## 1 Introduction  
Brazil is a country rich in biodiversity, and much concern has been focused on the preservation of its five native biomes, as degradation of these biomes could have serious consequences, such as contributing to climate change, for the whole world. The Cerrado biome, which is located in the midwestern region of the country, currently contains approximately 22% of the natural vegetation [1]. Thus, efforts have been made to enhance awareness and better use of the native species to ensure their preservation [1, 2, 3]. In this biome, there are several species of native fruits that are considered to be sensorially and nutritionally attractive but are commercially devalued, mostly consumed in nature, and rarely processed and used technologically [4]. _Arccomia aculeata_ (Jacq.) Lodd., known as macauba or bocaitiva, is one of the species that occur naturally in the Cerrado biome and has shown potential as a major source of daily nutrient intake. The epicarp of the fruit has a thin, hard, brittle, fibrous structure,and light brown color, while the mesocarp has a yellowish color due to the presence of bioactive color compounds such as carotenoids (\(\sim\)200 \(\mu\)g/g) [5], mainly \(\beta\)-carotene [6]. Bocaiiova pulp is also rich in lipids (\(\sim\)29%) [5], especially fatty acids such as oleic (\(\sim\)53%), palmitic (\(\sim\)25%), and linoleic (\(\sim\)14%) [7,8]. Deficiency of oleic and linoleic acid has been associated with morbidity and mortality outcomes, including all causes, coronary heart disease, stroke, and cardiovascular disease [9], while the presence of palmitic acids has demonstrated a hypercholesterolemia effect [10]. In addition, the pulp of bocaiiova has a large amount of fibers (\(\sim\)20%) [5], which can contribute to the recommended daily intake for this nutrient. Fibers can promote rapid gastric emptying, decrease intestinal transit time, and increase fecal bulk, promoting actions beneficial to the health of the human body [11]. _A. aculeata_ (Jacq.) Lodd. fruits have been used in regional cuisine; are consumed by local people in preparations such as ice cream, cakes, and sweets; and have been used in cosmetics and energy production [5,7,8,12]. Soybean is a legume that has been used to develop food products because of its high nutritional value, mainly its protein contents, and its health benefits, mainly due to the presence of phenolic compounds and isoflav, as well as its low potential for adverse health effects [13]. Although this chemical composition in terms of health potential is known, investigating forms of processing that provide a greater amount of these nutrients, such as fermented soy products, is still a priority. Soymilk is one soybean product, which, with fermentation, can be a source of bioactive peptides as well as genistein and daidzein, which are responsible, in part, for the beneficial effects of soy products [14]. Several classes of microorganisms can be used for soymilk fermentation, including acidophilic bacteria, especially lactic acid bacteria such as _Lactobacillus_ and _Leuconostoc_, and yeasts, such as _Kluyveromyces_, _Pichia_, and _Saccharomyces_ in their isolated form [15, 16, 17, 18] or symbiosis association from kombucha [19] or kefir [20]. Kefir has been used for the production of functional products for people with special dietary needs (lactose intolerant individuals and vegans) [20] because it can also be used to ferment non-dairy substrates, such as fruits and vegetables, and produce functional beverages with distinct sensory characteristics [21, 22, 23, 24]. The use of kefir in the soymilk fermentation process has been presented in the literature [25, 26, 27, 28, 29], and one of the benefits of the fermentation process using microorganisms is the release of aglycone isoflav, as well as the glycosylated phenolic compounds present in soymilk or soybean [30,31], which increases the bioavailability of these compounds for the human organism.