Foam-mat drying technology: A review

Impact of foam-mat drying conditions of "Gấc" aril on drying rate and bioactive compounds: Optimization by novel statistical approaches

This study was conducted to optimize the foam-mat drying conditions to maximize quality [β-carotene and total polyphenol content (TPC)] and drying rate of "Gấc" aril powder by using two novel statistical techniques as Response Surface Methodology (RSM) and Artificial Neural Network (ANN) couple with Genetic Algorithm (GA). During production process, level of egg albumin (EA) used for foaming process and drying temperature mainly influenced the drying rate and content of antioxidant compounds in powder. ANN model of 3-10-3 showed more accuracy and faster prediction capacity than RSM model did. ANN-GA model predicted the optimal conditions to be 13.31 % EA, 0.26 % xanthan gum and drying temperature of 73.1 °C, with the drying rate of 1.89 g-water/g-dry matter/min, β-carotene content of 395.88 μg/g, TPC of 1.68 mgGAE/g. These results confirmed the suitability and promising of foam-mat drying for "Gấc" aril powder production, to be producing food ingredient containing highly bioactive compounds.

Application of Carboxymethyl Cellulose and Glycerol Monostearate as Binder Agents for Protein Powder Production from Honey Bee Brood Using Foam-Mat Drying Technique

This study investigates the development of protein powder from honey bee drone broods using foam-mat drying, a scalable method suitable for community enterprises, as well as the preservation of bee broods as a food ingredient. Initially, honey bee broods were pre-treated by boiling and steaming, with steamed bee brood (S_BB) showing the highest protein content (44.71 g/100 g dry basis). A factorial design optimized the powder formulation through the foam-mat drying process, incorporating varying concentrations of S_BB, glycerol monostearate (GMS), and carboxymethyl cellulose (CMC). The physicochemical properties of the resulting powder, including yield, color spaces, water activity, solubility, protein content, and total amino acids, were evaluated. The results showed that foam-mat drying produced a stable protein powder. The binders (CMC and GMS) increased the powder's yield and lightness but negatively affected the hue angle (yellow-brown), protein content, and amino acid content. The optimal quantities of the three variables (S_BB, GMS, and CMC) were determined to be 30 g, 6 g, and 1.5 g, or 80%, 16%, and 4%, respectively. Under this formulation, the protein powder exhibited a protein content of 19.89 g/100 g. This research highlights the potential of bee brood protein powder as a sustainable and nutritious alternative protein source, enhancing food diversification and security.

Development of 3D-Printable Albumin-Alginate Foam for Wound Dressing Applications

In this article, a method to develop 3D printable hybrid sodium alginate and albumin foam, crosslinked with calcium chloride mist is introduced. Using this method, highly porous structures are produced without the need of further postprocessing (such as freeze drying). The proposed method is particularly beneficial in the development of wound dressing as the printed foams show excellent lift-off and water absorption properties. Compared with methods that use liquid crosslinker, the use of mist prevents the leaching of biocompounds into the liquid crosslinker. 3D printing technique was chosen to provide more versatility over the wound dressing geometry. Calcium chloride and rhodamine B were used as the crosslinking material and the model drug, respectively. Various biomaterial inks were prepared by different concentrations of sodium alginate and albumin, and the fabricated scaffolds were crosslinked in mist, liquid, or kept without crosslinking. The effects of biomaterial composition and the crosslinking density on the wound dressing properties were assessed through printability studies. The mist-crosslinked biomaterial ink composed of 1% (w/v) sodium alginate and 12% (w/v) albumin showed the superior printability. The fabricated scaffolds were also characterized through porosity, mechanical, degradation, and drug release tests. The mist-crosslinked scaffolds showed superior mechanical properties and provided relatively prolonged drug release.

