title: Changes in volatile profile of soybean residue (okara) upon solid-state fermentation by yeasts.
abstract: BACKGROUND
  Soybean residue (okara), a by-product of soymilk, is produced in large volumes by the soy food industry and is often discarded due to its undesirable flavour. As it contains a considerable amount of protein and fats, biotransformation of okara to improve its flavour presents an opportunity for alternative utilisation. This paper evaluated 10 yeasts in the solid-state fermentation of okara based on their volatile profiles as analysed with HS-SPME GC-MS/FID. Four 'dairy yeasts' (Geotrichum candidum, Yarrowia lipolytica, Debaryomyces hansenii and Kluyveromyces lactis) and six 'wine yeasts' (Saccharomyces cerevisiae, Lachancea thermotolerans, Metschnikowia pulcherrima, Pichia kluyveri, Torulaspora delbrueckii, and Williopsis saturnus) were studied.
  
  
  RESULTS
  The main off-odourants in okara, hexanal and trans-2-hexenal, significantly decreased after fermentation due to their bioconversion into methyl ketones and/or esters. The okara fermented by dairy yeasts contained greater proportions of methyl ketones, while that by wine yeasts contained more ethyl and acetyl esters. Notably, the okara fermented by W. saturnus contained 13 esters and the total GC-FID peak area of esters was about 380 times that in fresh okara, leading to a perceptible fruity note.
  
  
  CONCLUSIONS
  Okara can be exploited as an inexpensive substrate for bioflavour extraction and/or a more pleasant food ingredient via yeast fermentation. © 2016 Society of Chemical Industry.
authors.affiliation: Food Science and Technology Programme, Department of Chemistry, National University of Singapore, 3 Science Drive, Singapore 117543, Singapore.
authors.forename: Weng Chan
authors.initials: WC
authors.lastname: Vong
authors.affiliation: Food Science and Technology Programme, Department of Chemistry, National University of Singapore, 3 Science Drive, Singapore 117543, Singapore.|National University of Singapore (Suzhou) Research Institute, No. 377 Linquan Street, Suzhou Industrial Park, Suzhou, Jiangsu 215123, China.
authors.forename: Shao-Quan
authors.initials: SQ
authors.lastname: Liu
mesh_terms: D005285:Fermentation; D005421:Flavoring Agents / Q000737:chemistry / Q000378:metabolism; D045730:Soy Foods / Q000032:analysis / Q000382:microbiology*; D013025:Glycine max / Q000737:chemistry / Q000382:microbiology*; D055549:Volatile Organic Compounds / Q000737:chemistry* / Q000378:metabolism; D014866:Waste Products / Q000032:analysis*; D015003:Yeasts / Q000378:metabolism*
chemical_list: D005421:Flavoring Agents; D055549:Volatile Organic Compounds; D014866:Waste Products
keywords: fermentation; okara; soybean curd residue; volatiles; yeast