Research on color changes during bulgur production and the development of new systems to obtain yellow bulgur

Bulgur were tempered with two different methods: spray and steam tempering, followed by polishing with four different method: UV/Sun-light treatments, mechanical polisher, microwave/infrared and additives. In the first method, bulgur was exposed the UV/Sun-light simulation for 12, 24, 36, 48, 60 and 72 hours. In the second method, bulgur were polished using electrical heater aided mechanical polisher (EHA-MP) and modified EHA-MP with preheating systems (microwave and infrared) at 40, 60 and 80°C. In the third method, bulgur were applied to microwave with 350, 490 and 700 W for 120, 240, 360, 480 and 600 seconds. In the last method, ascorbic acid, benzoyl peroxide, potassium hydroxide, lutein and riboflavin were added separately at 5 different amounts. After tempering and polishing, moisture content (%, d. b.), ash content (%, d. b.), protein content (%, d. b.), total carotenoid content (TCC, expressed as µg/g lutein equivalent), color values (CIE L*, a*, b* and YI) and energy consumption (kJ/kg) of process were determined. It was found that steam tempering was better method than spray tempering according to CIE b* values. UV-light resulted in a noticeable (P≤0.05) improvement on the color (CIE L* and CIE b*). The strongest relationship between CIE b* (yellowness) and TCC (pigment) were obtained with steam and UV-light applied bulgur (r2=0.62). Additives increased (P≤0.05) yellowness and most of them increased the TCC. EHA-MP, UV-light treatment and microwaving consume less energy than current mechanical polishing method. As a conclusion, steam tempering and UV-light treatments should be preferred instead of current polishing method.