Comparative Effects of Freeze-Drying and Sun-Drying on Phenolic Composition, Antioxidant Capacity, Microbial Characteristics, and Aroma Profile of Purple Sweet Potato-Enriched Tarhana

This study investigated the effects of drying method and ingredient form on the quality characteristics of tarhana enriched with purple sweet potato (Ipomoea batatas L.). Tarhana samples were formulated with purple sweet potato in two forms (puree and freeze-dried powder) at incorporation levels of 5% and 10%, and subjected to either traditional sun-drying or freeze-drying. The drying method emerged as the dominant factor influencing product quality. Freeze-dried samples exhibited significantly lower moisture content and water activity along with a highly porous microstructure, indicating favorable physicochemical characteristics associated with product stability. Purple sweet potato incorporation enriched the phenolic profile and improved antioxidant capacity, with greater retention observed under freeze-drying conditions, particularly in powder-based formulations. Microbiological analysis revealed that freeze-drying preserved higher populations of lactic acid bacteria while suppressing yeast and mold growth. Instrumental aroma analysis demonstrated a clear shift in volatile composition depending on processing conditions, with freeze-drying yielding a more favorable aroma profile compared to sun-drying. Freeze-drying was identified as a superior method for preserving bioactive compounds, microbial viability, and aroma quality in purple sweet potato-enriched tarhana. These findings highlight the functional potential of purple sweet potato as an ingredient in traditional fermented foods and provide a basis for the development of high-quality tarhana formulations.