Study Of β-Lactoglobulin Glycation In Intermediate Moisture System

Intermediate moisture foods (IMF) enjoy a wild consumption for its excellent functional and nutritional properties. However, the high portion of proteins and reducing sugars in the formulation lead to glycation and Maillard rection, resulting in detrimental effects on the sensory and nutritional properties of the products.The structure of proteins and reducing sugars could affect the glycation progress. On the one hand, the glycation reactivities of the potential glycated sites of one protein differ because of its primary sequence and tertiary structure. On the other hand, the glycation reactivities of reducing sugars also differ, resulting from their differences on structure. The glycation progress could be detected by methods such as sodium dodecyl sulfate-polyacryamide gel electrophoresis (SDS-PAGE) and O-phthalaldehyde (OPA). These traditional approaches, however, could not recognize the glycation site accurately. Different from these means, liquid chromatography-mass spectrometry (LC-MS) and data-independent acquisition LC-MS (LC-MSE) could be used to study the glycation reactivities of the potential glycated sites of the protein, as well as the effect of sugar structure on protein glycation. The results provided theoretical basis for alleviating or even inhibiting the glycation. In addition, the tertiary structures of glycated proteins might be changed and the effects various due to the sugars used. The studies on structural changes of the modified β-lg provided evidence for predicting the changes on the nutritional and functional properties of the food systems. In the present work, IMF model systems established to study the reactivity of the potential glycated sites of β-lactoglobulin (β-lg) and the effect of sugar structures on the glycation extent and site of β-lg. Furthermore, the structural changes of glycated β-lg had been preliminarily studied by circular dichroism spectrum (CD) and differential scanning calorimetry (DSC).The MSE results showed that the glycation reactivities of the16potential glycated sites of P-lg varied in the IMF system. The glycation reactivities of potential glycated sites ranked from high to low was L1> K91> K47,77,100>K70,75,83,135> K8,14,60,69,101,138,141.The sugar structures did affect the glycation extent and the site preference towards β-lg. The studies on glycation extent showed that the increasing molecular size, negative charge state of reducing sugars and decreased eletrophilicity of carbonyl groups would reduce the glycation speed and extent. Open-ring proportion and deoxy would not affect the glycation extent. The studies on glycation site showed that ribose, glucose, mannose, galactose and rhamnose could react with L1, K8,47,70,75,77,83,91,100and135in the IMF systems,. Maltose could react with the nine sites except K75. Maltotriose could react with the seven sites except K8,70and77. Galacturonic acid could react with the nine sites except K77. Fructose could react with the nine sites except K8. The results indicated that molecular size, negative charge state of reducing sugars and electrophilicity of carbonyl groups would affect the glycation site preference of reducing sugars.In addition, the studies on the structures of glycated β-lg showed glycation would not change the secondary structure, yet could change the spatial structure of β-lg. Glycaiton by galacturonic acid unfolded the tertiary structure of β-lg, while glycation by the other8 reducing sugars slightly changed the tertiary structure and increased the rigidity of the β-lg molecule.