# Optimization of the Drying Temperature for High Quality Dried Melissa officinalis
## 1 Introduction  
_Melissa officinalis_ (i.e., lemon balm) is a medicinal and aromatic plant (MAP) belonging to the Lamiaceae family. Despite its origins in southern Europe and Asia, it is cultivated worldwide for its culinary and health-promoting properties [1, 2]. Lemon balm is most frequently used as an anti-anxiety remedy, but recent research has also explored its effects on the nervous system and neurocognitive processes in cases of depression, insomnia, and stress [3, 4, 5]. In addition to its use as an infusion/tea, Melissa's essential oil (EO) is widely utilized in traditional medicine for the treatment of various ailments [6]. The industry employs both fresh and dried MAPs to produce new, natural (less synthetic) and eco-friendly products, including medicines, cosmetics, food and dietary supplements, etc. [5, 7, 8]. Scientific research focuses on the development of high-quality plant materials [9, 10, 11] and their derivatives, as well as the preservation of these products [12, 13].  
Fresh herbs have a relatively high moisture content (up to 75-80%), which must be reduced to below 15% (ideally between 5 and 13% to ensure optimal storage and preservation [14]. The moisture content of dried plant materials should be monitored and kept as low as possible (with a maximum referenced value of 12%) to prevent microbialcontamination and deterioration [15]. According to [PERSON] et al. [16], a low moisture level enhances stability, reducing the risk of product degradation while preserving of important compounds. Additionally, reducing moisture content decreases the weight and volume of the dried product, facilitating packaging and storage while lowering transportation cost [17].  
The drying process and conditions are crucial for maintaining the final product's quality, as they can cause undesirable changes such as alterations in color, texture, flavor, and aroma, as well as reductions in phytochemicals and nutraceuticals [18; 19]. The extent of these changes depends on the drying method and parameters used [20; 21]. Standard drying techniques, including sun, shade, and oven drying, are commonly applied to MAPs without considering the potential loss of bioactive compounds and the resulting decline in the quality of the final product [22]. Furthermore, the energy consumption associated with the drying process is a critical factor due to its financial implications [23]. Optimizing the balance between dryer design, operational efficiency, energy consumption, and product quality requires significant managerial decision-making [24]. While increasing the drying temperature can accelerate the process, previous studies have reported adverse effects on the dried product and the extracted EO, particularly at temperatures between 50 and 60 \({}^{\circ}\)C [22; 25]. Research has shown that drying temperatures between 35 and 50 \({}^{\circ}\)C can help preserve heat-sensitive compounds [18; 26]. For _M. officialis_, previous reports show that drying at temperatures higher than 45 \({}^{\circ}\)C contributed to color degradation, while plants dried at 30-40 \({}^{\circ}\)C resembled the green color of the fresh product [27; 28]. Therefore, optimizing drying methods for specific MAPs is essential.  
This study aimed to examine the effects of different drying temperatures (20, 35, 42, and 49 \({}^{\circ}\)C) on the quality attributes (moisture content, color, chlorophyll content) and the EO composition of _M. officialis_. Additionally, the environmental impact (energy consumption and carbon footprint) was assessed to determine the optimum drying temperature for this herb.