Preliminary Study On The Browning Mechanism Of Xuanhua Mare’s Milk Grapes

Browning is the characters of mature and ageing of fruits, browning would cause thedecline of fruit quality, and even made the fruits loss their storage value and digestive value.Browning is divided into two categories: non-enzymatic browning caused by Maillardreaction and the enzymatic browning caused by PPO and POD.Catechin (C) and Epicatechin (EC) in grape fruits were the research objects of the study,model enzymatic reaction systems of different pH values were build, and the compoundsgenerated from different pH values and different reaction systems were studied with theestablished extraction and detection method. The related products of Mare’s milk grapes fromXuanhua, China in different storage periods were analyzed, and the results were as following:1. The dimers generated in the enzymatic reaction systems of EGGC and EG underdifferent pH values are quite different. A-type Proanthocyanidin dimers were generated underthe pH values of5,6, and7, while B-type Proanthocyanidin dimers were generated under thepH values of4and5, no enzymatic reaction product was identified under the pH values of3.2. The generation of products and the colors under different pH values indicated that A-typeProanthocyanidin dimers maybe has relationship with browning, while B-typeProanthocyanidin dimers is to the contrary.3. B-type Proanthocyanidin dimers was generated persistently in Xuanhua Mare’s milkgrapes under different storage periods, while the browning degree during grape storageindicated that B-type Proanthocyanidin dimers had contribution to the browning of the grapesas the intermediate product or precursor of the further reactions even though it is colorless.4.5-HMF (the markers of Maillard reaction) was not identified during the whole storageperiods of grape samples. Maybe the Maillard reaction was extremely slow under the lowtemperature storage condition (about1℃), so the concentration of5-HMF was quite low andwas not able to identified, which speculated that the browning of grapes stored under lowtemperature condition had no relationship with Maillard reaction.