Relationships between cocoa mass percentage, surface color, free phenolic compounds content and antioxidant capacity of commercially available dark chocolate bars

The aim of the study was to assess the relationships between cocoa mass percentage declared by producer and color, free phenolic compounds content and antioxidant capacity of chocolate bars. The research materials were commercially available 2 dessert (with 30 and 50% of cocoa mass) and 10 bitter chocolate bars (with 40–90% of cocoa mass). The scope of analysis included determining chocolate bars surface color using digital image analysis, content of free phenolic compounds (total, flavonoids and proanthocyanidins) using spectrophotometric methods and antioxidant capacity using the Cuprac method. Based on the results, it was generally found that bitter chocolate bars were characterized by a darker color and a higher content of free phenolic compounds (252.38–703.13 mg/100 g), including flavonoids (29.01–89.55 mg/100 g) and proanthocyanidins (52.23–224.47 mg/100 g), compared to dessert chocolate bars (241.70, 38.58 and 58.99 mg/100 g on average, respectively). The study showed that the cocoa mass content in the chocolate bars was strongly positively correlated with the phenolic compounds content (in particular flavonoids) and the antioxidant capacity. On the other hand, these properties of the chocolate bars were less dependent on the surface color.