Investigation into the roles of yeasts in wet coffee beans fermentation Elhalis, Hosam en_US 2022-03-15T12:51:00Z 2022-03-15T12:51:00Z 2021 en_US
dc.description.abstract This thesis investigated the ecology and metabolism of microorganisms, especially yeasts, during the wet fermentation of Australian coffee beans, and their contribution to coffee quality. Pulped coffee beans were fermented underwater for 36 h where yeast growth was suppressed by the addition of Natamycin at 300 mg/L. Spontaneous fermentation without the addition of Natamycin was conducted as control. The growth and diversity of microorganisms during fermentation were monitored by both culture dependent and independent methods. Major non-volatile metabolites during fermentation were monitored by high performance liquid chromatography (HPLC) and volatiles in the green and roasted beans were measured by solid phase microextraction coupled with gas chromatography tandem mass spectrometry (SPME GC-MS). Both bacteria and yeasts grew significantly during spontaneous fermentation while yeast growth was restricted in the Natamycin treated fermentation without significant impact on bacterial growth. The bacterial community was dominated by Citrobacter sp., Gluconobacter cerinus, Leuconostoc mesenteroides and Lactococcus lactis with maximum populations between 4-7.2 log CFU/g, while Hanseniaspora uvarum and Pichia kudriavzevii were the predominant yeasts at 4.5-5 CFU/g. During fermentation, the microflora utilized sugars in the mucilage and produced mannitol, glycerol and essential volatiles, mainly alcohols, esters, aldehydes and organic acids, with their concentrations generally lower in beans fermented with yeast suppression. Coffee produced from yeast suppressed fermentation received lower sensory scores in flavour and aroma and overall quality by 3 Q-Grade coffee masters. When H. uvarum and P. kudriavzevii were inoculated individually and in combination, they dominated the fermentation by growing to 9-10 log CFU/ml, and produced greater amounts of glycerol and flavour volatiles in the green beans which remained in higher levels after roasting compared with the control. Coffee brewed from these beans received significantly high scores of flavour, aroma, acidity and overall quality. Mucilage degradation seems to be initiated by endogenous enzymes and microbial contributions to the process occurred subsequently either enzymatically or by acidification. These findings demonstrated the crucial contribution of yeasts to successful coffee fermentation and high-quality coffee, and the potential of developing the two yeasts into starter cultures for coffee fermentation. en_US
dc.language English
dc.language.iso EN en_US
dc.publisher UNSW, Sydney en_US
dc.rights CC BY-NC-ND 3.0 en_US
dc.rights.uri en_US
dc.subject.other Flavour en_US
dc.subject.other Yeasts en_US
dc.subject.other Coffee en_US
dc.subject.other Mucilage degradation en_US
dc.title Investigation into the roles of yeasts in wet coffee beans fermentation en_US
dc.type Thesis en_US
dcterms.accessRights open access
dcterms.rightsHolder Elhalis, Hosam
dspace.entity.type Publication en_US
unsw.accessRights.uri 2022-02-02 en_US
unsw.description.embargoNote Embargoed until 2022-02-02
unsw.relation.faculty Engineering
unsw.relation.originalPublicationAffiliation Elhalis, Hosam, Chemical Engineering, Faculty of Engineering, UNSW en_US School of Chemical Engineering *
unsw.thesis.degreetype PhD Doctorate en_US
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