Releasing characteristics of anthocyanins extract in pectin–whey protein complex microcapsules coated with zein

This study investigated pectin-based capsules as delivery systems for purple rice bran anthocyanin extract (AE) during exposure to simulated gastrointestinal conditions. Four different capsules loaded with AE were prepared by ionotropic gelation/extrusion, including (1) pectin capsules (PE), (2) pectin capsules coated with zein (PE/ZE), (3) pectin-whey protein isolate complex capsules (PE + WP), and (4) pectin-whey protein isolate complex capsules coated with zein (PE + WP/ZE). CaCl in an ethanol solution with or without zein was used as a crosslinking solution. Swelling and release characteristics of all capsules under simulated gastric fluid at pH 1.2 (SGF) and simulated intestinal fluid at pH 6.8 (SIF) for 120 and 180 min, respectively, were examined. PE + WP, PE + WP/ZE, and PE/ZE capsules had higher encapsulation efficiency than PE capsules. After incubation, PE + WP/ZE and PE capsules had the lowest swelling ratio in SGF and SIF, respectively. PE + WP/ZE capsules had the lowest AE release in SGF, while PE capsules had the highest. Both PE + WP and PE + WP/ZE capsules had significantly lower AE release in SIF than PE and PE/ZE capsules. The study demonstrated that PE + WP and PE + WP/ZE capsules have potential to function as a slow release delivery system for AE

The unravelling of the complex pattern of tyrosinase inhibition

Tyrosinases are responsible for melanin formation in all life domains. Tyrosinase inhibitors are used for the prevention of severe skin diseases, in skin-whitening creams and to avoid fruit browning, however continued use of many such inhibitors is considered unsafe. In this study we provide conclusive evidence of the inhibition mechanism of two well studied tyrosinase inhibitors, KA (kojic acid) and HQ (hydroquinone), which are extensively used in hyperpigmentation treatment. KA is reported in the literature with contradicting inhibition mechanisms, while HQ is described as both a tyrosinase inhibitor and a substrate. By visualization of KA and HQ in the active site of TyrBm crystals, together with molecular modeling, binding constant analysis and kinetic experiments, we have elucidated their mechanisms of inhibition, which was ambiguous for both inhibitors. We confirm that while KA acts as a mixed inhibitor, HQ can act both as a TyrBm substrate and as an inhibitor