Blue turmeric (Curcuma caesia Roxb.): phenolic profile, bioaccessibility after in vitro gastrointestinal digestion, and chondroprotective effects in IL-1β-stimulated human chondrocytes

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by progressive cartilage breakdown driven by inflammatory and oxidative stress mechanisms. Blue turmeric (Curcuma caesia Roxb.), a rare and understudied spice, represents a source of bioactive compounds with anti-inflammatory properties. This study aimed to characterize the phenolic profile of a blue turmeric rhizome extract (BTE) and its bioaccessible fraction obtained after in vitro gastrointestinal digestion, and to assess their biological effects on human chondrocytes (C-28/I2) exposed to interleukin-1 β (IL-1β). HPLC-MS/MS analyses revealed a phytochemical profile rich in phenolic acids and flavan-3-ols, with partial stability maintained after in vitro digestion. Pre-treatment with both native BTE and digested BTE (dBTE) protected chondrocytes against IL-1β-induced cytotoxicity, mitochondrial dysfunction, and nuclear factor erythroid 2-related factor 2 (Nrf2) inactivation. Furthermore, BTE pre-treatment significantly reduced tumour necrosis factor-α (TNF-α) release and preserved cellular morphology. These findings demonstrate that BTE phenolic compounds are partially bioaccessible and exert chondroprotective effects, supporting further preclinical investigation of BTE as a potential functional ingredient for joint health maintenance and OA prevention strategies.