Effects of ball-milling on the glass transition of wheat flour constituents

BACKGROUND: Starch and gluten, the major components of wheat flour, greatly influence the structural characteristics of food products made with wheat flour. The effects of ball-milling on the change in the semicrystalline structure of starch granules to the amorphous state have been reported. However, the effects of ball-milling of native wheat flour on physicochemical changes in wheat flour constituents have not been elucidated. Therefore in this study the effects of ball-milling on the glass transition of wheat flour constituents were investigated. RESULTS: Crude gluten, non-gluten proteins and separated starch were obtained from wheat flour ball-milled for 0-10 h, and the glass transition temperature (T(g)) of these constituents was evaluated. The T(g) of all wheat flour constituents decreased with increasing ball-milling time. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that changes in band position and intensity did not occur for gluten but did occur for non-gluten proteins. X-ray diffraction revealed decreased crystallinity and greater plasticisation by water in separated starch as the ball-milling time was prolonged. CONCLUSION: The results showed that the ball-milling process decreased the T(g) of wheat flour constituents as a function of milling time. The decrease in T(g) was probably due to changes in conformation of protein subunits in gluten and depolymerisation of the non-gluten protein fraction. The information obtained here about the physical alteration of wheat flour constituents may enhance the ability to successfully use ball-milled wheat flour in food applications. (C) 2008 Society of Chemical Industry