Laura Analía Campañone

Microwave (MW) drying offers rapid processing but poses challenges in controlling thermal exposure, which can degrade heat-sensitive bioactive compounds such as ascorbic acid (AA) and anthocyanins. Although conventional and hybrid MW configurations have been explored, real-time temperature-based power modulation remains underexplored as a strategy to balance drying efficiency and bioactive retention. This study evaluated a temperature-controlled MW drying mode (Tcon), in which magnetron power was dynamically regulated via infrared thermography surface feedback, and compared it against conventional MW, fluidized-bed (FB), and hybrid FB–MW configurations for drying acerola ( Malpighia emarginata ). Drying kinetics, drying rate, and thermal histories were assessed alongside the retention of total polyphenol content (TPC), antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl), anthocyanins, and AA. The Tcon mode achieved the shortest drying time among the treatments evaluated while maintaining moderate surface temperatures, and showed higher retention of TPC, antioxidant capacity, and AA compared to fixed-power MW and hybrid processes. Hybrid configurations accelerated drying relative to FB alone; however, longer residence times led to greater cumulative thermal exposure and reduced bioactive retention. These findings suggest that real-time infrared-based power modulation is a promising strategy for improving bioactive preservation during MW drying of thermally sensitive fruit products.

Microwave technology offers a sustainable alternative to fossil fuel-based drying of particulate materials. Its combination with fluidized bed systems enhances process efficiency and product quality. A pilot-scale dryer with two magnetrons was used to study soybean and pumpkin seed drying. Samples were dried at 50 °C with air velocities twice the minimum fluidization value. Microwave power levels of 0, 350, and 750 W were applied. Weight loss after 30 min reached 32.2–42.5% for soybeans and 42.0–48.2% for pumpkin seeds. Moderate microwave power improved drying efficiency, highlighting the potential of microwave-assisted fluidized bed drying for food processing sustainability.

Microwave-assisted hydrodistillation (MAHD) method was employed to extract cinnamon oil and hydrosol (a byproduct). The total polyphenol content (TPC) of the cinnamon hydrosol (CH) was determined using the Folin-Ciocalteu method, and its antioxidant power was assessed through the DPPH radical reduction method. Gas chromatography was utilized to quantify the main bioactive compound (cinnamaldehyde). The disc agar diffusion method was applied to evaluate the inhibition of pathogenic microorganisms. To protect the bioactive compound, an encapsulation method involving cross-linking with calcium alginate was utilized. The capsules were examined using environmental scanning electron microscopy (ESEM). The TPC content was found to be 15.63 ± 0.21 mg gallic acid/g dry matter, and the DPPH radical inhibition rate was 84.26 ± 1.35%. CH exhibited a significant inhibitory effect against Escherichia coli, and a moderate inhibition effect against Shigella flexneri, Salmonella spp., Salmonella typhimurium, and Escherichia coli EPEC. Finally, successful encapsulation of CH was achieved using sodium alginate, resulting in bead sizes ranging between 1.75 and 2.75 mm.

Summary: The present study aimed to evaluate the combined application of edible coatings (alginate or pectin) and the osmotic dehydration process (glucose solution at 40 °Brix and 60 °Brix, solution temperatures of 20 and 40 °C, and process times of 1, 2, 4, 8, and 16 h) on mass transfer kinetics and physicochemical parameters (weight reduction (WR), water loss (WL), solids gain (SG), and optical and mechanical properties) of pear cubes. The best dehydration performance was observed in the coated samples treated at 60 °Brix‐40 °C. At the end of this process, the coated samples showed higher values of WR (77.30% and 75.13%) and WL (77.39%; 74.38%) and lower values of SG (1.69% and 1.24%) than the uncoated samples (WR: 65.97%, WL: 68.38%, and SG: 4.12%). Additionally, optimal retention of optical and mechanical properties was achieved in the coated samples exposed to the 40 °Brix‐40 °C condition.

