Occurrence of galactosyl isomaltol and galactosyl beta-pyranone in commercial drinking milk

Occurrence of galactosyl isomaltol (GAI) and galactosyl beta -pyranone (GAP ), two advanced glycosylation end products arising from the Maillard reacti on of lactose via 1-deoxyosone pathway, was studied in commercial drinking milk. Galactosyl isomaltol was extracted from milk spiked with this isomalt ol glycoside avoiding usage of any deproteinizing agent and was determined by a sensitive and interference-free HPLC method. No quantifiable amount of GAI proved to be present in any type of drinking milk, suggesting that som e data reported in literature arise from uncontrolled conversion of GAP int o GAI. The standard molecule of GAP was produced by heating a model system contain ing lysine and [U-14C]lactose, purified by solid phase extraction (SPE) on a C18 cartridge eluting with water, separated by the inverse distance funct ion (IDF) standard HPLC method specified for lactulose determination, and c haracterized by both spectroscopic data and tandem mass spectrometry. The behaviour of formation of GAP and GAI in model systems containing lysin e and lactose, heated under conditions of in bottle sterilization of milk, was studied in a wide range of values of the molar ratio lysine to lactose. While GAP easily forms as soon as lysine is present in the system, GAI doe s not form below a value of 0.1 of this molar ratio, so explaining why this compound is not present in commercial drinking milk. Amounts of GAP varying from 0.04 to 43.1 mu mol/l were found in the differe nt types of drinking milk ranging from high temperature pasteurized to in b ottle sterilized, proving that this compound is a stable and sensible marke r for evaluating the extent of the advanced Maillard reaction, hence the he ating severity of commercial drinking milk. Moreover, GAP can be determined after conversion into GAI under acid warm c onditions with a yield of 0.5 mol GAI from 1 mol GAP. Values of GAP obtaine d on commercial milk samples either by the direct HPLC method or after conv ersion into GAI were rather comparable, but the latter method needs further study in view of routine application.