Effect of toasting time on the browning of sliced bread

Slices of wheat bread were toasted for different times until a distinct intensity of brown colour was reached. Two assays were carried out: prolonged toasting times (5–60 min) and reduced toasting times (0.5–5 min). The browning indicators (furosine, available lysine, hydroxymethylfurfural (HMF), colour and absorbance at 284 and 420 nm) were determined. The precision of all indicators used was high (CV < 4%). No furosine or HMF was detected in the dough before baking. The furosine content increased until 7 min (299 mg per 100 g protein) and then decreased to 2.9 mg per 100 g protein at 60 minutes. For the first toasting times (0.5, 1 and 2 min) the furosine content decreased slightly. Available lysine reached losses of 50% after 25 min of heating. The toasting of bread increased HMF values from 12 to 2025 mg kg −1 for the assay at prolonged times of heating and from 1.3 to 4.2 mg kg −1 at reduced times (0.5–5 min). The HMF content decreased (1000 mg kg −1 ) when the sliced bread was toasted until it burnt. Colour (Δ E , 100 − L *) and absorbance at 284 and 420 nm always increased. High linear correlations ( r 2 > 0.860) were obtained between browning indicators and time ( A 284 /time, A 420 /time, 100 − L */time and HMF/time).