Release of Cinnamaldehyde and Thymol from PLA/Tilapia Fish Gelatin-Sodium Alginate Bilayer Films to Liquid and Solid Food Simulants, and Japanese Sea Bass: A Comparative Study

This study aimed to develop an active biodegradable bilayer film and to investigate the release behaviors of active compounds into different food matrices. Cinnamaldehyde (CI) or thymol (Ty) was encapsulated in β-cyclodextrin (β-CD) to prepare the active β-CD inclusion complex (β-CD-CI/β-CD-Ty). The tilapia fish gelatin-sodium alginate composite (FGSA) containing β-CD-CI or β-CD-Ty was coated on the surface of PLA film to obtain the active bilayer film. Different food simulants including liquid food simulants (water, 3% acetic acid, 10% ethanol, and 95% ethanol), solid dry food simulant (modified polyphenylene oxide (Tenax TA)), and the real food (Japanese sea bass) were selected to investigate the release behaviors of bilayer films into different food matrixes. The results showed that the prepared β-CD inclusion complexes distributed evenly in the cross-linking structure of FGSA and improved the thickness and water contact angle of the bilayer films. Active compounds possessed the lowest release rates in Tenax TA, compared to the release to liquid simulants and sea bass. CI and Ty sustained the release to the sea bass matrix with a similar behavior to the release to 95% ethanol. The bilayer film containing β-CD-Ty exhibited stronger active antibacterial and antioxidant activities, probably due to the higher release efficiency of Ty in test mediums.

Seawater Culture Increases Omega-3 Long-Chain Polyunsaturated Fatty Acids (N-3 LC-PUFA) Levels in Japanese Sea Bass (Lateolabrax japonicus), Probably by Upregulating Elovl5

The fatty acid compositions of the fish muscle and liver are substantially affected by rearing environment. However, the mechanisms underlying this effect have not been thoroughly described. In this study, we investigated the effects of different culture patterns, i.e., marine cage culture and freshwater pond culture, on long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis in an aquaculturally important fish, the Japanese sea bass (Lateolabrax japonicus). Fish were obtained from two commercial farms in the Guangdong province, one of which raises Japanese sea bass in freshwater, while the other cultures sea bass in marine cages. Fish were fed the same commercial diet. We found that omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) levels in the livers and muscles of the marine cage cultured fish were significantly higher than those in the livers and muscles of the freshwater pond cultured fish. Quantitative real-time PCRs indicated that fatty acid desaturase 2 (FADS2) transcript abundance was significantly lower in the livers of the marine cage reared fish as compared to the freshwater pond reared fish, but that fatty acid elongase 5 (Elovl5) transcript abundance was significantly higher. Consistent with this, two of the 28 CpG loci in the FADS2 promoter region were heavily methylated in the marine cage cultured fish, but were only slightly methylated in freshwater pond cultured fish (n = 5 per group). Although the Elovl5 promoter was less methylated in the marine cage reared fish as compared to the freshwater pond reared fish, this difference was not significant. Thus, our results might indicate that Elovl5, not FADS2, plays an important role in the enhancing LC-PUFA synthesis in marine cage cultures.