Effect of ultrasound treatment on the water state in kiwifruit during osmotic dehydration

The Effect of Gliding Arc Discharge Low-Temperature Plasma Pretreatment on Blueberry Drying

This study evaluates the effects of gliding arc discharge low-temperature plasma (GAD-LTP) pretreatment on the drying performance and quality attributes of blueberries. Fresh blueberries were pretreated under varying conditions-treatment durations of 6 s, 12 s, and 18 s and power levels of 300 W, 600 W, and 900 W-prior to convective hot air drying at 65 °C. Results demonstrate that plasma pretreatment significantly reduced drying time, with an 18 s treatment at 900 W reducing drying time by 31.25%. Moisture diffusion coefficients increased with both treatment duration and power. Under optimal conditions, total phenolic content improved by up to 33.47%, while anthocyanin retention initially declined then recovered, reaching a 7.9% increase over the control. However, plasma-treated samples exhibited darker color due to surface etching and oxidation. Rehydration capacity improved, with a maximum enhancement of 27.94%. Texture analysis indicated increased hardness and decreased adhesiveness and chewiness in treated samples. Overall, GAD-LTP pretreatment enhances drying efficiency and preserves bioactive compounds in dried blueberries, offering a scalable approach for industrial application.

Exploring Osmotic Dehydration for Food Preservation: Methods, Modelling, and Modern Applications

This study summarizes the most recent findings on osmotic dehydration, a crucial step in food preservation. The many benefits of osmotic dehydration are listed, including longer shelf life and preserved nutritional value. Mass transfer dynamics, which are critical to understanding osmotic dehydration, are explored alongside mathematical models essential for comprehending this process. The effect of osmotic agents and process parameters on efficacy, such as temperature, agitation and osmotic agent concentration, is closely examined. Pre-treatment techniques are emphasized in order to improve process effectiveness and product quality. The increasing demand for sustainability is a critical factor driving research into eco-friendly osmotic agents, waste valorization, and energy-efficient methods. The review also provides practical insights into process optimization and discusses the energy consumption and viability of osmotic dehydration compared to other drying methods. Future applications and improvements are highlighted, making it an invaluable tool for the food industry.

Review of osmotic dehydration: Promising technologies for enhancing products' attributes, opportunities, and challenges for the food industries

Osmotic dehydration (OD) is an efficient preservation technology in that water is removed by immersing the food in a solution with a higher concentration of solutes. The application of OD in food processing offers more benefits than conventional drying technologies. Notably, OD can effectively remove a significant amount of water without a phase change, which reduces the energy demand associated with latent heat and high temperatures. A specific feature of OD is its ability to introduce solutes from the hypertonic solution into the food matrix, thereby influencing the attributes of the final product. This review comprehensively discusses the fundamental principles governing OD, emphasizing the role of chemical potential differences as the driving force behind the molecular diffusion occurring between the food and the osmotic solution. The kinetics of OD are described using mathematical models and the Biot number. The critical factors essential for optimizing OD efficiency are discussed, including product characteristics, osmotic solution properties, and process conditions. In addition, several promising technologies are introduced to enhance OD performance, such as coating, skin treatments, freeze-thawing, ultrasound, high hydrostatic pressure, centrifugation, and pulsed electric field. Reusing osmotic solutions to produce innovative products offers an opportunity to reduce food wastes. This review explores the prospects of valorizing food wastes from various food industries when formulating osmotic solutions for enhancing the quality and nutritional value of osmotically dehydrated foods while mitigating environmental impacts.

Combined effect of ultrasound and vacuum impregnation for the modification of apple tissue enriched with aloe vera juice

The aim of the work was to investigate how ultrasonic (US) treatment impacts on the physical and chemical properties of vacuum-impregnated apples. Apple slices were subjected to vacuum impregnation (VI) in an Aloe vera juice solution without additional treatments, serving as the reference material. Alternatively, ultrasound (US) treatments, at frequencies of 25 or 45 kHz, and durations of 10, 20, or 30 min, were employed as a pre-treatments before the VI process. The use of US processing enabled a significant increase in the efficiency of VI, without influencing in a significant way the color of the VI samples. The VI process led to a reduction in the content of bioactive compounds, in particular vitamin C and TPC decreased by 34 and 32 %, respectively. The use of US as a pre-treatment, in particular at 45 kHz for 20 or 30 min, led to a better preservation of these compounds (unchanged values for vitamin C and decrease by 23-26 % for TPC in comparison to the fresh samples). Through cluster analysis encompassing all assessed properties, it was evident that US treatment was beneficial for the processing, however the application of appropriate parameters of US treatment (frequency and time) had an impact on achieving similar quality to VI samples. The ultrasound treatment before vacuum impregnation may be suitable, however, the specific processing parameters should be defined for the obtained high quality of the final product.

