The binding of Cresol Red and of Acid Orange 10 (in the absence and presence of urea) to unheated and progressively heated, defatted soy meal was compared with their NSI values, urease activities, in vitro digestibilities, unreactive lysine contents, and foaming and emulsifying capacities. These results suggested that increased amounts of Cresol Red and of Acid Orange 10 (in the presence of urea) bound to the heated samples were due to the progressive exposure of hydrophobic residues caused by thermal denaturation. High statistical correlations were obtained between dye-binding, the duration of heating, and functional properties. Our results indicate that dye-binding has potential for predicting certain funr tional properties as well as for monitoring thermal denaturation of soy proteins.

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A dye binding procedure has been developed for the estimation of protein in seed extracts and solutions of seed protein isolates. The method was evaluated using extracts of five seed materials, viz. field beans (Phaseolus vulgaris), rapeseed (Brassica napus) , sesame seed (Sesame indicum), cowpeas ( Vigna unguiculata) and cottonseed (Gossypiurn hirsutum L.). A high correlation between the dye binding measurements and analyses obtained by the Kjeldahl procedure has been demonstrated and the suitability of the dye binding method for routine protein estimations in this work has been confirmed.

During the last 20 years, the estimation of proteins in foods by dye binding has progressively increased in popularity and, mainly because of adaptations to suit a wide range of food commodities, many different procedures are in existence. However, despite variations in methodology, these procedures are all characterised by the formation of an insoluble dye-protein coagulum at about pH 2, which is removed from the reaction mixture before a photometric measurement is made on the supernatant. The reduction in absorbance effected by samples (on account of their proteins reacting with the dye) is directly related to their content of protein and this value is interpolated from data previously obtained with other samples which have also been analysed by a reference procedure, usually based on a Kjeldahl estimation of nitrogen.Practical details of dye-binding procedures may be obtained by reference to reviews by Cole' and Lakin.2The principal mechanism operating in these methods is an electrostatic association between dye anions and the basic groups of proteins, which are positively charged at the low pH of the reaction mixture. An additional amount of dye is also removed from solution because of hydrophobic associations with proteins and with dye already bound to proteins by the electrostatic and hydrophobic forces. The extent to which this additional, secondary binding occurs is mainly a function of the strucuture of the dye molecule and with some dyes it occurs to a considerable degree. For example, CI Acid Black 1, a fast-reacting dye commonly used for the analysis of milk, is bound by proteins in amounts which may be 150 % greater than their total content of basic groups.Because of the complex nature of the dye-protein interaction dye-binding procedures are highly empirical, but even so, when the experimental conditions are rigorously standardised, the amounts of acid azo dyes bound by proteins are remarkably constant. Accordingly, these