Functional interaction components of protein isolates and glucomannan in food bars by FTIR and SEM studies

Abstract

Functional compounds between soya, wheat, corn protein isolates, and konjac glucomannan (KGM) and these dough mixtures were investigated by FTIR studies. The results showed that fragments–CONH2, were assigned to absorption bands in the region of 1634 - 1650 cm-1, and fragments–carboxyl groups of protein matrix were exhibited at the region of 3235 – 3460 cm-1. Whereas, the molecular structures of KGM were confirmed by fragments –CH appeared at the wave length of 808 - 875 cm-1, which representated the mannose and glucose units. Fragments C=O (aceto compounds) exhibited at the region of 1636 - 1666 cm-1showed the existence of β-1,4 linked glucose and mannose. Fragments C-O-C represented acetyl residue of KGM were exhibited at the absorption region of 1027 - 1244 cm-1, and free –OH hydroxyl groups of KGM were strongly appeared at absorption bands of 3100 - 3391 cm-1. Surprisingly, the deconvolated spectra of a dough mixtures of protein isolates with KGM was almost identical to IR spectrum of each ingredient. The presence of overlapping absorption bands at 3435.95 and3488.99 cm-1 which were assigned to –OH and NH2 stretch vibration, from protein matrix and –OH vibration from KGM intermingled to form a smooth surface of SEM image of the dough mixtures. Smooth surface plates were observed for the microstructure of food bar with konjac flour; on the contrary, that without konjac flour showed rough fracture plates. Textural studies showed increasing breaking force as the increased level of konjac flour in food bar. Key words: Interaction components, protein isolates, glucomannan, konjac flour, food bar, FTIR, and SEM.