Bioactivity of Heat-Processed Korean Curcuma longa is Preserved Despite Extensive Curcuminoid Degradation

Ulgeum is a Korean-cultivated variety of Curcuma longa L. that is commonly consumed after heat processing, such as drying or decoction. Although the bioactivity of unheated or mildly heated C. longa extracts (CLEs) has been widely investigated, the functional consequences of high-temperature processing remain poorly understood. Heat treatment at 180°C markedly reduced curcuminoid levels, while sesquiterpenoids, such as ar-turmerone, exhibited comparatively greater thermal resistance, and these changes were accompanied by the formation of low-molecular-weight phenolic degradation products. Despite these compositional shifts, heat-treated CLEs retained substantial biological activity. In LPS-induced RAW 264.7 macrophages, CLEs suppressed nitric oxide production through the selective attenuation of NF-κB signaling, without significantly affecting MAPK pathways. In parallel, antioxidant activity was preserved across heat-treatment durations up to 90 min, as evidenced by a sustained suppression of intracellular reactive oxygen species production and activation of Nrf2-dependent antioxidant responses. Collectively, these findings demonstrate that the bioactivity of ulgeum is resilient to high-temperature processing and is maintained through a coordinated modulation of inflammatory and redox signaling pathways rather than through the preservation of curcuminoids alone.