Interfacial Behaviour of Secalin and Rye Flour-milling Streams in Comparison with Gliadin

Secalin was extracted from rye flour and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The SDS-gel pattern showed that some proteins were composed of disulphide linked polypeptide chains. However, a gliadin sample contained more polymeric protein. The behaviour of gliadin and secalin at the air–water interface was compared using the surface balance technique. It was found that secalin was more surface active than gliadin, spreading faster and to a higher surface pressure. The influence of pH on the interfacial behaviour was also studied. The surface pressure after 45 min equilibrium of both gliadin and secalin decreased with decreasing pH. The effect was independent of the acid (hydrochloric acid, lactic acid or ascorbic acid) when compared at the same pH. The behaviour at the gas–liquid interface of five different rye flour-milling streams together with the whole (straight run) flour was also investigated. The fraction with highest protein content spread fastest and reached the highest surface pressure value. When spread on ascorbic acid at pH 3·7 the surface pressure of the flour stream with lowest protein content decreased to the greatest extent, whereas the fraction with the highest protein content was not affected. It was thus found that, although secalin showed an interfacial behaviour similar to gliadin, this behaviour was not necessarily shown by the total protein mixture in a rye flour.