Biodiversity Of Yeast Associated With Longan Grape Variety In Shacheng Region And Fine Wine Yeast Strains Selection

Wine fermentation is a complex process carried out by the action of microorganisms. Yeasts play a most important role in wine fermentation. Longan is the unique grape variety in China. In this study, yeast were isolated from ecological environment of Longan vineyard and winery in Shacheng wine region. We used traditional method to separate yeast strains. Then we used molecular method for further distinction and identification. Finally, wine fermentation experiment was conducted by using selected yeast strains. The purpose of wine fermentation experiment was screening for local yeast strains adapted for Longan dry white wine production. This study is important for the information of yeast resource in Shacheng wine region and fine wine yeast selection.First, yeast isolation and preliminary morphological distinction:In this study, samples were collected from different sources of Shacheng wine region in Hebei province in 2008 and 2009 two consecutive years. Then yeast isolates were isolated from these samples. The different sources were grape berry, grape juice, four phases of nature fermentation, vineyard soil, winery equipment in 2008 and grape berry, grape juice, four phases of nature fermentation, vineyard soil from 3 different vineyard in 2009. By using morphological distinction method, yeast strains were divided into 16 categories. Vineyard soil was most rich in yeast species, there are 9 categories. Nature fermentation process was followed, 8 categories. However, only three categories of yeast were isolated from the surface of winery equipment.Second, using molecular methods to distinguish and identify different types of yeasts isolated from different sources: In this study, two molecular methods were used, that were analysis of the restriction pattern of amplified 5.8S-ITS rRNA gene (RFLP) and analysis of the restriction pattern of amplified 26S D1/D2 rRNA gene (RFLP). By using 5.8S-ITS rRNA gene (RFLP), 16 restriction patterns were obtained through the study of the yeast isolated from two consecutive years. Sequence analysis of 5.8S-ITS rRNA gene were applied for identify yeast strains to species level. They were Metschnikowia spp., Saccharomyces bayanus×Saccharomyces cerevisiae, Issatchenkia occidentalis, Candida zemplinina, Issatchenkia orientalis, Candida tropicalis, Pichia membranaefacien, Cryptocococcus flavescens, Hanseniaspora uvarum. The study shows that samples collected from different source were composed of different types of yeast. But the most common yeast was Saccharomyces bayanus×Saccharomyces cerevisiae. The study also used 26S D1/D2 rRNA gene (RFLP) to distinguish the yeast isolated in 2008. This method can differentiate and indentificate yeast species very effectively.Finally, wine fermentation test was conducted by using selected yeast strains: DHS-1 and CZ-1. And commercial active dry wine yeast CY3079 as control. The following conclusions can be obtained: the selected yeast CZ-1 performed a faster rate of inoculation but slower rate of hypoglycemic. The wine has the maximum amount of acid. However the selected yeast DHS-1 performed a faster rate of hypoglycemic during fermentation and the minimum amount of acid. Residual sugar of wine was less than 2 g / l. The wine was taste more coordinate. The study preliminary showed that DHS-1 was the suitable local wine yeast strains for Longan grape wine. For these three kinds of red grape varieties of Zibeisai, Yan 73 and Cabernet Sauvignon, we incubated DHS-1 to ferment Zibeisai and Yan 73 grape and we can see that the parameters of reduction rate of glucose and soluble solids, acidity and color degree of original wine are better than that when we incubated Anqi dry wine yeast. But fermentation using Cabernet Sauvignon performed the opposite result. That is to say the selected yeast of DHS-1 also adapte to brew Zibeisai and Yan 73 grape wine.All in all, in this study, by using morphological distinction method, yeast strains were divided into 16 categories. The result showed the high diversity of yeast composition. Then molecular method was used for further distinction and identification. The result showed the high gene diversity of yeast recource in Shacheng wine region. Through wine fermentation test, DHS-1 was the suitable local wine yeast strains for Longan grape wine. At the same time, this kind of yeast is also adapte to brew Zibeisai and Yan 73 grape wine.