Comparative Evaluation of Artemisia-ZnO NPs and Chemically Synthesized ZnO NPs in Kefir: Effects on Quality and Probiotic Viability

The growing interest in functional foods, such as kefir, has encouraged the investigation of green-synthesized nanoparticles as bioactive ingredients. This study investigated green-synthesized Artemisia absinthium L.-derived zinc oxide nanoparticles (Artemisia-ZnO NPs) incorporated into kefir at 0.25%, 0.50%, and 0.75% (w/w), with plain kefir and 0.25% chemically synthesized ZnO NPs as comparison formulations. Microbiological, physicochemical, and antioxidant properties were evaluated during 28 days of refrigerated storage at 4 °C. Structural characteristics of kefir samples were assessed using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), particle size distribution analysis, and Fourier transform infrared spectroscopy (FTIR). Sensory properties were evaluated at the end of storage using a nine-point hedonic scale. Artemisia-ZnO NPs significantly affected the microbiological, physicochemical, and sensory characteristics of kefir (p < 0.05). The 0.25% Artemisia-ZnO NP formulation exhibited higher DPPH radical-scavenging activity than plain kefir and 0.25% chemically synthesized ZnO NPs. This higher DPPH activity may reflect the combined effects of the Artemisia-ZnO NP system and the kefir matrix; however, the specific contribution of Artemisia-derived phytochemicals could not be established because their concentrations were not quantified in the final kefir, and differences in sample pH may also have influenced the DPPH response. Sensory evaluation showed that plain kefir received the highest scores, while higher Artemisia-ZnO NP concentrations reduced flavor and overall acceptability. Overall, the 0.25% Artemisia-ZnO NP formulation provided the most favorable balance of probiotic viability, physicochemical properties and sensory acceptability. However, further studies are required to evaluate zinc exposure, bioavailability, in vivo safety, and thujone content before its suitability as a functional ingredient can be established.