Golden oats - Natural fortification of oat milk with riboflavin through fermentation.

Plant-based beverages are often fortified with different vitamins, especially B-vitamins, as the raw materials used for their production have a low content of these. Recently, we reported a simple and natural approach for obtaining vitamin B2 (riboflavin) secreting derivatives of the lactic acid bacterium (LAB) Lactococcus lactis, based on the observation that riboflavin can alleviate heat-induced oxidative stress. Here, we explore the potential of these strains for enriching plant-based beverages based on soy and oats, with riboflavin. Three riboflavin producing L. lactis strains were selected for the study: ER10, ALE13, and LDH13, where the latter is a lactate dehydrogenase-deficient derivative of ALE13. We found that ER10 produced more than 50 % more riboflavin in soy milk than ALE13 under static conditions (i.e. with no active aeration). Aerated culturing, in general, increased riboflavin production, especially for LDH13. The protein in oat milk is mostly insoluble and thus unavailable for the L. lactis strains used. To address this, oat milk was treated with food grade proteases, Alcalase® and Flavourzyme®, generating soluble peptides. When LDH13 was grown in the enzymatically treated oat milk with aeration, this resulted in a 600 % increase in riboflavin content (∼6 mg/L), demonstrating that the bioavailability of amino acids limits riboflavin production in oat milk. Here, we found that arginine played a special role in riboflavin production. By supplementing enzymatically treated oat milk with arginine, the riboflavin content could be further increased to 8 mg/L.