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Starch gelatinisation and texture effects during vacuum cooling
T. MORSKY (1) (1) Campden BRI, Chipping Campden, Gloucestershire, United Kingdom.

Vacuum cooling is a batch process whereby products containing free water are cooled by evaporation of moisture under vacuum. The aim of the project was to study if vacuum cooling could be used to shorten baking and cooling time of 800g sandwich loaves. The impact of a reduction in bake time and vacuum cooling process on bread texture, structure, volume, starch gelatinisation and enzyme activity was studied. Sandwich loaves were cooled using a vacuum cooler and compared with those cooled at ambient conditions. Weight loss of vacuum cooled products was significantly higher than ambient cooled products, depending on the vacuum cooling program. The crust was thicker and harder in the vacuum cooled products. Reduced baking time was used to compensate for these changes by reducing moisture loss from the loaves. A baking time reduction of 20% resulted in greater moisture retention but the crumb texture was significantly less resilient. The effects on starch gelatinisation and retrogradation were studied, together with amylase activity. Differential scanning calorimetry (DSC) analysis of bread crumb showed that when baking time was reduced by 44–56% vacuum cooled samples had higher levels of enthalpy of amylopectin compared to their respective ambient cooled counterparts. Enzymatic activity of the loaves was studied by making a slurry from dried bread samples and the slurry viscosity measured using the Rapid Visco Analyser (RVA). Vacuum cooled samples were significantly less viscous after 30 minutes suggesting they had higher enzyme activity compared to ambient cooled counterparts. These results show the importance of the residual heat in early stages of ambient cooling finishes the gelatinising process and inactivates the enzymes.

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