## 4 Discussion  
In summary, the analysis of the results described above highlights some important aspects of RSLDE that improve the features of conventional solid-liquid extraction techniques:  
1. The comparison of the extraction kinetics of different vegetable matrices by maceration and RSLDE showed that RSLDE allows obtaining, in just 72 h, more than 50% of product compared to what is obtained with maceration in two months. 2. The analysis of the kinetic curves shows that the maximum extraction yield occurs in just 12/24 h for the majority of vegetables compared to that obtained from maceration. It could be objected that the extract obtained using NE is slightly defective (5%), but this figure could be improved by squeezing the soaked plant material, or by lengthening the extraction time. Furthermore, the antioxidant capacity of the sample obtained by RSLDE is eight points higher than the sample extracted by maceration. 3. The study carried out on three types of extractive mixtures highlights the speed of RSLDE, as the maximum extractive yield of the products was reached in a maximum of 16 h. Due to its characteristics, RSLDE can be used in various sectors, such as pharmaceuticals, cosmetics, herbs, and food and beverages [17]. In the cosmetic sector, it is possible to produce extracts from vegetable matrices that contain pigments and odorous substances for the production and formulation of creams and perfumes [30; 31]. In this context, a further resource is represented by the possibility of using the processing waste of vegetable matrices such as grape skins, rich in polyphenols, which can be easily reused in many different ways through RSLDE without adding any organic solvent or by applying heating or cooling processes that can cause loss of substances of interest [32; 33]. In the herbal sector, RSLDE can be used to extract fluid bioactive molecules useful for herbal teas and/or infusions from plants and official herbs and for the production of liqueurs and elixins. Running the process at room temperature keeps the active ingredients unaltered. Comparing the product obtained using RSLDE with that derived from the traditionally used method, namely maceration, the organoleptic tests performed show that the bitters produced with RSLDE were more appreciated than the bitters prepared by maceration [34]. The same comparison was made for the preparation of lemon liqueur (_limoncello_), a typical liqueur of Campania, famous all over the world, which is made with lemon peels macerated in ethyl alcohol. In fact, the use of RSLDE makes it possible to produce limoncello in just 2 h, avoiding the long traditional maceration that takes 7-14 days [35; 36]. Furthermore, the efficiency of RSLDE was compared with another extraction technique that uses supercritical fluids (SFE), to obtain the extraction of acid compounds contained in hop flowers [37]. However, the sector where RSLDE is increasingly being applied is the food sector [17]. The previously cited work by [PERSON] et al. [37] reports a cyclically pressurized soaking process for the rapid hydration of cannellini beans at room temperature. The hydration process using RSLDE is approximately ten times faster than the traditional soaking procedure and the microbial load developed at the end of the process is much  
Figure 8: Comparison of the staining of a solution with artificial dye (**left**) and with Karkade extract (right). lower than that obtained using the traditional process [38]. Another sector where RSLDE finds application is in the recovery of processing waste, such as agri-food waste products, which can be important sources of bioactive compounds. Several studies have shown that tomato by-products contain significant amounts of bioactive phytochemicals, including lycopene, which when extracted from tomato peel could be used as natural antioxidants for the formulation of functional foods or as additives in food systems to extend their service life. RSLDE has been used to extract lycopene from tomato peel waste [39].