demands for healthy, natural, high-quality convenience foods, especially within the fish and seafood sector. Traditional processing technologies such as drying or extensive heating can cause deterioration of nutrients and sensory quality uncompilable with these demands. This has led to development of many novel processing technologies, which include several mild technologies. The present review highlights the potential of mild thermal, and nonthermal physical, and chemical technologies, either used alone or in combination, to obtain safe seafood products with good shelf life and preference among consumers. Moreover, applications and limitations are discussed to provide a clear view of the potential for future development and applications. Some of the reviewed technologies, or combinations thereof, have shown great potential for non-seafood products, yet data are missing for fish and seafood in general. The present paper visualizes these knowledge gaps and the potential for new technology developments in the seafood sector. Among identified gaps, the combination of mild heating (e.g., sous vide or microwave) with more novel technologies such as pulsed electric field, pulsed light, soluble gas stabilization, cold plasma, or Ohmic heat must be highlighted. However, before industrial applications are available, more research is needed.

Strategies to Improve the Potential Functionality of Fruit-Based Fermented Beverages

It is only recently that fermentation has been facing a dynamic revival in the food industry. Fermented fruit-based beverages are among the most ancient products consumed worldwide, while in recent years special research attention has been granted to assess their functionality. This review highlights the functional potential of alcoholic and non-alcoholic fermented fruit beverages in terms of chemical and nutritional profiles that impact on human health, considering the natural occurrence and enrichment of fermented fruit-based beverages in phenolic compounds, vitamins and minerals, and pro/prebiotics. The health benefits of fruit-based beverages that resulted from lactic, acetic, alcoholic, or symbiotic fermentation and specific daily recommended doses of each claimed bioactive compound were also highlighted. The latest trends on pre-fermentative methods used to optimize the extraction of bioactive compounds (maceration, decoction, and extraction assisted by supercritical fluids, microwave, ultrasound, pulsed electric fields, high pressure homogenization, or enzymes) are critically assessed. As such, optimized fermentation processes and post-fermentative operations, reviewed in an industrial scale-up, can prolong the shelf life and the quality of fermented fruit beverages.

Modeling time-temperature history and sterilization value of mango puree under conventional and microwave assisted pasteurization

Continuous pasteurization of liquid foods has to provide the desired lethality level to guarantee food safety with minimum degradation of quality attributes (sensorial and nutritional characteristics) and high energy efficiency. To optimize quality and cost, a thermal process should be modeled considering flow, heat transfer and mass dispersion principles; however, flow through helical tubes and microwave heating require a complex 3D multiphysics approach. Herein a simplified 2D approach is presented to model a hybrid pasteurization unit with conventional and microwave heating under laminar flow to predict axial and radial distributions of temperature and residual activity of a microorganism or enzyme. A study case of 20 °Brix mango puree (power law fluid) processing is used to test the model based on an existing pilot plant unit. Results were useful to compare conventional and microwave heating regarding the process sterilization value and model can be used for process analysis, design and optimization.

Electromagnetic properties of crayfish and its responses of temperature and moisture under microwave field

To reveal the application potential of microwave heating in the thermal processing of crayfish, this work explored the electromagnetic properties of different parts of crayfish and the patterns of temperature and moisture responses in crayfish during microwave heating. The results of electromagnetic analysis demonstrated that the electromagnetic properties of different parts of crayfish were different, and the tail had higher dielectric properties and reflective loss than other parts, but the maximum thickness of each part of crayfish was almost within their heating depth of microwave. The visual imaging and numerical simulation of temperature and moisture responses showed there were nonuniform temperature and moisture distributions in crayfish during microwave heating. The crayfish tail was selectively heated and rapidly cooked, but its moisture loss was far less than the mass loss of whole crayfish. Furthermore, the immobilized water in crayfish tail meat was continuously converted to free water, while the bound water was relatively stable during microwave heating. This work provided the theoretical references for the assumption that cooking the crayfish by microwave to overcome the shortcomings of boiling. PRACTICAL APPLICATION: In this work, we innovatively applied microwave heating to the heat processing of crayfish, and analyzed the electromagnetic properties of different parts in crayfish and explored its temperature and moisture responses under microwave field. Although this is a basic research, which provided some theoretical references for the assumption that microwave heating of crayfish (Procambarus clarkia) may be a clean and efficient means of overcoming the shortcomings associated with boiling. In particular, the simulation model of crayfish was established according to its real size and shape, which provided an option for the prediction of temperature response of crayfish in the microwave field.

