Degradation kinetics of carotenoids and visual colour in pumpkin (<i>Cucurbita maxima</i> L.) slices during microwave-vacuum drying

<p>The degradation kinetics of colour and individual carotenoids including lutein, α-carotene and <i>β</i>-carotene in pumpkin slices was investigated during microwave-vacuum drying (MVD) at selected microwave powers (4–8 W/g). The contents of lutein, α-carotene and <i>β</i>-carotene significantly decreased, while visual colour parameters such as the Hunter L* value decreased and the total colour difference (<i>ΔE</i>) value increased with the increase of processing time and microwave power. Degradation of lutein, α-carotene, <i>β</i>-carotene and Hunter L* value followed the first-order reaction kinetics; however, zero-order reaction kinetics was found adequate to describe changes in <i>ΔE</i> with <i>R²</i> ≥ 0.9027. The relationship between individual carotenoid content and Hunter L* value was found to be more consistent through one-dimensional linear regression analysis with <i>R²</i> ranging from 0.8697 to 0.9701. These results indicated that visual colour might be used to predict the lutein, α-carotene and <i>β</i>-carotene contents during drying pumpkin slices.