In situ enzymatic cyclodextrin generation enhances hot oat-milk foamability and stability

The increasing popularity of oat milk is hindered by its inferior foaming performance, particularly as "clean-label" requirements restrict the use of additives. In this study, we evaluated an enzymatic in situ strategy in which cyclodextrins (CDs) are generated directly in oat milk using cyclodextrin glucanotransferase (CGT) in combination with α-amylase (AA). Systematic variation of CGT/AA ratios revealed a strong, near-linear relationship between foamability and total CD content (R² = 0.92). Under a representative enzyme condition (6.5 U/g CGT and 5.3 U/g AA), dynamic surface tension measurements showed a faster reduction in surface tension in the enzyme-treated oat milk than in the control. Size-exclusion chromatography with refractive-index and 210-nm UV detection showed an early-eluting feature in lipid-containing, enzyme-treated oat milk. The corresponding early-eluting fraction showed markedly elevated Nile Red fluorescence, a time-dependent decrease in surface tension, and measurable foamability. Dynamic foam analysis demonstrated slower foam-height decay, slower liquid drainage, and a doubling of foam half-life (t_1/2; 600 s vs. 300 s). The onset of non-drainage decay (t_dev) occurred later (20 s vs. 8.5 s), and the transition to rapid collapse (t_tr) was prolonged (660 s vs. 270 s) compared with the control. These findings indicate that, under the present conditions, in situ CD generation was associated with improved hot oat-milk foaming, accompanied by CD-related interfacial and lipid-associated changes, while maintaining a label-friendly formulation.