Drying Kinetics, Microstructure and Antioxidant Properties of Basil Treated by Ultrasound

Recent processing of fruits and vegetables using emerging thermal and non-thermal technologies. A critical review of their potentialities and limitations on bioactives, structure, and drying performance

Fruits and vegetables have rich bioactive compounds and antioxidants that are vital for the human body and prevent the cell from disease-causing free radicals. Therefore, there is a growing demand for high-quality fruits and vegetables. Nevertheless, fruits and vegetables deteriorate due to their high moisture content, resulting in a 40-50% loss. Drying is a common food preservation technique in the food industry to increase fruits and vegetables' shelf-life. However, drying causes chemical modifications, changes in microstructure, and bioactives, thus, lowering the final product's quality as a considerable amount of bioactives compounds and antioxidants are lost. Conventional pretreatments such as hot water blanching, and osmotic pretreatment have improved fruit and vegetable drying performance. However, these conventional pretreatments affect fruits' bioactive compounds retention and microstructure. Hence, emerging thermal (infrared blanching, microwave blanching, and high-humidity hot-air impingement blanching) and non-thermal pretreatments (cold plasma, ultrasound, pulsed electric field, and edible films and coatings) have been researched. So the question is; (1) what are the mechanisms behind emerging non-thermal and thermal technologies' ability to improve fruits and vegetables' microstructure, texture, and drying performance? (2) how do emerging thermal and non-thermal technologies affect fruits and vegetables' bioactive compounds and antioxidant activity? and (3) what are preventing the large-scale commercialization of these emerging thermal and non-thermal technologies' for fruits and vegetables, and what are the future recommendations? Hence, this article reviewed emerging thermal blanching and non-thermal pretreatment technologies, emphasizing their efficacy in improving dried fruits and vegetables' bioactive compounds, structural properties, and drying performance. The fundamental mechanisms in emerging thermal and non-thermal blanching pretreatment methods on the fruits and vegetables' microstructure and drying performance were delved in, as well as what are preventing the large-scale commercialization of these emerging thermal and non-thermal blanching for fruits and vegetables, and the future recommendations. Emerging pretreatment approaches not only improve the drying performance but further significantly improve the retention of bioactive compounds and antioxidants and enhance the microstructure of the dried fruits and vegetables.

The impact of ultrasound-assisted thawing on the bioactive components in juices obtained from blue honeysuckle (Lonicera caerulea L.)

Ultrasound (US) assisted thawing of blue honeysuckle berry was utilized in order to reduce the losses of bioactive components (ascorbic acid, anthocyanins, phenolic acids, iridoids, proanthocyanins) and increase the extraction efficiency during juice processing. It was analysed whether it was more beneficial to apply US (alone or with enzymatic treatment) to the frozen state, until reaching the cryoscopic temperature or thawed state. Both the US and enzymatic treatment significantly increased the extraction efficiency, extract content, acidity and the content of iridoids and chlorogenic acid in juices, especially if the US was applied to 50 °C. It was probably due to a higher extractivity by the greater damage of the tissue and detexturation. Enzymatic treatment due to long heating contributed to a higher degradation of anthocyanins, ascorbic acid and proanthocyanidins, which are more heat-sensitive. The results of the study mainly indicated the possibility of including ultrasound-assisted thawing in the fruit processing before pressing the juices. This may replace costly enzymatic treatment.

Postharvest Microwave Drying of Basil (Ocimum basilicum L.): The Influence of Treatments on the Quality of Dried Products

Edible herbs are widely used in the human diet due to their pleasant flavors and countless health benefits associated with their components having, mainly, antioxidant and anti-inflammatory therapeutic functions. Since herbs are highly perishable materials because of their high water content, to guarantee products are safe and stable over time, it is necessary that they undergo stabilization operations. The application of microwave-assisted drying, a promising technique in terms of process sustainability, for the stabilization of the aromatic herb, Ocimum basilicum L., was investigated. The activities were carried out by applying different operating conditions in order to evaluate the impact of the time/temperature combination on the final quality of dried basil. The latter was investigated via the chemical characterization of extracted essential oils and tissue damages. Conventional convective processes were also applied to perform comparisons between dried basil products both under production and the quality preservation points of view. Results showed that microwave heating is suitable as a drying method, as expected, due to the well-known interaction between vegetable tissue (rich in water) and the electromagnetic field; and that drying methods have a different influence on the chemical composition of the essential oils extracted from dried products, in terms of the number (ranging from 41 to 18 components in different dried samples) and percentage (until 67% in linalool and 21% in α-trans-bergamotene in different dried samples) of its’ constituents.

