Quality characteristics of frozen horse mackerel (Trachurus trachurus) treated with starch–glycerol coatings containing plant extracts

Starch-based coatings are biodegradable food-contact materials, but their performance depends on plasticizer level, incorporated active compounds, and the food surface to which they are applied. This study developed starch-glycerol polysaccharide coating formulations containing aqueous extracts from persimmon fruit calyces, cherry laurel leaves, and bilberry/likapa leaves and evaluated their application to whole horse mackerel ( Trachurus trachurus ) during frozen storage at -20 ± 2 °C for 6 months. Extract-level antioxidant activity was determined by the DPPH assay and expressed as percentage inhibition and Trolox equivalent antioxidant capacity. Comparable starch-glycerol films containing the same plant extracts had previously been characterized by Gurdal and Caglak and were used here only as formulation-characterization background. During frozen storage, TVB-N values increased but remained below 35 mg/100 g in all groups. Lipid oxidation responses were formulation-dependent: the lowest final TBA values were observed in PA and PB, whereas BA and VC showed the highest final values. pH, water activity, color, texture, and microbial results varied among treatments and storage months without supporting a uniform concentration-dependent response. The findings suggest that selected starch-glycerol formulations containing plant extracts may help modulate lipid oxidation and quality changes in frozen horse mackerel. However, the absence of a plain starch-glycerol-coated fish control, coating-uptake measurements, compound-level extract characterization, and composite-film antioxidant testing limits direct attribution of the observed effects to specific bioactive mechanisms.