Loss of ordered molecular structure in proteins is known to increase their adhesion to surfaces. The aim of this work was to study the stability of norovirus secondary and tertiary structures and its implications for viral adhesion to fresh foods and agrifood surfaces. The pH, ionic strength, and temperature conditions studied correspond to those prevalent in the principal vehicles of viral transmission (vomit and feces) and in the food processing and handling environment (pasteurization and refrigeration). The structures of virus-like particles representing GI.1, GII.4, and feline calicivirus (FCV) were studied using circular dichroism and intrinsic UV fluorescence. The particles were remarkably stable under most of the conditions. However, heating to 65°C caused losses of ␤-strand structure, notably in GI.1 and FCV, while at 75°C the ␣-helix content of GII.4 and FCV decreased and tertiary structures unfolded in all three cases. Combining temperature with pH or ionic strength caused variable losses of structure depending on the particle type. Regardless of pH, heating to pasteurization temperatures or higher would be required to increase GII.4 and FCV adhesion, while either low or high temperatures would favor GI.1 adhesion. Regardless of temperature, increased ionic strength would increase GII.4 adhesion but would decrease GI.1 adhesion. FCV adsorption would be greater at refrigeration, pasteurization, or high temperature combined with a low salt concentration or at a higher NaCl concentration regardless of temperature. Norovirus adhesion mediated by hydrophobic interaction may depend on hydrophobic residues normally exposed on the capsid surface at pH 3, pH 8, physiological ionic strength, and low temperature, while at pasteurization temperatures it may rely more on buried hydrophobic residues exposed upon structural rearrangement. N oroviruses are the main cause of acute nonbacterial gastroenteritis in the United States, accounting for nearly 58% of all food-borne illnesses reported in 2011 (1). Most European countries experienced repeated outbreaks of norovirus gastroenteritis during the period 2002 to 2006 (2). Multiple outbreaks were also reported in Canada (3) and numerous other countries throughout the world (4). Noroviruses are classified in the calicivirus family (5). Human illness usually involves genogroup I or II. The former is frequently involved in transmission via shellfish (6), while the latter is transmitted person to person (7). The norovirus structure comprises a single positive strand of RNA with an icosahedral nonenveloped capsid about 28 to 35 nm in diameter (8).The infectiousness of noroviruses is strongly correlated with their capacity to adhere to food preparation or processing surface materials, such as stainless steel (9), and to remain infectious over time. Biophysical and biochemical parameters such as pH tolerance, isoelectric pH, ionic strength, temperature tolerance, and electrostatic/hydrophobic interactions are reportedly important factors for adhesion to food surfaces (6) and...