Exploring conventional and emerging dehydration technologies for slurry/liquid food matrices and their impact on porosity of powders: A comprehensive review

The contribution of dehydration to the growing market of food powders from slurry/liquid matrices is inevitable. To overcome the challenges posed by conventional drying technologies, several innovative approaches have emerged. However, industrial implementation is limited due to insufficient information on the best-suited drying technologies for targeted products. Therefore, this review aimed to compare various conventional and emerging dehydration technologies (such as active freeze, supercritical, agitated thin-film, and vortex chamber drying) based on their fundamental principles, potential applications, and limitations. Additionally, this article reviewed the effects of drying technologies on porosity, which greatly influence the solubility, rehydration, and stability of powder. The comparison between different drying technologies enables informed decision-making in selecting the appropriate one. It was found that active freeze drying is effective in producing free-flowing powders, unlike conventional freeze drying. Vortex chamber drying could be considered a viable alternative to spray drying, requiring a compact chamber than the large tower needed for spray drying. Freeze-dried, spray freeze-dried, and foam mat-dried powders exhibit higher porosity than spray-dried ones, whereas supercritical drying produces nano-porous interconnected powders. Notably, several factors like glass transition temperature, drying technologies, particle aggregation, agglomeration, and sintering impact powder porosity. However, some binders, such as maltodextrin, sucrose, and lactose, could be applied in controlled agglomeration to enhance powder porosity. Further investigation on the effect of emerging technologies on powder properties and their commercial feasibility is required to discover their potential in liquid drying. Moreover, utilizing clean-label drying ingredients like dietary fibers, derived from agricultural waste, presents promising opportunities.

Optimization of foaming process for development of modified aloe polysaccharide (MAP) juice and powder using foam-mat drying

The present study was performed to optimize the modified aloe polysaccharide (MAP) foaming process and to determine the effect of drying process parameters on the quality of obtained MAP powder. The studied process parameters were glycerol monostearate (GMS), carboxymethyl cellulose (CMC), and whipping time (WT) which was varied between 1 and 4% w/v, 0.1-0.5% w/v, and 1-5 min, respectively. The optimized values of foaming process parameters were 3.87% GMS, 0.39% CMC, and 4.89 min WT with a desirability of 0.889. The optimized foamed MAP juice was dried at different foam thicknesses (FT) (1, 3, and 5 mm) and drying temperatures (DT) (50, 60, and 70 °C) to develop MAP powder and compared with non-foamed aloe powder developed under the same drying condition. Based on functional properties, the best GMS foamed MAP powder was achieved at 50 °C DT and 1 mm FT, recording powder yield (16%), solubility (20.85%), and polysaccharide content (282 mg/L).

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01354-6.

Effect of Foam-mat Drying on Bioactive, Powder and Thermal Properties of Carrot Juice Powders

Foam-mat drying is a promising method due to involvement of proteins as foaming agent which acts like a wall material wrapping around bioactives and retards their degradation. In this study, powder properties of foam-mat dried carrot juice powders including 15% egg albumen (EA) and 15% egg albumen+ 10% whey protein isolate (WPI) during 90 days of storage at room conditions were evaluated by means of physical, chemical, thermal (DSC and TGA) and microstructural (SEM) analyses. The powder flow properties (wettability, hygroscopicity, degree of caking, Carr index and Hausner ratio) have been significantly affected from the moisture uptake during storage; however, powder flow properties of 15% EA+ 10% WPI powders were found to be better than 15% EA powders as it was also confirmed by particle diameter distributions that remained the same before and after the storage period. Besides, the total antioxidant, phenolic and carotenoid contents of 15% EA+ 10% WPI carrot powder was found comparably higher than 15% EA powders due to possible encapsulating mechanism of whey proteins. In addition to delaying of physical and chemical deteriorations in powders with WPI incorporation, thermal stability of the foam-mat dried carrot juice powders was also improved in 15% EA+ 10% WPI powder.

Preparation of egg white powder using electrohydrodynamic drying method and its effect on quality characteristics and functional properties

This research investigated the effects of spray drying (SD, set at 180 °C), freeze-drying (FD, set at -35 °C), and electrohydrodynamic drying (EHD) with and without the foam-mat method on egg white. The configuration used in EHD was a wire-to-plate type at room temperature. The results showed no significant difference in gel hardness and WHC% (P ≥ 0.05). Also, the foam-mat EHD powders resembled the FD powders in microstructure, appearance, flowability, and absorption intensity of the Amide I and II bands. Furthermore, the foam-mat EHD (DC-) powder had the highest protein content (66.1%), enthalpy (-183.06 J/g), and foaming capacity (725%) (P < 0.05). This finding was proved by FTIR, Raman, and SDS-PAGE tests, which revealed the minor structural changes in proteins (peptide chain structure, Amide I, Amide II, α-helix, and β-sheet). FD powder demonstrated good protein stability in zeta potential and foam stability tests.

