Effect of ultrasound pre-treatment on the kinetics and thermodynamic properties of guava slices drying process

Effects of ultrasonic pretreatment on drying characteristics and water migration characteristics of freeze-dried strawberry

The effects of ultrasonic pretreatment on the drying characteristics and microstructure of strawberry slices were investigated. The rehydration characteristics of freeze-dried products, which were pre-frozen at -20 °C and - 80 °C were explored, with a focus on water mobility and distribution. The ultrasonic pretreatment significantly increased the water mobility of the strawberry slices, resulting in a reduction in their water content. However, the application of ultrasound significantly decreased the rehydration speed, indicating a lower moisture absorption capacity in the pretreated sample. The micrographs revealed that the structure of the tissue was more uniform after ultrasonic treatment, and water loss was accelerated. In addition, the contact angle measurements showed that the samples were more hydrophobic after ultrasonic treatment, and the eutectic temperature and fold point of the samples increased. Therefore, this study found that ultrasonic-assisted freeze vacuum drying technology effectively reduces hygroscopicity, improves product storage, and represents a potential method for dried production.

Osmotic and convective hot air drying of sweet gourd

Kinetics of osmotic dehydration (OD) and insights into the effect of salt concentration (5%, 10%, 15%, 20%), drying temperature (50 ∘ C, 60 ∘ C, 70 ∘ C), and sample thickness (4 mm, 6 mm, 8 mm) on the drying kinetics of sweet gourd of two varieties (SGV-1 and SGV-2) were investigated based on the Fick's second law of diffusion model. Quality attributes (chemical and organoleptic) of biscuit formulated with osmotic dehydrated sweet gourd powder were assessed. Results showed that, significant changes occurred during the first 2 h of process where mass transfer kinetics were increased with increasing salt concentration. With increasing time, drying rate was proportional to the temperature, inversely proportional to the sample thickness as well as salt concentration. Moreover, sweet gourd variety has shown impact on formulated products quality and consumer acceptability which could serve as a ground to diversify the use of sweet gourd towards industrial application.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01193-x.

Ultrasonic pre-treatment to enhance drying of potentially probiotic guava (Psidium guajava): Impact on drying kinetics, Lacticaseibacillus rhamnosus GG viability, and functional quality

This study aimed to evaluate the effects of ultrasound (US) on the drying acceleration of potentially probiotic guava, including its impact on drying kinetics, probiotic (Lacticaseibacillus rhamnosus GG) viability, and functional quality of the product during drying. To perform US pre-treatments, one group of samples were first pre-treated by US (38 W/L, 25 kHz) for 15 and 30 min and then immersed in the probiotic solution for 15 or 30 min, and another group of samples were submerged in the probiotic solution simultaneously applying US (US-assisted) for 15 and 30 min. After pre-treatments, the samples were convectively dried at 60 °C. Based on the results, all US pre-treatments improved the drying rate (up to 59%) and reduced the drying time (up to 31%) to reach 25% moisture compared to non-sonicated samples. The reduction in drying time (from ∼6 h to ∼4 h for US pre-treated samples) was crucial for maintaining the probiotic viability in the dehydrated guavas. These samples showed counts of 6.15 to 7.00 CFU∙g-1 after 4 h, while the control samples reached counts of 4.17 to 4.45 CFU∙g-1 after 6 h. US pre-treatment did not affect the color parameters of the samples before drying (p > 0.05). The functional compounds were reduced during drying (p < 0.05), however, all US pre-treated samples had lower reductions in vitamin C content (up to 20%), phenolic compounds (up to 41%) and antioxidant capacity (up to 47%) compared to control samples (up to 52%, 81% and 61%, respectively). Therefore, US pre-treatment (highlighting the US-assisted probiotic incorporation for 30 min) reduced the drying time for guava slices and minimized the thermal impact on probiotic viability and functional compounds, being a strategy to produce potentially probiotic dehydrated guava.

Ultrasound applications in drying of fruits from a sustainable development goals perspective

This review focuses on the many contributions of ultrasound technologies for fruit drying toward the United Nations Sustainable Development Goals (SDG). Along this review, several aspects attained from the application of ultrasound technologies are correlated with the SDGs. The main ultrasonic technologies applied for fruit drying, such as ultrasonic bath, probe ultrasound, air-borne ultrasound air-drying, and ultrasound-assisted contact air-drying, are presented. An in-depth discussion on ultrasound contributions, its advantages, disadvantages, and limitations are made. The effects of ultrasound on water diffusivity in several fruits are presented by correlating this effect with drying time and cost of energy. Ultrasound-assisted fruit drying, like other food processing technologies, directly impacts Zero Hunger, but ultrasound technologies contribute to much more than delivering long shelf-life food. This technology can be used to produce healthy foods and provide well-being, which will be discussed by correlating the effects of ultrasound-assisted air-drying with the concentration of nutritional compounds. Ultrasound-assisted fruit drying reduces wastewater toxicity and energy consumption and improves productivity, potentially improving workplaces and salaries. A walk through the technology is presented from Zero Hunger to No Poverty.

