Bleaching of defatted flaxseed meal to improve its usage as ingredient in food applications

Brown defatted flaxseed meal (FM) was decolourised by dilute hydrogen peroxide (HP). The bleachability was evaluated as function of the FM concentration (2.5%, 5% and 10%), HP concentrations (1%, 2% and 3%), pH (3, 6, 7 and 9), temperature (25, 50 and 75 degrees C) and reaction time (2, 5 and 10 min). The product whiteness and yellowness were better at pH 9% and 3% HP concentration. The bleachability was enhanced by increasing the temperature but was inversely proportional to the meal concentration. The colour L* value was the highest at 2.5% FM, 3% HP, pH 9 and 10 min at 75 degrees C (L* = 74.82 +/- 0.56) and was the lowest at 10% FM, 1% HP, pH 3 at 25 degrees C during 10 min (L* = 36.17 +/- 0.45). These results may be exploited to improve the profitability of the flax sector using bleached meal as ingredient in food formulations. (Authors abstract)

It is important to investigate uses for flaxseed meal (FM) especially food applications. FM can compensate for the lack of amino acids like lysine in some grains and can be also used to improve some functional properties of different food matrices. FM proteins are the dominant component of the defatted meal and are comparable in nutritional quality and amino acid composition too the high-quality plant proteins such as soya protein.  Incorporation of FM to food matrices will result in product with altered colour.  The application of UV⁄ozone treatments for cleaning and bleaching purposes has been reported, and it was found that good oxidative efficiency can be achieved by coupling both UV radiation and ozone. Hydrogen peroxide (HP) is also known as efficient bleaching agent and is approved and generally recognised to be safe for use in the production of annatto-coloured whey.  The aim of the present work was to study the effectiveness of dilute HP as a bleaching agent to produce discoloured brown FM. The bleaching was studied according to the following independent variables: defatted FM concentration, HP concentration, bleaching time, bleaching pH and temperature. Key observations a decrease in the total phenolics content which suggests that bleaching agents such as HP affect pigments that cause dark coloration in plant material. The L* value represents the whiteness (lightness) and the highest the L* value the whiter is the sample. According to the LMS analysis method, it appeared that the effect of HP concentration on the L* value followed a quasi-linear behaviour. The L* colour parameter was significantly affected by the FM concentration, and it decreased quasi-linearly as the meal concentration was increased.  (Editors comments)