HPLC of anthocyanins in port wines: <p>Determination of ageing rates</p>

Abstract

The total and individual anthocyanin contents in several port wines ageing at different rates were determined by HPLC at regular intervals during the first 46 weeks of storage at 15 °C. The losses of anthocyanins were logarithmic with time. There were small differences in the rate of ageing of the major anthocyanins (malvidin 3-glucoside, malvidin 3-acetylglucoside and malvidin 3-p-cownarylglucoside), but no firm conclusions could be drawn after consideration of all factors involved. The rate of loss of total known anthocyanins best reflected the rate of ageing of anthocyanins in port wines. During the initial ageing in the presence of free acetaldehyde, the molar loss of anthocyanins was higher than the molar loss of acetaldehyde, indicating that both acetaldehyde condensation and direct condensation not involving acetaldehyde occurred at this stage. Increasing acetaldehyde contents increased the rate of loss of anthocyanins. Acetaldehyde was still reacting when little anthocyanins remained, indicating the formation of complex branched polymers. The percentage of colour due to polymeric material was between 23 and 30 % in the young ports, while after 46 weeks it was between 78 and 98 %; the port with the highest free acetaldehyde content showed the fastest increase in the percentage of polmeric pigment colour. The absorbance due to polymers and the st ability of its colour was dependent on the free acetaldehyde concentration.