Butter aroma compounds in plant-based milk alternatives through fermentation: screening of potential starter cultures and enhanced production in oat milk with Lactococcus cremoris

Acetoin and diacetyl are aromatic compounds that confer creamy and butter aroma to products such as yogurt and cheese. As such, they can also impart desired sensory properties to plant-based products such as dairy analogues. These compounds are produced by lactic acid bacteria, but few strains can produce amounts high enough to be considered relevant strains for its use as fermentation starters. Therefore, in this study we aimed to identify a great acetoin and diacetyl bacteria producer using different reported methods. We identified the Lactococcus cremoris strain CNTA 939 as a great producer of these compounds and optimized its production in synthetic medium and in plant-based milk alternatives. In the latter, it was detected that the availability of free amino acids is crucial for allowing good fermentation performance by strain CNTA 939, and it was demonstrated that relevant acetoin and diacetyl titers (115 and 8 mg/L, respectively) can be achieved without adding external supplements. • Voges-Proskauer, not Kempler & McKay, suits detecting butter aroma-producing LAB. • Wild type Lactococcus cremoris CNTA 939 excelled in acetoin/diacetyl production. • Protease treatment of oat milk boosts fermentation for acetoin/diacetyl production. • Strain CNTA 939 in oat milk produced acetoin/diacetyl above water aroma thresholds.