Production of riboflavin by lactic acid bacteria in soymilk.

JUÁREZ DEL VALLE, M; LEBLANC, JG; SAVOY DE GIORI, G

Clermont-Ferrand

Congreso; 18ème Colloque du Club des Bactéries Lactiques,; 2012

l'unité de recherche Calityss de VetAgro Sup, avec la participation de l'Inra.

Riboflavin (vitamin B2) is one of the B-group water-soluble vitamins and is an essential component of energy metabolism since it is the precursor of two important coenzymes: flavin mononucleotide (FMN) and flavin adenin dinucleotide (FAD). Humans need to obtain riboflavin in their diet regularly because they lack the ability to synthesize this vitamin and the body is unable to store this vitamin. Although riboflavin is found in a wide variety of foods, subclinical deficiency of riboflavin is common in many parts of the world, even in highly industrialized countries. In order to prevent riboflavin deficiencies, many countries include this vitamin in generalized fortification programs using the chemically produced enzyme. Recently, there has been an increase interest in the search for more natural methods of increasing vitamin concentrations in foods, including riboflavin, in order to prevent deficiencies. Soymilk, the water extract of soybean, is a rich source of high quality proteins, amino acids and unsaturated fatty acids; however, it contains very low concentrations of riboflavin. Furthermore, it has previously been shown, that some lactic acid bacteria (LAB) can synthesize riboflavin, making these ideal candidates to increase B2 concentrations in fermented foods; however, riboflavin production is a strain dependent trait. Taking into account all of these observations, the objective of this study was to evaluate the potential of LAB to increase the concentrations of riboflavin in soymilk. From the 180 strains of LAB belonging to CERELA culture collection, that were isolated from a large variety of fermented foods from Northwestern Argentina,46 showed the ability to grow in a riboflavin-free chemically defined medium. All of these strains produced riboflavin, determined by means of a microbiological method using L. rhamnosus ATCC7469 as the reference strain, in a strain dependent manner. From these results, 12 LAB strains were selected according to their riboflavin production pertaining to the following species: Lactobacillus (L.) bulgaricus (2 strains), St. thermophilus (2), L. reuteri (1), L. plantarum (2), L. fermentum (2), L. paracasei (2), Lactoccocus lactis (1). These strains were used to inoculated (OD: 0.1) soymilk (that was freshly prepared and sterilized in our laboratory) and incubated at 37ºC during 24 h. Samples were withdrawn at the start incubation and after 24 h to determine bacterial growth and riboflavin concentrations. Since some strains were unable to grow in soymilk, glucose (0.1 g/l) or yeast extract (5 g/l) were added. In our laboratory conditions, soymilk supplemented with glucose or yeast extract contained around 60 or 300 ng B2/ml, respectively. After the incubation time, some strains were able to significantly increase the riboflavin concentration with respect to initial concentration reaching values >150 ng B2/ml in soymilk + glucose and >600 ng B2/ml in soymilk + yeast extract whereas others did not modify B2 levels. These LABs could thus be used to elaborate riboflavin enriched soy-based foods that could form part of a balanced diet in order to prevent deficiencies of this essential vitamin.