APPLICATION OF THE DYE-BINDING TECHNIQUE FOR QUANTITATIVE AND QUALITATIVE ESTIMATION OF RAPESEED MEAL PROTEIN

Abstract

The linear equation Y = 2.2 + 0.27X relating dye-binding capacity with Acid Orange 12 (X) and Kjeldahl crude protein content (Y) of rapeseed meal, derived previously, was applied to 126 commercial samples for estimating the protein contents of the meals. Results indicated that the means of crude protein contents obtained by both dye-binding and Kjeldahl nitrogen analyses were comparable. However, comparisons based on individual samples showed that the dye-binding method underestimated or overestimated the protein content of about 20% of the samples by 1% or more. The deviation was caused mainly by the atypical content of basic amino acids, particularly of lysine, in these meals. Application of the equation for quantitative prediction should, therefore, be limited to rapeseed meals which have been properly processed. On the other hand, the correlations noted between the dye-binding capacity of protein (DBCP, mg Acid Orange 12/g protein) of 21 selected rapeseed meals and the lysine and available lysine contents of the meals (r = 0.84 and 0.79) showed that the ability of the protein to bind Acid Orange 12 may be used as a protein quality index of the samples. This potential was further investigated by studying the effects of autoclaving for varying periods of time at 121 °C on the DBCP of rapeseed meal protein. In this regard, a significant reduction in DBCP of the meals was noted after 45 min of heating. Available lysine values were reduced by autoclaving at a more rapid rate than DBCP values.