Bioaccessibility of phytochemicals and nutrients in nixtamalized Cucurbita spp.: An in vitro and microstructural...

Cucurbits contain functional and nutritional compounds that could be potentiated by nixtamalization. The objective was to evaluate the effect of nixtamalization on the bioaccessibility of phytochemicals (oxalates, carotenoids, polyphenols) and nutrients in Cucurbita pepo, Cucurbita argyrosperma, and Cucurbita maxima. Cucurbit cubes (side: 2 cm) were nixtamalized for 6 min and subsequently dehydrated (60 °C, 24 h), obtaining some flour. Determined proximal chemical composition, total oxalates, total carotenoids, individual polyphenols (HPLC), and antioxidant capacity; subsequently, in vitro digestions were performed. Calcium, oxalates, carotenoids, polyphenols, and antioxidant capacity were quantified in the accessible fraction. The bioaccessibility index (BI) was calculated from this data. The microstructure of the non-digestible fraction was also analyzed, where specific nutrients and carotenoids were identified. Nixtamalization caused increases in ash (>70 %), fat (13 %), crude fiber (19 %), carotenoids (9-27 %), and antioxidant capacity (16-20 %), and reduced carbohydrates (13 %) and oxalates (>63 %). An increase in the IB of calcium (39-66 %), carotenoids (33-48 %), and antioxidant capacity (20-24 %) was observed. In addition, after nixtamalization, the IB of individual polyphenols increased: gallic (43 %) and chlorogenic acids (76 %), epicatechin (85 %) catechin (84 %), and quercetin (90 %). In the non-digestible fraction, the most homogeneous dispersion of carbohydrates, lipids, and carotenoids was observed in the cellular tissue after nixtamalization. In conclusion, nixtamalization of cucurbits decreased the concentration of oxalates and improved the bioaccessibility of calcium and polyphenols. This process represents a viable strategy to valorize cucurbits and develop innovative functional ingredients.