| This paper mainly studied the effects of ice-structuring protein(ISP) extracted from winter wheat on the freeze-thaw stability of corn and wheat starch, stability of frozen hydrated gluten and cell viability and gas production of yeast.Differential scanning calorimetry (DSC), centrifugation, scanning electron microscopy (SEM), textural analysis (TA) and X-ray were employed to explore the effects of ISP at level of solids (0.5% w/w) on the freeze-thaw stability of starch-water system. DSC results showed that addition of 0.5% ISP inhibited the retrogradation of starch. With increasing of freeze-thaw cycles (FTC), rate of retrogradation was increased. When it comes to 9thfreeze-thaw cycle, rate of retrogradation of corn and wheat starch decreased from 39.6% to 35.6% and from 37.5% to 35.3%. The results of texture analysis indicated that there are an increase in hardness for samples with and without 0.5% ISP during freeze-thaw cycles, compared with the control starches. Additionly, starch with 0.5% ISP had smaller hardness. Synerisis shows that the repeated FTC increased the syneresis for all starch gels from 1st to 7th FTC, Other than 1st FTC, addition of ISP to starch gels significantly reduced the syneresis at any given FTC for both corn and wheat starch gels. The re-crystallization was continuously occurred by the repeated FTC, at the same time, WS with ISP had less re-crystallization compared to that of the WS without ISP at the same FTC.The freezable water, water holding capacity (WHC), rheological properties and microstructure of hydrated gluten and the hydrated gluten with ISP after frozen storage at -18℃for 1, 2, 4, 7 and 9 week were determined by differential scanning calorimetry (DSC), Rheometer and scanning electron microscopy (SEM) of hydrated. The results showed that: (1) The amount of freezable water in hydrated gluten increased with increase of frozen storage time, however, the addition of 0.5% ISP lowered the amount of freezable water, when frozen time was same, the melting enthapy of hydrated gluten containing ISP was lower than the control one. (2) The WHC of wet hydrated gluten decreased with increase of frozen storage time, Compared to the control, the wet hydrated gluten containing ISP had a higher WHC. (3) G'were higher than G''at all frozen time for hydrated gluten. Both the G'and G''decreased with frozen time increasing, while G'change greater than G''with time increasing. In terms of creep test, Increasing duration of frozen storage results in a considerable increase of compliance values. Introduction of ISP to the system resulted in a considerable decrease of the corresponding compliance values. (4) After a certain period of frozen storage, ice formed in hydrated gluten containing ISP were smaller than the control one, in line with the less damage of microstructure of frozen hydrated gluten with ISP caused by ice growth and recrystallization.The results of microscope and rheofermentometer experiments showed that pretreatment of yeast with ice-structuring protein effectively improved the anti-freezing property of yeast, improving the cell viability and gas production of yeast. SDS-PAGE showed that the substances leached from frozen yeast caused an increase in the solubility of some gluten proteins.
|
PDF Full Text Request