The effect of drying methods on the color, chlorophyll, total phenolic, flavonoids, and macro and micronutrients of thyme plant

Effect of drying methods on phenolic compounds and antioxidant activity of Capparis spinosa L. fruits

BACKGROUND

Drying is a critical post-harvest process for medicinal plants, which are typically high in moisture and microorganisms. To prevent spoilage and quality loss, it is essential to dry these plants promptly. The drying method significantly impacts the levels of secondary metabolites and the organoleptic characteristics of medicinal plants. This study aimed to investigate the effects of various drying methods on the total phenolics, flavonoids, anthocyanins, antioxidant activity, and phenolic acids in caper (Capparis spinosa L.) fruits. The experiment was performed using a completely randomized design with three replications and included 11 treatments: shade drying, sun drying, oven drying (at 50 °C, 60 °C, and 70 °C), microwave drying (at 300 W, 600 W, and 900 W), freeze-drying, salt-drying, and a fresh plant sample as a control.

RESULTS

Among the drying methods tested, microwave drying consistently produced the highest levels of flavonoids, anthocyanins, and antioxidant activity, regardless of wattage. Specifically, the highest total phenol content was observed in samples dried at 900 W microwave, 600 W microwave, and 70 °C in the oven (5.3, 5.37, and 5.31 mg GAE/g DW, respectively). Drying at 600 W microwave yielded the highest levels of caffeic, cinnamic, ferulic, vanillic, and protocatechuic acids (13.03, 3.85, 4.28, 9.73, and 5.6 µg/g, respectively) while drying at 900 W microwave also resulted in elevated levels of caffeic, ferulic, protocatechuic, and p-coumaric acids. The 70 °C oven drying method also showed high levels of caffeic, cinnamic, ferulic, vanillic, and protocatechuic acids. Freeze-drying achieved the highest levels of rosmarinic, gallic, and m-coumaric acids (320.17, 175.3, and 12.99 µg/g, respectively), while shade drying produced high levels of p-hydroxybenzoic, cinnamic, ferulic, m-coumaric, protocatechuic, and p-coumaric acids.

CONCLUSIONS

Overall, microwave drying (especially at 600 W), oven drying at 70 °C, and freeze-drying emerged as effective alternatives to traditional drying methods. These methods not only preserved the color, texture, and taste of the fruits but also enhanced their bioactive compound levels.

Effects of Drying Treatments on Nutritional Compositions, Volatile Flavor Compounds, and Bioactive Substances of Broad Beans

In this study, different drying methods, including hot air drying, sun drying, and freeze drying were employed to dry fresh broad beans. The nutritional composition, volatile organic components and bioactive substances of the dried broad beans were systematically compared. The results indicated significant differences (p < 0.05) in nutritional composition, such as protein and soluble sugar content. Among the 66 identified volatile organic compounds, freeze drying and hot air drying significantly promote the production of alcohols and aldehydes, while sun drying effectively preserves esters. In terms of bioactive substances, broad beans dried by freeze drying exhibit the highest total phenol content as well as the strongest antioxidant capacity and gallic acid, followed by sun drying. The chemometric analysis revealed that the bioactive compounds in broad beans dried by three different methods were primarily composed of flavonoids, organic acids, and amino acids with significant differentiation. Notably, freeze-dried and sun-dried broad beans exhibited a higher concentration of differential substances.

UHPLC-QTOF-HRMS metabolomics insight on the origin and processing authentication of thyme by comprehensive fingerprinting and chemometrics

The metabolic composition of thyme, one of the most used aromatic herbs, is influenced by environmental and post-harvest processing factors, presenting the possibility of exploiting thyme fingerprint to assess its authenticity. In this study, a comprehensive UHPLC-QTOF-HRMS fingerprinting approach was applied with a dual objective: (1) tracing thyme from three regions of production (Spain, Morocco, and Poland) and (2) evaluating the metabolic differences in response to processing, considering sterilized thyme samples. Multivariate statistics reveal 37 and 33 key origin and processing differentiation compounds, respectively. The findings highlighted the remarkable "terroir" influence on thyme fingerprint, noticing flavonoids, amino acids, and peptides among the most discriminant chemical classes. Thyme sterilization led to an overall metabolite enrichment, most likely due to the facilitated compound accessibility as a result of processing. The findings provide a comprehensive metabolomics insight into the origin and processing effect on thyme composition for product traceability and quality assessment.