The effect of conventional and ohmic heating as pasteurization methods on the mechanical and rheological properties of edible whey-based films

Edible film-forming solutions typically undergo thermal treatment to ensure microbial safety before being applied to food products. The aim of this study was to assess the effects of two different heating methods—conventional heating (CH) and ohmic heating (OH)—on the physical, chemical, and microbiological properties of liquid acid whey permeate (AWP) and liquid acid whey protein concentrate (AWPC) edible films. Composition of edible film-forming solutions consisted of AWPC, sunflower oil, sugar beet pectin, and glycerol, whereas AWP-based films were produced with sugar beet pectin and glycerol. The following parameters were tested to assess the effect of heating treatments on the film-forming solutions: rheology, contact angle [CA] and microbial counts and mechanical properties (tensile strength [TS] and elongation at break [EB]), water vapor permeability [WVP], moisture content [MC], solubility (Sol), and thickness with optical properties of produced edible films. In addition, film surface was investigated by scanning electron microscopy [SEM]. Microbiological analysis of the untreated film-forming solutions revealed that the AWPC-based solution had a higher initial load of lactic acid bacteria (3.96 log₁₀ CFU/mL) (p < 0.05). Both heating treatments successfully reduced microbial counts to below detection limits in both film-forming solutions. Additionally, OH treatment resulted in lower CA values in both solutions (p < 0.05). OH also led to an increase in TS for AWP-based edible films (p < 0.05) and significantly reduced the thickness of both AWP and AWPC films, while reducing the Sol of AWP-based films and increasing the Sol of AWPC-based films (p < 0.05). The study highlights the effectiveness of the two pasteurization methods and offers insights into improving whey-based edible films.