Some nutritional, thermal and pasting properties of buckwheat flours and its wet milling fractions

In this study, the native hulled buckwheat cultivars (Aktaş cv. and Güneş cv.) were milled by using wet milling technique in order to separate into seed components and then some physical, chemical, nutritional (enzyme resistant starch, phytic acid, total phenolic compound and antioxidant activity) and physicochemical properties (pasting-viscosity and thermal) were investigated and compared with the properties of hulled and hull-less buckwheat flours of same cultivars. In wet milling processing, hulled buckwheat were soaked in 0.25% Na2SO3 solution adjusted to pH 4 at 30°C for 16 hours. Then, buckwheat samples were sieved from the sieves with sizes of 600, 300, 75 and 53 µm in order to separate hull, germ + dietary fibre and protein, respectively. Remaining starch fraction was separated with centrifugation method. Hull, germ + dietary fibre, total protein and starch fractions were dried in the oven at 40°C for 24 hours, and then their yields were calculated. The total recovery of hulled Aktaş cv. and Güneş cv. buckwheat cultivars were found as 98.1% and 96.1%; total starch yields were found as 51.6% and 49.7%, respectively. Retrogradation properties of Aktaş cv. and Güneş cv. starches were investigated during storage at +4°C and their retrogradation indexes were found as 50.3 and 56.6, respectively. The pasting temperatures of the same starches measured on rapid visco analyzer were found as 83.7 and 85.7°C; and final viscosity values were determined as 3.5 and 3.4 Pa•s, respectively. The enzyme resistant starch contents of starch fractions of Aktaş cv. ve Güneş cv. buckwheat were detected as 3.28% and 3.62%, respectively. The phytic acid contents of germ + dietary fibre fractions of Aktaş cv. and Güneş cv. buckwheat were found as 0.74 and 0.96 g/100 g, respectively; besides the phytic acid contents of protein fractions were 0.62 and 0.69 g/100 g, respectively. The highest total phenolic compound contents detected in dimethyl sulfoxide extraction condition were found in the germ + dietary fibre fractions of Aktaş cv. and Güneş cv. buckwheat's as 12.4 and 10.8 mg ferulic acid/g sample, respectively. The highest DPPH radical scavenging activity and TEAC antioxidant capacity were found in the hull fraction (as 81.7%) and germ + dietary fibre fraction (as 11.8 mmol/kg) of Aktaş cv. cultivar.