Production of type 5 resistant starch and determination of its effects on bread quality characteristics

In this thesis study, the effects of type 5 resistant starch (RS5), produced using enzymatically hydrolyzed flaxseed oil and high-amylose corn starch, on the in vitro starch digestibility, estimated glycemic index (GI), physical properties [differential scanning calorimetry (DSC) and X-ray diffraction (XRD)], quality attributes (color, specific volume, crumb structure, texture profile), and sensory characteristics of bread were investigated. Initially, crude flaxseed oil was subjected to enzymatic hydrolysis, and free fatty acidity, peroxide value, p-anisidine value, and fatty acid profile of the oils were determined. As a result of enzymatic hydrolysis, without promoting the accumulation of oxidative precursors, the free fatty acidity increased from 0.56% to 45.92%. The hydrolysis process did not alter the fatty acid composition of the oil. The RS5 samples produced with enzymatically hydrolyzed flaxseed oil were analyzed for in vitro starch digestibility, dry matter content, water holding capacity (WHC), solubility, swelling power, and characterized by DSC and XRD. Rapidly digestible starch (RDS) and slowly digestible starch (SDS) contents were higher in the control samples, whereas samples produced with hydrolyzed oil (EHK-RS5) exhibited lower values. The highest resistant starch (RS) content was found in the EHK-RS5 sample at 69.12%. Water holding capacity was determined as 95.12% in the control, 284.20% in HK-RS5, and 280.95% in EHK-RS5. Solubility values of RS5 samples ranged between 0.0% and 1.15% at 55°C, and between 1.31% and 2.08% at 75°C. Despite high WHC values, the lowest solubility was observed in the EHK-RS5 sample. DSC results indicated that the peak height index (PHI) of the control starch sample was the lowest among all samples. HK-RS5 and EHK-RS5 exhibited the highest PHI values, which were higher than that of the control. According to DSC thermograms, PHI values were 25.33 for the control and 30.24 for EHK-RS5. In the XRD pattern of the EHK-RS5 sample, typical peaks of V-type starches were identified at 13°, 17°, and 20°. In the second phase of the study, EHK-RS5 was incorporated into bread formulations at levels of 5%, 10%, 15%, and 20%. It was found that RS5 addition significantly (p<0.01) affected the glycemic index (GI) of the breads. The highest GI value (77.31) was observed in the control bread, while the lowest GI value (67.19) was determined in the bread containing 20% RS5. Hydrolysis values were 68.48% in the control and 50.06% in the 20% RS5-added bread. Specific volumes of breads ranged from 4.75 cm³/g to 2.76 cm³/g, with the lowest volume observed in breads with the highest RS5 content. RS5 addition led to an increase in crust lightness (L*) values (p<0.05). The L*, a*, and b* values of the bread crumb increased linearly with RS5 addition. While the number of air cells in the crumb decreased with RS5, the average pore area increased significantly (p<0.05). According to texture profile analysis, RS5 addition increased the hardness and chewiness of bread crumb. Hardness was recorded as 1558.25 in the control and 4744.60 in the bread containing 20% RS5. The lowest springiness value (0.67) was observed in the bread with 10% RS5, while other samples ranged between 0.93 and 0.96. Cohesiveness was slightly lower in the bread with 5% RS5 (0.65) compared to the control (0.69). Elasticity values were determined as 0.31 for the control and 0.37 for the bread containing 20% RS5. According to DSC results, the incorporation of RS5 did not significantly affect the thermal properties of bread (p>0.05). XRD patterns of the bread samples showed single peaks at 15°, double peaks at 17°, and single peaks at 20° and 23° in the control. In breads with 5% and 10% RS5, peaks were observed at 17° and 20°, while in those with 15% and 20% RS5, peaks appeared at 13°, 17°, and 20°. Sensory analysis revealed that the control and 10% RS5-containing bread samples had similar sensory characteristics. In terms of appearance, crumb structure, and overall acceptability, the breads with 5% and 10% RS5 were found to be comparable to the control.