Ultrasound pretreatment application in dehydration: its influence on the microstructure, antioxidant activity and carotenoid retention of biofortified Beauregard sweet potato (Ipomoea batatas Lam)

This work aimed to evaluate the effects of ultrasound pretreatment on the microstructure, antioxidant activity, and carotenoid retention of biofortified Beauregard sweet potato (BBSP). The pretreatment was carried out in an ultrasonic bath at 30 °C for 10 min, and it was evaluated in terms of water loss and solid gain. The drying process was performed at two different temperatures (50 and 70 °C). Six different semi-theoretical mathematical models were examined to characterize the drying curves, and quality analyses were executed. The two-terms exponential model provided the best simulation of the drying curves. Drying time was reduced by performing ultrasound pretreatment and by increasing drying temperature. The ultrasound treatment caused greater agglomeration, breakage, or strangulation of the BBSP structure, increasing porosity, and thus increasing drying rates. Drying caused a diminution of total carotenoids content and influenced antioxidant activity. However, the samples pretreated with ultrasound and dried produced lower total carotenoids loss.

Influence of Drying Type of Selected Fermented Vegetables Pomace on the Natural Colorants and Concentration of Lactic Acid Bacteria

Nowadays, foods with probiotic bacteria are valuable and desired, because of their influence on human gut and health. Currently, in the era of zero waste, the food industry is interested in managing its waste. Therefore, the aim of the study was to determine the influence of drying process on the physicochemical properties of fermented vegetable pomace. The work included examining the influence of the lactic acid bacteria (Levilactobacillus brevis, Lactiplantibacillus plantarum, Limosilactobacillus fermentum and its mixture in the ratio 1:1:1) used for vegetable fermentation (beetroot, red pepper, carrot), obtaining pomace from fermented vegetables, and then selection of drying technique using the following methods: convection drying (CD) or freeze-drying (FD) on the physical and chemical properties of pomace. In the obtained pomace and its dried form, dry substance, water activity, color, and active substances such as betalains and carotenoids by spectrophotometric method and also bacteria concentration were evaluated. After fermentation of pomace from the same vegetable, a similar concentration of lactic acid bacteria was found as well as dry substances, color and colorants. Results of physico-chemical properties were related to the used vegetable type. After drying of pomace, it could be seen a high decrease in bacteria and colorant concentration (betalains, carotenoids) independently from drying and vegetable type as well as used starter cultures. The smallest change was observed for spontaneously fermented vegetables compared to those in which the starter culture was used.

Influence of Ultrasound and the Conditions of Convective Drying with Dehumidified Air on the Course of the Process and Selected Properties of Apple Tissue

The conditions of convective drying induce a negative effect on the quality of the dried products, and thus, innovative solutions, such as the utilization of ultrasound and dehumidified air are gaining importance. Therefore, the aim of this study was to evaluate the impact of ultrasound pretreatment and variable air temperature on the kinetics of convective drying with dehumidified air and the quality of dried apples. Apples were dried with dehumidified and non-dehumidified air at 55, 70 and 85 °C. Preliminary ultrasound treatment was conducted by immersion for 60 min. The effect of both ultrasound and dehumidified air utilization was more prominent in the terms of drying time reduction, when lower drying temperatures were used. Drying of apples with dehumidified air, preceded by ultrasound pretreatment, resulted in a greater rehydration capacity of the products, and limited the browning process. Dehumidified air increased the lightness of the dried products, while sonication darkened them. The use of ultrasound before drying coupled with a drying with dehumidified medium at a temperature of 70 °C reduced the exposure of the product to a high temperature and oxygen. Products treated before dehumidified air drying with ultrasounds were characterized by high total phenolic content and the greatest antioxidant activity. This was because such technological treatment reduced exposure of the product to a high temperature and oxygen.

