Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences-SGGW, 02-787 Warsaw, Poland.
Department of Petroleum Engineering, College of Engineering, Knowledge University, Erbil 44001, Iraq.
Molecules. 2022 Mar 27;27(7):2164. doi: 10.3390/molecules27072164.
The drying process preserves the surplus of perishable food. However, to obtain a good-quality final product, different pretreatments are conducted before drying. Thus, the aim of the study was the evaluation of the effect of thermal (blanching treatments with hot water) and non-thermal technologies (pulsed electric field (PEF) and ultrasound (US)) on the kinetics of the drying process of red bell pepper. The convective and microwave-convective drying were compared based on quality parameters, such as physical (water activity, porosity, rehydration rate, and color) and chemical properties (total phenolic content, total carotenoids content, antioxidant activity, and total sugars content). The results showed that all of the investigated methods reduced drying time. However, the most effective was blanching, followed by PEF and US treatment, regardless of the drying technique. Non-thermal methods allowed for better preservation of bioactive compounds, such as vitamin C in the range of 8.2% to 22.5% or total carotenoid content in the range of 0.4% to 48%, in comparison to untreated dried material. Moreover, PEF-treated red bell peppers exhibited superior antioxidant activity (higher of about 15.2-30.8%) when compared to untreated dried samples, whereas sonication decreased the free radical scavenging potential by ca. 10%. In most cases, the pretreatment influenced the physical properties, such as porosity, color, or rehydration properties. Samples subjected to PEF and US treatment and dried by using a microwave-assisted method exhibited a significantly higher porosity of 2-4 folds in comparison to untreated material; this result was also confirmed by visual inspection of microtomography scans. Among tested methods, blanched samples had the most similar optical properties to untreated materials; however non-thermally treated bell peppers exhibited the highest saturation of the color.
干燥过程可以保存易腐食物的剩余部分。然而，为了获得高质量的最终产品，在干燥之前需要进行不同的预处理。因此，本研究的目的是评估热（热水烫漂处理）和非热（脉冲电场（PEF）和超声（US））技术对红甜椒干燥过程动力学的影响。基于物理（水分活度、孔隙率、复水率和颜色）和化学性质（总酚含量、总类胡萝卜素含量、抗氧化活性和总糖含量）等质量参数，比较了对流和微波对流干燥。结果表明，所有研究的方法都缩短了干燥时间。然而，最有效的方法是烫漂，其次是 PEF 和 US 处理，无论采用哪种干燥技术。与未处理的干燥材料相比，非热方法可以更好地保留生物活性化合物，如维生素 C（8.2%至 22.5%）或总类胡萝卜素含量（0.4%至 48%）。此外，与未处理的干燥样品相比，PEF 处理的红甜椒表现出更高的抗氧化活性（高约 15.2-30.8%），而超声处理则降低了自由基清除潜力约 10%。在大多数情况下，预处理会影响物理性质，如孔隙率、颜色或复水性能。经 PEF 和 US 处理并采用微波辅助干燥方法的样品的孔隙率显著提高了 2-4 倍，与未经处理的材料相比；这一结果也通过微断层扫描的目视检查得到了证实。在测试的方法中，烫漂样品的光学性质与未经处理的材料最相似；然而，未经热处理的甜椒表现出最高的颜色饱和度。
