Oxidative stability of plant sterols in a new enriched bakery product

Food enrichment with plant sterols (PS) is a common practice in the development of functional foods aimed at reducing the risk of cardiovascular diseases due to their known hypocholesterolemic effect. The addition of PS is authorized in rye bread, which is an interesting matrix due to its healthy nutritional profile and its growing consumption trend. However, PS are prone to oxidation and this may affect their content and/or bioavailability in PS-enriched products which are subjected to heating during baking/cooking, such as bread. In the present study, PS stability was assessed in a PS-enriched wholemeal rye bread by determining PS and their oxidation products (POP). PS and POP contents were determined in the microencapsulated free-PS powder ingredient (Lipophytol® Me Dispersible Lipofoods), wholemeal rye flour, and wholemeal rye bread (enriched with 2.3 g PS/100 g of bread or non-enriched). Gas chromatography-mass spectrometry (GC-MS) was used for PS and POP quantification. In all samples, the most abundant PS was β-sitosterol (44.5-76.4%), followed by β-sitostanol (15.0-16.1%), and campesterol (7.3-18.7%). POP were not present in the flour and PS ingredient, while only traces of 7β-hydroxysitosterol and 7-ketositosterol were found in the non-enriched bread. As expected, baking promoted PS oxidation and the consequent POP formation in the PS-enriched bread (732.0 µg POP/100 g of bread). Only POP deriving from β-sitosterol were found, with triol (163.62 µg/100 g of bread) and α-epoxysitosterol (150.31 µg/100 g of bread) as the most abundant oxysterols, followed by 7α-hydroxy (143.42 µg/100 g of bread), 7-keto (139.74 µg/100 g of bread) and 7β-hydroxy (134.94 µg/100 g of bread) derivatives. To exert their hypocholesterolemic effect, about 1.5 g/day of PS must be ingested, which corresponds to about 6 slices (12.5 g each) of PS-enriched bread. Regarding ingested oxysterols, the POP content (0.55-0.73 mg) found in 75-100 g of PS-enriched bread, was similar to the one detected in a PS-enriched beverage where no cytotoxicity was observed.