Document Type : Research Paper

• food industry

Encapsulation of curcumin by chia seed protein and mucilage hydrogels: Evaluation of stability and kinetic release

EXTENDED ABSTRACT

Introduction

Curcumin is a lipophilic bioactive ingredient found in turmeric. Due to its excellent antioxidant properties and high safety curcumin is known to possess anti-cancer and anti-microbial properties. However, curcumin is insoluble in water and has low stability and low bio-availability. Also, curcumin in the presence of light, heat, and oxygen is unstable and undergoes degradation via oxidation and isomerization. To overcome these problems, many researchers employed curcumin in carriers, such as nanoparticles and hydrogels. Among various delivery systems, hydrogels stand out for their ability to encapsulate, load, and release bioactive compounds. The swelling body known as a hydrogel is suited for use as a flexible material due to its high-water content and softness. They are employed in the food industry as carriers for bioactive substances because of their good biodegradability, and specific biological activity. So, encapsulation of biologically active ingredients in hydrogels with uniform network structures can improve their stability and bio-availability. For bioactive delivery, natural food-grade polymers such as proteins or polysaccharides are used as building blocks of hydrogels.  Proteins, as natural biopolymers, are secure and inexpensive carriers for the loading of curcumin with high nutrition value. According, in this research, chia protein was used as a carrier for the encapsulation of curcumin. Due to the weak mechanical characteristics of protein-based cold-set hydrogels and their sensitivity to enzymatic degradation, scientists have concentrated on developing protein/polysaccharide binary gels. Chia mucilage is a hydrophilic heteropolysaccharide. Chia mucilage can be employed as an encapsulating agent of probiotics. Our main aim was to determine whether encapsulation affects the release of curcumin from the delivery system and to study the release kinetics of curcumin in simulated gastrointestinal situations.

Materials and Methods

Chia seeds were purchased from Jam Noor Talai Company Iran and kept at room temperature. In the Transfer Phenomena Lab, mucilage and protein isolates were extracted and purified. Protein solutions were prepared by dissolving in double-distilled water for 2 hours at room temperature while using magnetic stirring to achieve various protein concentrations (7.5%, 10%, 12.5%, 15%, 20%, 25%, and 30% w/v). Furthermore, solutions were created by using a magnetic stirrer for 2 hours while adding the mucilage stock solution at various concentrations (7.5%, 10%, 12.5%, 15%). The solutions' pH was raised to 7.3 ± 0.12 with 1 M NaOH, followed by an overnight chill in the fridge to complete hydration. The protein and mucilage solutions were heated at 90 °C for 20 minutes the next day. As a result, tap water was used to bring the vials' temperature down to room temperature. They were stored in the refrigerator for 24 hours. A curcumin suspension with a concentration of 80 mg/mL was prepared in 50 % aqueous ethanol solution. The final ratio of curcumin to protein is 1:350 (w/w). The mixture was stirred on a magnetic stirrer for 1 hour at room temperature.

Results and Discussion

The results indicated that the gel made with 12.5% protein and 12.5% mucilage exhibited better mechanical properties, so it was selected for curcumin recovery and other evaluations. The encapsulation efficiency and loading amount of curcumin in chia protein isolate and mucilage were 90.15 ± 0.05% and 9.76 ± 0.08 µg.mg^-1, respectively. The instability index of protein and mucilage hydrogel 12.5 % was smaller than the instability index of free curcumin and it indicates better stability of curcumin in the protein and mucilage hydrogel 12.5%. The mean diameter by volume and the number of particles during the time after the heating process at pH 7 in protein, curcumin, and mucilage hydrogel 12.5% decreased. However, the polydispersity indices of protein and mucilage hydrogel solutions were significantly affected by curcumin loading (p ˂ 0.05).

Conclusion

Our study indicated that chia seed protein isolates /chia seed mucilage gels had high entrapment efficiency and could preserve curcumin in the upper gastrointestinal tract. The results of release in vitro conditions showed that the overall release of curcumin during gastrointestinal digestion for the sample containing 7.5% protein and mucilage was 60.71% and for the sample containing 12.5% protein and mucilage was 27.30%. Therefore, protein hydrogels and mucilage can prevent the spread and demolition of curcumin loaded in the upper gastrointestinal tract. Hydrogels are therefore useful in delivering biological compounds to the colon.