# Volatilome and Bioaccessible Phenolics Profiles in Lab-Scale Fermented Bee Pollen
## 1 Introduction  
Bee-collected pollen (BCP) is currently receiving increasing attention due to its remarkable levels of valuable nutrients and bioactive compounds [1, 2, 3, 4]. BCP is rich in proteins (5-60%), essential amino acids, simple sugars (13-55%), unsaturated and saturated fatty acids (1-10%), and crude fibre (0.3-20%). Other minor constituents include minerals (Ca, Mg, Fe, Zn, Cu, and with a high K/Na ratio), vitamins (provitamin A, vitamin E, niacin, thiamine, biotin and folic acid), phenolics (flavonoids and phenolic acids), carotenoid pigments, and phytosterols [2]. According to [PERSON] and [PERSON] [2], fifteen grams of BCP may account for a significant part of the required daily intake for sugars, proteins, and some vitamins and minerals. Even though BCP is mainly exploited as a dietary supplement, it is not easily digestible by humans, and more than 50% of its nutrients are not bioaccessible due to the intine-exine complex of pollen grain wall. The exine mostly consists of sporopolenin, which provides strong chemical and physical resistances and protects the compounds inside the pollen grains [3, 4, 5]. Therefore, BCP needs to be processed before human consumption, in order to impair the pollen wall and to increase the accessibility of nutrients for intestinal absorption. Several biotechnological options have been proposed for BCP processing, including physical, chemical and biological treatments [6, 7, 8, 9, 10]. Fermentation is one of the most attractive opportunities, because it emulates the natural maturation process of bee-head, which is mediated by bee-associated microbial communities [11]. Within the beehive, the conversion of BCP to bee bread results from several biochemical changes, including the modification of the intine-exine complex, which in turn leads to an increased accessibility of nutrients and bioactive compounds [3; 4]. The predominance of lactic acid bacteria in bee bread was previously reported, with _Apilactobacillus kunkeei_, _Fructobacillus fructosus_, and _Lactiplantiobacillus plantarum_ as dominant species. The occurrence of yeasts, molds, and other aerobic and anaerobic bacteria has also been described. Many of these microorganisms are metabolically relevant during bee bread maturation, while some of them are simply contaminants [12; 13; 14; 15]. Due to the prominent role of this complex microbial consortium, the emulation of bee bread fermentation through a controlled lab-scale process is difficult. Several studies investigated the aptitude of selected microbial starters to ferment BCP in order to obtain dietary supplements with improved nutritional and functional features compared to the raw BCP [16; 17; 18]. During BCP fermentation, innumerable biochemical reactions are mediated by the primary and secondary metabolisms of microorganisms. Such metabolic pathways frequently are connected to the adaptive growth and survival of microorganisms [19]. Most importantly, some microbial metabolic traits may modify the bioaccessibility and bioavailability of phytochemicals. Other than taking part in breakdown of pollen walls, microorganisms may drive the degradation of complex molecules, which in turn release smaller molecules often characterized by greater bioaccessibility and bioavailability. For instance, free volatile terpen may be released upon hydrolysis of glycosylated conjugated precursors. Similarly, microbial enzymes may contribute to the release of proteins- and carbohydrates-associated phenolics. To the best of our knowledge, there is a lack of data on the metabolite changes during BCP fermentation, especially with regard phenolics and other secondary vegetables metabolites. This study proposed an integrated metabolomic approach to investigate how the use of starters may affect the volatilome and the profile of bioaccessible phenolics during fermentation of BCP.