Preparation of Light-Colored Botanical Sunscreen from Pink Birch Lignin

Lignin holds significant potential in UV-blocking and skincare products. However, its application has been hindered by the dark color. Herein, a pink lignin (PL) is successfully extracted from birch under mild condition, with molecular weight and polydispersity index of 4680 Da and 1.38, respectively. As PL preserves the native structure of lignin, it retains 57.14% of β-O-4 linkages and 19.09% of methoxy groups, and possesses a whiteness index (WI) of -25. To address its limited absorption in long-wave UV irradiation, PL capsules with broad-spectrum UV absorption are developed by encapsulating chemical sunscreen actives via one-step ultrasonic cavitation. Optimal capsules with an average diameter of 180 nm are obtained using 3 wt% PL solution concentration, 8:2 mass ratio of PL to chemical sunscreen actives, and 7.5 wt% surfactant. Formulating sun creams with 10% and 15% PL capsules as the sole active ingredient achieves sun protection factor (SPF) values of 130+ and 180+, respectively. And their WIs maintain -18 and -22. Due to the excellent photostability of PL, the SPF value of the capsule-based sun cream decreases by only 18% after 7.5 h UV exposure. Moreover, the PL capsules exhibit good biocompatibility and have promising application potential.