A review on the environment-friendly emerging techniques for pretreatment of lignocellulosic biomass: Mechanistic insight and advancements

The process of pretreatment is considered as an indispensable unit operation in the field of lignocellulosic conversion. The traditional pretreatment operations of lignocellulosic biomass are observed as inefficient to meet the demand for an industrial adaptation. In view of that, numerous investigations are reported on various conventional pretreatment methods but very limited information's are available on the advanced technologies. The present review article provides an exclusive discussion on various emerging and environment-friendly pretreatment methods applied on a number of different feedstock materials. Further, an insight on the reaction mechanism involved with each of the technologies such as microwave, ultrasound, deep eutectic solvent, irradiation, and high force assisted pretreatment methods are elucidated for an effective valorization of lignocellulosic biomass. Hence, in a single article, the readers of this paper will get to know all important aspects of the emerging pretreatment techniques of lignocellulosic biomass including the advancements, and the mechanistic insight which will be highly beneficial towards the selection of an efficient pretreatment method for large scale of commercial implementation in a lignocellulosic biorefinery.

Effect of Microwave Heating on the Acrylamide Formation in Foods

Acrylamide (AA) is a neurotoxic and carcinogenic substance that has recently been discovered in food. One of the factors affecting its formation is the heat treatment method. This review discusses the microwave heating as one of the methods of thermal food processing and the influence of microwave radiation on the acrylamide formation in food. In addition, conventional and microwave heating were compared, especially the way they affect the AA formation in food. Available studies demonstrate differences in the mechanisms of microwave and conventional heating. These differences may be beneficial or detrimental depending on different processes. The published studies showed that microwave heating at a high power level can cause greater AA formation in products than conventional food heat treatment. The higher content of acrylamide in microwave-heated foods may be due to differences in its formation during microwave heating and conventional methods. At the same time, short exposure to microwaves (during blanching and thawing) at low power may even limit the formation of acrylamide during the final heat treatment. Considering the possible harmful effects of microwave heating on food quality (e.g., intensive formation of acrylamide), further research in this direction should be carried out.

Bioconversion of bamboo shoot shell to methane assisted by microwave irradiation and fungus metabolism

Bamboo shoot shell (BSS), a major byproduct from bamboo shoot industries with a high amount of output annually, needs to be sustainably management due to its impact on environment and human health. Anaerobic digestion is an eco-friendly and sustainable option, but its efficiency is limited by recalcitrance of lignocellulose structure. A cascade pretreatment (CP) using microwave irradiation and fungus metabolism was developed in this work to reduce the recalcitrance of BSS and enhance its methane production. The results showed significant synergistic effects of microwave irradiation and fungus metabolism on anaerobic digestion of BBS. The methane yield by CP increased by 162.9% (reached to 223.4 mL/g VS) when compared to control group. This was higher than both the values of fungal pretreatment (101.0 mL/g VS, 18.9% increase), and microwave pretreatment (110.5 mL/g VS, 30.1% increase) alone. Further mechanisms of the synergistic effects were revealed. Microwave irradiation provided dissolved products and more accessible BBS for fungus action. In particular, the GC-MS analysis indicated the dissolved products induced fungal laccase activity effectively, and the highest activity in CP was 1.91-fold higher than that in fungal pretreatment alone. The fungus in cascade process further increased accessible surface area and reducing sugars (20.2-43.2%, which compared to fungal pretreatment alone), and reduced significantly the lignin content (42.2-49.1%) and crystallinity (4.5-8.1%) of BSS.

Dielectric characterization of raw and packed soy milks from 0.5 to 20 GHz at temperatures from 20 to 70 ºC

For microwave heating pasteurization processes, knowledge of the dielectric characteristics of foods are very important. In this paper, we present the dielectric properties of raw soy milk and commercial packed soy milk of four different flavors (light, natural, chocolate and pecan) from 500 MHz to 20 GHz, covering most of the assigned frequencies by the Federal Communications Commission for heating purposes. Experiments were performed using an open-ended-coaxial probe and a vector network analyzer. This characterization was carried out for temperatures ranging from 20 to 70 °C in steps of 10 °C. The dielectric constant of soy milks decreased with increasing frequency, while increasing temperature resulted in decreasing of the values. The dielectric loss factor presents a U shape behavior, where the loss started decreasing from 500 MHz to about 3 GHz and then, it increased again up to 20 GHz. In addition, higher temperatures decreased the dielectric loss. Applying the higher order Debye´s equation, two relaxation times were calculated for the soymilks, with good agreement with the measured properties. Deeper penetration of microwaves were obtained for raw soy milk at 915 MHz, making it suitable for microwave pasteurization.