Mass transfer kinetics (soluble solids gain and water loss) of ultrasound-assisted osmotic dehydration of apple slices

Ultrasound (sonication) treatment can be used directly for dehydration or pre-treatment before the osmotic dehydration (OD) procedure of fruit or vegetable particles. The combination of this technique with the OD technique can further improve the dehydration process efficiencies by increasing the mass transfer rates and enhancing final product quality. In this study, apple slices were osmotically dehydrated in different hypertonic sucrose solutions and assisted with or without ultrasound. Sucrose concentrations (in three levels of 30, 40, and 50° Brix), sonication power (in three levels of 0, 75, and 150 W), and treatment time (in six time intervals: 10, 20, 30, 40, 50, and 60 min) were the factors investigated concerning weight reduction, soluble solids gain, water loss and rehydration. Also, mass transfer kinetics were modelled according to Page, Newton, Midilli, Logarithmic, Verma, and Two terms equations. Increased sucrose solution concentration resulted in higher weight reduction, soluble solids gain and water loss. Also, increased sonication power levels resulted in higher weight reduction, soluble solids gain and water loss. The average rehydration ratio of apple slices decreased from 237.7 to 177.5%, by increasing osmotic solution concentration from 30 to 50%. The Page equation showed the best fitting for water loss data. The effective moisture diffusivity (D_eff) of apple slices during OD calculated using Fick’s second law applied to a slab geometry was found to be in the range of 1.48 × 10^–10 and 4.62 × 10^–10 m²s⁻¹ for water loss.

Measurement of microstructural changes promoted by ultrasound application on plant materials with different porosity

This research investigated the effects of ultrasound application (192 ± 6 W/L) on the microstructure of vegetables/fruits with different porosities, cell sizes and patterns (eggplants, beetroots, and apples), submitted to an immersion treatment in different liquids: distilled water, citric acid (1% w/v), and the vegetable/fruit juice, at 25 °C during 5 min. The ultrasound application did not significantly (p > 0.05) affect the size of the cells of the most porous material (eggplant) compared to the samples immersed without ultrasound assistance. The apple samples (with a middle-high porosity and the largest cells) were the most affected by ultrasound application. The median cell areas of samples treated with ultrasound in water and apple juice were 26 and 20% larger than those of samples treated without ultrasound, mainly because of cell wall disruption which caused the cells to merge into bigger clusters, but no effect was observed with the citric acid. Ultrasound application significantly (p < 0.05) increased the median cell area of the less porous raw matter (beetroot) only when the treatment was carried out in the vegetable juice (cells were 26% larger after treatment assisted with ultrasound than without it). Thus, the effects of ultrasound differ in materials with initially different characteristics.

Effect of an Ultrasound Pre-Treatment on the Characteristics and Quality of Far-Infrared Vacuum Drying with Cistanche Slices

In this study, the effect of an ultrasound (US) pre-treatment on the process of drying Cistanche slices through far-infrared vacuum drying was investigated with various experimental factors, including the US treatment time (25, 35, 45 min), frequency (20, 40, 60 kHz) and power (150, 180, 210 W). The results showed that compared with the samples without US, the material drying time after the US treatment was reduced by 16–36.8%. The effective moisture diffusion coefficients of Cistanche slices under different US conditions ranged from 1.61122 × 10⁻⁸ to 2.39274 × 10⁻⁸ m²/s, which agreed with food processing ranges. In addition, the phenylethanoid glycoside, iridoid, polysaccharide, total phenol and total flavonoid contents in Cistanche were significantly increased after US pre-treatment. However, the dried products obtained with the 45 min US treatment had greatly damaged internal structures, collapsed and seriously deformed surfaces, and low contents of active ingredients. Overall, the US pre-treatment could significantly improve the drying quality of Cistanche slices.

Study of Water Distribution, Textural and Colour Properties of Cold Formulated and Air-Dried Apple Snacks

Vacuum impregnation is considered a cold formulation technology since it allows the incorporation of a desired functional compound into porous plant tissue without applying any heat. It is widely used in combination with the drying process to obtain added-value snacks. The aim of this work was to evaluate the effect of two trehalose concentrations (5 and 10% w/w) on: (i) the water state and texture evolution during the air drying (50 °C, 8 h) of apple snacks vacuum impregnated with blueberry juice, and on (ii) the colour of the final dried apple snacks. The results of nuclear magnetic resonance (NMR) showed that trehalose affects the water mobility of the samples during drying especially after 200–300 min of drying. In terms of textural properties, trehalose could increase the crispier characteristic of the samples impregnated with trehalose at the end of drying. Significative changes were found in terms of chroma and hue angle.