Production of tomato powder from tomato puree with foam-mat drying using green pea aquafaba: drying parameters and bioaccessibility of bioactive compounds

BACKGROUND

The purpose of this study was to valorize green pea cooking water (aquafaba) as a foaming agent in foam-mat drying of tomato. For this aim, density of foam-mats (green pea aquafaba+tomato puree) changed between 1.06 and 0.45 g/mL depending on the aquafaba concentration. Foam-mats with 5 mm thickness were dried at 50, 60 and 70°C at 1.3 m/s air velocity.

RESULTS

The results showed that the porous structure of foams with lower densities resulted in higher drying rates and moisture diffusivities. Redness (a* ) value decreased with increasing aquafaba content (p < 0.05). Total phenolic content (TPC) and antioxidant activity (CUPRAC, DPPH and FRAP) of the resulting tomato powders were also determined. Moreover, bioaccessibility of phenolics and antioxidant activities were also determined using in vitro digestion.

CONCLUSIONS

All of the bioactive parameters are positively affected by foam-mat drying process. Using aquafaba as a foaming agent accelerated the drying period and improved bioactive characteristics of the powders. © 2022 Society of Chemical Industry.

Study of functional, biochemical, and sensory qualities of jackfruit pulp powder produced through optimized foam-mat drying parameters

Jackfruit (Artocarpus heterophyllus) production is abundant during the summer season in Southeast Asia and is also produced throughout the year in some parts of South India. Attributed to the absence of viable process technology, the pulp is predominantly consumed fresh and has not been used effectively for other applications such as in ice cream, beverages, custard preparations, or as a flavor enhancer. The conversion of the high sugar-containing pulp to powder is difficult. Hence, the foam-mat drying of jackfruit pulp was carried out using different foaming agents and stabilizers. The effect of maltodextrin (MD; 3%, 4%, and 5% w/w), glycerol-monostearate (GMS; 2%, 3%, and 4% w/w), or soy protein (SP; 0.5%, 1%, and 1.5% w/w), and 0.5% methylcellulose added to the pulp at a concentration of 8 °Brix on foam expansion (FE; %), foam retention (FR; %), total carotenoids (TC; mg/100 g pulp), and overall acceptability (OA) were investigated, and their levels were optimized using central composite design of response surface methodology. The foam mats were dried at a drying air temperature of 70°C along with a foam thickness of 4 mm. The samples were evaluated based on drying time, foaming, functional, biochemical, and sensory qualities. The optimum levels of MD and GMS were 3.96% (4.0%) and 3.01% (3.0%), respectively, which led to the foam-mat-dried jackfruit powder with properties within the desirable range. At these optimum conditions, the predicted FE, FR, TC, and OA were 69.84%, 89.42%, 0.152 mg/100 g pulp, and 7.73, respectively. The optimum levels of MD and SP were 3.95% (4.0%) and 1.02% (1.0%), respectively, and the corresponding properties (considered as responses) of this foam-mat-dried jackfruit powder such as FE, FR, TC, and OA were 74.45%, 84.80%, 0.14 mg/100 g pulp, and 7.6, respectively. PRACTICAL APPLICATION: This study is one of the few studies that is focused on the development of a technique for the long-term preservation of jackfruit powder for further applications that will also reduce the wastage of jackfruit attributed to its fast perishability. This technology can be replicated in other parts of the world. This article has demonstrated foam-mat drying as a useful technique to achieve high-quality jackfruit pulp powders with desirable drying, foaming, functional, biochemical, and sensory qualities using different foaming agents and stabilizers.

