Functional Properties of an Oat-Based Postbiotic Aimed at a Potential Cosmetic Formulation

The concept of postbiotic has been attracting the attention of the scientific community and several industrial realities to develop new claims and new market segments for functional fermented products. The aim of this work was to develop a process to produce an oat-based postbiotic ingredient to be used in personal care cosmetic formulations. A hydrolyzed oatmeal suspension was fermented using Lacticaseibacillus paracasei CBA L74 as starter culture, at 37 °C for 48 h by controlling the pH; then the bacterial charge was inactivated by a mild thermal treatment at 80 °C for 30 s, obtaining a postbiotic. The effect of different process steps, hydrolysis, sterilization, fermentation, and inactivation phases, on lactic acid concentration, total polyphenolic content, antioxidant activity, tyrosinase inhibition activity and Sun Protection Factor value was investigated, demonstrating the potential cosmetic applications. The maximum bacterial growth and lactic acid production were achieved after 24 h of process, with a cell density and a lactic acid concentration of 3.05 × 109 CFU/mL and 8.60 g/L, respectively. The total phenolic content and the antioxidant activity reached their maximum values (2.5 mgGAE/mL, EC50 = 2.2 mg/mL and 1.38 × 10−2 mmol Fe2+/g and 7.3 × 10−3 mmol TE/g, respectively) after the sterilization treatment; the maximum tyrosinase inhibition of 50.6%, corresponding to a sample concentration of 16 mg/mL, was found after 24 h of fermentation process. Fermentation did not show an impact on UV shielding ability and the SPF value decreased during the process