Reformulation of gluten-free sponge cakes with pulsed electric field-treated kiwifruit pomace: Unravelling the nutritional and functional impact through a foodomics-based in vitro digestion approach

Gluten-free (GF) bakery products are often nutritionally poor in dietary fiber and bioactive compounds compared to their gluten-containing counterparts. Kiwifruit pomace, a by-product of juice processing, represents an underexploited source of such compounds, and pulsed electric field (PEF) pretreatment offers a green strategy to further modulate its phytochemical profile. This study evaluated the incorporation of control and PEF-treated kiwifruit pomace (2.5% and 5%) into GF sponge cakes, assessing nutritional composition, descriptive sensory analysis, total phenolic content (TPC), antioxidant activity, and untargeted metabolomics coupled with chemometrics, both in raw sponge cakes and after in vitro gastrointestinal digestion. Pomace addition significantly increased total dietary fiber content (up to 77% at the highest inclusion level) and TPC, enhancing antioxidant capacity across all digestion phases, particularly in the intestinal fraction. Metabolomic profiling showed that kiwifruit pomace enriched the sponge cakes with flavones, flavonoids, and phenolic glycosides, whereas PEF-treated pomace additionally increased the abundance of saponins and steroidal alkaloids; in vitro digestion further amplified these effects by increasing the bioaccessibility of terpenoids and lignans and enhancing antioxidant activity. Sponge cakes containing 2.5% kiwifruit pomace showed only minor sensory changes while retaining the nutritional benefits of reformulation, and PEF treatment additionally attenuated the textural changes associated with higher incorporation levels. Overall, these findings identify 2.5% PEF-treated kiwifruit pomace as the optimal formulation for balancing nutritional enrichment, phytochemical bioaccessibility, and sensory acceptability, supporting PEF-assisted by-product valorization as a sustainable, foodomics-guided strategy for designing next-generation functional GF bakery products aligned with circular economy principles.