Optimization and Bioaccessibility Evaluation of Black Myrtle ( <i>Myrtus communis</i> L.) Juice: Antioxidant Properties and Processing Effects

Black myrtle (Myrtus communis L.) is a valuable raw material for the functional food industry due to its rich phytochemical composition and strong antioxidant potential. However, a significant research gap exists regarding the integrated impact of industrial processing and gastrointestinal (GI) digestion dynamics on the bioaccessibility of these bioactive compounds. The aim of the study was to optimize the extraction conditions of pasteurized and concentrated clear myrtle juice, to monitor changes in total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacities (2,2-diphenyl-1-picrylhydrazyl [DPPH], 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) [ABTS], ferric reducing antioxidant power [FRAP], and cupric ion reducing antioxidant capacity [CUPRAC]) during processing, and to evaluate the bioaccessibility of these properties under in vitro GI digestion. Production protocols were mathematically validated utilizing response surface methodology (RSM), in vitro GI simulations, and principal component analysis (PCA)-based multivariate analysis. The findings confirmed that optimized extraction conditions maximize bioactive recovery. Pasteurization significantly (p < 0.05) enhanced phenolic bioaccessibility compared to concentrated juices by facilitating matrix destabilization. Conversely, thermal concentration induced substantial anthocyanin degradation, whereas the high antioxidant potential retained in the pomace underscored its viability for value-added valorization. These findings provide critical technological and industrial implications, indicating that mild thermal processing offers a strategic pathway for formulating black myrtle as a scientifically substantiated nutraceutical ingredient while supporting the development of innovative, functionally optimized beverage products.