Antibiotics have been widely supplemented in feeds at subtherapeutic concentrations to prevent postweaning diarrhea and increase the overall productivity of pigs. However, the emergence of antimicrobial-resistant bacteria worldwide has made it urgent to minimize the use of in-feed antibiotics. The development of promising alternatives to in-feed antibiotics is crucial for maintaining the sustainability of swine production. Both medium-chain fatty acids (MCFA) and essential oils exhibit great potential to postweaning diarrhea; however, their direct inclusion has compromised efficacy because of several factors including low stability, poor palatability, and low availability in the lower gut. Therefore, the objective of this study was to develop a formulation of microparticles to deliver a model of essential oil (thymol) and MCFA (lauric acid). The composite microparticles were produced by the incorporation of starch and alginate through a melt-granulation process. The release of thymol and lauric acid from the microparticles was in vitro determined using simulated salivary fluid (SSF), simulated gastric fluid (SGF), and simulated intestinal fluid (SIF), consecutively. The microparticles prepared with 2% alginate solution displayed a slow release of thymol and lauric acid in the SSF (21.2 ± 2.3%; 36 ± 1.1%), SGF (73.7 ± 6.9%; 54.8 ± 1.7%), and SIF (99.1 ± 1.2%; 99.1 ± 0.6%), respectively, whereas, the microparticles without alginate showed a rapid release of thymol and lauric acid from the SSF (79.9 ± 11.8%; 84.9 ± 9.4%), SGF (92.5 ± 3.5%; 75.8 ± 5.9%), and SIF (93.3 ± 9.4%; 93.3 ± 4.6%), respectively. The thymol and lauric acid in the developed microparticles with or without alginate both exhibited excellent stabilities (>90%) during being stored at 4 °C for 12 weeks and after being stored at room temperature for 2 weeks. These results evidenced that the approach developed in the present study could be potentially employed to deliver thymol and lauric acid to the lower gut of pigs, although further in vivo investigations are necessary to validate the efficacy of the microparticles.
Keywords: encapsulation; gut; lauric acid; microparticles; slow release; thymol.