This work presents the fluidized bed drying process combined with microwaves applied to Parchment coffee. In order to study different parameters that affect the quality of the grains, a mathematical model that describes energy and mass transfer during the drying process is presented and solved using Finite Elements Method (FEM) through COMSOL Multiphysics software. The model also considered the shrinkage of the grains due to water removal. Experiments were carried out in experimental prototype equipment obtaining the drying curves, which were utilized to validate the mathematical model. To study the impact of the operating conditions on the quality of the processed coffee, total polyphenolic content and antioxidant capacity were determined by Folin-Ciocalteau and free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods, respectively. Finally, nutritional parameters were related to operating conditions by the polynomial regression and desirability function methodology. Optimal operating conditions (1.4 m/s and 500 W) were found, which provides a product of excellent final quality.

Summary: The objective of the present work was to evaluate the combined effect of the application of edible coatings (sodium alginate and low methoxyl pectin) and different osmotic dehydration conditions (sucrose solution: 40 and 60 °Brix, temperatures: 20 and 40°C and times: 1, 2, 4, 8 and 16 h) on pear cubes (water loss, solid gain, performance ratio, the total colour differences, mechanical properties, phenolic content and sensory analysis). The results indicated that samples coated with low methoxyl pectin and treated under 60 °Brix for 16 h at both temperatures (20 and 40°C) presented the best process performance. Statistical analysis showed that the application of the coatings resulted in greater firmness and stiffness of the pear cubes at the end of osmotic dehydration. Besides, alginate coating best preserved the phenolic content (31.4%) than uncoated (26.04%) and pectin‐coated (20.77%) ones. However, total colour differences were not improved with the use of edible coatings (alginate or pectin). In terms of quality, the samples coated with both hydrogels had good overall acceptability by the evaluators and good mechanical properties. However, further studies are required to decrease the difference in colour and leaching of bioactive compounds in pear cubes due to the osmotic dehydration treatment.

The aim of the present study was to evaluate the effect of solar and microwave drying on raspberries (Rubus Idaeus) cv. Heritage. The efficiency of drying was evaluated in terms of weight reduction in function of the time. The quality properties evaluated were color, texture, antioxidant capacity and total polyphenols content. The results showed that solar drying and microwave drying allowed a good preservation of surface color in the final product. However, the solar drying achieved a desirable texture in dried raspberries compared to microwave drying. Neither solar drying nor microwave drying allowed a high retention of the antioxidant capacity. Nevertheless, both processes allow obtaining final stable fruits (low water activity) at any time of the year.

In fruits, strawberries in particular, appearance is an attribute of great importance. Appearance, which can be defined by color, shape, size and visual texture, not only determines the degree of maturation or the presence or absence of impurities, but also indicates the application of technological processes or prolonged storage conditions. In most cases, an excessive shrinkage of fruits negatively affects the preference and acceptance of these products by consumers. Particularly, in the case of dehydrated fruits, the geometric modifications (shape and size) caused by the process are a matter of great concern to the industry. Traditional techniques for monitoring physical and physico-chemical parameters of quality usually are time consuming, costly, laborious, invasive and impracticable during in-line monitoring at the industry. Computer vision techniques and digital image analysis are an attractive and economical alternative to evaluate the appearance changes of foodstuffs during processing. Therefore, the present work aims the evaluation and correlation of morphological characteristics area (A), by digital image analysis techniques, and thickness (L) measured by caliber in strawberries subjected to combined treatments that include application of edible coatings (alginate-lactate), osmotic dehydration (sucrose, 60 degrees Bx, 40 degrees C, 4h) and microwave assisted drying (1,2 W/g). Related to thickness, reductions of 60% (retention 40%) were obtained for fresh (FR+ MW) and fresh coated (FR_R+MW) samples. OD pre-treated samples (DO+MW and DO_R+MW) reached values of 37% (retention 63%). The digital processing of images showed cross sectional area reductions up to 56% for FR+ MW and FR_R+MW samples, being significatively higher (up to 18%) for samples previously osmo-dehydrated (DO+ MW and DO_R+MW). By correlating the L and A percentage retention, during MW-drying, excellent correlations were attained for FR+ MW and FR_R+MW samples (R-2: 97 and 98%).