The Influence of Polyols on the Process Kinetics and Bioactive Substance Content in Osmotic Dehydrated Organic Strawberries

In recent years, an increasing interest in reducing sugar consumption has been observed and many studies are conducted on the use of polyols in the osmotic dehydration process to obtain candied or dried fruits. The studies in the literature have focused on the kinetics of the process as well as the basic physical properties. In the scientific literature, there is a lack of investigation of the influence of such polyol solutions such as sorbitol and mannitol used as osmotic substances during the osmotic dehydration process on the contents of bioactive components, including natural colourants. Thus, the aim of the study was to evaluate the impact of polyols (mannitol and sorbitol) in different concentrations on the process kinetics and on chosen physical (colour and structural changes) as well as chemical (sugars and polyol content, total anthocyanin content, total polyphenol content, vitamin C, antioxidant activity) properties of osmotic-dehydrated organic strawberries. Generally, the results showed that the best solution for osmotic dehydration is 30% or 40% sorbitol solutions, while mannitol solution is not recommended due to difficulties with preparing a high-concentration solution and its crystallization in the tissue. In the case of sorbitol, the changes of bioactive compounds, as well as colour change, were similar to the sucrose solution. However, the profile of the sugar changed significantly, in which sucrose, glucose, and fructose were reduced in organic strawberries and were partially replaced by polyols.

Multi-Analytical Approach to Study Fresh-Cut Apples Vacuum Impregnated with Different Solutions

The aim of this study was to evaluate the effect of different solutions for vacuum impregnation (VI) of fresh-cut (FC) apples through an innovative multi-analytical approach. In particular, the individual and synergistic effects of ascorbic acid and calcium lactate on the preservation of freshness of FC apples was assessed through color, texture, microscopy, isothermal calorimetry, and time-domain nuclear magnetic resonance (TD-NMR) evaluations. The analysis was performed immediately after VI and after 24 h of refrigerated storage. The obtained results showed a good preservation of color and higher firmness in the impregnated samples. Concerning the metabolic heat production, a decrease following the VI treatment was observed, especially when the combined solution was used for the impregnation. The TD-NMR studies showed higher changes in terms of signal intensity and transversal relaxation time T2 after 24 h of storage, evidencing the meta-stability of the plant material for its dynamic tissue nature, and the dewatering/impregnation processes evolution until the achievement of dynamic equilibrium.

An overview of different homogenizers, their working mechanisms and impact on processing of fruits and vegetables

Fruits and vegetables (F&V) are the second highest recommended foods, rich in antioxidants, vitamins and minerals, vital for building immunity against chronic diseases. F&V processing involves particle size reduction, for which different types of homogenizers, categorized as mechanical homogenizers, pressure homogenizers and ultrasonic homogenizers are used. The review discusses different types of homogenizers, their working mechanism, and application in F&V processing. Among mechanical homogenizers, knife mills are used for primary size reduction, ball mills for the micronization of dried F&V and rotor-stator homogenizers for emulsification. Use of the ultrasonic homogenizer is limited to extraction of bioactive compounds or as a pre-treatment for dehydration of F&V. High-pressure homogenizers are most widely used and reported due to the synergistic effect of homogenization and temperature increase, resulting in longer shelf-life and better physicochemical properties of the product. Additionally, the review also explains the effect of homogenization on the physicochemical, sensory and nutraceutical properties of the product.

Selected Quality Parameters of Air-Dried Apples Pretreated by High Pressure, Ultrasounds and Pulsed Electric Field-A Comparison Study

The aim of this work was to compare selected physicochemical properties of air dried ‘Golden Delicious’ apples, pretreated either by high-pressure processing (HPP), ultrasound (US) or pulsed electric field (PEF). Following parameters of pretreatment were used: HPP–400 MPa for 15 min, US–21 kHz, 180 W for 45 min, PEF–1 kV/cm, 3.5 kJ/kg. The quality of materials was evaluated by their rehydration properties, hygroscopicity, color and total phenolic content. To compare the effectiveness of the utilized methods, determined properties were expressed as relative comparison values against the reference sample obtained without any pretreatment in the same conditions. The performed research demonstrated that properties can be shaped by the application of proper pretreatment methods. For instance, PEF was shown to be the best method for improving water uptake during rehydration, whereas HPP was the most effective in decreasing hygroscopic properties in comparison with untreated dried apples. Among the investigated methods, HPP resulted in the deepest browning and thus total color difference, while the effects of US and PEF were comparable. For all pretreated dried apples, the total phenolic content was lower when compared with reference material, though the smallest drop was found in sonicated samples.

