Lemon Balm as a Source of Potentially Bioaccessible Rosmarinic Acid: The Effect of Herbal Preparation Type, Dosage, and Digestion-Related Factors

This study aimed to evaluate how the dosage, type of herbal preparation (plant material, dry extract, or isolated compound), along with simulated digestion-related factors, i.e., digestion stage (gastric vs. intestinal) and corresponding physicochemical and biochemical environment, influence the in vitro bioaccessibility of lemon balm phytochemicals. Simulated in vitro digestion revealed that the bioaccessibility of rosmarinic acid (RA), total phenolics, and antioxidant activity strongly depended on the application form, dose, and digestion stage. Isolated RA exhibited the highest gastric in vitro bioaccessibility, which markedly decreased during intestinal digestion. Dry extracts provided consistently higher in vitro bioaccessibility of RA, TPC (Total Phenolic Content), ABTS (ABTS scavenging activity), and FRAP (Ferric Reducing Antioxidant Power) than powdered plant material, particularly at doses of ≥25 mg. Intestinal digestion enhanced the in vitro bioaccessibility of phenolics and antioxidant activity from plant material under physicochemical conditions, whereas biochemical digestion factors generally reduced in vitro bioaccessibility, especially at lower doses. Overall, higher doses ensured more stable in vitro bioaccessibility across all analysed parameters.