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 bacteria (LAB) Lactococcus lactis (L. 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 almost 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 enzyme treated oat milk with aeration, this resulted in an almost 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 enzyme hydrolyzed oat milk with arginine, the riboflavin content could be further increased to 8 mg/L.