Introduction:  Cake is one of the most popular flour products among all age groups especially in children with different types and calories. The high-energy content of various cake is often attributed to the oil, eggs and sugar in their formulation. Sugar is one of the principle ingredients of sponge cake batter that acts as a stabilizer and tenderizer by retarding and restricting the gluten formation and increasing the temperature of egg protein denaturation and starch gelatinization. In addition to making sweets, sugar keeps air bubbles in the texture of the cake and increases the volume of the cake. Despite all the functional benefits of sugar, due to the association with health risks such as high blood pressure, cardiovascular diseases, non-alcoholic fatty liver disease, tooth decay, obesity and diabetes, these days, the demand for low-sugar foods has increased. The replacing sugar with kinds of sweeteners such as natural and artificial ones in cake formulation for reducing amount of sugar is particularly important. Iran is the tenth largest grape producer in the world and grape syrup is one of the grape products with high nutritional and sweetening value that is produced in different regions of Iran. It is an important food product in human nutrition because of the high amounts of monosaccharides and minerals it contains and it is especially an excellent source of iron. The objective of this study was to use the grape syrup powder as a sugar substitute in cup cake.
Material and methods: The grape syrup without any added sugar or additives with brix 71 was obtained from Tuyserkan (Hamadan province, Iran) and powdered using a spray dryer and maltodextrin to prevent it from sticking to the machine. Cake flour with 72% extraction rate was purchased from Jonoob Factory (Ahwaz, Khuzestan).  In order to make a spongy cake, the grape syrup powder at the five ratios of 0%, 25%, 50%, 75% and 100% were substituted with the sugar in the formulation of cake. The batter of cupcake in this research was prepared using the sugar – dough method. The cake batter was poured into mold and cooked in an oven at 325 °C for 25 minutes. The cakes were exposed to air for 40 minutes to cool. The cakes were then packed in polyethylene bags and stored at ambient temperature and away from direct light. The specific gravity of cake batter was determined by dividing the weight of 240 mL of cake batter by the weight of 240 mL water. Then the physicochemical properties including the moisture content, firmness, volume, porosity, and color and sensory characteristics of the cakes were evaluated weekly during twenty-one days of storage. The moisture content of the samples was evaluated using a hot air oven at 105°C until constant weight. The cake volume was measured using the rapeseed displacement method. A Texture Analyzer was used to calculate the firmness of samples. The porosity of the crumb was investigated by imaging using Image J software. Color determinations of cake crust, including lightness (L), redness (a*), and yellowness (b*) were determined using the digital colorimeter system. A panel of ten trained panelists evaluated the cakes, ages 24–37 years (six females and four male), with sensory evaluation experience in descriptive evaluation of various food products. The sensory features including taste, odor, appearance, texture, and overall acceptability of cakes were performed using a descriptive profile test based on a scale of 1-5; where: 0 = extremely low intensity and 5 = extremely high intensity.
 
Results and discussion: The findings observed that increasing the grape syrup powder ratio caused an increase in specific gravity of the cakes batter, although in each case it was lower than the specific gravity of the control sample. The results showed that replacing sugar with different ratios of grape syrup powder as well as storage time had a significant effect on the characteristics of the cake. The moisture content increased significantly with increasing ratio of grape syrup powder to cake formulation. However, in all treatments, the moisture content of cake samples decreased during storage (p < 0.05). By the time of cake storage up to 21 days, the firmness of all cake samples decreased but the firmness of the cakes made from grape syrup powder was lower than the control sample on all days. On the last day, the samples containing 25% and 50% powder did not differ in firmness but were significantly softer than the control. The volume and porosity of cake samples were affected by sugar substitution with grape syrup powder as it decreased with increasing grape syrup powder ratio but the highest porosity and cake volume were observed in the sample containing 25% powder. By raising the ratio of grape syrup powder to the cake formula, the lightness of the cakes decreased and in other words, the cakes became darker and the redness and yellowness of the cakes increased and decreased, respectively. The sensory evaluation results showed that the samples containing 25% and 100% of the grape syrup powder had the highest and the lowest appearance, respectively. Replacement of sugar with grape syrup powder also improved the cake odor, which was significantly different from the control sample. The control sample and the cake sample containing 25% grape syrup powder had the highest softness and elasticity values. On the other hand, the addition of grape syrup powder produced a better taste than the control sample, with the cake containing 75% of the powder having the highest taste score. The highest and lowest overall acceptability scores were obtained in samples containing 25 and 50% grape syrup powder, respectively. In general, the results of sensory evaluation showed that replacing sugar with ratios of 25 to 50% of grape syrup powder improved some of the sensory properties of the cake.
Conclusion: Based on the findings of this study, up to 25% grape syrup powder as a natural sweetener can be replaced with sugar in the cupcake formula.