Functionalization of sodium carboxymethylated yeast β‐glucan by epigallocatechin gallate: Antioxidant activity and color stability

Sodium carboxymethylated yeast β‐glucan (SC‐GLUCAN) was functionalized with epigallocatechin gallate (EGCG) by esterification. EGCG was first succinylized and then grafted onto SC‐GLUCAN through an N, N′ carbonyldiimidazole mediated reaction. The graft of EGCG with SC‐GLUCAN (SC‐GLUCAN‐g‐EGCG) was verified by spectroscopic (UV, FTIR) and thermal (derivative thermogravimetric [DTG] and thermogravimetric analysis [TGA]) analyses. The grafting ratio of SC‐GLUCAN‐g‐EGCG was determined by the Folin–Ciocalteu procedure and up to 100.25 mg/g SC‐GLUCAN‐g‐EGCG. The antioxidant activity of SC‐GLUCAN‐g‐EGCG was evaluated by scavenging activity of DPPH and ABTS radical, reducing power, and iron chelating ability. SC‐GLUCAN‐g‐EGCG exhibited dramatical increases in DPPH and ABTS radical scavenging activity. In addition, the color development of SC‐GLUCAN‐g‐EGCG solution was studied through sun irradiation. SC‐GLUCAN‐g‐EGCG solutions presented better color stability at 0.2 and 0.4 mg/mL, especially within 4 hr of the sun. TGA and DTG showed that SC‐GLUCAN‐g‐EGCG had good thermal stability. Therefore, SC‐GLUCAN‐g‐EGCG might show potential in active food packaging, and could be further used as cosmetics ingredient. Highlights 1. The hydroxyl group of SC‐GLUCAN and the carboxyl group of succinylized EGCG were grafted by chemical coupling method. 2. SC‐GLUCAN‐g‐EGCG has good thermal stability at temperatures above 150°C. 3. SC‐GLUCAN‐g‐EGCG presented excellent antioxidant activity, better than blank SC‐GLUCAN. 4. SC‐GLUCAN‐g‐EGCG solutions presented good color stability, especially within 4 hours sun irradiation.