Application of ultrasound in combination with other technologies in food processing: A review

The use of non-thermal processing technologies has been on the surge due to ever increasing demand for highest quality convenient foods containing the natural taste & flavor and being free of chemical additives and preservatives. Among the various non-thermal processing methods, ultrasound technology has proven to be very valuable. Ultrasound processing, being used alone or in combination with other processing methods, yields significant positive results on the quality of foods, thus has been considered efficacious. Food processes performed under the action of ultrasound are believed to be affected in part by cavitation phenomenon and mass transfer enhancement. It is considered to be an emerging and promising technology and has been applied efficiently in food processing industry for several processes such as freezing, filtration, drying, separation, emulsion, sterilization, and extraction. Various researches have opined that ultrasound leads to an increase in the performance of the process and improves the quality factors of the food. The present paper will discuss the mechanical, chemical and biochemical effects produced by the propagation of high intensity ultrasonic waves through the medium. This review outlines the current knowledge about application of ultrasound in food technology including processing, preservation and extraction. In addition, the several advantages of ultrasound processing, which when combined with other different technologies (such as microwave, supercritical CO2, high pressure processing, enzymatic extraction, etc.) are being examined. These include an array of effects such as effective mixing, retention of food characteristics, faster energy and mass transfer, reduced thermal and concentration gradients, effective extraction, increased production, and efficient alternative to conventional techniques. Furthermore, the paper presents the necessary theoretical background and details of the technology, technique, and safety precautions about ultrasound.

Osmotic dehydration and convective drying of kiwifruit (Actinidia deliciosa) - The influence of ultrasound on process kinetics and product quality

The aim of this study was to assess the impact of ultrasound on two subsequent processes - initial osmotic dehydration and convective drying of kiwifruit (Actinidia deliciosa). The effect of ultrasound (at a frequency of 25 kHz) was assessed both in terms of process kinetics and product quality. During the study, three different osmotic agents were used - erythritol, sorbitol, and sucrose - in an aqueous solution at a concentration of 50% (w/w). The essential kinetic parameters were analyzed - water loss and increase of dry matter during osmotic dehydration, and evolution of moisture content and temperature of samples during convective drying (drying curves). Product quality was assessed on the basis of color, water activity, and content of relevant bioactive components - polyphenols and carotenoids. It was found that the application of ultrasound during osmotic dehydration resulted in higher water loss and solid gain. This surely results from the phenomena occurring during the propagation of the elastic waves in the liquid medium (mainly related to cavitation) and enhancement of the mass transfer. The use of ultrasound during convective drying also had a positive effect on the kinetics of this process. In most cases, during the ultrasonically assisted drying operations, a significant increase in drying rate was observed, leading to a reduction in drying time. This may be due to the intensification of both heat and mass transfer as a result of the mechanical and thermal effects of ultrasound. The assessment of product quality showed that the use of sugar alcohols was a good alternative to sucrose, and ultrasound-assisted convective drying increased the retention of valuable carotenoids and polyphenols. Moreover, in all dried kiwifruit slices, water activity was below 0.6, which can guarantee the microbiological stability of the tested samples.

The influence of osmotic treatment assisted by ultrasound on the physico-chemical characteristics of blueberries (Vaccinium myrtillus L.)

The aim of the study was to analyse the effect of osmotic treatment assisted by ultrasound on the physico-chemical properties of blueberries from Suceava county, Romania. Ultrasound treatment was conducted at the frequency of 25 kHz (using different values of amplitude - 20, 60 and 100%, respectively) in 61.5% sucrose solution at 30, 40 and 50 °C for 20, 40 and 60 min. The Box-Behnken design was used to investigate the influence of independent variables (time, temperature and amplitude) on the osmotic dehydration. The results showed that for physico-chemical characteristics (mass transfer parameters; moisture content; total content of anthocyanins, flavonoids and polyphenols; DPPH assay scavenging activity) that optimal conditions were obtained at 30 °C for 40 min at a 100% amplitude. Ultrasound treatment stimulated changes in the main characteristics, especially of colour leading to a higher lightness (L*), decreasing AsA-POD and water activity. The results indicated that the higher the values of independent variables are, the more representative is the correlation between them.

Current Applications of Ultrasound in Fruit and Vegetables Osmotic Dehydration Processes

Ultrasound (US) is a promising technology, which can be used to improve the efficacy of the processes in food technology and the quality of final product. US technique is used, e.g., to support mass and heat transfer processes, such as osmotic dehydration, drying and freezing, as well as extraction, crystallization, emulsification, filtration, etc. Osmotic dehydration (OD) is a well-known process applied in food processing; however, improvements are required due to the long duration of the process. Therefore, many recent studies focus on the development of OD combined with sonication as a pretreatment method and support during the OD process. The article describes the mechanism of the OD process as well as those of US and changes in microstructure caused by sonication. Furthermore, it focuses on current applications of US in fruits and vegetables OD processes, comparison of ultrasound-assisted osmotic dehydration to sonication treatment and synergic effect of US and other innovative technics/treatments in OD (such as innovative osmotic solutions, blanching, pulsed electric field, reduced pressure and edible coatings). Additionally, the physical and functional properties of tissue subjected to ultrasound pretreatment before OD as well as ultrasound-assisted osmotic dehydration are described.

