Unraveling the bioaccessibility of plant sterol oxidation products from plant sterol-enriched rye bread under young adult and senior digestion conditions.

Food enrichment with plant sterols (PS) is a common approach in developing functional foods to reduce the risk of cardiovascular disease [1]. Due to its nutritional properties and increasing popularity, rye bread is an attractive choice for incorporating PS [2]. However, PS can undergo oxidation during baking, raising concerns about potential toxic effects. Therefore, understanding the bioaccessibility of PS oxidation products (POPs) can provide essential information for consumers [3]. The aim of this study was to evaluate POP bioaccessibility from a PS-enriched (1.6 g/100 g) wholemeal rye bread subjected to different digestion conditions. The effect of gastric lipase (GL) and/or cholesterol esterase (CE) under young adult digestion conditions, as well as the adaptation to simulate senior population digestion conditions, were investigated. Bread digestions were performed as follows : i) for young adult conditions [4], INFOGEST method as control digestion (AC), INFOGEST 2.0 method for GL incorporation (A1) and Makran et al. [4] protocol for GL+CE addition (A2) were used; ii) for senior digestion assays[5], digestion with GL+CE was used as control digestion (SC), and adaptations for gastric (S1) and gastric and intestinal (S2) senior conditions were carried out. POPs in bread and bioaccessible fractions (BFs) were analyzed by gas chromatography-mass spectrometry to assess bioaccessibility [6]. In bread, only POPs derivatives from b-sitosterol were observed (mg/100 g) : triol (163.62), a-epoxy (150.31), 7a-hydroxy (143.42), 7-keto (139.74) and 7b-hydroxy (134.94). However, only 7a-hydroxy was detected in BFs from all digestion conditions. In young adult conditions assay, 7a-hydroxy contents were 87.26, 109.42, and 106.97 mg/ 100 g of bread for AC, A1, and A2, respectively. 7a-hydroxy bioaccessibility significantly increased with the addition of GL (A1, 25.45%) and GL+CE (A2, 22.59%) compared to AC. In the digestion assays under senior conditions, 7a-hydroxy content in BF ranged from 125.51 to 148.72 mg/100 g of bread for SC and S1, respectively, while it reached values of 98.40 mg/100 g of bread under S2 conditions. The bioaccessibility of 7a-hydroxy was 25.67% for SC, 30.41% for S1, and 20.12% for S2. Thus, the inclusion of lipid metabolism enzymes, like GL and CE, improved digestion conditions to better mimic the physiological environment. Moreover, the resulting lipolysis products can act as emulsifying agents, potentially facilitating the incorporation of POP into bile salt micelles. However, complete adaptation to senior population conditions reduced POP solubility, likely due to decreased lipolytic effect resulting from reduced enzyme activities. These findings provide valuable insights into the POPs fate under various digestion conditions, giving crucial information for consumers regarding the safety and potential health implications.