Effects of Freeze Drying and Storage of Oat Sourdough Starter on Volatile Flavor Compounds of Bread

Oat breads made with non-freeze-dried L.sanfranscensis containing sourdough starter and freeze-dried ones stored at 4 ℃ for 0 and 30 days were analyzed for their volatile compound composition by solid phase micro-extraction/gas chromatography-mass spectrometry(SPME/GC-MS) in order to explore the effects of freeze drying and storage of sourdough starter on volatile flavor compounds of bread.A total of 87 compounds were identified in the three oat breads and acids,alcohols,aldehydes,aromatic and heterocyclic compounds were of most importance in the volatile profile.The most abundant volatile compound category in all samples was acids,followed by alcohols,aromatic and heterocyclic compounds and aldehydes.Through freeze-drying and subsequent storage,aldehydes and alcohols contents first increased and then decreased;while acid,esters,ketones and aliphatic compounds experienced an opposite process,and the concentration of aromatic and heterocyclic compounds rose up.Breads made with both freeze-dried starters were also rich in volatile flavor compounds.Acetic acid and ethanol contents showed opposite changes due to the competition between L.sanfranscensis and yeast.The relative abundance of furfural increased in both cases.However,hexanal content significantly decreased after freeze-drying and was not detected in bread made with 30-day stored freeze-dried starter.