The　assessment　of　total　antioxidant　capacity　(TAC),　a　critical　marker　of　food　quality　in　terms　of　antioxidant　efficacy,　has　garnered　considerable　attention　in　human　health　management.　The　development　of　an　in　situ　technique　that　does　not　require　complex　apparatus　can　facilitate　accurate　and　rapid　TAC　detection.　Herein,　we　developed　a　specific　and　sensitive　colorimetric　assay　to　evaluate　the　TAC　of　fruit　juices　using　the　red-green-blue　(RGB)　model.　We　synthesized　a　copper-poly(tannic　acid)　(Cu-PTA)　coordination　polymer　that　exhibits　enhanced　peroxidase　(POD)-like　activity　in　the　presence　of　H2O2.　This　Cu-PTA　nanozyme,　along　with　H2O2,　enhances　the　conversion　of　the　colorless　compound　3,3　＇,5,5　＇-tetramethyl-benzidine　(TMB)　into　a　visually　perceptible　oxTMB　product.　This　chromogenic　reaction　is　suppressed　in　the　presence　of　antioxidants,　such　as　ascorbic　acid　(AA).　This　colorimetric　assay　achieved　a　limit　of　detection　of　0.06　mu　M　across　a　concentration　range　of　0.90-5.40　mu　M　for　AA.　Our　findings　enable　the　development　of　nanozymes　for　convenient　in　situ　TAC　analysis　to　assess　the　nutritional　value　of　food　items.