Polymer Degradation and Stability 191 (2021) 109660 Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polymdegradstab Dual pH responsive via double - layered microencapsulation for controlled release of active ingredients in simulated gastrointestinal tract: A model case of chitosan-alginate microcapsules containing basil oil (Ocimum basilicum Linn.) Sureerat Thuekeaw a , Kris Angkanaporn d , Suwabun Chirachanchai b,c,∗ , Chackrit Nuengjamnong a,e,∗ a Department of Animal Husbandry, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, 10330, Thailand b The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, 10330, Thailand c Bio-to-advanced Materials (B2A) Research Unit, Chulalongkorn University, Bangkok, 10330, Thailand d Department of Veterinary Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, 10330, Thailand e Food Risk Hub, Research Unit of Chulalongkorn University, Bangkok, 10330, Thailand a r t i c l e i n f o Article history: Received 13 May 2021 Revised 16 June 2021 Accepted 20 June 2021 Available online 23 June 2021 Keywords: Basil oil Controlled release Double-layered Dual pH responsive Microcapsule Chitosan Alginate a b s t r a c t Phytogenic feed additives (PFAs) have gained more attention to replace antibiotic growth promoters (AGPs) in poultry industry. However, the efficiency of PEAs might be lost during feed pelleting, storage and gastrointestinal (GI) tract resulting in an insufficient level at the small intestine. The present work demonstrates the use of double-layered polymers with opposite charges leading to a dual pH responsive- ness where the encapsulated ingredients are remained active through the acidic gastric stage and ready to be released at the intestine. Anionic sodium alginate (SA) and cationic chitosan (CS) are a good com- bination to represent double-layered polymer of which an effective incorporation of active ingredient, i.e. basil oil (BO), a model PEA, can be achieved. By simply fabricating SA porous microcapsules followed by the absorption of BO before the surface coating with CS, the double-layered microcapsules, CS-SA, are obtained. The release performances confirm that CS-SA retains the antioxidant and antimicrobial activ- ities of BO under storage in addition to a great tolerance of acids, bile, trypsin, including the thermal conditions. The present work, for the first time, proposes the concept of porous double-layered polymer in microcapsule form which shows the dual pH responsive for controlled release application. The use of ionic polysaccharides is simple, biocompatible and environmentally friendly, whereas the plausible up- scaling for wide range of controlled release applications has to be further investigated. © 2021 Elsevier Ltd. All rights reserved. 1. Introduction In poultry production, the awareness of the negative effects of antibiotic growth promoters (AGPs) in animal feed is important [1] and several feed additives to replace AGPs are proposed. Phy- togenic feed additives (PFAs) such as essential oils (EOs) are pos- sible alternatives in animal industry [2]. Currently, EOs are gaining a good attention in accordance with their wide range of antiox- Abbreviations: : SEM, scanning electron microscopy; FTIR, Fourier transform in- frared; TGA, Thermogravimetric analysis; DPPH, 2,2-diphenyl-1-picrylhydrazyl radi- cal, CFU, colony forming units; MHA, Mueller-hinton agar. ∗ Corresponding author. E-mail addresses: csuwabun@chula.ac.th (S. Chirachanchai), Chackrit.n@chula.ac.th (C. Nuengjamnong). idant and antimicrobial attributes, non-toxic and environmentally friendly properties [3]. However, EOs are highly heat labile sub- stances particularly during feed pelleting (at 70°C - 85°C) or expo- sure to the harsh environment during transportation and storage. In addition, most EOs are low aqueous soluble and the entering to the GI tract is quite limited [4,5]. Microencapsulation is recognized as a process to fabricate the microcapsules covering the active species with polymers, organic and inorganic compounds, and therefore it is a practical technique to perpetuate the activity of EOs [6]. The microcapsules are ben- eficial for the delivery system of EOs into animal body with a minimum damage [4]. Numerous microencapsulation techniques have been proposed e.g. spray drying, emulsions, and coacerva- tion methods [7]. Among these techniques, spray-drying is com- paratively ease to scale up, cost effective, and less time consump- https://doi.org/10.1016/j.polymdegradstab.2021.109660 0141-3910/© 2021 Elsevier Ltd. All rights reserved.