Optimization of the Preparation Process and Ameliorative Efficacy in Osteoporotic Rats of Peptide–Calcium Chelates from Skipjack Tuna (Katsuwonus pelamis) Meat

This study aimed to establish the preparation process of peptide-calcium chelates (TMP-Ca) using skipjack tuna meat and investigate the function and mechanism of TMP-Ca in an osteoporosis model of rats. The results indicated that trypsin is more suitable for preparing the Ca-chelating hydrolysates of tuna meat, and the optimal hydrolysis conditions were derived as follows: digestion time 4 h, material-liquid ratio 1:10, and enzyme dose 3%. The conditions for chelating Ca with tuna meat hydrolysate were optimized to be chelation time 50 min, temperature 50 °C, pH 8.0, and a peptide-Ca ratio 1:10. The prepared hydrolysate was subjected to ultrafiltration, and the fraction (TMP) (MW <1 kDa) showed the highest Ca chelation rate (51.27 ± 1.42%) and was made into the peptide-Ca chelates (TMP-Ca). In osteoporotic rats, TMP-Ca significantly improved the decrease in ovarian indexes caused by retinoic acid. It also elevated serum Ca, phosphorus, and bone turnover indexes, increased the number of bone trabeculae, and improved bone microstructure. In addition, we confirmed that TMP-Ca could regulate the OPG/TRAF6 pathway to reduce osteoclast differentiation, inhibit bone resorption, and promote bone formation. Therefore, TMP-Ca could significantly ameliorate osteoporosis, and this study provides a functional component for the preparation of healthcare products using skipjack tuna meat to treat osteoporosis.