# Some Plant Food Products Present on the Polish Market Are a Source of Vitamin B12
## 1 Introduction  
Vitamin B12, also called cobalamin, is the most complex of all vitamins [1]. It is a key cofactor for the methylation process, essential in reactions related to DNA and in the metabolism of cells [2], as well as a key ingredient in the process of erythropoiesis. Therefore, its insufficient intake can cause negative effects on the homeostasis of the human body [3]. Mild deficiency is manifested by fatigue and anemia. Moderate deficiency is often associated with the occurrence of macrocytic anemia and the initial stage of neurological problems manifesting, among others, polyneuropathy. With a significant deficiency, the suppression of bone marrow function occurs along with serious neurological problems and an increased risk of cardiomyopathy [4; 5]. Deficiency of vitamin B12 also increases the risk of DNA damage [6]. Human requirements for vitamin B12 vary and depend, among others, on age and physiological condition. According to data from the European Food Safety Authority (EFSA), a daily intake of 1.5-2 \(\upmu\)cobalamin is the minimum requirement for maintaining a healthy hematological condition. Based on various factors and on the estimation of daily cobalamin losses, it was suggested that the daily requirement of cobalamin ranges from 4 to 20 \(\upmu\)g. Therefore, an adult should intake 4.0 \(\upmu\)g of cobalamin per day with food. The demand for this vitamin increases in pregnant women (4.5 \(\upmu\)g of cobalamin per day) and lactating women (5.0 \(\upmu\)g of cobalamin per day) [7]. People consume vitamin B12 from food. It is present in negligible amounts, if at all, in some plants, including vegetables, fruits and algae [1; 8; 9; 10; 11; 12; 13; 14], but mostly occurs as a result of the activity of microbes inhabiting the digestive tract of mammals, mainly ruminants. Therefore, meat and animal products are considered the best source of vitamin B12 in the human diet [15; 16]. People on a restrictive vegetarian diet, in particular vegans, are most at risk of vitamin B12 deficiency. The complete exclusion of the richest source of cobalamin, i.e., animal products, may be associated with negative health consequences. Conscious vegans support their diet by supplementation or by pharmaceutical preparations. In order to avoid vitamin B12 deficiency, some food producers fortify their products. However, many vegetarians tend to avoid processed foods [17]. Because vitamin B12 can be produced by bacteria found in the digestive tract of animals, it should also be synthesized during the lactic acid fermentation process. Lactic acid bacteria (LAB) are naturally present in the human digestive system and manifest the ability to synthesize B vitamins [18; 19]. Recently, selected bacteria were shown to be able to synthesize cobalamin. In 2003, there were indications that bacteria from the _Lactobacillus_ genus, in particular _Lactobacillus reuteri_, could effectively produce vitamin B12 [20]. An even greater amount of vitamin B12 was obtained by the controlled fermentation of plant products using a combination of LAB and propionibacteria [21]. In 2007 [PERSON] et al. showed that _Lactobacillus reuteri_ is able to produce pseudocvitamin B12 under beta-oxygen conditions. Pseudovitamin B12 differs from cobalamin in the \(\alpha\)-ligand where it has adenine in place of the 5,6-dimethylbenzimidazole \(\alpha\)-linked with the C-1 ribose [22]. Lactic fermentation is a natural food preservation method that has been applied for a long time. It is used to preserve and extend the shelf life and improve the taste, texture and functional properties of foods [23]. Both animal and vegetable products can be fermented. In Poland, the most popular fermented vegetables are white cabbage (sauerkraut) and cucumbers. Besides these plant materials, red cabbage, red beets, sorrel, tomatoes, peppers, carrots and many other vegetables can be also used. Fermented vegetable, fruit and vegetable-fruit juices are also quite popular in Poland. They are produced by the lactic fermentation of juices obtained from vegetables and fruits.