# Extraction of Galactolipids from Waste By-Products:
## 1 Introduction  
Galactolipids are a group of lipids that occur mainly in the thylakoids of higher plants and algae [1]. It is the main class of lipids found in plastid membranes, and their presence is crucial for the synthesis of the photosynthetic apparatus. Two main groups of galactolipids are distinguished: monogalactosyldiacylglycerols (MGDGs), which account for 50% of all lipids in thylakoids, and digalacosyldiacylglycers (DGDGs), which in turn account for 30% [2]; their structures are presented in Figure 1. Their synthesis takes place in the plastid envelope membranes by galactosyltransferase enzymes [3] An impact of a balanced diet rich in vegetables and fruits on consumers' health due to the presence of bioactive compounds has been known for decades. These compounds include galactolipids, which are considered to be an important class of nutraceuticals. So far, several positive effects have been attributed to galactolipids, e.g., MGDGs isolated from fresh spinach leaves inhibit the activation of the Epstein-Barr virus (EBV) [4]. Another study by [PERSON] et al. showed that the glycolipid fraction of spinach, containing, among other things, MGDGs and DGDGs, shows potential anti-cancerogenic features [5]. Moreover, the presence of galactolipids along with other compounds (such as carotenoids or terpenoids) present in rosehip (_Rosa canina_ L.) counteract osteoarthritis [6]. Its anti-inflammatory as well as anti-rheumatic properties were attributed to a galactolipid named GOPO. So far, many studies have been carried out that clearly show that in patients suffering from chronic inflammation of the bones and joints, there was a reduction in pain and an improvement injoint mobility after the administration of powdered rosehips [7]. More importantly, no side effects of the administered substances have been observed so far [8]. Products containing GOPO are commercially available on the pharmaceutical market; producers claim that thanks to the presence of this galactolipid, they can delay arthritic changes and slow down the degradation of cartilage tissue. It must, however, be noted, that the EFSA has so far not made any health claims connected with galactolipids. The details of the methods used by the manufacturers of galactolipid-based diet supplements are confidential; however, based on chemical properties of galactolipids, it can be assumed that extraction with organic solvents is the method of choice. In recent decades, there has been an increasing awareness of the environmental impact of production and processing, which has led to a global tendency to ensure the sustainability of such operations. The term \"green chemistry\" was coined to describe an alternative approach to the operations that were developed to be more environmentally friendly, often at the price of their profitability. The main principles of green extraction include the use of alternative solvents, innovative technologies, and the selection of renewable resources [10]. Some of the techniques have already found a place as the methods of choice in industrial applications, while others are still in the first testing stage. A broader description of the various methods of green extraction can be found in excellent reviews on the subject [11; 12]. Ultrasound-assisted extraction (UAE) refers to the modification of a typical solid-liquid extraction by applying high-intensity ultrasonic waves to the sample. Typical implementations of the process include the use of baths, with generators built in the wall of the vessel, and horns, which are immersed in the sample. Compared to other novel processing techniques, UAE is very inexpensive. The main driving force of the process is acoustic cavitation--the creation, expansion, and implosive collapse of microbubbles in ultrasound-irradiated liquids. The use of ultrasound also causes agitation, vibrations, shockwaves, microjets, and radical formation. The UAE benefits from enhanced mass transfer and an increase of the surface area due to the disintegration of the solid matrix [13].