Cold plasma modification of food biopolymers: The protein–polysaccharide rheological dichotomy

Cold atmospheric plasma (CAP) has emerged as a versatile non-thermal technology for modifying food biopolymers. However, a critical pattern has remained largely unrecognized: under similar plasma conditions, protein-based systems tend to exhibit enhanced viscoelasticity, while polysaccharide-based systems undergo significant viscosity reduction. This trend is condition-dependent, with deviations observed depending on plasma parameters, polymer chemistry, and environmental factors. Evidence from the literature was classified according to plasma mode and material state to ensure comparability, and the proposed dichotomy is presented as a condition-dependent tendency rather than a universal rule . This dichotomy emerges from fundamental differences in how reactive oxygen and nitrogen species (RONS) interact with each polymer class at the hydrated interface. The critical determinant is the competition between bond formation and bond scission at the polymer-water interface. In proteins, RONS oxidize sulfur-containing side chains, which can promote disulfide crosslinking and hydrophobic exposure—both of which enhance network elasticity. In polysaccharides, the response is dose-dependent: mild plasma exposure induces surface oxidation and electrostatic restructuring without backbone damage, intermediate doses alter chain entanglement and hydration dynamics, and only high doses drive significant glycosidic bond cleavage and depolymerization . A further argument concerns methodology. The widespread reliance on small amplitude oscillatory shear (SAOS) within the linear viscoelastic region may obscure the protein-polysaccharide dichotomy. Because plasma modification is inherently heterogeneous—creating a modified surface layer over an unmodified bulk—SAOS averages over this gradient. While SAOS provides linear viscoelastic characterization, large amplitude oscillatory shear (LAOS) offers critical insights into non-linear network dynamics—such as yielding, strain stiffening/softening, and network breakdown. However, LAOS remains a volume-averaged technique; true spatial resolution requires complementary approaches such as microrheology, AFM nanomechanics, and in situ spectroscopic imaging (e.g., Rheo-IR, Rheo-SANS). The combination of LAOS for non-linear dynamics and spatially resolved techniques for heterogeneity mapping provides a comprehensive characterization strategy for plasma-modified biopolymers . This review provides a unified framework that predicts rheological outcomes based on polymer chemistry and hydration state. The findings suggest that cold plasma is not a universal texturizing tool but a selective rheological architect: it strengthens proteins while weakening polysaccharides. Recognizing this dichotomy enables rational, predictive design of plasma-modified food systems.