Influence of foam mat drying on the nutritional and technological potential of fruits - a review

The consumption of fruits and vegetables is strongly encouraged in the nutritional recommendations presented in national and international guidelines, which strongly advise the intake of these elements as part of a healthy diet. However, this type of food matrix has a low post-harvest durability, making it necessary to apply techniques that extend its shelf life. Among the methods that can be applied, drying acts as a unitary operation of wide use, presenting low operational cost, ease of handling and wide variation of procedural techniques. However, it still remains a methodology seen as "critical" in the food sector, especially when the maximum focus of efforts is to obtain a material of high quality, nutritional and sensorial. In this context, foam layer drying has gained recognition as an effective and low-cost technique, where foam porosity and higher surface area-volume ratio provide high heat and mass transfer rates, reducing process time and improving the physical-chemical quality of the final product. We provide information capable of elucidating that drying requires a large amount of energy for the operation, and that many studies are still needed in order to optimize the process and guarantee the economic, nutritional and functional viability of the final product.

Effect of cellulose and gum derivatives on physicochemical, microstructural and prebiotic properties of foam-mat dried red banana powder

Fruit sugars are gaining attention for their nutraceutical benefits. High sugar in ripe and over-ripe bananas makes them difficult for convective drying. In this study, red banana (RB) pulp was added with different gum derivatives as foaming agent (FA) (4 % w/w) viz., acacia gum(GA), carrageenan (CG) and gelatine(GE). Maltodextrin and carboxymethyl-cellulose were added as foam-stabilizers (FS). FA addition resulted in low density foam (RBGE-50 % reduction) with improved foam stability (RBGA-94.42 %). Powders were low in hygroscopicity (RBGA-18.62 g 100 g ^-1) with optimum flowability. The particle size (54.95 to 69.86 μm) of RB powder increased with gum derivatives addition. Secondary metabolites varied significantly in powder samples. Positive correlation of secondary metabolites with DPPH assay was observed. RBGA showed higher prebiotic activity (0.68) and supported the growth of tested Lactobacillus strain. Therefore, foam-mat dried RB powder with GA could be used in food formulation as low-cost alternative fruit sugar with higher nutritional, functional and prebiotic properties.

Foam mat drying: Recent advances on foam dynamics, mechanistic modeling and hybrid drying approach

Drying is one of the oldest and most widely used methods for food preservation. It reduces the availability of moisture and inhibits microbial and enzymatic spoilage in food products. Foam mat drying is a mild drying technique used for semiliquid and liquid foodstuff. It is useful for heat-sensitive and sticky liquid food products. In this process, liquid food is converted into foam using surfactant additives, which can be a foaming agent or foam stabilizer. These additives are surface-active compounds of vegetative and animal origins. The foamed material is then convectively dried using hot air. The foam mat drying is an efficient and economical technique. With the emergence of different hybrid techniques such as foam mat freeze drying, foamed spray drying, foamed vacuum drying, and microwave assisted foam mat drying, the powders' physical, chemical, and functional properties have enhanced many folds. These strategies have shown very promising results in terms of cost and time efficiency in almost all the cases barring a few exceptions. This review article attempts to comprehensively summarize the mechanisms dictating the foam mat drying process, novel technological tools for modeling, mathematical and computational modeling, effects of various foaming additives, and various hybrid techniques employed to foam mat drying.

Nonconventional Hydrocolloids’ Technological and Functional Potential for Food Applications

This review aims to study the alternatives to conventional industrial starches, describing uncommon sources along with their technological characteristics, processing, and performance on food products. Minor components remaining after extraction play an important role in starch performance despite their low percentage, as happens with tuber starches, where minerals may affect gelatinization. This feature can be leveraged in favor of the different needs of the food industry, with diversified applications in the market being considered in the manufacture of both plant and animal-based products with different sensory attributes. Hydrocolloids, different from starch, may also modify the technological outcome of the amylaceous fraction; therefore, combinations should be considered, as advantages and disadvantages linked to biological origin, consumer perception, or technological performance may arise. Among water-based system modifiers, starches and nonstarch hydrocolloids are particularly interesting, as their use reaches millions of sales in a multiplicity of specialties, including nonfood businesses, and could promote a diversified scheme that may address current monocrop production drawbacks for the future sustainability of the food system.

