Effect of processing cycles on the composition of Polygonatum cyrtonema Hua during nine-steam-nine-bask processing

Nine-steam-nine-bask is a traditional method for the processing of polygonatum cyrtonema Hua , which is a homology plant of medicine and food, but why is nine cycles of steam-bask needed is still not clear. This study aims to investigate the changes of functional components caused by each processing cycle and optimize the best number of processing cycles for the preparation of polygonatum. It was found that the content of total polysaccharide decreased with the increase of processing cycles and stabled at about 5.2 g/100 g, which was reduced by 45.81% compared with raw polygonatum (10.899 g/100 g, p < 0.05). However, the contents of saponins, phenols and flavonoids as well as the in vitro antioxidant activity of polygonatum showed an increasing trend, which had slight fluctuations after the fourth processing cycle. Besides, a total of 48 volatile components and 221 non-volatile components were identified by GC-MS and UPLC-Q Exactive MS/MS, respectively. Among them, 2,3-butanediol was the major numb-taste component in polygonatum which could be eliminated by processing and 113 differential non-volatile components were screened. To sum up, the four processing cycles could be sufficient for edible and medicine without the need of nine-steam-nine-bask. • Functional component contents and in vitro antioxidant activity were determined. • 5-hydroxymethylfurfural was not existed in raw polygonatum rhizome and produced after processing. • 2,3-butanediol was the major numb-taste component and eliminated by processing. • A total of 113 differential non-volatile components were screened during processing. • Four processing cycles could replace the traditional nine-steam-nine-bask processing.