Physicochemical properties and sensory acceptability of beetroot chips pre-treated by osmotic dehydration and ultrasound

Abstract Red beet (or beetroot) is highly nutritious and can be preserved by drying, in order to avoid wastage, to take advantage of crop surpluses, and to add value during the off-season. The objective of this study was to evaluate the effects of osmotic dehydration (OD) and ultrasound (US) pre-treatments on the nutritional quality and sensory characteristics of dried beetroot chips. The kinetics of moisture loss during OD and US were predicted by fitting the experimental data with thin-layer models. The physicochemical parameters (moisture, protein, lipid, carbohydrate, energy, ash, sodium and nitrate) and sensory properties (affective preference-ordering and acceptance test) were determined. Correlations between the treatments and the sensory acceptability evaluated by consumer’s perceptions were performed by applying unsupervised chemometric techniques (Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA)). The two-term exponential model provided the best fit for the experimental drying data. The US treatment promoted a higher drying rate and lower lipid, ash and energy values, while the OD process resulted in higher ash and sodium values. Multivariate analysis revealed that the US and OD treatments improved the sensory properties of the beetroot chips. The US was more efficient pre-treatment for producing beet chips due to its leads a significant reduction on drying time and intermediate level of sensory preference.

Advances in application of ultrasound in food processing: A review

Food processing plays a crucial role in coping up with the challenges against food security by reducing wastage and preventing spoilage. The ultrasound technology has revolutionized the food processing industry with its wide application in various processes, serving as a sustainable and low-cost alternative. This non-destructive technology offers several advantages such as rapid processes, enhanced process efficiency, elimination of process steps, better quality product and retention of product characteristics (texture, nutrition value, organoleptic properties), improved shelf life. This review paper summarizes the various applications of ultrasound in different unit operations (filtration, freezing, thawing, brining, sterilization/pasteurization, cutting, etc.) and specific food divisions (meat, fruits and vegetables, cereals, dairy, etc.) along with, the advantages and drawbacks of the technology. The further scope of industrial implementation of ultrasound has also been discussed.

Tri-frequency ultrasound as pretreatment to infrared drying of carrots: impact on enzyme inactivation, color changes, nutrition quality parameters and microstructures

The effects of tri-frequency ultrasound as pretreatment on the peroxidase (POD) inactivation and infrared drying attributes of carrots were studied in the temperature range of 60–80 °C. Thermosonication (TS) treatment reduced 65.21, 73.33 and 81.43% POD activity after 5 min for the temperatures at 60, 70 and 80 °C, respectively, which were all higher than hot water (HW) blanching treated samples. The first-order kinetics fitted well for the POD inactivation curves. Similar retention ranges of vitamin C (VC) were observed after TS (88.41–82.51%) and HW (91.91–88.75%) treatments at the studied range of temperatures. Compared to HW treated samples, drying times of thermosonicated carrot slices were shortened by 13.6, 15 and 15.8% for blanching temperatures at 60, 70 and 80 °C, respectively. The aid of ultrasound showed a positive effect on the rehydration ration (RR) of samples. Sonicated dried samples exhibited higher hardness compared with thermal dried samples. No significant variation (p > 0.05) in the total color difference (ΔE) was attained for dried carrot slices pretreated by TS and HW processes.

Optimization of Osmotic Dehydration of Tomatoes in Solutions of Non-Conventional Sweeteners by Response Surface Methodology and Desirability Approach

The osmotic dehydration (OD) of tomatoes in solutions of alternative sweeteners was investigated using Response Surface Methodology (RSM), while selected desirability functions were implemented in order to define the optimum process parameters (temperature/duration of osmotic treatment, osmotic solution composition and concentration). Mass exchange, color and texture were measured during the process. Changes in color occurred rapidly at the beginning of the process, while firmness was significantly increased, indicating that OD processing led to tomato texture improvement. Color and firmness changes were adequately modeled using a polynomial model. RSM coupled with desirability functions was applied to optimize OD procedure in terms of color retention and maximum solid gain, a requirement for candied products. A maximum desirability was obtained by incorporating oligofructose into the osmotic solution, at relatively short treatment times. Results were validated and sensory analysis was conducted at the optimized conditions to assess samples’ organoleptic acceptance.

