The effect of different processing parameters on the final product quality in bozkir sesame paste production

In the Turkish Food Codex (TFC) Communiqué on sesame paste (Communiqué No: 2015/27), sesame paste is defined as "The product obtained by crushing sesame (Sesamum indicum L.) seeds suitable for sesame paste production in a mill after their shells are separated in accordance with the technique and dried and roasted in the oven". There is no standard method in sesame paste production. Traditional sesame paste production consists of sieving, soaking in water, peeling, soaking in salt water, rinsing and centrifugation, roasting, ventilation, grinding, packaging and storage. In 2021, the production steps of Bozkır sesame paste, which received the "protected geographical indication" by the Turkish Patent Institute, include soaking, peeling, roasting, ventilation, sieving, grinding, packaging and storage. For this reason, products produced with the Bozkır sesame paste production method have different characteristics compared to sesame paste produced with the traditional method. Besides, different applications are made in the processing stages of the Bozkır sesame paste production method. In this study, 9 sesame paste samples were obtained from different sesame paste production plants from Bozkır district in Konya. The quality of Bozkır sesame paste samples produced by using imported or local sesame seeds and applying different processing parameters such as soaking time (6-24 h), shell separation rate (0-95%), roasting method (wood fire-roasting drum), ventilation time (10-30 min) were evaluated in terms of dry matter content, ash content, fat ratio, color characteristics, rheological and sensorial properties. The dry matter content of sesame paste samples was determined in the range of 99.65-98.87%, and the highest dry matter content (99.65%) was determined in the sesame paste sample (KS2) produced by roasting and grinding imported sesame in a drum with 85% shell separation rate. The sample with the highest ash content (4.16%) and the lowest fat content (50.07%) (KL1) was sesame paste roasted and ground in a stone oven with wood fire with 100% shell separation rate. The sesame paste sample with only grinding process (BYZ) had the lightest color. With 85% shell separation rate, the most yellowish sample (KS1) was obtained by roasting in wood fire and using imported sesame seeds. Sesame paste samples were non-Newtonian fluid and shear thinning characteristics was detected. The rheological properties of the flow behavior were determined using the power law model. The K values of sesame paste samples at 15°C, 30°C, 45°C were 3.10-8.90, 1.60-4.50, 1.29-2.98, n values were 0.77-0.84, 0.73-0.82, 0.67-0.81 and R2 values were 0.993-0.999, 0.991-0.998, 0.987, 0.997 respectively. The viscosity of sesame paste samples decreased with increasing temperature at all three shear rates (1, 10, 100 s-1). The K0 value obtained by using Arrhenius equation for shear rate of 1, 10, 100 s-1 was in the range of 5.84x10-04-7.53x10-06; 1.07x10-04-4.60x10-06; 6.06x10-06-1.54x10-06, Ea value was in the range of 18.84-30.65; 23.03-31.48; 30.28-32.97, and R2 value was in the range of 0.991- 0.999; 0.990-0.999; 0.997-0.999, respectively. According to the consumer preference test, the most preferred sesame paste samples were KS2 (18.91%) with 85% shell separation rate from the hulled sesame paste group, KL3 (16.21%), KL1 (14.2%) and KL4 (11.15%) from unhulled sesame paste group. Color and taste data were similar in sesame paste samples. In terms of aroma and smell as well as color value, the BYZ sample, which was only grinded, was generally least liked. Although samples of KL1 with no shell separation and KS3 with 95% shell separation rate were liked the most in terms of appearance, similar results were obtained in KL2, KL3 from unhulled sesame paste group and KS2 from hulled sesame paste group. Therefore, it was determined that many parameters such as sesame type, soaking time, shell separation rate, roasting method, ventilation time and grinding speed had an effect on product quality. Due to the differences in traditional and Bozkır sesame paste production methods, some samples produced with Bozkır sesame paste production method did not comply with the TFC Tahini Communiqué. It would be in the best interest of the producers to improve the codex for Bozkır sesame paste in order to comply with TFC.