Response Surface Approach to Optimize the Conditions of Foam Mat Drying of Plum in relation to the Physical-Chemical and Antioxidant Properties of Plum Powder

This research was done to optimize the influence of various egg albumin (EA) concentrations of 2, 4, and 6% as a foaming agent and whipping times of 5, 10, and 15 minutes, on physicochemical and antioxidant properties of plum powder produced using response surface methodology (RSM). Physical properties of the foam such as density, porosity, and expansion were determined. After drying and powder manufacturing, physical properties, namely, the water absorption index (WAI) and water solubility index (WSI), as well as chemical characteristics such as pH, titratable acidity, and browning index, were assessed. Finally, antioxidant capabilities such as the total phenol content (TPC), DPPH scavenging activity, beta carotene, and total flavonoid content (TFC) were measured. According to the findings, both whipping duration and EA concentration had a substantial effect on the foam forming characteristics. Foam expansion increased significantly with EA concentration and whipping time increase, but foam density exhibited an inverse relationship as expected. Increases in EA concentration and whipping duration both raised pH values whereas titratable acidity exhibited an inverse tendency as variable quantity rose. The browning index dropped as EA concentration increased. Antioxidant qualities were retained in dried sample powder as compared with the fresh sample, and they were also altered by variable changes. Overall, a 4% EA concentration for 10 to 15 minutes produced the best dehydration effects with the most antioxidant retention.

Effect of Three Types of Drying on the Viability of Lactic Acid Bacteria in Foam-Mat Dried Yogurt

In this research, foaming technology was applied to obtain powdered yogurt from commercial yogurt at lower temperatures than the typical temperatures used during the dehydration process; the viability of lactic acid bacteria (LAB) was evaluated after the application of different drying techniques (conventional drying, freeze drying, and vacuum drying). Three different formulas (F1, F2, and F3) based on a foaming agent (albumen), stabilizers (guar gum), and prebiotics sources (inulin and agave syrup) were developed. Foam stability was evaluated at different pH values through optimum time of foam (OTF), medium drainage time (MDT), and drainage volume (DV). Foam expansion (FE) and foam density (FD) were measured. The OTF ranged from 6 to 10 min. The MDT ranged from 4.3 to 27.3 min, depending on pH, while the DV varied from 14.1 to 16.2 mL only in F1. No drainage was evidenced in F2 and F3, showing the best stability. The F2 and F3 produced the best FE and FD values. The dried yogurt with different techniques showed a survival rate (SR) of up to 85% Log-CFU/mL, even with the conventional drying method. Sensorial trials were carried out in reconstituted product, with the freeze-dried yogurt showing higher scores. The foam formulas developed demonstrate the efficacy of both the dehydration of yogurt and the preservation of LAB.

Foaming process optimization, drying kinetics and quality of foam mat dried papaya pulp

This study was performed to optimize the papaya pulp foaming process and determine the effect of drying conditions on the drying kinetics and the quality of the obtained powder. Thus, the one- factor-at-a-time experimental method, followed by 2 ^k full factorial design was implemented to determine the optimal conditions of the foaming process. The factors studied were egg white percentage (EW%), xanthan gum percentage (XG%), and whipping time (WT) which varied between 5-20%, 0-0.5%, and 5-20 min, respectively. The optimum conditions (EW% of 15%, XG% of 0.3% and WT of 15 min) for papaya foam expansion percentage (FE%) resulted in a foam with the highest FE% (275.64%) and desirability of 0.916. Foamed and non-foamed papaya pulp in thickness layers of 2-, 4- and 6-mm were dried at 60° and 80° C. Foaming papaya pulp reduced drying time at various layer thicknesses from 140-400 min to 60-160 min, and from 70-160 min to 30-100 min at 60° and 80° C, respectively. Foamed powder samples had the lowest dissolution times and hygroscopicity values; in addition, reconstituted solutions were lighter than non-foamed solutions. Ascorbic acid retention and total phenolic compound content was adversely affected by increased drying time. The obtained papaya powder was classified into six groups based on its quality parameters via hierarchical cluster analysis. In general, foam mat drying is a promising method for producing papaya pulp powder due to its high drying rates and better-quality product.

