###### Abstract  
Drying herbs is a crucial method for stabilizing and preserving their essential properties and bioactive compounds. Although freeze drying is the preferred method for most herbs, it is expensive due to high energy consumption and operating costs. Biflavonoids are dimeric flavonoids that have recently been recognized as potential molecules possessing biological activities, such as antiviral and antimicrobial activity, and as effective molecules for the treatment of neurodegenerative and metabolic diseases and for cancer therapies. In this study, we performed a comparative analysis of freeze drying, air drying and oven drying to evaluate their effects on biflavonoid content in yellow ginkgo leaves (_Ginkgo biloba_ L.). After drying, we performed spectrophotometric analysis to determine the browning index, pigments, phenolic compounds and antioxidant activity, while HPLC-DAD was used for the identification and quantification of individual biflavones (amentoflavone, bilobetin, ginkgeetin, isoginkgeetin and sciadoptiysin). The most abundant biflavonoids were isoginkgeetin and bilobetin, the amounts of which exceeded 1000 \(\upmu\)g/g dw in all leaf samples. They were followed by ginkgeetin and sciadoptiysin, the amounts of which were about 30% lower. The drying method did not influence biflavone content or the total carotenoids, total polyphenols and total flavonoids. Consequently, our study suggests that all three methods may be used for the preparation of yellow ginkgo leaves as a source of biflavones and other bioactive compounds. air drying; biflavonoids; freeze drying; ginkgo; oven drying +
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Drying of herbs is a crucial technological process primarily aimed at removing the water content and enabling longer preservation of raw materials [11]. The drying process of plant material facilitates the removal of water, effectively suppresses metabolic processes and ensures the stability of the chemical composition of the plant material [11]. In addition, it helps to minimize the presence of microorganisms so that the full range of physicochemical and sensory properties of the plant product is preserved [12]. Drying processes can take place under natural conditions, such as air drying, or in controlled artificial environments with temperature control (either high or low) and vacuum. Considering the time required and the need to prevent the possible contamination or damage of samples by external factors, artificial drying systems are increasingly preferred, especially drying chambers and freeze drying [13]. As elevated drying temperatures can lead to degradation of and reductions in the desired components, freeze drying is increasingly being used [11; 14]. Drying methods have a major impact on the various properties of the final product, including the presence and composition of bioactive components as well as physicochemical and organoleptic properties [15]. In high temperature drying, a hot air circulation system is used to vaporize water, while in freeze drying, also known as vacuum drying, the water is suppressed under low pressure after the plant material has been previously frozen [11]. Freeze drying allows high efficiency in removing water from the plant matrix while keeping all bioactive components stable and preserving their chemical structure. It is often the method of choice to extract flavonoids [13]. Although heat and freeze drying techniques shorten the drying time, they also have their limitations. For example, freeze drying is energy-intensive, while heat drying can affect quality [14]. The use of an appropriate drying method can therefore reduce production costs, preserve the bioactive compounds in the material and improve the quality of the final products. However, the literature shows that the effect of leaf drying depends on the type of leaves. In the case of mulberry leaves, [PERSON] et al. [16] reported that air drying and freeze drying are the best methods to preserve the antioxidant activity of flavonoids.