The authors, who published the results of their research in the Journal of the Science of Food and Agriculture, found that the antioxidant activity and free phenolic acid content were reduced by mixing but recovered after fermentation and baking.
Phenolic acid recovery after baking, they added, was between 74 and 80 per cent.
The researchers note that increasing consumer awareness of the health benefits of fruits and vegetables has prompted the development of bakery products containing whole wheat flour and the fortification of bakery products with fruits and vegetables with high antioxidant potentials.
But they report that their study was triggered by that fact that, to date, no studies have been published on the effect of baking on the phenolic acid content and antioxidant activity of wheat flour.
“Although the biological effects of phenolic acids in fresh vegetables and fruits have been studied, little is known about the biological effects of phenolic acids in bakery products such as cookies and bread,” said the authors.
Phenolic acid, a type of antioxidant, is abundant in whole grains and is present in high concentrations in aleurone cell walls and in the seed coat and embryo of wheat, which are removed during milling, but is not present in significant quantities in the endosperm.
As phenolic acids are susceptible to oxidation and degradation, exposure to light, oxygen and heat, conditions normally present during food processing, may accelerate the destruction of phenolic acids. “Therefore information on the stability of phenolic acids during food processing is important for evaluating the potential health benefits of foods containing phenolic acids,” said the team.
The researchers said that they investigated changes in the antioxidant potential of wheat flour when exposed to mechanical mixing, fermentation and baking. “In this model system, instead of adding vegetables and fruits as antioxidant sources, four different phenolic acids were added individually to the wheat flour and their antioxidant activities were determined at each step of the breadmaking process,” said the scientists involved.
Four phenolic acids, caffeic acid, ferulic acid, syringic acid and gallic acid, were mixed with wheat flour at a concentration of 4.44 µmol/g of flour, said the authors.
“This level of added phenolic acid was calculated to induce rapid breakdown of hard wheat flour dough in mixograph studies,” said the team.
The researchers said that optimum-mixed dough was defined as dough mixed until maximum elasticity was attained. It was divided into three portions. The first portion was lyophilised immediately, the second was fermented and then lyophilised and the third was fermented, baked and then lyophilised.
The team said that dough was fermented for 1 h at 30 °C and 85 ± 5 per cent relative humidity (RH) in a proofer. The fermented dough was then baked in the electrically heated deck oven, which had independently operated decks, at 200 °C (top) and 190 °C (bottom) for 20 minutes, they added.
The lyophilised unfermented dough, fermented dough and bread were ground, sieved through a 20-mesh screen, sealed in plastic bags and frozen until analysis, said the researchers.
They explained that the antioxidant potential of the acids was determined using the β-carotene-bleaching activity assay, and free phenolic acid levels were determined by high-performance liquid chromatography.
Of the phenolic acids, caffeic acid had the most pronounced antioxidant effect, followed by ferulic acid, gallic acid and syringic acid, found the researchers.
“The initial antioxidant activity of caffeic acid (45.8 per cent) was not significantly changed by processing,” noted the team.
They added that their results showed the concentration of ferulic acid was the highest of the residual free phenolic acids after the baking process. “Although less added caffeic acid was recovered than added ferulic acid, caffeic acid made the greatest contribution to the antioxidant activity of bread,” concluded the researchers.
Source: Journal of the Science of Food and Agriculture
Published online ahead of print: DOI: 10.1002/jsfa.4188
Title: Antioxidant activity of hard wheat flour, dough and bread prepared using various processes with the addition of different phenolic acids
Authors: Hye-Min Han, Bong-Kyung Koh