Inactivation of Lipase in Grains: Processing Methods, Kinetics, and Storage Stability

Lipase activity in grains is a critical factor limiting the shelf-life of whole-grain flours and brans. Inside intact kernels, lipase and its substrates are separated by structural barriers. Once lipase is in contact with the substrate (triacylglycerols, TAGs) after milling, it hydrolyzes TAGs into free fatty acids (FFAs), and the grain matrices become rancid, a condition known as hydrolytic rancidity. Further oxidation of FFAs produces aldehydes and ketones, generating off-flavors and compromising sensory quality and product acceptability. This review consolidates recent advances in lipase inactivation using various thermal, nonthermal, ozone exposure, and salt conditioning across different grain matrices. Superheated steam and atmospheric cold plasma were the most effective thermal and nonthermal treatments, respectively, achieving 100% and 97% lipase inactivation in wheat, while salt conditioning provided only partial activity (55%) suppression. The extent of inactivation depends on the matrices and grain type, treatment type, and intensity. Lipase inactivation kinetics were described using first, fractional, and nth-order models, and the rate constants (k, min^-1) were compared across treatments and grain types. The effects of residual lipase activity and storage stability of lipids in grain-based matrices were evaluated using mixed correlation and multivariate analyses. The unifying mechanistic outcome was disruption of the lipase lid domain and catalytic triad, and changes in conformational structures, though the reversibility of these structural changes varied across treatments. Thus, this review provides a cross-grain comparative framework to guide the design of grain-specific lipase stabilization strategies for producing shelf-stable whole-grain flour and bran products.