Usability of soapwort and horse chestnut saponin extracts as foaming agents in foam mat drying of pomegranate juice

BACKGROUND

This study evaluated the usability of saponin-rich extracts (soapwort and horse chestnut) as a foaming agent for foam mat drying of pomegranate juice.

RESULTS

According to the foaming and stabilization studies, the optimum conditions were determined as 0.4% of soapwort extract, 0.03% of carboxymethyl cellulose as a stabilizer, and 3 min of whipping time. The foams produced using these conditions were dried at different spreading thicknesses and drying temperatures. The results showed that the thicker spreading thicknesses provided a higher antioxidant activity. On the other hand, drying temperature had a significant effect on all measured parameters except moisture content and water activity. The higher drying temperature caused a greater colour change and a lower content of total phenolics, total monomeric anthocyanins, cyanidin-3-glucoside, and delphinidin-3-glucoside. On the other hand, a higher content of ascorbic acid and better antioxidant activity was determined in the samples dried at 70 °C.

CONCLUSION

According to the results obtained, spreading thickness of 2 mm and drying temperature of 70 °C were suggested for pomegranate juice powder production by foam mat drying. Overall, it was demonstrated that saponin-rich extracts are a good foaming agent alternative that provides foaming at very low concentrations and a product with high quality. © 2020 Society of Chemical Industry.

Process optimization and ethanol use for obtaining white and red dragon fruit powder by foam mat drying

Dragon fruit shows good sensory and nutritional attributes, but it is also highly perishable. Drying is a unitary operation that promotes the reduction of moisture content, extending the useful life of the product. In this study, the elaboration of white and red dragon fruit powder by foam mat drying was studied with optimization of the proportion of foaming agent and stirring time. The use of ethanol and air temperature were evaluated on drying kinetics, effective moisture diffusivity (D_eff ), and drying rate (DR). The study was divided into two steps. In the first, density, stability, porosity and overrun foam were evaluated and the optimal condition was determined. For the white and red pulp foams, the optimal conditions were, respectively, 26.88 min and 4.12 kg 100 kg^-1 and 23.5 min and 3.44 kg 100 kg^-1 . In the second step, the foam was subjected to ethanol pretreatment and convective drying (50 or 70 °C). The best condition involved pretreatment and the highest tested temperature, with the shortest drying time and the highest D_eff and DR. PRACTICAL APPLICATION: Foam mat drying is a suitable method for drying perishable fruits, such as dragon fruit. The foam properties need to be optimized to ensure the success of the drying process. The ethanol pretreatment and the drying air temperature influence the drying kinetics. Therefore, determining the optimal process conditions is very important.

Comparison of bioactive compounds and nutrient contents in whey protein concentrate admixture of turmeric extract produced by spray drying and foam mat drying

We developed a whey protein admixture of turmeric extract by spray drying (TWPC-SD) and by foam mat drying (TWPC-FMD) and compared its bioactive compounds and nutrients contents. TWPC samples were evaluated for preference and acceptability. Vitamins and carotenoids were determined by high-performance liquid chromatography. Total phenolics, curcumin and antioxidant capacity were determined by spectrophotometry. Centesimal composition was performed according to the Association of Official Analytical Chemists. Chemical elements were determined by inductively coupled plasma optical emission spectrometry. TWPC containing 3.6 mg of curcumin showed good acceptability. Carotenoids and riboflavin were not detected in either TWPC. Vitamin C content was maintained, and antioxidant capacity was increased in both products (p < 0.05). TWPC-SD showed higher total phenolic and curcumin contents compared to TWPC-FMD (p < 0.05). Thus, the TWPC-SD is a good alternative for human consumption since it showed good sensory acceptability and its nutrients and bioactive compounds can contribute to human health.

