Heat-induced chemical, physical and functional changes during grape must cooking

Cooked must is a product that could be used in food formulations, directly or after fermentation, to obtain many traditional foods. Must cooking was conducted in boilers of different materials (copper and stainless steel) for different times in order to obtain differently concentrated products.The concentration of many constituents (sugars, organic acids, nitrogen compounds, metal ions and polyphenols) was observed upon cooking, together with the increase of neo-formation compounds, such as hydroxymethylfurfural and melanoidins, which give, to the musts, the typical brown colour and caramel-like odour. The concentration of metal ions, in particular, determined high levels of lead and copper (in the case of use of copper boilers) in the final products.Polyphenol heat concentration determined the degradation of simple phenolics, such as catechins, and the formation of condensed tannins, which determined a loss of the antioxidant activity of the phenolic fraction, whereas the formation of melanoidins improved the total antioxidant activity of the product.