Different inoculation methods for semi-dry processed coffee using yeasts as starter cultures

Abstract

This study evaluates the behavior of Saccharomyces (S.) cerevisiae (CCMA 0543), Candida (C.) parapsilosis (CCMA 0544), and Torulaspora (T.) delbrueckii (CCMA 0684) as starter cultures for semi-dry processed coffee using two inoculation methods: (1) direct inoculation and (2) bucket inoculation. The microbial population was evaluated by plating and real-time polymerase chain reaction (qPCR). The microbial metabolic changes of both bucket and direct inoculation methods during fermentation were evaluated using high performance liquid chromatography (HPLC), and gas chromatography–mass spectrometry (GC–MS). A sensorial test was also carried out. Citric and succinic acids were detected throughout the fermentation period. Chlorogenic acid concentration levels were higher for the bucket method after roasting. Roasted coffee beans also had a higher caffeine concentration, with the exception of the T. delbrueckii (CCMA0684) assay. Acids, pyrazines and pyridines were the main volatile compounds in both green and roasted coffee beans. Coffee cupping results proved that both inoculation methods scored well in terms of coffee quality. The bucket method favored the permanence of the microorganisms during coffee processing, especially the treatment inoculated with S. cerevisiae.