Thermal stability and bioaccessibility of apple phenolics in starch systems are governed by their molecular motifs, plant cell walls, and cell wall pre-loading

Wheat starch (S), an apple cell wall analogue (aACW), and an apple pomace phenolic extract (PP) were formulated into blends-S-PP, S-aACW, S-aACW-PP, and phenolic pre-loaded wall composites S-(aACW:PP)-then hydrothermally processed and digested to elucidate the molecular determinants of phenolic thermal degradation and gastrointestinal bioaccessibility in starch-fibre systems. Processing-induced phenolic loss and bioaccessibility decreased with starch, declined further with aACW, and were most suppressed in S-(aACW:PP). Single-compound analysis revealed distinct lability clusters. Group-1 included heat-labile phenolics, slightly stabilized by starch but strongly protected by aACW, particularly when preloaded. Group-2 showed pronounced matrix dependence, with starch additionally exerting a stabilizing effect. A small group exhibited stochastic matrix effects. During digestion, small phenolics benefited from aACW retention. In contrast, larger flavanols were prone to precipitation by starch and aACW, reducing their bioaccesibility. Phenolic structure, interactions with S and aACW, and aACW pre-loading together determined thermal and digestive stability and gastrointestinal release.