Investigating the effect of cooking temperature and cooking time on the thickening ability, absorption of oil, thermal properties and microscopic property of roux
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Date
2021
Authors
Wang, Bailin
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Abstract
Roux is made from cooking a mixture of wheat flour and butter, and this is commonly used to create a thick sauce by cooking the roux with excess water. Roux were made from mixtures of canola oil and one of four types of starch or flour (wheat starch, wheat flour, pea starch, and pea flour) which was cooked at one of five temperatures (100, 116, 134, 153, 175 °C) for 0, 4, 8, 12, or 16 min. The oil content of the roux, and the pasting properties of the sauce made from the roux (by rapid viscoamylograph) were determined. The thermal properties (determined in excess water by differential scanning calorimetry (DSC)) and microscopic analyses of roux made from wheat starch and canola oil cooked at one of three temperatures (100, 134, 175 °C) for 0, 8, or 16 min were also determined.
The thickening abilities of all types of roux decreased with an increase in cooking time when the roux was cooked at 154 and 175 °C, but cooking time did not influence the thickening ability at the three lower cooking temperatures. The pasting viscosity of roux made from wheat flour, pea starch, and pea flour was enhanced when cooking temperature increased from 116 to 134 °C, but such an enhancement was not observed with the roux made from wheat starch. Roux made from flour, regardless of the flour type, had significantly higher oil content than roux made from starch.
DSC property changes were slight with changes in roux making conditions. Starch granule integrity and birefringence was maintained regardless of cooking time and temperature.
In conclusion, the cooking process changed the thickening ability of a roux, but no starch gelatinization was observed during the roux making process. Ingredients of a roux, especially protein, significantly affected some physicochemical properties, such as the thickening ability and residual oil content of the roux during the cooking process. Pea starch and flour are suitable thickening ingredients for making a roux when cooking temperatures were at 134 or 154 °C, but not at higher temperatures.
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Roux, starch and flour pasting