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Edible coatings provide an alternative way to reduce packaging requirements and extend the shelf life of foods by delaying oxidation and microbial spoilage. Hydrogels, oleogels and bigels were applied as coatings on fresh sardine fillets. The effectiveness of these coatings as delivery systems of rosemary extract (RE) was also evaluated. Three groups of sardine fillet treatments were prepared: (i) the control (C), which comprised sardine fillets without coating, (ii) sardine fillets with plain hydrogel (H), oleogel (O) or bigel (BG) coatings, and (iii) sardine fillets with RE incorporated into the H, O and BG coatings. The different treatments were evaluated for lipid oxidation (TBA test), total volatile basic nitrogen (TVB-N) and microbiological growth during cold storage at 4 °C. Results showed that hydrogel, oleogel and bigel coatings delayed oxidation. The incorporation of RE into coatings significantly retarded lipid oxidation but did not affect the proliferation of microorganisms during storage. When RE was incorporated in the oleogel phase of the bigel coating, it produced significantly lower TVB-N values compared to the control and BG treatments. The incorporation of RE into the oleogel phase of the bigel coating may be a promising method of maintaining the storage quality of the sardine fillets stored at refrigerated temperatures.

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The 2-thiobarbituric acid (TBA) method has been used for the spectrophotometric determination of secondary lipid oxidation products, such as malonaldehyde (MA), due to its good correlation with sensorial perception of lipid oxidation. Other approaches have been proposed over time. Direct distillation can result in artificially increased MA concentrations due to intense heating. Extraction is a milder and faster method, but it suffers from false color development in the presence of sugars or other compounds. A novel approach using steam distillation for the recovery of MA was developed. Validation and optimization studies were conducted, aiming to maximize MA recovery from various meat product samples by adjusting the steam distillation parameters. For the optimal MA recovery, 10 g of the sample, 25 mL of H2O, and 5 mL of 2 N HCl were used. The sample was distilled using a stream of water vapor until 50 mL of the distillate was collected in less than 3 min. Subsequently, 5 mL of the distillate was reacted with 5 mL of 0.02 M TBA, and the absorbance was measured at 532 nm. MA recovery was 61.8%. Experimentation with varying nitrite levels suggested that the addition of sulfanilamide is necessary when NaNO2 is more than 50 mg MA/kg. The proposed method is fast, milder than direct distillation, and eliminates the issue of TBA interacting with sugars and other compounds.