Effects and mechanism of modified starches on the gel properties of myofibrillar protein from grass carp.

The effects and mechanism of cassava starch (CS), hydroxypropylated cassava starch (HCS) and cross-linked hydroxypropylated cassava starch (CHCS), on gel properties of myofibrillar protein (MP) from grass carp were investigated using texture analyzer, dynamic rheometer, scanning electron microscopy (SEM) and circular dichroism (CD). Water holding capacity (WHC) of MP gels increased from 70% to ca. 90% with an increase in additive amount of modified starches (MS) and HCS improved WHC most effectively. The MS (HCS and CS) at proper additive amount (1.5 wt%) improved the textural properties of MP gels significantly (P<0.05). In rheological test, all MS-MP solutions showed viscoelastic nature of MP, but adding MS resulted in much higher G', suggesting the effect of MS (especially 2.5 wt% CHCS) was considerable and equal to increasing protein concentration. The SEM photographs showed the MP gel with 2.5 wt% CHCS or 0.5 wt% HCS formed compact and homogeneous network, while the gel with CS agglomerated and the agglomerate phenomenon occurred more obviously with increasing additive amount. The addition of MS, especially CHCS, promoted the heat-induced conformational transition from the α-helix companied with β-turn to β-sheet, leading to the MP molecules stretching out.