Osmodehydrofreezing: An Integrated Process for Food Preservation during Frozen Storage

Osmodehydrofreezing (ODF), a combined preservation process where osmotic dehydration is applied prior to freezing, achieves several advantages, especially in plant tissues, sensitive to freezing. OD pre-treatment can lead to the selective impregnation of solutes with special characteristics that reduce the freezing time and improve the quality and stability of frozen foods. ODF research has extensively focused on the effect of the osmotic process conditions (e.g., temperature, duration/composition/concentration of the hypertonic solution) on the properties of the osmodehydrofrozen tissue. A number of complimentary treatments (e.g., vacuum/pulsed vacuum, pulsed electric fields, high pressure, ultrasound) that accelerate mass transfer phenomena have been also investigated. Less research has been reported with regards the benefits of ODF during the subsequent storage of products, in comparison with their conventionally frozen counterparts. It is important to critically review, via a holistic approach, all parameters involved during the first (osmotic dehydration), second (freezing process), and third stage (storage at subfreezing temperatures) when assessing the advantages of the ODF integrated process. Mathematical modeling of the improved food quality and stability of ODF products during storage in the cold chain, as a function of the main process variables, is presented as a quantitative tool for optimal ODF process design.

Application of ultrasound technology in processing of ready-to-eat fresh food: A review

With the increase in food standardization and the pace of modern life, the demand for ready-to-eat foods is growing. The strong processing conditions of traditional technology often accelerate the rate of deterioration of quality, and microbes are the safety hazard of ready-to-eat foods. Ultrasound technology is an environmentally friendly technology that hardly causes thermal damage to raw materials. In this paper, the ultrasound technology is used in the disinfection, sterilization, enzyme inactivation, desensitization, dehydration, curing, tenderization and cooking process of fresh food from the perspective of microbial safety and quality of fresh food. The cavitation effect of ultrasound can improve the mass transfer rate of infiltration processes such as dehydration and curing, promote the oxidation of lipids and proteins for enrich the flavor of meat products, improve the microbiological safety and reduce the sensitization by destroying the integrity of the microbial cells and the conformation of the protein. In addition, ultrasound as an auxiliary processing technology can reduce the damage of traditional production technology to reserve the quality and nutritional value of food. Ultrasound has proved to be an efficient and green processing technology for ready-to-eat food.

Application of non-thermal pretreatment techniques on agricultural products prior to drying: a review

BACKGROUND

Most agricultural crops contain high moisture content (80-95% wet basis (wb)) which makes them very susceptible to microbial damage leading to shorter shelf-life and high postharvest losses. The high perishability of these agricultural products requires preservation techniques to prolong their shelf-lives. Drying remains an important component of processing in this regard. Therefore, any pretreatment methods for drying agricultural product that decreases the moisture content and minimizes drying time by conserving the quality of the crop product is of prime significance. This article is a comprehensive review of recent developments of non-thermal pretreatment (NTP) methods. A summary of their significance, emerging and innovative methods of this technology together with its applications and limitations are discussed. This article further examines the environmental impact of NTP techniques.

RESULTS

NTP techniques, such as high pressure, ultrasound, pulsed electric field and osmotic dehydration methods are essential operations for pre-dehydration of agricultural products prior to drying. These techniques can avoid the deleterious effects of heat on nutritive value, colour and flavour of agricultural products compared to thermal pretreatments. They also enhance the inactivation of the enzymes, improve energy efficiency and mass transfer, reduce processing time, preserve bioactive compounds, improve drying kinetics and drying rate, minimize enzymatic browning, and enhance product quality.

CONCLUSION

These findings will provide a better understanding of different NTP methods and also make available more information for selecting pretreatment techniques for drying of agricultural products. © 2020 Society of Chemical Industry.

Sono-physical and sono-chemical effects of ultrasound: Primary applications in extraction and freezing operations and influence on food components

Ultrasound is an advanced non-thermal food-processing technology that has received increasing amounts of interest as an alternative to, or an adjuvant method for, conventional processing techniques. This review explores the sono-physical and sono-chemical effects of ultrasound on food processing as it reviews two typical food-processing applications that are predominantly driven by sono-physical effects, namely ultrasound-assisted extraction (UAE) and ultrasound-assisted freezing (UAF), and the components modifications to food matrices that can be triggered by sono-chemical effects. Efficiency enhancements and quality improvements in products (and extracts) using ultrasound are discussed in terms of mechanism and principles for a range of food-matrix categories, while efforts to improve existing ultrasound-assist patterns was also seen. Furthermore, the progress of experimental ultrasonic equipments for UAE and UAF as food-processing technologies, the core of the development in food-processing techniques is considered. Moreover, sono-chemical reactions that are usually overlooked, such as degradation, oxidation and other particular chemical modifications that occur in common food components under specific conditions, and the influence on bioactivity, which was also affected by food processing to varying degrees, are also summarised. Further trends as well as some challenges for, and limitations of, ultrasound technology for food processing, with UAE and UAF used as examples herein, are also taken into consideration and possible future recommendations were made.

