Enhanced proanthocyanidin-mediated starch crosslinking and resistant starch formation using electron beam energy

Proanthocyanidins (PA) complex with starch via non-covalent interactions, reducing starch digestibility. However, these complexes are unstable under hydrothermal processing, limiting their potential use as natural resistant starch (RS) ingredients. The present study aimed to demonstrate the effect of electron beam irradiation (Ebeam) on PA-mediated starch crosslinking. Starch-PA treatments were subjected to Ebeam energy (0–50 kGy), and products characterized for M_W (size-exclusion chromatography/multi-angle light scattering detector), pasting properties (Rapid Visco Analyzer), granule integrity (X-ray diffraction and microscopy), and in vitro digestibility. Although Ebeam resulted in dose-dependent decrease in starch M_W, the starch-PA complexes had 5–102 % higher (p < 0.05) M_W than their respective controls. Furthermore, extractable PA from Ebeam treatments decreased dramatically (p < 0.01) to 8.3–16 % vs non-irradiated control (82.4 %). The evidence suggests that PA-facilitated starch covalent crosslinking, likely via electron transfer reactions catalyzed by Ebeam free radical generation. Amylose fractions showed higher increase in M_W in presence of PA (e.g., doubling from 5.35 × 10⁴ vs 10.8 × 10⁴ kDa at 50 kGy vs 37–44 % increase in M_W for amylopectin fractions), indicating higher degree of PA-induced crosslinking. Changes in starch crystallinity or granule integrity were not detected. PA-crosslinked starches were highly resistant (p < 0.001) to enzyme digestion (84–87 %, RS) at all Ebeam doses but had wide variation in viscosity profiles (e.g., 52–2465 cP final viscosity). Ebeam facilitates covalent PA-mediated starch crosslinking to produce starches with broad variation in rheological properties, while retaining high level of RS that could benefit diverse applications.