Influence of pulsed light exposure on the structure, physicochemical properties, and antimicrobial activity of pectin films with thymol

The growing demand for safe and sustainable foods provides opportunities for the development of active films from various sources. One example is citric pectin, a renewable material that can be combined with antimicrobials such as essential oils. At the same time, non-conventional technologies have been developed and studied for their compatibility with food applications. Pulsed Light (PL) is a non-thermal technology that does not require the use of sanitizers or water and offers the advantage of rapid processing, making it suitable for use with food. Therefore, the objective of this study is to investigate the effects of PL on active films used in food applications. The citric pectin and thyme essential oil were homogenized using an ultrasonic sonicator, and the films were produced using the casting technique. Subsequently, the films were treated using PL, applying 6, 12, 18, and 24 pulses (each pulse ~1.56 J/cm²). The films were characterized in terms of their physicochemical and structural properties, as well as their antimicrobial activity. The FTIR spectra showed changes in the intensity and sharpness of the bands depending on the number of pulses: the 1450–1400 cm^-1 region possibly indicated structural changes in the polymer chain and interaction between the matrix and the active compounds in thyme. Regarding light transmission, the active pectin films remained transparent even with increased PL intensity, showing little change in light transmission. In contrast, the b* color values increased proportionally with PL intensity (control: 2.32; 24 pulses: 2.98). The mechanical properties showed changes, in the elongation at break (31.8% for the control to 23.7% with 6 pulses). PL treatment increased the elasticity of the films, except for the 18 pulses treatment; the best result was obtained with the 6 pulses treatment (5.12 MPa in the control to 6.82 MPa with 6 pulses). In the evaluation of antimicrobial activity against Staphylococcus aureus ATCC 25923, all treatments exhibited inhibitory activity, particularly with 6 pulses (23.38 mm in the control and 25.25 mm with 6 pulses). The application of PL had favorable effects on the active pectin film, enhancing the material and demonstrating its potential for use in food products.