Progresses in processing technologies for special foods with ultra-long shelf life

Foods for special applications have recently received much attention due to rapid development of space and military industries as well as to frequent occurrence of natural and man-made disasters. Since the way such foods are processed clearly and directly affects their consumer's acceptability and shelf life, it is of interest to explore in detail how these special foods can be processed. This article presents a review on the difficulties in the processing, application and storage as well as on how to ensure the shelf life and acceptability of special foods through the use of efficient processing technologies. Emphasis is made on the use of both conventional and alternative thermal processing and irradiation technologies. Appropriate packaging technologies for each of the discussed special foods are also mentioned along with the way to overcome the problem of product quality degradation. Through comparison and analysis, it is found that foods with different attributes require different technologies and processes to achieve desirable results. Combined use of multiple technologies has also noted to be advantageous.

Prototype continuous microwave foam-mat dryer: design and fabrication

A prototype microwave foam mat dryer with continuous operation was fabricated for tomato and guava. Results of preliminary studies on microwave foam mat drying of tomato and guava were used to design the prototype. The continuous foaming operation was achieved with the help of a submersible pump controlled by a time switch which ensured the delivery of pulp into foaming container and streamlined the delivery of foam on the drying surface (belt). The drying section presented a combination of hot air and microwaves, which resulted in accelerated heating and subsequently drying of the foam. Dried flakes were collected at the exit with the scrapper blade, which ensured appreciable recovery. The quality evaluation of guava pulp and tomato pulp dried at different microwave powers and inlet air temperatures revealed that the products dried at 1000 W microwave power and 50 °C exhibited excellent physicochemical properties in both the cases. Performance evaluation study depicted that the capacity of the dryer for guava drying was 4.84 l/h, the final moisture retention in the dried powder was 0.059 g H₂O/g d.m, recovery was 98.34% and energy consumption was 1.32 kWh/l. Similarly, for tomato drying the capacity, final moisture content, recovery and energy consumption were 4.03 l/h, 0.062 g H₂O/g d.m, 91.29% and 1.49 kWh/l respectively.

Microwave Foaming of Materials: An Emerging Field

In the last two decades, the application of microwave heating to the processing of materials has to become increasingly widespread. Microwave-assisted foaming processes show promise for industrial commercialization due to the potential advantages that microwaves have shown compared to conventional methods. These include reducing process time, improved energy efficiency, solvent-free foaming, reduced processing steps, and improved product quality. However, the interaction of microwave energy with foaming materials, the effects of critical processing factors on microwave foaming behavior, and the foamed product's final properties are still not well-explored. This article reviews the mechanism and principles of microwave foaming of different materials. The article critically evaluates the impact of influential foaming parameters such as blowing agent, viscosity, precursor properties, microwave conditions, additives, and filler on the interaction of microwave, foaming material, physical (expansion, cellular structure, and density), mechanical, and thermal properties of the resultant foamed product. Finally, the key challenges and opportunities for developing industrial microwave foaming processes are identified, and areas for potential future research works are highlighted.

Analysis of the Anthocyanin Degradation in Blue Honeysuckle Berry under Microwave Assisted Foam-Mat Drying

Changes in nutrient content and bioactivity are important indicators to evaluate the quality of products. Berries are rich in antioxidant anthocyanins, which are prone to degradation during drying. The effects of different variables on the stability of anthocyanins in berry puree during microwave assisted foam-mat drying (MFD) was investigated by path analysis and degradation kinetics analysis. The experimental results showed that the degradation of anthocyanins mainly occurred in the last drying stage. The temperature and the moisture content have both direct and indirect effects on the anthocyanin stability. The direct path coefficient of the moisture content on anthocyanins was 0.985, and the direct path coefficient of temperature on anthocyanins was −0.933. The moisture content to temperature ratio (M/T) was first put forward to estimate the anthocyanin degradation. The results of the regression analysis confirmed that the anthocyanins were stable at M/T of 0.96–3.60. A finite element simulation model was established to predict the anthocyanin degradation rate and content. These research results could provide a theoretical reference for use in optimizing the MFD processing technologies.

