Evaluation of the use of stevia (stevia rebaudiana) and its products as a sugar substitute in cake and cookies

ABSTRACT EVALUATION OF THE USE OF STEVIA (Stevia rebaudiana) AND ITS PRODUCTS AS A SUGAR SUBSTITUTE IN CAKE AND COOKIES Gülsüm Nur Yüksel M.Sc. Thesis in Food Engineering Supervisor: Prof. Dr. Muharrem Certel February 2019; 196 Pages In this study, it was aimed to reduce the energy value of cakes and cookies by using stevia products as sugar substitution. Use of stevia products instead of sugar in the recipe causes structural problems as a result of the decrease in the amount of solid matter. It is aimed to eliminate this problem by adding isomalt or wheat starch with stevia products to the cake and cookie formulations and examine the shelf life characteristics of the products with the chosen formulation. For these purposes, stevia leaf powder (SLP) or 90% pure commercial stevia powder (CSP) with the addition of isomalt (both cakes and cookies) and wheat starch (in cookies) were used as sugar substitutes. Cakes and cookies were produced by reducing sugar level by 0%, 25%, 50%, 75%, and 100% and using stevia products with other ingredients as a sugar substitute. Physical, structural and sensory analyses were performed to the produced cakes and cookies. For shelf life analysis, the control sample produced without reducing sugar, cakes and cookies which sugar was reduced by 50% and 25% (separately for SYT and TST) were reproduced in 2 replicates. The samples were packed in a modified atmosphere (75% N2 and 25% CO2) stored for two months at 25 °C. Every 15 days for two months, shelf life analyses were applied to these samples and the changes in the moisture, aw, color, texture, sensory evaluation, TBA, p-anisidine, peroxide value, free fatty acid values and the number of yeast molds during the storage period were examined. It was observed that the effect of the sweetener groups on the raw fat, crude protein, raw fiber, and HMF values were statistically not significant while the effects of the sweetener groups on energy values were statistically significant. It is determined that the control cake and control cookies have the highest energy values and the energy content decreased as sugar content decreased. When the results of the texture profile analysis (TPA) of the cakes were evaluated, the effect of the sweetening groups on the cohesive viscosity and elasticity values was statistically not significant; the effect of sweetener groups on hardness, gumminess, and chewiness values was observed to be significant. The effect of the sweetener groups on the hardness and fragility values of the cookies was statistically not significant. During the storage period, the textural values of the cakes were generally varied During the storage period, it is observed that the hardness values of the cookies increased, while the fragility values could not be read by the device The sensory evaluation scores of cakes and cookies were reduced during the storage period. The least-favored cakes and cookies were the ones produced by reducing the sugar by 25% and using SYT. It was determined that TBA reagents and p-anisidine contents of cakes and cookies increased during the storage period. The peroxide number and free fatty acid content of cakes and cookies decreased during the storage period. When the results are evaluated decrease at the energy value of both cakes and cookies was determined. Additionally, it is observed that the resulting problems can be eliminated to a great extent with the addition of isomalt or wheat starch to the cake and cookie formulations. KEYWORDS: Isomalt, cake, cookies, rebaudioside A, Stevia, Stevia rebaudiana, stevioside. COMMITTEE: Prof. Dr. Muharrem CERTEL Prof. Dr. Mustafa ERBAŞ Prof. Dr. Sebahattin NAS