title: Effects of wort gravity and nitrogen level on fermentation performance of brewer's yeast and the formation of flavor volatiles.
abstract: Normal gravity wort and high gravity wort with different nitrogen levels were used to examine their effects on the fermentation performance of brewer's yeast and the formation of flavor volatiles. Results showed that both the wort gravity and nitrogen level had significant impacts on the growth rate, viability, flocculation, and gene expression of brewer's yeast and the levels of flavor volatiles. The sugar (glucose, maltose, and maltotriose) consumption rates and net cell growth decreased when high gravity worts were used, while these increased with increasing nitrogen level. Moreover, high gravity resulted in lower expression levels of ATF1, BAP2, BAT1, HSP12, and TDH, whereas the higher nitrogen level caused higher expression levels for these genes. Furthermore, the lower nitrogen level resulted in increases in the levels of higher alcohols and esters at high wort gravity. All these results demonstrated that yeast physiology and flavor balance during beer brewing were significantly affected by the wort gravity and nitrogen level.
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou, 510640, China.
authors.forename: Hongjie
authors.initials: H
authors.lastname: Lei
authors.forename: Haifeng
authors.initials: H
authors.lastname: Zhao
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Yu
authors.forename: Mouming
authors.initials: M
authors.lastname: Zhao
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001515:Beer / Q000382:microbiology; D050260:Carbohydrate Metabolism; D015169:Colony Count, Microbial; D004952:Esters / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D005421:Flavoring Agents / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D006112:Gravitation; D009584:Nitrogen / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012440:Saccharomyces / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D055549:Volatile Organic Compounds / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D004952:Esters; D005421:Flavoring Agents; D011506:Proteins; D055549:Volatile Organic Compounds; D000431:Ethanol; C079238:alcohol O-acetyltransferase; D009584:Nitrogen