Abstract
China is one of the main producers in the worldwide raisin market. Most China’s raisins are produced in Xinjiang where the Thompson seedless grape (Vitis vinifera L.cv.Thompson seedless) is the main variety of green raisin. However, the browning of Thompson seedless grape during drying has been well-acknowledged as the primary factor affecting the development of the raisin industry. Data independent acquisition (DIA)-based protein profiling was performed on fresh and shade-dried Thompson seedless grapes. As a result, 5431 proteins were identified, among which the amounts of 739 proteins in fresh grape were found to be significantly different with those in dried grape. The functional annotation based on the Blast2GO showed that the ‘organic substance metabolic process’, ‘regulation of molecular function’, ‘enzyme regulator activity’, and ‘isomerase activity’ related proteins became very active during browning. Further analyses revealed that the browning-related proteins, which with significant different amounts in fresh and in dried grapes, are primarily involved in the phenylpropanoid biosynthesis, tyrosine metabolism, phenylalanine metabolism, oxidative phosphorylation metabolism, plutathione metabolism, peroxisome pathway, and fatty acid degradation. And five random differential proteins were verified with parallel reaction monitoring (PRM). The PRM results were in agreement with the DIA data. The main browning-related proteins of Thompson seedless grape were identified in this study. Their properties were tested, and their roles in the browning mechanism were indicated. This will lay base to a better understanding on the enzymatic browning of Thompson seedless grape, and it will also provide guidance for controlling the quality of Thompson seedless grapes in industry.
Highlights
Thompson seedless grape (Vitis vinifera L.cv.Thompson seedless) has been a major raisin grape variety worldwide for over a century [1]
Chemicals and reagents Sucrose, Tromethane hydrochloride (Tris–HCl), Ethylenediamine tetraacetic Acid (EDTA), Lauryl sodium sulfate (SDS), Phenol, Acetone, Formic acid, Potassium chloride (KCl) were purchased from Sinopharm (Beijing, China); 1,4-Dithiothreitol (DTT), Trypsin, Bond-BreakerTM TCEP Solution (TCEP), Iodoacetamide and Acetonitrile were purchased from Sigma-Aldrich (Johannesburg, South Africa); 1× Protease Inhibitor Cocktail was purchased from Roche Ltd. (Basel, Switzerland); iRT peptides were purchased from Biognosys (Schlieren, Switzerland)
739 proteins were identified as significantly changed proteins (SCP)
Summary
Thompson seedless grape (Vitis vinifera L.cv.Thompson seedless) has been a major raisin grape variety worldwide for over a century [1]. China’s raisin production accounts for about 15% of the world’s total output, ranking third after the United States and Turkey. Due to Xinjiang, the largest raisin producing area in China, possess the output of 180,000 tons in 2018, among which 60% were green raisins. The main variety of green raisins is Thompson seedless grape [3], which is mainly produced in Turpan region of Xinjiang. Due to the superior photothermal conditions and unique climate in Turpan, shade-dry is the most common drying method used in the production of raisins. The browning of the raisins prepared in this way is very common. The browning rate of raisins in different regions of Xinjiang varies from 40 to 65%
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