Influence of tragacanth gum and oat bran fiber on physicochemical, and sensory properties of toast

Bread is one of the oldest foods that it is widely used in the world. Since the quality properties of breads are great interest to consumers. Bread during the storage period has undesirable physicochemical changes that it's called staling. Increase in hardness of bread core during the storage period is one of the most important to the staling index that the main reason for this is starch retrogradation (Guarda et al. 2004). It is recommended to delay staling by various pathways including additives such as proteins, carbohydrates, enzymes, fats, fibers, emulsifiers and hydrocolloids (gums) (Rajabzadeh, 2008). Today, the usage of dietary fiber is one of interest for food consumers due to its beneficial, physiological effects.  Its importance in reducing fat and blood sugar, reducing the risk of colon and gastrointestinal cancers and treating obesity is well known (Basman and Köksel, 1999). Oat bran is a soluble dietary fiber source and its known for its high beta-glucan levels. It is effective in lowering cholesterol and slowing glycemic responses (Klopfenstein, 1988). For a long time ago flour and bran of oat has been used in breakfast cereals or bakery products (Webster, 1986). Adding sources of fiber to the bread formula is often accompanied by problems in the properties of the dough and the quality of the bread. Adding fiber reduces the volume, hardness and darkness of the bread color and sometimes changes the taste (wang et al., 2002). Negative effects of fiber on bread structure is related to the decrease in gluten content and the increase in bran particles in bread texture (Verbeken et al. 2003). Due to low consumption of fiber in the daily diet that is usually lower than the recommended dose (30 grams of fiber per day), enriching bread with fiber can play an important role in achieving its health benefits (wang et al., 2002). The use of hydrocolloids increasing in recent years due to the desirable characteristics of baking (Kiumarsi, 1997). Tragacanth gum, as one of the herbal gums, is ejected from several species of Astragalus. Tragacanth is listed as a quality hydrocolloid in the GRAS list and is one of the food additives (Kiumarsi, 1997). This gum has wide application properties in the food industry, especially in the baking products, it has wide application properties including emulsifying properties, stability and thickening in food products (Verbeken et al. 2003). In this research, the effects of replacing oat bran fiber (4 and 8%), as well as tragacanth gum (0.5% and 1%) alone and in combination include 0.75% tragacanth gum + 6% oat bran fiber and 0.25% tragacanth gum + 2% oat bran fiber were used in preparation and formulation of toast bread formulation.  

Six treatments were designed according to a completely randomized design. The physicochemical tests included: bread volume, moisture content, ash, pH, fat percentage, colorimetric (brightness index (L*), redness index (a*), jaundice index (b*), hardness, sensory characteristics (Volume, Shape, Crust color, cooking uniformity, Crust Properties, Crack and tear properties, Hollow and grainy properties, Crump color, Aroma, Taste, Chewiness, Texture) were analyzed 2 hours after production and staling at 1, 2 and 3 days intervals were evaluated in three replications. The results of the tests were analyzed by Duncan's one-way mean comparison at 95% confidence level and training. Sensory data also evaluated using Kruskal-Wallis nonparametric test, charts were drawn with Excel software version 2013. 

The results showed that there was none significant difference in fat percentage index and pH of treatments compared to control (p>0.05). By increasing the amount of tragacanth gum, as well as oat bran fiber ash percentage, jaundice and redness index significantly increased and brightness index, texture hardness and staling significantly (P ≤ 0.05) decreased. By using tragacanth gum and oat bran fiber and increase their concentration the moisture content of toast bread compare to the control significantly (P≤0.05) increased. In fact, the addition of tragacanth gum significantly increased the absorption of water in the dough as compared to the control, which is due to the hydrophilic nature of the hydrocolloids, including tragacanth gum. Oat bran fiber due to the high protein content of beta-glucan, it is also able to absorb a large amount of water in the early stages of dough preparation and increase the amount of water used to make the dough. This increase in water absorption caused decreases the hardness of the bread texture. Reason of staling decrease by adding oat bran fiber it is also due to the presence of starch degrading enzymes such as amylase, which causes delay in the staling and hardening of the bread's kernel. The results of the evaluation of the volume of tested treatments showed that the use of oat barley fiber alone increased the bread volume up to 4%, and decreased the bread volume in quantities higher than 4%. The reason for reducing volume by increasing the amount of oat bran fiber can be due to less airborne bubbles during the mixing of the dough and thus to reduce the volume of the samples. The use of tragacanth gum and increase its concentration also increased the specific volume of the toast breads compared to the control sample. Tragacanth gum due to the presence of hydroxyl groups in their structure, they can interact with the water molecules in the bread dough, which increases the viscosity of the dough, develops the dough and, consequently, improves the maintenance of gases and increases the volume of the product. The highest proportion of volume belonged to the treatment containing 0.75% tragacanth gum and 6% oat bran fiber and then the treatment containing 0.25% tragacanth gum and 2% oat bran fiber. The sensory evaluation results showed that all sensory features were evaluated including volume, shape, crust color, cooking uniformity, crust properties, crack and tear properties, hollow and grainy properties, crump color, aroma, taste, chewiness, texture did not have a significant difference with the control sample and even got higher score.

Toasting treatment containing 0.75% tragacanth gum and 6% oat bran fiber due to having more volume, less stale and desirable sensory properties were introduced as superior treatment. Therefore, the use of tragacanth gum and oat bran fiber can improve the qualitative (physicochemical and sensory properties) of the toast bread.