Potential bioaccessibility and bioavailability of polyphenols and functional properties of tiger nut beverage and its by-product during in vitro digestion†

“Horchata de chufa” is a beverage produced from tiger nut tubers, which yields a high amount of by-product. This study explored the functional properties of the Spanish tiger nut beverage (TNB) and its by-product (TNBP) together with the bioaccessibility and bioavailability of polyphenols in vitro. TNB and TNBP were characterized for polyphenols via LC/MS/MS and underwent in vitro digestion (INFOGEST). The total antioxidant capacity (TAC) of all bioaccessible fractions and digestion residues was assessed. Intestinal bioaccessible fractions were tested for the ability to inhibit the activity of digestive enzymes (α-amylase, α-glucosidase, and lipase) and the content of polyphenols, whose bioavailability was assessed in a Caco-2 cell model. Thirteen polyphenols were quantified and found to be more abundant in TNB (603 ± 1.4 μg g⁻¹ DW) than in TNBP (187 ± 1.0 μg g⁻¹ DW). Polyphenol bioaccessibility was higher for TNBP than that for TNB (57% vs. 27%), and despite a similar TAC of the intestinal bioaccessible fractions (10.2 ± 0.1 μmoL vs. 9.2 ± 0.03 μmoL eq. Trolox per g DW for TNB and TNBP, respectively), the different patterns of polyphenols released upon digestion suggested the higher ability of TNBP fraction to inhibit α-glucosidase and lipase. TNBP digestion residue showed higher TAC than TNB. Moreover, TNB polyphenols exhibited over 80% bioavailability, whereas TNBP polyphenols’ bioavailability ranged from 62% to 84%. Overall, the findings demonstrated that TNBP maintains a high nutritional value, thus suggesting its possible reuse in innovative, healthy, and sustainable foods.