Effects of enzymatic modification of soybean protein on the pasting and rheological profile of starch-protein systems

Reformulation of traditional food systems to introduce new ingredients may change their structure and perceived texture. Interactions between proteins and starch during processing can markedly influence starch gel network structure and rheological profile. The present work aimed to study the effects of soybean protein and the products of enzymatic modification on the pasting and rheological profile of corn and cassava starch. The behaviour of those protein enriched gels during storage was also assessed. Soybean protein isolate (SPI) was incubated with endopeptidase (AL) or food grade microbial transglutaminase (TG). Pasting and rheological behaviour, water retention capacity and structure of proteinand hydrolysed protein-starch gels were analyzed. Protein incorporation increased the viscosity of starch suspension during and after heating. SPImodified proteins increased peak viscosity. Only the structural modifications brought by TG on SPI increased the final viscosity during starch pasting and the storage modulus (G′). This modulus (G′) of the gelled systems decreased with the addition of AL-treated protein isolate. Light and fluorescence microscopy showed that SPI formed a continuous phase, like a network, in the gelled system. Different network structures and rheological properties can be obtained when SPI are modified by protease and transglutaminase enzymes, which may be very useful for designing new food products. INTRODUCTION Reformulation of traditional food systems to introduce new ingredients may change their structure and perceived texture, since products result from interactions between different components. The development of protein enriched products has focussed the attention of food technologist when aimed at the design of innovative food with improved nutritional properties. Interactions between proteins and starch during processing can markedly influence starch gel network structure and rheological profile.