Research On The Screening Of Advanced Glycation End Products Of Green Tea And Influence Factors

Advanced glycation end products(AGEs) has posed a potential threat to human health, due to their relationship with chronic diseases, such as diabetes and inflammation. Diet-AGEs is one of important sources for biological-AGEs. Therefore, it is valuable to monitor levels of AGEs in different food sytems, the influence factors and control of the generation. This thesis had investigated the contents of typical AGEs, such as N?-(carboxymethyl) lysine(CML) and N?-(carboxyethyl) lysine(CEL) in commercial green tea. The effects of processing conditions and storage on the formation of them were also studied, moreover, a model system was designed to explore the influence factors of AGEs formation.Firstly, liquid chromatography-tandem mass spectrometry(LC-MS/MS) was usd to determine the content of CML and CEL in green tea. The levels of CML and CEL in 43 kinds of green tea produced in China and Japan were largely different. The levels of CML and CEL ranged from 46.94 μg/g protein to 472.52 μg/g protein and 4.33 μg/g protein to 118.76 μg/g protein, respectively. The average contents of CML and CEL were 136.50 μg/g protein and 49.06 μg/g protein. Compared with other kinds of food, AGEs content in tea was relatively high. A significant negative correlation was presented between CML/CEL and epigallocatechin gallate(EGCG) or total catechins.Then, effects of processing techniques and storage on AGEs were investigated. Three kinds of green tea were harvested from three different varieties of Camellia. GT 1 was produced through four steps, including rotary drum-firing, pan-firing, rolling and drying. GT 2 and GT 3 were manufactured without rotary drum-firing compared to GT 1. Most AGEs were formed in the drying stage of green tea processing. In GT 1, CML and CEL accumulated stepwise, whereas in GT 2 and GT 3, the contents of CML and CEL changed little during firing and rolling. In general, significant negative correlations were found between CML and EGCG, epigallocatechin(EGC), epicatechin gallate(ECG) and total monomeric catechins, which implied that these catechins might have an inhibition effect on CML formation. Green tea was stored at 4oC and 25 oC, respectively. During the period of 12 months, CML and CEL content increased quickly at the later storage time, compared with early storage time, especially, when green tea was stored at 25 oC. After 12 months, the level of CML and CEL increased by 39.91% and 32.78%, respectively.In order to further study the influence factors(catechines, temperature, water content and time) of CML and CEL formation, a model system of glucose-fructose-lysine was designed, according to the main components in green tea and processing conditions during drying. Catechins of EGCG, EGC and ECG inhibited the formation of CML. While, effects of three kinds of catechins on CEL formation depended on kinds of catechins and quantity. When catechins existed in the system, content of CML and CEL increased with higher reaction temperature, lower water content and longer reation time. Catechins could affect the generation of intermediates of glyoxal(GO) and methylglyoxal(MGO) and anti-oxidantion capacity to influence formation of AGEs.Thus, reaction conditions had an important effect on AGEs formation, and it maybe the reason of high AGEs levels, although there were lots of catechins in green tea during processing.