Evaluation of heat-induced changes in Spanish commercial milk: Hydroxymethylfurfural and available lysine content

Hydroxymethyfurfural (HMF) content and loss of available lysine were measured as indices of heat damage in various Spanish commercial milks (pasteurized, UHT sterilized and in-bottle sterilized milks) with similar processing dates. HMF level was determined by the traditional colorimetric procedure and by the reversed-phase HPLC method. Available lysine was measured by an alternative method with o-phthaldialdehyde as fluorescent marker. A significative relationship has been found between the HMF content and loss of available lysine and both are suitable for use as heat-induced indices. When loss of lysine (y) was expressed as percentage and HMF (x) as mu M, the function of the correlation line was, y = 0.47x - 0.089 (r = 0.958, P < 0.005).