The Effect of Inulin and Resistant Starch on Rheological Properties of Baguette Dough

The rheological properties of a bread dough describe its behavior under different process conditions. They are also central to its formulation, optimization, quality control, and better process capacity. A number of additives can improve the rheological properties of dough and breads. Fiber-based compounds and prebiotics in addition to gluten and starch, which have a large tendency to absorb the flour water, can affect the moisture distribution across the dough structure. Inulin and resistant starch are two types of prebiotics. Inulin is a water-soluble dietary fiber that is not absorbed by the enzymes at the upper section of he the digestive system and is partially fermented and metabolized by the microbial flora of the colon. Digestion-resistant starch is another prebiotic that acts as a food fiber and adds to the nutritional value. It can also improve the structure of the final product. In recent years, the rise in consumer awareness about health benefits of prebiotics has increased interests in functional foods particularly in bakery products. The present study qualitatively analyzed the effect of the prebiotics (i.e. inulin and resistant starch) on rheological properties of baguette bread doughs.
The study treatments are: Baking dough w/o inulin and resistant starch (Control); baking dough w 2.5% inulin (based on flour weight); baking dough w 5% inulin (based on flour weight); baking dough w 2.5% resistant starch (based on flour weight); baking dough w 5% inulin (based on flour weight); baking dough w 2.5% inulin 2.5% resistant starch (based on flour weight); baking dough w 2.5% inulin 5% resistant starch (based on flour weight); baking dough w 5% inulin 2.5% resistant starch (based on flour weight); baking dough w 5% inulin 5% resistant starch (based on flour weight). The treatments were rheologically tested by farinograph and extensograph after preparation. Study data were then analyzed using the completely randomized design. Means of data were also compared by Duncan's multiple-range test (α = 5%) in SPSS 16.
According to the results, the different levels of prebiotics (inulin and resistant starch) significantly improved dough water absorption compared to the control samples. This can be due to the presence of hydroxyl groups in the structure of the prebiotics, which increased the number of hydrogen bonds and thus water absorption in all treatments compared to the control. Moreover, these additives led to significantly higher dough development time than the control. This can be due to the hydroxyl groups in the structure of inulin and resistant starch, which increased the number of hydrogen bonds and thus cross-bonding with water. These additives also significantly increased the dough stability time compared to the control.This is a result of hydrogen attachments and hydroxyl bonding between gluten proteins (made up of glutenin and gliadin) and the prebiotics (inulin and resistant starch) that in turn improved the stability and strength of the doughs. As the dough stability increased, the dough softening degree after 10 and 12 minutes was also reduced, which was due to the hydrogen bonds resulting from hydroxyl cross-links of gluten with inulin and resistant starch. Note that the quality index increased when the stability and strength were improved compared to the control dough. According to the results, by adding different levels of inulin and resistant starch, the dough energy rised higher than the control sample after 45, 90 and 135 minutes. This is again due to (OH) hydroxyl bonds with hydrogen attachments between glutens and the prebiotics. In this regard, the highest resistance to extension after 45, 90 and 135 min was recorded for the treatments containing inulin and resistant starch whereas its lowest value was recorded for the control. This is due to the stable continuous lattice made by amylose in resistant starch granules, which led to the higher strength of other treatments than the control. Additionally, the increased dough resistance to extension can be due to the interaction of inulin and resistant starch with flour proteins. Regarding extensibility, significant differences were observed between the treatments and the control within all three time intervals. Accordingly, after 45, 90 and 135 min, the control treatment had the highest extensibility whereas the treatment with 5% inulin 5% resistant starch (based on flour weight) had the lowest level of this parameter within these times. The increases in strength and stability of the doughs were caused by strong links between glutens and these prebiotics, which reduced the dough extensibility. The results showed that the highest dough ratio number after 45, 90 and 135 min belonged to the treatment with 5% inulin 5% resistant starch (based on flour weight). The lowest ratio number was recorded for the control in these time periods. The gluten was the main factor behind dough stability. The large amount of hydroxyl groups in the structure of inulin and resistant starch led to formation of a better structured three-dimensional gluten lattice. In general, by taking all parameters into account, the treatment with 5% inulin 5% resistant starch was selected as the best treatment.