Phenolic compounds and antioxidant activity are differentially affected by drying processes in celery, coriander and parsley leaves

Coriander (Coriandrum sativum) Polyphenols and Their Nutraceutical Value against Obesity and Metabolic Syndrome

Coriander is a widely used plant for its medicinal and biological properties. Both coriander essential oil and extracts are interesting sources of bioactive compounds and are widely used as spices in culinary practice due to their exclusive aroma and flavour. We focus our attention on coriander extracts that are rich in polyphenols. It is well known that plant polyphenols possess different biological activities and several functional foods contain this class of compounds. The polyphenol profile in an extract can be influenced by the plant part studied, the method of extraction and other parameters. This study performs a literature review using the words "coriander", "polyphenols" and "extraction" or "biological activity" in different databases such as PubMed, Google Scholar and Scopus. After that, we focus on the evidence of coriander polyphenols as protective agents against some inflammation-related diseases. Due to the bioactivities of coriander extract, this herb can be considered a valuable functional food against obesity, metabolic syndrome and diabetes.

Kinetic Modeling of Convective and Microwave Drying of Potato Peels and Their Effects on Antioxidant Content and Capacity

This study deals with drying properties and focuses on the drying kinetics of potato peels (PP) by two processes, namely convection drying (CD) at various temperatures (40, 60, 80, 100, and 120 °C) and microwave drying (MD) at different powers (200, 400, 600, and 800 W). In addition, the effectiveness of the adopted processes was evaluated in terms of antioxidant contents and antioxidant capacity. A total of 22 mathematical models were undertaken to predict the drying kinetics, and the best model was selected based on the highest R2 values and the lowest χ2 and RMSE values. The Sledz model was the more appropriate for both methods with values of 0.9995 ≤ R2 ≤ 0.9999, χ2 = 0.0000, and 0.0054 ≤ RMSE ≤ 0.0030 for CD, and the results of MD were 0.9829 ≤ R2 ≤ 0.9997, 0.0000 ≤ χ2 ≤ 0.0010, and 0.0304 ≤ RMSE ≤ 0.0053. The best drying rates (DR) of PP were assigned to a temperature of 120 °C and a power of 600 W with values of 0.05 and 0.20 kg water/kg dw min, respectively. A potential explanation is that as PP’s moisture content decreased during the drying process, there was a drop in absorption, which led to a reduction in the DR. The energy consumption of both processes was assessed, and it rose with increasing temperature or power. The microwave process reduced the drying time, consumed lower energy, and presented a higher drying efficiency at a moderate power level compared to the convection process. Furthermore, MD preserved antioxidants better compared to CD and improved the antioxidant capacity. Therefore, the proposed microwave process for drying PP is suggested for its expected use in various fields, including the food processing industries.

Drying Characteristics and Quality Analysis of Medicinal Herbs Dried by an Indirect Solar Dryer

Considering the solar radiation status in Oman, a low-cost, indirect, stand-alone, forced-convective solar dryer was developed to dry medicinal herbs, which are sensitive to direct sun. The hot air flow was obtained using a solar-panel-powered blower and air passing through a black-body solar collector. This drying process could extend the shelf life of herbs while preserving their medicinal and nutritional (physicochemical) properties and adhering to food safety and hygiene practices. This study investigated the benefits of an indirect solar drying technique on the retention of quality attributes of mint and basil used in medicinal applications. Herbs used during drying could be subjected to changes in their physicochemical properties such as color, water activity (Aw), total soluble solids (TSS), phenol content, antioxidant capacity, and moisture content (MC), and, thus, results were compared with fresh herb samples. The dryer chamber-maintained temperature and relative humidity regimes of 30-50 °C and 21-95% and the expected final moisture content (wet basis) was 10%. The dryer showed improved physicochemical quality parameters and the retention of green color with parameter ranges of Aw 0.44-0.63, phenol content (increase) 1705-8994 mg/100 g DM, and antioxidant capacity (increase) 0.61-0.67 µmol/g DM, respectively. This study showed the ability of developed solar dryers to preserve the physicochemical properties of medicinal herbs during drying and can extend to other food products.