Effect of different milling systems on selected quality parameters of bulgur

ABSTRACT EFFECT OF DIFFERENT MILLING SYSTEMS ON SELECTED QUALITY PARAMETERS OF BULGUR YILDIRIM, Ali M.Sc. in Food Engineering Supervisor: Prof. Dr. Mehmet Durdu ÖNER April 2004, 83 pages Effect of different milling systems on selected quality parameters of bulgur was searched in this study. Studies were made with disc and roller mills, horizontal helical polisher and color sorting systems for bulgur production. Conventional disc mill and newly improved roller mill (with four rolls and three passing) used in bulgur production were compared based on; energy, capacity, yield, loss, milling characteristics, ash content, hectoliter weight, color and protein contents. The gaps of first-second rolls, second-third rolls and third-fourth rolls were adjusted to 1.90, 1.60 and 1.30 mm; 1.20, 1.00 and 0.80 mm, and 0.40, 0.50 and 0.60 mm, respectively, and twenty seven variations of those gaps were studied for roller mills. On the other hand, nine different gaps 1.90, 1.60, 1.30, 1.20, 1.00, 0.80, 0.60, 0.50 and 0.40 mm were studied for disc mill. The produced samples from both types of milling systems were screen analyzed using 3.50, 2.00, 1.00 and 0.50 mm size sieves. Screened fractions of (+/3.50), (3.50/2.00), (2.00/1.00), (1.00/0.50) and (0.50/-) mm named as coarse, pilaf, middle, fine sized bulgur and loss of bulgur, respectively. Also effect of the horizontal helical polishing system used in bulgur production line on quality factors such as color, protein content, loss, yield, moisture content and hectoliter weight of bulgur samples were researched. Color sorting system is applied on peeled intact, mixed and fine bulgur samples and effects of the system on percent purity (yield), loss and color values of the products were investigated. Yield values of 11samples from disc mill were found as 13.13, 72.33 and 84.84 % for gaps adjustments of 0.40, 0.50 and 0.60 mm, respectively. On the other hand, yield values of samples from roller mill were obtained between 84.77 and 99.75% for the same gaps. Especially for the fine bulgur, the yield values of the disc mill were found to be too low. The amount of loss in disc mill, especially for the 0.40 mm break was increased up to 86.87 %, was higher than that for improved roller mill. Even in the finest break of the improved roller mill system, the loss value was at most 15.23 %. The hectoliter weight values for the disc mill system were found to be higher than those of roller mill. In the roller system, coarse, pilaf, middle and fine bulgur products could have been produced simultaneously. The moisture and ash content were decreased from 13.08 to 11.15 % and 1.53 to 1.41% respectively, but hectoliter weight value measured on 2 mm sieve was increased from 67.16 to 85.35 kg/hi in horizontal helical polishing system. The measurements of color values from inlet and outlet of polisher were indicated decrease in L and increase in b values. Also, increase in YI (yellowness index) value which was parallel with this change reveals the fact that using polisher produces bulgur with desired amber color. Analysis of percent purity of intact, mixed and fine bulgur samples from color sorting system was showed that the highest value, 99.10 %, was obtained for intact bulgur. Key words: bulgur, roller mill, disc mill, polisher, color sorting system. m