The objective of this study was to investigate the effects of the enzymatic aided acid‐swelling process on gelatin obtained from fish by‐products. For this purpose, gelatin was extracted by an acidic swelling procedure in the presence of protease extracted from Rainbow trout pyloric caeca. The yield of gelatin extraction and the most important physicochemical characteristics of the fish gelatin samples were investigated and compared with those of commercial bovine gelatin (CBG). The yields of gelatin from Epinephelus coioides skin (ESG) either with or without crude protease from pyloric caeca (15 units/g alkaline treated) were 14.98% and 50.89%, respectively. The yields of gelatin from Cyprinus carpio scales (CSG) with crude protease from pyloric caeca (15 units/g) were 49.97%. The gel strength of the CSG (259.66 g) was significantly higher than that of CBG (228.30 g) and ESG (187.75 g). Similarly, the gelling and melting points, foaming capacity and stability, and the SDS‐PAGE pattern of gelatins were compared. The electrophoretic pattern confirmed the results of gel strength which was due to the narrower alpha and beta bands in fish skin and commercial bovine gelatins than that of fish scales gelatin. The results of this research showed that the production of high‐quality gelatin can be achieved by the enzymatically aided acid‐swelling procedure from fish scales and skin.

The dried pomegranate (Punica granatum L.) arils have several health benefits and are in demand worldwide. Therefore, in the current study, the wrapping effects of Poly L-lactide (PLA) activated with zinc oxide nanoparticles (ZnO NPs, 1.5% w/w) and Zataria multiflora Boiss. essential oil (ZEO, 1 and 1.5% w/w) was studied on pomegranate arils' storage-life extension in cold storage. The arils were analyzed periodically for properties of physiochemical (weight loss, pH, total soluble solids, color measurement, antioxidant activity and sensory attributes) and microbial (total aerobic bacteria and total fungi counts). Results showed that the ZEO causes to decrease and ZnO causes to increase of pH during storage. Also, the active films were more effective than the control film in maintaining TTS and preventing weight loss of arils. The PLA/ZnO/1.5% ZEO sample had the highest phenolic content (∼520 mg/100 ml in juice) and antioxidant activity (∼90%) on day 15. Nevertheless, the effect of ZEO on the color properties of arils was more than ZnO, and 0.5 and 1.5% ZEO-PLA, showed the highest a* (55.14) and b* (31.30) with fresh arils, respectively. The microbial test results showed that ZEO was more effective in controlling bacterial growth than ZnO. Based on atomic absorption spectrophotometer measurement, minimal amounts (∼29 mg Kg− 1 sample) of Zn2 + ions released into arils were observed. Generally, the active PLA could be used as a safe and effective way to prolong the storage life of arils in refrigerated conditions.