Atmospheric Cold Plasma Alters Surface Morphology, Hydration Behavior, and Phenolic Release in Philippine Pigmented Rice

Abstract Rice is a staple food for billions, and grain surface characteristics and bioactive content strongly influence its cooking quality and nutritional value. This study examined the effects of atmospheric cold plasma (ACP) treatment on Philippine rice varieties—brown (NSIC RC 222), black (97-SDS07041), and red (97-CAT006111)—with a focus on grain surface morphology, hydration and cooking behavior, and phenolic content. Rice grains were exposed to ACP for 1 and 2 minutes and analyzed using SEM, FTIR, total phenolic content (TPC) assay, water absorption tests, and contact angle measurements. SEM revealed that ACP progressively etched the bran surface, producing fissures and microcavities that enhanced moisture diffusion. Consistently, ACP-treated grains exhibited greater water uptake during soaking and cooking, supported by reduced contact angles in brown and black rice. FTIR spectra confirmed the preservation of starch and protein structures, while subtle intensity changes in –OH and C–O–C regions suggested disruption of polysaccharide–phenolic linkages. TPC analysis showed a two-stage response: free phenolics decreased after 1 min but increased after 2 min, particularly in pigmented rice, reflecting the release of bound phenolics from the bran matrix. Overall, ACP demonstrated its potential as a non-thermal, eco-friendly postharvest technology to engineer rice surfaces, improving hydration, cooking efficiency, and phenolic availability.