## 1 Introduction  
_Fagopyrum esculentum_ M., better known as common buckwheat, is a great source of proteins and fibers. However, secondary metabolites such as ruin or quercetin are also abundant in buckwheat grains, which have anti-tumor properties, e.g., lung adenocarcinoma [1]. According to [PERSON] et al. [2] quercetin extracted from buckwheat enhances autophagy against protein aggregation by suppressing mTOR activity. An experiment conducted by [PERSON] et al., altering the diet of rats, showed that buckwheat consumption led to a higher concentration of short fatty acids (SCFA) and increased levels of _Lactobacillus_, _Blautia_, and _Akkermansia_ strains in the gut. The same study also showed that supplementation of Tartary buckwheat improves colonic barrier function by initiating ZO-1 protein expression [3]. Moreover, buckwheat is considered to be involved in lipid metabolism and prevents obesity, fatty liver, and hypedimia [4]. Lately, buckwheat has been gaining popularity in beer production due to its gluten-free origin, making it suitable for those suffering from coeliac disease. However, brewing is only allowed if enzymes are incorporated into the process [5, 6, 7].  
Oligosaccharides are an interesting area due to their prebiotic potential and fermentability [8; 9]. Lactic acid bacteria (LAB) fermentation is known for increasing food biopreservation [10]. Organic acids, bacteriocins, biogenic amines, and other metabolites have antimicrobial properties. These properties are essential for the prevention of foodborne infections and for increasing overall human health [11; 12]  
Enzyme-assisted extraction is one of the most suitable ways to extract oligosaccharides from plant materials [13; 14]. It has mild extraction conditions, requiring relatively lower temperatures of 40-70 \({}^{\circ}\)C and no harsh solvents. Enzyme-assisted extraction also increases the stability of bioactive compounds during the extraction process [15]. However, enzymes need to be carefully tailored to the chosen plant material for extraction. Usually, for grain materials, amyloidtic and cellulolytic enzymes are selected. These enzymes cleave both starch and non-starch polysaccharides. They may cleave specifically, with the same bonds consistently cleaved between different grains, or randomly, where the cleaved bonds are inconsistent between different grains, requiring more scientific research to be implemented [16].  
Plant fermentation is a valuable source of volatile compounds [17]. The interest in probiotics and fermented products has risen in the past decade due to the discovery of a link with obesity, diabetes, cognitive function, and more. Although fermentation has been known for ages, scientists are now suggesting more specific metabolic mechanisms to explain its effects. Spontaneous fermentation usually encompasses a symbiotic relationship between bacteria and yeast colonies [18]. However, depending on the substrate, microbiological alteration may differ [19].  
Tibetan kefir grains (TFG) and birch sap (BS) contain LAB and yeast colonies, which induce spontaneous fermentation when an appropriate substrate and suitable conditions are prepared [20; 21]. In general, LAB fermentation is known for bio-preservative compound formation [22]. For example, acetic, lactic, and propionic acids form the media unfavorable for many pathogenic and spoilage bacteria [23; 24].  
This research aims to compare the effects of different hydrolytic enzymes on common buckwheat oligosaccharides before and after in-vitro digestion. The graphical experimental design is presented in Figure 1. Hydrolyzed buckwheat extracts were further fermented with TKG and BS. The fermented extracts were then collected for evaluation of potent antimicrobial properties against ten different pathogenic bacteria.  
Figure 1: Experimental design overview.