A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development

Thesis (M. Sc.) - Asian Institute of Technology, 2018

Currently, t he commercialized products of natural hydrogels are still shortage due to the accessibility and the prices . However, the demand for the natural products have been tremendously increase in several industries over the decade . The gears are shift to ward the bio - base ingredient and merchandises . The main purpose of this study is to develop the pH - responsive and thermal resistant hydrogel from the natural bio polymers and used for the encapsulation of valuable bioactive compounds . Due to the outstanding thermal resistance , non - digestible and biocompatible properties , xanthan gum and alginate were selected as the cationic polymers. For the anionic polymers, whey protein isolate was designated . The xanthan/ whey protein isolate and xanthan/ whey protein isolate /alginate beads were successfully developed via extrusion method , the synthesized beads are the oval - shape milky color and soft texture beads. From the pH - responsive test , the beads were shrinking when immersed in acid buffer and dispersing in basic buffer. In case of disintegration test, m ost of the developed beads were dispersed in SGF solutions after immersed for 2 hr. due to the diges tion of whey protein isolate expect 1.2/2.4 and 1.2/2.4/1.2 %w/v xanthan/whey protein isolate and xanthan/ whey protein isolate /alginate beads which can withstand the enzymatic digestion. Alginate polymers were successfully added in to the combination to make multi - layer hydrogel beads and protect the whey protein chain from enzymatic digestion. Thus, these compositions become the optimized conditions for hydrogel beads developing . The SEM images show the highly porous structure for hydrogel beads and multilayer beads with the sizes approximately around 2 . 074 mm and 1 . 485 mm . However, the 1.2/2.4 and 1.2/2.4/1.2 %w/v beads have different pore sizes approximately around 8.017 om and 1.992 om respectively . The presence of alginate in the structure can effectively enhance the binding potentials with the active compounds. The hydrogel scaffold which develop from the similar procedure illustrate the highly porous structure with the pore size within the suitable range for tissue engineering application. Th e encapsulation of curcumin compounds via the extrusion methods show the promising results, the encapsulation efficiency of the xanthan/WPI and xanthan/WPI/alginate beads w ere 65 and 75 % respectively. The active compounds were encapsulated via entrapping and binding reaction . Both WPI protein and alginate polymers h ave an ability to bind and conjugate with the curcumin compounds. Thus, the multilayer beads which contain alginate in the structure can in teract and bind more curcumin compounds within the structure. The acidic and basic stability of the curcumin - loaded beads were tested , t he synthesized beads completely stable in the acidic environment , and only 6.048 and 6.908 % of curcumin compounds were released from 1.2/2.4 and 1.2/2.4/1.2%w/v beads after immersed for 7 days . The releasing behavior of entrapped curcumin in acidic buffer goes according to first order kinetic s. In case of basic solutions, the bead completely di spersed after immersed for 1 days . Disintegration tests show that around 3 and 1 % of curcumin compounds were released during pre - incubation in SGF. The breakdown of WPI protein which occurred from enzymatic digestion are the main reason for the releasing . Then, the beads were transfer to SIF solutions and dispersed within 2 hr. For the thermal stability, the beads can easily withstand the processing temperature in HTST pasteurization treatment. Moreover, the curcumin compounds were released from the beads during treatment. The develop beads which response according to pH of the solutions have the potential to be used as the drug delivery machine to transport the active compounds or drug to the s mall intestinal tract. In addition, due to thermotolerant nature, the beads can effectively incorporate in food to develop the high - quality food products with health benefits from active compounds.