Otimização por Page do processo de secagem em leito de espuma para produção de café solúvel

Resumo A expansão da produção de café solúvel é uma alternativa ao consumo do café tradicional, tornando-se necessária para atender às novas exigências dos consumidores que buscam conveniência e praticidade. Diante desse cenário, o estudo de técnicas que simplificam e reduzem custos para a obtenção de café solúvel se torna mais pertinente. Portanto, o objetivo deste trabalho foi otimizar o processo de secagem de extrato de café em leito de espuma, por meio do ajuste ao Modelo de Page por regressão não linear. Foram avaliados dois métodos para a concentração do extrato: (A) em evaporador rotativo e (B) em recipiente de inox aberto. A cinética de secagem do extrato de café em leito de espuma sob as temperaturas de 40, 50, 60, 70 e 80 °C foi descrita pelo modelo. Além disso, foi proposta uma equação multivariada para a secagem mediante detecção da influência da temperatura no parâmetro k, do Modelo de Page, e posterior validação dos resultados. O tempo para obtenção do extrato concentrado foi próximo para os dois métodos de concnetração (A: 2 horas e 30 minutos; B: 2 horas e 40 minutos). O modelo de Page apresentou ótimo ajuste com valores de coeficientes de determinação acima de 99%. Por meio dos resultados obtidos, foi confirmado que a temperatura é um fator determinante na velocidade de perda de umidade do produto, apresentando tempos de secagem menores com o aumento da temperatura. A correlação entre os dados experimentais e preditos foi satisfatória para validar os resultados. O modelo matemático também pode auxiliar na correlação dos parâmetros de secagem com alterações físico-químicas e sensoriais do café solúvel, a fim de melhorar os parâmetros tecnológicos.

The Concept of Microwave Foam Drying Under Vacuum: A Gentle Preservation Method for Sensitive Biological Material

Microwave vacuum drying as compared to conventional vacuum drying has evinced advantages regarding drying time, while comparable product characteristics were achieved when drying sensitive biological material. Due to the volumetric microwave input, a time reduction of up to 90% is possible. When drying viscous liquids, a foamed structure that remains stable during drying exhibits further advantages as the diffusion-limited third drying step is enhanced by the porous structure. As foams not only have to be thermally resistant during microwave vacuum processing, but also withstand the vacuum, a specific process for foam drying by microwaves under low pressure conditions was developed. Foam formation and stabilization was achieved by using a synergistic mixture of proteins and carbohydrates; Lactobacillus paracasei ssp. paracasei F19 (L. paracasei) served as a model sensitive substance. Investigation of surface activity and foaming properties as a function of L. paracasei concentration revealed a significant positive contribution of the bacterial cells. It was shown that L. paracasei directly adsorbed at the air-water interface. Besides, a structuring of the liquid lamellae was assumed. Moreover, drying time was reduced to at least 50% compared to microwave vacuum drying without foaming. It was further observed that the slight loss in survival was mainly due to the relatively high moisture content and high vacuum levels at the beginning of the process. However, foaming, vacuum application, and final drying, respectively, did not affect viability of the bacterial cells. Thus, by incorporation of lactic acid bacteria into foam structures, drying can be carried out in a fraction of time, and further results in high-product quality. PRACTICAL APPLICATION: The application of continuous foam drying offers an efficient and energy-saving alternative to the currently applied techniques for the processing of sensitive material. The process could be applied for the preservation of starter cultures and probiotics as well as in the pharmaceutical industry, when sensitive material such as therapeutic proteins is dried. This process is especially suitable for freezing-sensitive and thermolabile substances.

Trends in foam mat drying of foods: Special emphasis on hybrid foam mat drying technology

Dehydration of foods is not simply a preservation technique in the present era, rather an important food processing operation which has many benefits in addition to enhancement of shelf life of foods. There are various methods of drying foods and most of them are unique in their own way. Liquid foods can be dried in many ways and foam mat drying is one such method which is being researched frequently for its potential use at commercial level. Foam mat drying has got almost all the features to be a commercially successful method of drying. It is a simple technique and has shown good results in drying of liquid foods with low glass transition temperature. Hybridization of this method has shown the results that make this technology look even more promising than the conventional one. Studies on freeze drying, vacuum drying and microwave drying of foam have indicated encouraging results with respect to drying kinetics and product quality. This review presents an overview of foam mat drying of foods. The procedure and technology of this method of drying have been summarized with an intention to make them easy to understand. The emphasis is, however, on the hybrid foam mat drying technology.