Effects of roasting with microwave oven, hot air oven and their combination on physical and chemical properties of carob powder

Carob powder is produced by roasting and milling of the kibbled carob and mainly used in food industry in cakes, biscuits and chocolates as a substitute or extender for cocoa and a sweetener. It is particularly suitable for the manufacture of caffeine-free and theobromine-free chocolate substitutes. The carob powder is also consumed as a hot drink directly after preparation in a similar way to the Turkish coffee or mixed with milk. In the present thesis, microwave, microwave + hot air and only hot air roasting applied for the production of carob powder and the effects of these processes on physicochemical properties of carob powder and energy consumption were determined. For this purpose, roasting of kibbled carob was performed by using microwave at different powers and times (3x4), combined microwave+hot air at different times (3x3) and only hot air at different periods and the effects of these treatments on moisture content, water activity, color change, sugar composition, D-pinitol content, total phenolics, antioxidant activity, browning properties (browning index, UV-A), sensory properties and aroma compounds of the carob powder were investigated. Moisture content, water activity and the pH values of the carob powders decreased with increase in microwave power and roasting time. Unroasted sample had 7-8% moisture content and 0.65-0.70 water activity of which decreased to 3-5% and 0.25-0.30, respectively, after roasting. At the end of the roasting pH values were 4.99-5.08, less than their initial values of 5.14-5.20. Total phenolics, total antioxidant activity, browning index and UV absorbance values of the sample were increased by an increase in microwave power and time. In roasted samples average values of total phenolics, total antioxidant activity, browning index and UV absorbance were 10.80 mg / g dm, 1.56 g / mg DPPH, 18.5 and 375.5 respectively. Hunter L and b values of carob powders were decreased by 28% and 26%, respectively, during roasting, whereas color value a has increased by 40%. Sugar composition and D-pinitol content of the samples were determined chromatographically and they changed significantly with the roasting process. By roasting sugar content decreased while D-pinitol content of the samples increased. Before roasting, averages for sucrose, glucose, fructose and D-pinitol were 350, 63, 90 and 65 g / kg, respectively, which were determined 330, 44, 76 and 78 g / kg, respectively, after roasting. The total number of volatile components of the carob powders were increased by roasting process. In all samples, "isobutyric acid" was the main volatile of which was decreased with by roasting degree. Roasted carob powders, on the other hand, had neo-formed compounds like furan, pyrrole and pyrazine compounds. Samples, roasted by only hot air and microwave + hot air combination showed similar volatile profile on gas chromatograms. According to the results of sensory analysis, roasting improved the sensory characteristics of the raw carob. Combined microwave + hot air roasted samples had the highest score in terms of purchasing trend.