Effect of storage temperature on the ageing of concentrated wheat starch gels

Abstract

Using differential thermal analysis (d.t.a.) the progress of ageing of concentrated wheat starch gels stored at temperatures from -l o to 43" has been investigated.A very close relationship has been found between the ageing of starch gels as measured by d.t.a. and the staling of bread as measured by crumb firmness at storage temperatures of -lo, 10" and 21" but some differences have been found at 32" and 43". The results at -lo, 10" and 21" provide very strong confirmatory evidence that starch crystallisation is the chief factor in the firming of bread. At elevated storage temperatures (32" and 43") the rBle of starch crystallisation in the firming of bread apparently gradually diminishes. Analysis of the results indicates that the mechanism of crystallisation of the starch, instantaneous nucleation followed by rod-like growth of crystals, is the same over the whole range of storage temperatures -1 to 43". Evidence is also presented to show that there is a possibility that at higher storage temperatures a more symmetrically perfect crystal structure is being formed. IntroductionAn important feature of bread staling is that the rate has a negative temperature coefficient, i.e. the rate of staling increases as the storage temperature is lowered. This characteristic of staling has been studied in detail by Cornford, Axford & E1ton.l They measured the rate of crumb firming of bread prepared by the bulk fermentation process and stored at temperatures ranging from --I" to 32". They found that, independently of temperature, the loaves all tended to the same ultimate value of crumb firmness but that the rate of attainment of this value was dependent on storage temperature. Time constants, the reciprocal of rate constants, of from 1.39 days at -1" to 5.51 days at 32" demonstrated the negative temperature coefficient of the rate.Included in the studies of Axford, Colwell, Cornford & Elton2 was an extension of the above work to bread prepared by the Chorleywood Bread Process3 and stored at temperatures from -1 " to 66". Time constants increased steadily over the range of temperatures, varying from 1.44 days at -1 " to 23.3 days at 66".

Interactions between amylopectin and lipid additives during retrogradation in a model system

“…The melting temperature of crystallised amylopectin increases with increasing storage temperature, indicating that more stable crystals are formed at higher storage temperatures. The storage temperature used in most experiments ( + 7°C) was chosen to give good conditions for crystallisation of amylopectin (Colwell et al 1969). The results obtained in the present work clearly show that the addition of a surfactant such as CTAB greatly reduces the rate of crystallisation during these conditions, the effect of the added surfactant being greater at + 25°C than at + 7°C (Fig 3).…”

The effect of hydroxypropylation on the structure and physicochemical properties of native, defatted and heat-moisture treated potato starches

“…Thus, nucleation rate increases with decrease in temperature down to Tg while the propagation rate increases with increasing temperature up to the Tm (Wunderlich, 1976). Several studies ' (Colwell et al, 1969;Fearn, & Russell, 1982;Jankowski, & Rha, 1986) have shown that the rate limiting step for starch retrogradation is nucleation and the rate of retrogradation as well as the properties ofretrograded starch gel depend on the storage temperature (Jankowski, & Rha, 1986 …”

Isothermal crystallization of concentrated amorphous starch systems measured by modulated differential scanning calorimetry

“…7 Colwell et al were the first to investigate the aging of wheat starch gels by differential thermal analysis. 8 Other techniques used are: differential scanning calorimetry (DSC), 9 -12 nuclear magnetic resonance, 13 rheometry, 14 microscopy, 7 Raman, 15 and infra-red spectroscopy. 16 Silverio et al used isothermal microcalorimetry to follow the crystallization of starch.…”