Sugar, d-pinitol, volatile composition, and antioxidant activity of carob powder roasted by microwave, hot air, and combined microwave/hot air

The effects of hot air, microwave, and combined microwave/hot air roasting on physical and chemical properties of carob powder were determined. The comparison of different roasting processes was evaluated whether the combined microwave/hot air roasting could be an alternative to other roasting methods or not. The moisture content (2.86%-5.03%), water activity (0.20-0.35), and pH (4.94-5.12) values of the carob powder decreased by increasing microwave power and roasting time; whereas total phenolic content (10.13-13.74 mg/g dm), total antioxidant activity (0.69-1.53 g/mg DPPH), browning index (23.57-70.30), and UV absorbance (427.41-701.05) increased. Hunter L (41.54-55.28) and b (16.45-20.91) values of the carob powder decreased after roasting while color value a (8.88-20.91) increased. The main sugar was sucrose (317.54-347.68 mg/kg), followed by fructose (80.98-90.11 mg/kg), and glucose (45.16-62.19 mg/kg). Roasting process reduced the sugar content while increased the d-pinitol (62.41-76.71 mg/kg) content. The main volatile was isobutyric acid (acidic/butter odor). Hot air and the combined microwave/hot air roasted samples showed similar volatile and sensorial profile. According to the results, the combined microwave/hot air roasting consumed 50% less energy than the hot air roasting and got the best sensory scores. Practical applications The effects of microwave, hot air, and the combined microwave/hot air roasting processes on the properties of carob powder were first investigated. d-pinitol content of carob was increased by roasting processes. Different roasting processes increased organoleptic properties of carob powder. Total phenolic content and antioxidant activity of carob powder increased by roasting. The combined microwave/hot air roasting consumed 50% less energy than the hot air roasting and it is recommended to produce carob powder with preferable product quality.