BACKGROUND: This study investigated the effects of supplementing maize and wheat with a combination of xylanase and cellulase on porcine in vitro digestibility, nonstarch polysaccharides (NSP) solubilization, and matrix structure. The latter was assessed using synchrotron-based micro-computed tomography (SR-μCT) and Fourier transform mid-infrared (FTMIR) spectroscopy after porcine in vitro degradation. Cereal grains were subjected to porcine in vitro digestion with or without enzyme supplementation (20 000 U kg RESULTS: In vitro dry matter digestibility (IVDDM) was lower for maize than for wheat (P <
0.05), and enzyme supplementation had no effect on IVDDM. Supplemental enzymes reduced arabinoxylan content in the undigested residue of wheat (53 vs 46 g kg CONCLUSION: Supplemental enzymes did not affect IVDDM for wheat, as they primarily degraded endosperm cell walls, the content of which was already released by pepsin and pancreatin digestion. Similarly, IVDDM for maize remained unaffected, which was probably due to the high phenolic content of its cell walls. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.