Changes in unfrozen water content and dielectric properties during pulse vacuum osmotic dehydration to improve microwave freeze-drying characteristics of Chinese yam

BACKGROUND

As a pretreatment before drying, the purpose of osmotic dehydration (OD) is to reduce the initial water content of samples and shorten the drying time. When OD is combined with pulse vacuum, the mass transfer is enhanced. Furthermore, the properties of materials, which affect the absorption and dissipation of microwaves, can be changed by OD. In this work, pulsed vacuum osmotic dehydration (PVOD) with sucrose solution was adopted before microwave freeze-drying (MFD). The effects of PVOD on the drying characteristics and quality of dried products were studied.

RESULTS

Results showed that the unfrozen water content was increased by PVOD, which made the dielectric constant and loss factor of Chinese yam larger than that of untreated samples, and the difference amplified with the increasing temperature. Thus, the shortened drying time (up to 38.5%) and increased average drying rate (up to 16.8%) were achieved by MFD combined with PVOD. While in traditional freeze-drying, PVOD resulted in slightly shortened drying time but decreased drying rate. The mechanism of PVOD on improving drying rate of MFD was analyzed from the perspective of unfrozen water content and dielectric properties. Furthermore, the quality assessments indicated that PVOD treatment retained a better color and improved the total phenolic content of dried yams compared to untreated and dried samples.

CONCLUSION

PVOD using sucrose solution was an effective method to change the characteristics of yam, enhancing the MFD rate and improving the product qualities. © 2019 Society of Chemical Industry.

Effect of ultrasonic vacuum pretreatment on mass transfer kinetics during osmotic dehydration of black jamun fruit

The study investigates the effects of novel combination of ultrasound and vacuum pre-treatment on osmotic dehydration of black jamun fruit. The osmotic dehydration was conducted under three different conditions namely atmospheric osmotic dehydration (AOD), vacuum pre-treated osmotic dehydration (VOD), ultrasonic vacuum pre-treated osmotic dehydration (USVOD). The changes in water and solute content during osmotic dehydration were fitted to Peleg model to predict the equilibrium moisture and solute content values. The adequacy of Weibull distribution model for predicting the moisture and solute contents during osmotic dehydration at different temperatures were assessed. The effective diffusivity of samples in AOD, VOD and USVOD were estimated by application of Fick's second law. The high regression coefficient (R² > 0.9) and low χ² value represented the suitability of Peleg model for predicting equilibrium moisture and solute content and Weibull model for predicting both moisture and solute fraction in jamum fruit during AOD, VOD and USVOD processes. Both vacuum and ultrasound vacuum pretreatment enhanced the moisture loss and solute uptake during osmotic dehydration. The results showed the osmotic drying rate was significantly influenced by different pre-treatment techniques and both vacuum and ultrasonic vacuum pretreatment process enhanced moisture loss and solute uptake during osmotic dehydration. The effective moisture and solute diffusivity were highest in ultrasonic vacuum pretreated samples and the values at 30-50 °C temperature were ranged from 8.53 × 10^-10 to 9.27 × 10^-10 m²/s and 3.81 × 10^-10 to 4.39 × 10^-10 m²/s respectively. The results were interrelated to changes in tissue structure caused by application of vacuum and ultrasonic vacuum pretreatment.

Effects of Various Nonthermal Pretreatments on the Physicochemical Properties of Dried Ginger (Zingiber officinale Roscoe) Slices from Two Geographical Locations

This study explored the effect of different nonthermal pretreatments, osmosonication (OS), osmotic dehydration, and ultrasound methods on the physical and chemical properties of China- and Ghana-sourced ginger samples under relative humidity convective drying. The chemical properties of pretreated dried ginger slices were assessed for antioxidant properties (ABTS and DPPH); total phenolic content; total flavonoids content; and 4-, 6-, 8-, and 10-gingerol and 6-shogaol levels. The physical properties compared were weight loss, rehydration ratio (RR), texture, and drying kinetics. Results revealed that OS pretreatment led to a higher preservation of the chemical properties with the Ghana-sourced ginger exhibiting the highest values. The OS-treated samples obtained the highest weight losses and RRs, but the RR was higher in the Chinese ginger. OS pretreatment also gave the lowest textural value with the China-sourced samples exhibiting the lowest firmness. Weibull model best fitted the experimental results (R2 > 0.99). PRACTICAL APPLICATION: Ginger remains among the most notable medicinal spices worldwide. It is used as a raw material for the pharmaceutical, beverage, cosmetics, and the food industries. Long-term storage of ginger is one of paramount importance, hence any pretreatment that reduces its moisture content and lessens its drying time but preserves its quality is ideal. In this study, we report the effect of different nonthermal pretreatments, osmosonication, osmotic dehydration, and ultrasound on the physical and chemical properties of China- and Ghana-sourced ginger samples under relative humidity convective drying. The present findings will offer more information in the selection of the best pretreatment technique for drying ginger.

