Effect of processing on the phenolic content and antioxidant activity of oat flour substituted breads

With the increasing population of the World and decreasing sources, reaching to the beneficial nutrients is getting harder. Especially, rich phenolic content foods of which healthy, anticarcinogic and anti-atherosclerosis effects are proven with many studies a tendency in consumers for alternative beneficial foods has occur. In this manner, oat has been discussed in many articles and studies because of its availability and its applicability in large variety of products. It is separated from other cereals by its high dietary fiber and rich phenolic contents. The antioxidants like vitamin E and phenolic contents which showed strong antioxidant activities both in vitro and in vivo is proven to be available in oat grain. Oats are unique among other cereals because their lipolytic enzyme is 10-15 times more active than wheat besides their high lipid and protein contents. In the literature there are many studies which states that oat contains many beneficial compounds for human health with respect to other cereals. Although there are many studies showing phenolic content and process effects on antioxidant capacity of fruits and vegetables, there are very few studies for the antioxidant activity and phenolic content of products which has oat flour. In a study; the effect of bread making processes on wheat bread phenolics has been searched. As a result the researchers reported that fermentation created positive effect on the antioxidant activity and phenolic content in wheat breads. When it is considered that the most consumed food is bread in our country and in the world, an innovative contribution may be made for both the industry and consumers' health by enrichment of traditional wheat bread with oat flour and enhance its health beneficial effects. The aim of this study is to understand how mixing, fermentation and baking stages effects the phenolic content and antioxidant activities in a bread which is substituted by 40% oat flour (to preserve the taste of bread reologic properties). In addition to that, to develop an acceptable functional bakery product by the addition of oat flour is another aim. By this way, an innovative functional food idea is presented to the industry. Sampling is done from 2 different treatments. Extractions were applied duplicately and for each experiemt three replicates were analyzed. The data is the avergae results for all those samples. Breads and dough samples are grinded under liquid nitrogen using a grinder after they are freeze dried. All the results are expressed in dry weight basis. Extractions are performed both for free and bound phenolics.Free phenolics are extracted by HCl and methanol, bound phenolics are extracted after heat application to the sediments from the free phenolic extraction in addition to the methanol and H2SO4. Extracts are preserved in -20°C until they are used in analysis. Phenolic content is determined by Folin-Ciocalteau method. Standard calibration curve has been obtained by measuring the absorbances for the known concentrations of gallic acid at a specific wavelength. As a result of analysis; free, bound and total phenolic contents for 40% oat flour bread is found to be higher than traditional white bread. In addition to this; while the fermentation process is increasing the phenolic xxiv content, ıt is observed that baking process decreased the phenolic content (free, bound and total) for both of the breads. The standard calibration graph for total flavonoid analysis is plotted by using rutin because it is dominantly found in oat. In the result of analysis; while fermentation process is increasing the total flavonoid content, baking process is decreasing the total flavonoid content. The reason for this situation is probably because of their heat sensitive properties. Antioxidant activity is tested by two methods. The standard curves for DPPH and CUPRAC methods are plotted by using Trolox. The standart calibration curves for both have been obtained by measuring the absorbances for the known concentrations of Trolox in a specific wavelength. The results of two analysis were close to each other. While antioxidant activity was increasing by fermentation process, antioxidant activity of traditional white bread was close to the oat bread as it is contrary to the expected. The reason for this might be the addition of Vitamin C as an oxidant to wheat flour. Phenolic profiles of the samples were also identified by HPLC/PDA. In the oat flour and the oat flour added bread samples, free ferulic, gallic, caffeic, p-cumaric, vanilic, t-cinammic, p-hydroxibenzoic acid, syringic and rutin have been detected by the HPLC/PDA analyses. In addition; in the samples of wheat flour and wheat flour bread free ferulic, gallic, caffeic acid and syringic has also been found. As it has been mentioned in the literature; avenantramids have been detected at the oat flour and oat bread samples. As a result of the phenolic profile analysis; it has been seen that in oat flour the most abundant free phenolic acid was gallic acid (34,46 mg/g) and the highest amount of bound phenolic acid was syringic acid (45,93 mg/g). In the wheat flour the most abundant free phenolic acid was syringic acid (21,31 mg/g) and the most abundant bound phenolic acid was gallic acid (5,15 mg/g). For the free phenolics; the result of the phenolic profile analysis showed that; fermentation had a positive effect at different rates on all the free phenolic acids and the baking prosess had a negative effect at different rates. In the oat bread samples; it has been found that; unlike free phenolic acid profile, there are no t-cinammic acid in the bound fraction. In the oat flour samples; it has been seen that the most abundant bound phenolic acid was ferulic acid (16,54 mg/g). Furthermore; it has been found that the wheat flour was rich in gallic acid (5,15 mg/g) in the bound fraction. In the oat and wheat breads for the bound fraction, in a contrast with the results of the free phenolic acid analyses, some of the phenolic acids didn't increase with the fermentation prosess. In the oat bread samples; bound vanilic acid increased 13-fold by the baking process. In addition to this; in the wheat breads in the bound fraction gallic acid increased 2-fold with the baking process. To determine the most efficient formula for producing oat bread with the highest amount of the total phenolic acid profile, further studies should be done to optimize the process parameters. As a result, more healthy foods which is also acceptable by consumers can be produced using functional ingredients in bread production. It is well known that oat has better health benefits, compared to wheat. In this study; oat flour, wheat flour, oat and wheat bread have been evaluated. Results showed that; oat bread, as it is expected, has better phenolic acid content and profile compared to wheat bread. This study suggested that; the use of oat flour in bread making will increase the health benefits of the most popular food consumed in our country. Further studies should be done for optimizing the conditions of the oat bread production.