Convective, vacuum and microwave drying kinetics of mallow leaves and comparison of color and ascorbic acid values of three drying methods

The Nutritional Potential of Avocado By-Products: A Focus on Fatty Acid Content and Drying Processes

The aim of this study was to analyze the content of fatty acids and tocopherols in various components (pulp, seeds, peel) of avocado (Persea americana), which are often neglected as by-products. In addition, the effects of different drying processes on these components were investigated and the health benefits of the main fatty acids contained in avocados were highlighted. The samples were subjected to three drying processes: hot air (HAD), vacuum (VD), and hot-air microwave (HAMD). In all parts of fresh avocado, oleic acid was the most abundant (41.28-57.93%), followed by palmitic acid (19.90-29.45%) and linoleic acid (8.44-14.95%). Drying led to a significant reduction in the oleic acid content, with palmitic acid showing the greatest stability. HAD resulted in higher levels of oleic acid and linoleic acid in dried pulp and peel samples compared with VD and HAMD, while HAMD had the highest content of α-linolenic acid in all parts. In addition, HAMD had the shortest drying time. HAMD duration was 35 min, which was 76.7% shorter than HAD (150 min) and 82.5% shorter than VD (200 min). Considering fatty acid retention and drying efficiency, HAMD appears to have been the most effective method, especially for the avocado peel. Remarkably, the avocado peel consistently contained higher total tocopherol, with δ-tocopherol generally being the most abundant form. The high content of tocopherols, oleic acid, and linoleic acid in the avocado peel suggests promising health benefits.

Thin layer drying kinetics and quality dynamics of persimmon (Diospyros kaki) treated with preservatives and solar dried under different temperatures

Poor postharvest handling, microbial infestation, and high respiration rate are some the factors are responsible for poor storage life of perishable commodities. Therefore, effective preservation of these commodities is needed to lower the damages and extend shelf life. Preservation is regarded as the action taken to maintain desired properties of a perishable commodity as long as possible. Persimmon (Diospyros kaki) is perishable fruit with high nutritive value; however, has very short shelf-life. Therefore, effective preservation and drying is needed to extend its storage life. Drying temperature and preservatives significantly influence the quality of perishable vegetables and fruits during drying. The current study investigated the effect of different temperatures and preservatives on drying kinetics and organoleptic quality attributes of persimmon. Persimmon fruits were treated with preservatives (25% honey, 25% aloe vera, 2% sodium benzoate, 1% potassium metabisulfite, and 2% citric acid solutions) under different drying temperatures (40, 45, and 50°C). All observed parameters were significantly affected by individual effects of temperatures and preservatives, except ash contents. Similarly, interactive effects were significant for all parameters except total soluble sugars, ash contents, and vitamin C. Generally, fruits treated with citric acid and dried under 50°C had 8.2% moisture loss hour^-1, 14.9 drying hours, 0.030 g H₂O g^-1 hr^-1, 1.23° Brix of total soluble solids, 6.71 pH, 1.35% acidity, and 6.3 mg vitamin C. These values were better than the rest of the preservatives and drying temperatures used in the study. Therefore, treating fruits with citric acid and drying at 50°C was found a promising technique to extend storage life of persimmon fruits. It is recommended that persimmon fruits dried at 50°C and preserved in citric acid can be used for longer storage period.

Effect of Microwave Drying on the Drying Characteristics, Color, Microstructure, and Thermal Properties of Trabzon Persimmon

In this study, changes in the drying kinetics, color change, and the energy consumption for microwave energy were investigated for Trabzon persimmon. In addition to that, the microstructure of the persimmon was also investigated by considering its thermal changes. It is important to be aware of the purpose of the drying process for determining the drying system. Results of this research showed that 460 W for 7 mm slice thickness depending on energy consumption, 600 W for 5 mm slice thickness depending on drying time, and 600 W depending on color changes were found as suitable drying processes depending on drying conditions. The effective diffusion values varied between 2.97 × 10⁻⁸ m² s⁻¹ and 4.63 × 10⁻⁶ m² s⁻¹. The activation energy values for 5 mm, 7 mm and 9 mm slice thickness were estimated as 32.82, 18.64, and 12.80 W g⁻¹, respectively. The drying time and energy consumption decreased, whereas drying rate increased with an increase in the microwave energy. The number of pores increased compared to structure of fresh sample, and the pores got to be larger for 5 mm slice thickness as the power level increased. Results showed that the applied microwave energy had an important effect on the heating of the material and the change in the microstructure.

Phenolic content and some physical properties of dried broccoli as affected by drying method

Broccoli samples ( Brassica oleracea) with an initial moisture content of 82.87% (wb) were dried using microwave technology (18, 36, and 54 W/g). Convective drying was used as a control group. The dependent variables investigated in the study were phenolic content, color, rehydration capacity, and microstructure of broccoli samples. Moreover, the best fitting thin layer model to the experimental moisture ratio was determined. The phenolic contents were found as 892.4, 740.6, and 759.8 mg gallic acid/100 g dry matter for fresh, convective dried, and microwave (MW) dried at 54 W/g broccoli samples, respectively. The total phenolic content of samples dried at 54 W/g was closest to fresh samples compared to other MW power intensities and convective drying. A similar result was obtained for color values too. L*, a*, and b* of microwave-dried samples at 54 W/g were comparable to fresh broccoli. Another important result obtained from the study was the insignificant effect of drying conditions on rehydration capacity. In addition, it was found that microwave power had a positive effect on drying time; as the microwave powers applied were compared, the shortest drying time was reached at 54 W/g. When the process durations of microwave drying and convective drying were compared, it can be reported that a much lower process time for microwave drying was obtained with respect to convective drying. Drying in microwave oven has reduced the drying time by 49-52%. In the light of the results obtained, it may be declared that it is possible to produce high-quality dried broccoli samples in a very short time by using microwave drying at 54 W/g.