The application of unconventional technologies as pulsed electric field, ultrasound and microwave-vacuum drying in the production of dried cranberry snacks

A lot of effort is put to decrease the energy consumption of drying. This effect might be achieved by shift of a drying technology e.g. from a hot-air to a microwave-vacuum method. Moreover, an unconventional pre-treatment such as ultrasound or pulsed electric field may modify a cellular tissue, what influences drying kinetics of plant tissue. The aim of the study was to analyse the quality of microwave-vacuum dried, osmodehydrated (OD) cranberries processed by the means of blanching and ultrasound (US) or blanching followed by pulsed electric field and sonication (PEF + US) in comparison to traditionally treated material. Physical, chemical and sensorial properties of cranberry fruits were assessed. What is more, the impact of aforementioned unconventional treatments on the kinetics of microwave-vacuum dried cranberries was studied. Microwave-vacuum drying process was very short (25-38 min) in comparison to convective drying, which lasted several hours (13.2 h). Most of the samples subjected to US and PEF + US treatments before OD and drying were characterized by similar or a higher amount of bioactive compounds such as polyphenols, anthocyanins and flavonoids, and better colour and taste, as compared to cut osmodehydrated cranberry fruits subjected to convective drying (reference samples).

Effects of ultrahigh pressure and ultrasound pretreatments on properties of strawberry chips prepared by vacuum-freeze drying

The present work investigated the influences of ultrahigh pressure (UHP), ultrasound (US) and their combination (UHP-US) as pretreatments on properties of vacuum-freeze dried strawberry slices. During vacuum-freeze drying, drying duration and total energy consumption of UHP sample, US sample and UHP-US sample was decreased. After the UHP or US pretreatments, a* value (redness), antioxidative substances (total anthocyanin content, total flavonoid content, total phenolic content, diphenyl picrylhydrazyl (DPPH), hydroxyl (-OH) radical-scavenging assay), hardness and cross-section areas of matrix in the dried slices were significantly (P < 0.05) increased. Transverse relaxation times and peak area corresponding to free water in the pretreated samples were obviously decreased, indicating lower mobility in the pretreated samples. As compared with UHP or US individually, UHP in combination with US increased those parameters more pronouncedly. Therefore, UHP and US are promising techniques for the vacuum-freeze drying processing of strawberry products.

The Application of Combined Pre-treatment with Utilization of Sonication and Reduced Pressure to Accelerate the Osmotic Dehydration Process and Modify the Selected Properties of Cranberries

The aim of this study was to investigate the effect of a pretreatment, performed by a combined method based on blanching, ultrasound, and vacuum application, on the kinetics of osmotic dehydration and selected quality properties such as water activity, color, and bioactive compound (polyphenols, flavonoids, and anthocyanins) content. The pretreatment was carried out using blanching, reduced pressure, and ultrasound (20 min, 21 kHz) in various combinations: Blanching at reduced pressure treatment conducted three times for 10 min in osmotic solution; blanching with reduced pressure for 10 min and sonicated for 20 min in osmotic solution; and blanching with 20 min of sonication and 10 min of reduced pressure. The osmotic dehydration was performed in different solutions (61.5% sucrose and 30% sucrose with the addition of 0.1% of steviol glycosides) to ensure the acceptable taste of the final product. The changes caused by the pretreatment affected the osmotic dehydration process by improving the efficiency of the process. The use of combined pretreatment led to an increase of dry matter from 9.3% to 28.4%, and soluble solids content from 21.2% to 41.5%, lightness around 17.3% to 56.9%, as well as to the reduction of bioactive compounds concentration until even 39.2% in comparison to the blanched sample not subjected to combined treatment. The osmotic dehydration caused further changes in all investigated properties.

Water state and sugars in cranberry fruits subjected to combined treatments: Cutting, blanching and sonication

To ease the mass exchange in fruit tissues, cutting and blanching are traditionally performed. However, recently, unconventional methods such as sonication are becoming more popular, which cause several alterations of physical and chemical properties as well as microstructure changes. The aim of this work was to evaluate the distribution of water inside the cranberry fruits, microstructural changes and sugars content, following traditional and sonication pre-treatments in osmotic solutions. TD-NMR spectroscopy was used to measure the transverse relaxation time (T₂) and intensity of proton pools in different cellular compartments. The microstructure of the samples was evaluated by SEM microscopy, sugars content by HPLC and sucrose melting temperature and enthalpy by DSC. Different pre-treatments appeared to promote microstructure alterations and loss of water from vacuole and cytoplasm/extracellular space, more pronounced in cut and blanched samples. Cutting and blanching followed by osmotic dehydration with assisted sonication eased sucrose penetration into the tissue.