Water retention improvement in frozen bullfrog meat: evaluating basic amino acids as clean-label phosphate alternatives

As a frozen raw material, bullfrog ( Rana catesbeiana ) thigh meat often exhibits severe moisture loss after thawing, which detrimentally affects product quality. This muscle is characterized by high water content and a delicate tissue structure, distinguishing it from other meats. Although conventional polyphosphates effectively improve water holding capacity (WHC), the demand for clean-label alternatives is increasing, yet viable options for such meat remain scarce. To address the challenges of bullfrog thigh meat, this study evaluated whether the basic amino acids L-arginine (Arg) and L-lysine (Lys), which are GRAS-approved meat flavor precursors, could function as phosphate substitutes, and clarified the mechanisms responsible for WHC improvement under controlled pH conditions. Among the individual and combined treatments, 0.5% Arg +0.5% Lys +2% NaCl exhibited the best improvement effect, significantly increasing meat yield and WHC compared with the control ( P < 0.05), as reflected by improved cooking and thawing yields, reduced drip loss, and decreased centrifugal loss from 40.77% to 29.22%, with its overall WHC performance approaching that of the phosphate treatment. Color measurements further showed reduced surface yellowness, as indicated by lower b* values, consistent with decreased free water at the surface. These improvements coincided with a more compact muscle microstructure, reduced interfiber gaps, and a shift in water distribution toward immobilized water, as reflected by a shorter T₂₁ relaxation time. Such structural densification was underpinned by enhanced myofibrillar protein hydration, as partial α-helix unfolding, decreased surface hydrophobicity, and increased solubility from 51.54% to over 78% strengthened electrostatic repulsion and water entrapment within the myofibrillar lattice. These results indicate that Arg and Lys, particularly when combined with NaCl, improve WHC close to but less than phosphates under pH 8.5 conditions, yet still have potential as clean-label phosphate alternatives for frozen bullfrog thigh meat. Future studies will focus on formulation cost and storage stability to enhance industrial applicability.