Abstract This study investigated the physicochemical, structural, and textural properties of whey protein isolate (WPI) modified by dry heat treatment, as well as pretreatments with ethanol and cold plasma. Ethanol pretreatment was conducted at three concentrations (40%, 50%, and 60% ethanol), and cold plasma pretreatment at 18 kV for different durations (10, 15, and 20 minutes). Following the pretreatments, the samples were subjected to dry heat treatment for varying durations (24, 48, 72, and 96 hours). The changes in functional properties were eva‎luated through measurements of solubility, surface hydrophobicity, emulsifying capacity and stability, interfacial tension, zeta potential, and content of free sulfhydryl and tyrosine. Additionally, SDS-PAGE, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and rheology were employed to assess the modifications to WPI during the treatments. The results indicated that cold plasma pretreatment influenced the structure and functional groups of WPI, as evident from alterations in FTIR and FESEM. This pretreatment led to increased levels of free sulfhydryl and tyrosine content, while zeta potential, surface hydrophobicity, and interfacial tension decreased. However, solubility and emulsifying activity increased, and the apparent viscosity decreased. Based on the favorable functional properties exhibited in the 15-minute plasma pretreatment, this sample underwent subsequent heat treatment. The results revealed that applying 48 hours of heat treatment after plasma pretreatment helped maintain or slightly improve functional properties, while significantly enhancing textural properties. Solubility, emulsifying capacity, and free sulfhydryl content increased, whereas zeta potential and surface hydrophobicity decreased. Apparent viscosity improved and gel stability increased. In contrast, ethanol pretreatment had no positive impact on the functional properties of WPI. It resulted in decreased solubility and emulsifying capacity, as well as increased surface tension and hydrophobicity—although the textural properties improved and apparent viscosity increased, exhibiting good stability. Applying dry heat to ethanol pretreated samples yielded different outcomes, with slight improvements in functional properties and increased emulsifying activity, but severe weakening of texture and significant decrease in apparent viscosity. In conclusion, cold plasma pretreatment, whether applied alone or in combination with dry heat, had positive effects on the functional, structural, and textural characteristics of WPI. Conversely, ethanol pretreatment only improved the textural and structural properties while adversely affecting the functional characteristics. Adding dry heat further exacerbated the negative effects on textural and functional properties.

نفيسه سلطاني زاده

مهدي كديور , مهرنوش جعفري