Extraction and Antioxidative, Antihypertensive, and Antidiabetic Properties of Gelatin Hydrolysates From Lethrinid Fish Scales

Valorization of fish processing waste has gained attention due to the demand for sustainable biomaterials and environmental management. Fish scales contain collagen, which can be converted to gelatin and further hydrolyzed into bioactive peptides, which have several health benefits and industrial applications. This study is aimed at exploring gelatin extraction and enzymatic hydrolysis from Lethrinus sp. scales and evaluate bioactivities of hydrolysates. Fish scale gelatin was extracted from Lethrinus sp. using a hydrothermal extraction method at 121°C and 15 psi for 90 min. This resulted in a gelatin yield of 22.58 ± 0.97% with a 17.58% protein recovery rate. Papain enzyme was used to prepare fish scale gelatin hydrolysate by maintaining an enzyme-to-substrate ratio (E:S) of 1:100 (v/w) at 55°C and pH 7.0 in a water bath for 1 h. The resulting crude fish scale gelatin hydrolysate (CFSGH) had a degree of hydrolysis of 17.71 ± 1.02% and an average PCL of 5.64. Furthermore, the crude gelatin hydrolysate was subjected to fractionation based on 10 (10FSGH and 3–10FSGH) and 3 kDa (3FSGH) molecular weight cut-off filters using a tangential flow filtration (TFF) system. Antioxidant ability was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and sardine meat model methods. Further antihypertensive and antidiabetic potentials were measured using the Angiotensin-Converting Enzyme I (ACE) inhibitory activity and α-amylase inhibitory method, respectively. Among the peptide fractions, the crude fraction showed the highest DPPH radical scavenging activity, with an IC₅₀ value of 2.58 mg/mL. Furthermore, a sardine meat model study showed that the crude fraction had the highest antioxidant ability compared to the other three fractions of fish scale gelatin hydrolysate. The 10FSGH fraction showed the highest ACE inhibitory activity (58.12 ± 0.47%) and α-amylase inhibitory activity (67.61 ± 1.4%) at a concentration of 2 mg/mL. This study revealed that gelatin peptides with different molecular weights have different bioactivities, as CFSGH has higher antioxidant activity, whereas 10FSGH fractions have higher antihypertensive and antidiabetic activities. Fish scale gelatin hydrolyzate shows distinct bioactivities based on molecular weight, with enhanced antioxidant activity in crude hydrolysate and higher ACE and α-amylase inhibition in 10 kDa fractions. This study helps to develop functional biomaterials from fish waste, supporting environmental sustainability and human health benefits.