The Quality of Infrared Rotary Dried Terebinth (Pistacia atlantica L.)-Optimization and Prediction Approach Using Response Surface Methodology

Most agricultural products are harvested with a moisture content that is not suitable for storage. Therefore, the products are subjected to a drying process to prevent spoilage. This study evaluates an infrared rotary dryer (IRRD) with three levels of infrared power (250, 500, and 750 W) and three levels of rotation speed (5, 10, and 15 rpm) to dry terebinth. Response surface methodology (RSM) was used to illustrate and optimize the interaction between the independent variables (infrared power and rotation speed) and the response variables (drying time, moisture diffusivity, shrinkage, color change, rehydration rate, total phenolic content, and antioxidant activity). As infrared power and rotation speed increased, drying time, rehydration rate, antioxidant activity, and total phenolic content decreased, while the other parameters were increased. According to the results, the optimum drying conditions of terebinth were determined in the IRRD at an infrared power of 250 W and drum rotation speed of 5 rpm. The optimum values of the response variables were 49.5 min for drying time, 8.27 × 10⁻⁹ m²/s for effective moisture diffusivity, 2.26 for lightness, 21.60 for total color changes, 34.75% for shrinkage, 2.4 for rehydration rate, 124.76 mg GAE/g d.m. for total phenolic content and 81% for antioxidant activity.

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.

The Quality of Red Bell Pepper Subjected to Freeze-Drying Preceded by Traditional and Novel Pretreatment

It has been demonstrated previously in the literature that utilization of PEF or a combination of a pulsed electric field (PEF) and ultrasounds (US) can facilitate dehydration processes and improve the quality of dried products even better than the application of thermal methods such as blanching. The aim of the study was to evaluate the quality of red bell pepper subjected to freeze-drying preceded by blanching or PEF or US treatment applied in a single and combined mode. Furthermore, the freeze-drying was preceded by shock freezing or vacuum freezing performed inside the freeze-dryer as a result of pressure drop during the first stage of freeze-drying. All of the analyzed technological variants enhanced the drying kinetics when compared to the intact material. Freeze-dried bell pepper subjected to non-thermal pretreatment exhibited higher vitamin C, total phenolic and carotenoids content than blanched material despite the fact that blanching reduced drying time the most compared to all other analyzed methods.

The Assessment of the Possibility of Using Ethanol and Ultrasound to Design the Properties of Dried Carrot Tissue

The purpose of this study was to investigate the effect of pre-treatment in ethyl alcohol for 5, 15, 60 and 180 s with the application of ultrasound on the course of convective drying and properties of carrot tissue directly after the treatment and after the drying process. The treatment in ethanol resulted in loss of mass, increase of dry matter, ethanol conductivity, extractivity of carotenoids with a slight effect on the colour of carrot tissue after the treatment. The utilization of ultrasound during immersion in ethanol contributed to additional increase of conductivity of ethanol, and extractivity of carotenoids. The immersion in ethanol virtually did not affect the drying kinetics, which can be explained by the increase of shrinkage of the tissue in relation to the untreated dried tissue. Despite the lack of the influence on the drying course in the ethanol-immersed carrot, an increase of the carotenoid content (up to 135%) and the rehydration ability (up to 19%) was noted with the simultaneously unchanged colour of dried carrot in comparison to untreated dried material, which indicates the possibility to improve the quality of dried carrot after immersion in ethanol.

The Impact of the Pre-Treatment in Ethanol Solution on the Drying Kinetics and Selected Properties of Convective Dried Apples

The aim of this study was to investigate the effects of pre-treatment in ethanol solution carried out in variable time with and without ultrasound (US) assistance on convective drying kinetics, total phenolic content (TPC) and hygroscopicity of an apple. The drying time after immersion in ethanol solution was shorter up to 13.4 (without US) and 18.3 % (with US) in comparison to intact slices. The most appropriate model that described kinetics of drying was the one proposed by Sledz et al. Drying of the untreated apple resulted in a decrease of the TPC by 18 %, compared with raw apples and the pre-treatment led to further losses. The tissue after ethanol pre-treatment was less hygroscopic, which proves the possibility to maintain a characteristic texture of the dried apple with prolonged storage stability. The best quality of dried apples was obtained after 1 min of ethanolic pre-treatment with US.

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).

Influence of applied time and power of ultrasonic pretreatment on convective drying of potato slices

Ultrasound is a novel technology that can be applied as a pretreatment for the convective drying in order to reduce its undeniable shortcomings. The objectives of the present study are to ascertain the influence of sonication time (10, 20, and 30 min) and sonication power (100 and 300 W) on the performance of drying potato slices with regard to the drying kinetics and energy efficiency as well as the final product quality. The results showed that the application of ultrasound pretreatments significantly increased the drying rate of potato slices during the initial period of the drying process. Furthermore, ANOVA showed that the decrease in the sonication time and power gave rise to a significant reduction in drying time, specific energy consumption (SEC), and shear strength. In addition, compared to the control (pure convective drying), ultrasound pretreatments reduced the drying time, SEC, and the shear strength of dried potato slices.