The bio-accessibility of β-cyclodextrin encapsulated polyphenol mixtures post in vitro simulated digestion

Abstract

Polyphenols are inversely associated with the incidence of chronic diseases, but therapeutic use is limited by poor stability and bioaccessibility. Encapsulation has been shown to overcome some limitations facing polyphenols. This current study aimed at exploring the encapsulation of three polyphenols alone and in combination using the lyophilisation method in an attempt to improve their bioactivity following digestion. The study aim was achieved by encapsulating a sample of polyphenols (catechin (CAT), gallic acid (GA), and epigallocatechin gallate (EGCG)) in beta-cyclodextrin (βCD) through molecular inclusion complexation with subsequent lyophilisation. Inclusion complexation was confirmed, encapsulation yield and efficiency determined, and the morphology of the inclusion complexes observed. Thermal and storage stability was studied using the Trolox equivalent antioxidant capacity (TEAC) assay. The samples were then subjected to in vitro digestion using a simple and a complex method, thereafter, the antioxidant, antiglycation and anti-inflammatory activities were quantified. Inclusion complexes were formed at 1:1 mole ratio with a high encapsulation yield and efficiency. Encapsulated samples showed a change in morphology and a mix of morphologies was observed in combined samples. Inclusion complexation significantly improved thermal stability only for CAT and EGCG, and storage stability for all non-combination samples. Regarding antioxidant activity following in vitro digestion, encapsulation did not provide significant protection from digestion. An exception was seen with the antiglycation activity of non-encapsulated CAT in the bovine serum albumin (BSA)-methylglyoxal model, non-encapsulated CAT and GA in the BSA-fructose model and non-encapsulated CAT/GA in both models where the antiglycation activity was significantly higher compared with the respective inclusion complexes. Encapsulated EGCG exhibited significantly higher activity than non-encapsulated EGCG in the BSA-methylglyoxal model. Importantly, antiglycation activity generally increased in both models following in vitro digestion except for free EGCG and its inclusion complex that generally maintained activity. Inclusion complexation improved polyphenol-polyphenol interactions in the CAT/EGCG and CAT/GA/EGCG combination samples in the BSA-MGO model. Following simple digestion, free GA completely lost cellular antioxidant activity while its inclusion complex was not affected at 100 µM. All combinations exhibited additive interactions at 100 µM while the 10 µM samples revealed synergistic interactions in the CAT/GA, GA/EGCG and CAT/GA/EGCG triple combination samples. The non-digested and simple digested GA inclusion complexes had significantly higher nitric oxide (NO) scavenging activity compared to free GA. None of the combination samples exhibited any synergistic or additive interactions towards NO scavenging. The tested samples inhibited NO production in lipopolysaccharide stimulated RAW 264.7 macrophages. Inclusion complexation did not improve the activities of the samples following in vitro digestion, nor did it improve polyphenol-polyphenol interactions towards inhibiting NO in lipopolysaccharide stimulated macrophages. In conclusion, βCD formed 1:1 inclusion complexes with polyphenols and exhibited potential for improving the physicochemical properties as well as bioactivity of the polyphenols. Following digestion, inclusion complexation did not show overall improvement in activity. The findings of this study shed light into the bioaccessibility of polyphenols encapsulated in βCD. Further, this study could serve as the basis for future studies that may attempt to significantly improve the bioaccessibility of the polyphenols through encapsulation.