Apple pomace is a by-product of apple processing industries with low value and thus frequent disposal, although with valuable compounds. Acidified hot water extraction has been suggested as a clean, feasible, and easy approach for the recovery of polyphenols. This type of extraction allowed us to obtain 296 g of extract per kg of dry apple pomace, including 3.3 g of polyphenols and 281 g of carbohydrates. Ultrafiltration and solid-phase extraction using C18 cartridges of the hot water extract suggested that, in addition to the apple native polyphenols detected by ultra-high-pressure liquid chromatography coupled to a diode-array detector and mass spectrometry UHPLC-DAD-ESI-MSⁿ, polyphenols could also be present as complexes with carbohydrates. For the water-soluble polyphenols, antioxidant and anti-inflammatory effects were observed by inhibiting chemically generated hydroxyl radicals (OH•) and nitrogen monoxide radicals (NO•) produced in lipopolysaccharide-stimulated macrophages. The water-soluble polyphenols, when incorporated into yogurt formulations, were not affected by fermentation and improved the antioxidant properties of the final product. This in vitro research paves the way for agro-food industries to achieve more diversified and sustainable solutions towards their main by-products.

Yeast cell walls undergo modifications during the brewing process, leading to a remodelling of their architecture. One significant change is the increased insolubility of the cell wall glycogen pool, likely due to the formation of covalent bonds between glycogen and cell wall polysaccharides . To verify this hypothesis, we extracted the brewer's spent yeast with 4 M KOH, obtaining an insoluble glucan fraction (AE.4 M) primarily composed of ( α1 → 4)- and (1 → 3)-linked Glc residues. Dynamic nuclear polarization solid-state NMR of AE.4 M revealed distinct glucan resonances that helped to differentiate between α- and β glucosyl (1 → 4)-linked residues, and confirm covalent linkages between (β1 → 3)-glucans and glycogen through a (β1 → 4)-linkage. The hydrolysis with different endo-glucanases (zymolyase, cellulase , and lichenase) was used to obtain solubilized high molecular weight glycogen fractions. NMR analysis showed that covalent links between glycogen and ( β1 → 6)-glucans through (α1 → 6) glycosidic linkage, with branching at the C6 position involving (β1 → 3), and (β1 → 6)-glucans. HPAEC-PAD analysis of the enzymatically released oligosaccharides confirmed covalent linkages of (β1 → 3), (β1 → 6)-, and (β1 → 4)-glucan motifs with (α1 → 4)-glucans. This combination of multiple enzymatic approaches and NMR methods shed light into the role of yeast cell wall glycogen as a structural core covalently linked to other cell wall components during the brewing process.