Influence of Ultrasound-Assisted Vacuum Drying on Physicochemical Characteristics, Antioxidant Activity, and α-Glucosidase Inhibition Activity of Flos Sophorae Immaturus

Flos Sophorae Immaturus (FSI) contains a large number of bioactive substances with antioxidant and hypoglycaemic activity. However, a feasible drying process plays an important role in the retention of its biological activity. The present work investigated the effects of ultrasound-assisted vacuum drying (UAVD) on FSI samples in terms of drying time, colour, microstructure, and total flavonoid content (TFC). Meanwhile, the antioxidant activity and α-glucosidase inhibition activity were also evaluated. The results show that the drying time of UVAD samples was decreased by 40% compared to that of the single vacuum-dried (VD) samples (600 W for 10 min). The cellular porous structures of FSI tissue were formed by UAVD, which promoted the migration of water from the inside to the outside. Furthermore, samples treated by UAVD exhibited better antioxidant activities and α-glucosidase and α-amylase inhibition capacities, with DPPH (81.86%), ABTS (88.61%), FRAP (83.05%), α-glucosidase inhibition capacity (89%), α-amylase (85%), drying time (3 h), and total aberration (ΔE) (1.63) being the highest characteristic traits. In this condition, the highest levels of total flavonoid content (TFC), rutin, quercetin, kaempferol, isorhamnetin, and genistein were obtained with 266.94, 239.46, 35.56, 8.54, 10.37, and 5.64 mg/g DW, respectively. The results confirm that UAVD is a novel method that significantly reduced the VD time and promoted the release of the bioactive substances of FSI.

Impact of pretreatments with ethanol and freezing on drying slice papaya: drying performance and kinetic of ultrasound-assisted extraction of phenolics compounds

BACKGROUND

Pretreatments of drying can represent an alternative to minimize the negative aspect process on the dry samples. Thus, the influence of ethanol (ET) and freezing (FG) as drying pretreatments was analyzed for slices of papaya. The slices (5 mm) were submitted for drying kinetics (60 °C and 1.5 m s^-1 ). Drying kinetics experimental data were fitted using Page's model and a diffusive model with boundary condition of types I and III. Also the thermophysical properties (thermal conductivity and specific heat) were determined and finally, the kinetics of ultrasound-assisted (40 kHz and 132 W) extraction of total phenolic compounds (TPCs) were realized.

RESULTS

The combined method (ET + FG) was more efficient in reducing the drying time of papaya slices (48%) and the model 2 simulating the boundary condition of the third type (type III) showed the best fit to the experimental data. Effective diffusivity and convective coefficient were higher for ET + FG, where the maximum reduction in water content was 91% compared to fresh slices. The pretreatments did not influence the thermal conductivity, however, they were significant in the specific heat and in the extraction of TPCs, being higher in the time of 180 min.

CONCLUSION

It was confirmed in the results presented that the combined pretreatment ET + FG is the most viable for drying papaya slices. Furthermore, it was found to be the most efficient in minimizing the loss of TPCs. Therefore, this pretreatment has great potential for application in the development of high value-added foods. © 2022 Society of Chemical Industry.

Controlled Germination of Faba Beans: Drying, Thermodynamic Properties and Physical-Chemical Composition

The objective of this work was to determine the drying kinetics and the thermodynamic properties of the drying process of germinated seeds from faba beans of the Olho-de-Vó Preta (OVP), Raio-de-Sol (RS) and Branca (B) varieties. Additionally, the physicochemical properties of the germinated seeds and subsequent dried flours were determined. A thin layer of seeds were dried using a convective dryer at temperatures of 50, 60, 70 and 80 °C. Mathematical models were applied to the drying experimental data. The samples were further characterized for water content, water activity, ash, pH, alcohol-soluble acidity, total and reducing sugars, proteins, and starch. Page and Midilli models revealed the best predictions of the drying kinetics for all evaluated conditions. The effective diffusion coefficient increased with increasing temperature and presented magnitude in the order of 10−9 m²/s. The activation energy presented results in the range of 19 and 27 kJ/mol, falling within the range reported for agricultural products. The entropy and enthalpy values were higher in the OVP, followed by RS, higher than in the B variety. The increase in drying temperature resulted in a reduction of enthalpy and entropy and an increase in Gibbs free energy, indicating that the drying process is endothermic and requires external energy. Samples have acidic pH and acidity decreased with drying; the RS and B varieties had higher sugar contents; the B variety had the highest protein contents, and these were obtained from the in natura germinated samples; in the B variety the highest starch content was obtained. All flours showed good characteristics, presenting themselves as an alternative for diversifying the supply of beans.

Foaming characteristics and impact of ethanol pretreatment in drying behavior and physical characteristics for avocado pulp powder obtained by foam mat drying

The objective of this study was to optimize the production of powdered avocado using foam mat drying. In order to achieve this, the effect of Emustab^® (4, 6, and 8% w/w), goat's milk (10, 15, and 20% w/w), and whipping time (15, 20, and 25 min) on the foam physical properties of avocado pulp were evaluated. In addition, the influence of ethanol pretreatment on the drying kinetics, thermodynamic properties, and physicochemical characteristics of the powders was also assessed. An experimental design 2³ with three central points was used in this study and optimized foam conditions were dried at 50, 60, and 70°C, with a fixed air speed of 1.5 m/s. Empirical and diffusive models (boundary conditions of the third type) were adjusted to the experimental data to describe the drying kinetics and to determine the process activation energy and thermodynamic properties. The final products were characterized regarding their physical properties. Optimized foam mat drying conditions were achieved when avocado pulp was whipped for 15 min and 8% of Emustab^® and 20% of powdered goat milk were used as foaming agents. The use of an ethanol pretreatment and higher drying temperature (70°C) resulted in higher drying rate (1.6 × 10² /min) and shorter processing time (270 min). The ethanol pretreatment reduced the activation energy and Biot number and led to more uniform moisture distribution. The physical properties, such as water content, water activity, bulk, and tapped densities decreased with an increase in drying temperature and pretreatment with ethanol, whereas water absorption capacity increased. PRACTICAL APPLICATION: In this work, new information about the drying kinetics and mass transfer of the foam mat avocado pulp using ethanol as pretreatment is obtained. The results will contribute to the optimization production avocado foaming and powder. Ethanol pretreatment can represent an alternative to minimize the negative impacts on drying process and can be surely suggested as an industrial application.