The Role of Microbes in Coffee Fermentation and Their Impact on Coffee Quality

Coffee is one of the most important and widely used commercial crops in the world. After ripe coffee cherries are harvested, coffee must pass through several steps to become (green) raw coffee beans. Commonly, there are three different processing methods used to obtain green coffee beans from coffee cherries, namely, the wet, dry, and semidry methods. Microorganisms (yeasts and bacteria) play a major role in coffee fermentation process by degrading mucilage by producing different enzymes (pectinase), acids, and alcohols. Starter culture development is crucial and is done by selecting microorganisms that have certain characteristics, such as mucilage degradation ability, tolerance to stress during fermentation, the ability to suppress the growth of pathogenic fungi, and a positive impact on the sensory quality of the coffee. Currently, green coffee beans obtained from farms that use any of the above processing methods are fermented with selected microorganisms to improve the flavour and aroma of the coffee. This is the result of a new insight into the development of unique flavoured coffee and into engaging with the coffee market to better benefit. This review gives a comprehensive overview of the fermentation process, microorganisms and starter cultures, and fermentation’s impact on coffee quality. Future prospects are also discussed through the incorporation of recent research.

Download Full-text

Behaviour and reduction of ochratoxin A in green coffee beans in response to various processing methods

European Food Research and Technology ◽

10.1007/s002170050497 ◽

1999 ◽

Vol 209 (3-4) ◽

pp. 297-300 ◽

Cited By ~ 24

Author(s):

W. Heilmann ◽

A. G. Rehfeldt ◽

F. Rotzoll

Keyword(s):

Ochratoxin A ◽

Green Coffee ◽

Processing Methods ◽

Green Coffee Beans ◽

Coffee Beans

Download Full-text

Effect of the Post-Harvest Processing on Protein Modification in Green Coffee Beans by Phenolic Compounds

Foods ◽

10.3390/foods11020159 ◽

2022 ◽

Vol 11 (2) ◽

pp. 159

Author(s):

Gustavo A. Figueroa Campos ◽

Johannes G. K. T. Kruizenga ◽

Sorel Tchewonpi Sagu ◽

Steffen Schwarz ◽

Thomas Homann ◽

...

Keyword(s):

Phenolic Compounds ◽

Storage Protein ◽

Protein Fraction ◽

Protein Modification ◽

Green Coffee ◽

Processing Methods ◽

Green Coffee Beans ◽

Coffee Beans ◽

Modified Peptides ◽

Cup Quality

The protein fraction, important for coffee cup quality, is modified during post-harvest treatment prior to roasting. Proteins may interact with phenolic compounds, which constitute the major metabolites of coffee, where the processing affects these interactions. This allows the hypothesis that the proteins are denatured and modified via enzymatic and/or redox activation steps. The present study was initiated to encompass changes in the protein fraction. The investigations were limited to major storage protein of green coffee beans. Fourteen Coffea arabica samples from various processing methods and countries were used. Different extraction protocols were compared to maintain the status quo of the protein modification. The extracts contained about 4–8 µg of chlorogenic acid derivatives per mg of extracted protein. High-resolution chromatography with multiple reaction monitoring was used to detect lysine modifications in the coffee protein. Marker peptides were allocated for the storage protein of the coffee beans. Among these, the modified peptides K.FFLANGPQQGGK.E and R.LGGK.T of the α-chain and R.ITTVNSQK.I and K.VFDDEVK.Q of β-chain were detected. Results showed a significant increase (p < 0.05) of modified peptides from wet processed green beans as compared to the dry ones. The present study contributes to a better understanding of the influence of the different processing methods on protein quality and its role in the scope of coffee cup quality and aroma.

Download Full-text

Antioxidant properties and proximate analysis of green coffee beans from different plantations and processing methods in Thailand

Acta Horticulturae ◽

10.17660/actahortic.2017.1179.40 ◽

2017 ◽

pp. 255-260

Author(s):

N. Kanitnuntakul ◽

P. Meeasa ◽

C. Borompichaichartkul

Keyword(s):

Antioxidant Properties ◽

Proximate Analysis ◽

Green Coffee ◽

Processing Methods ◽

Green Coffee Beans ◽

Coffee Beans

Download Full-text

Influence of Environmental Microbiota on the Activity and Metabolism of Starter Cultures Used in Coffee Beans Fermentation

Fermentation ◽

10.3390/fermentation7040278 ◽

2021 ◽

Vol 7 (4) ◽

pp. 278

Author(s):

Vanessa Bassi Pregolini ◽

Gilberto Vinícius de Melo Pereira ◽

Alexander da Silva Vale ◽

Dão Pedro de Carvalho Neto ◽

Carlos Ricardo Soccol

Keyword(s):

Fermentation Process ◽

Starter Culture ◽

Amplicon Sequencing ◽

Isoamyl Acetate ◽

Starter Cultures ◽

Positive Interaction ◽

Coffee Beans ◽

Fermentation Tank ◽

Coffee Farm ◽

Food Commodities

Microbial activity is an integral part of agricultural ecosystems and can influence the quality of food commodities. During on-farm processing, coffee growers use a traditional method of fermentation to remove the cherry pulp surrounding the beans. Here, we investigated the influence of the coffee farm microbiome and the resulting fermentation process conducted with selected starter cultures (Pichia fermentans YC5.2 and Pediococcus acidilactici LPBC161). The microbiota of the coffee farm (coffee fruits and leaves, over-ripe fruits, cherries before de-pulping, depulped beans, and water used for de-pulping beans) was dominated by Enterobacteriaceae and Saccharomycetales, as determined by llumina-based amplicon sequencing. In addition, 299 prokaryotes and 189 eukaryotes were identified. Following the fermentation process, Pichia and the family Lactobacillaceae (which includes P. acidilactici) represented more than 70% of the total microbial community. The positive interaction between the starters resulted in the formation of primary metabolites (such as ethanol and lactic acid) and important aroma-impacting compounds (ethyl acetate, isoamyl acetate, and ethyl isobutyrate). The success competitiveness of the starters towards the wild microbiota indicated that coffee farm microbiota has little influence on starter culture-added coffee fermentation. However, hygiene requirements in the fermentation process should be indicated to prevent the high microbial loads present in coffee farm soil, leaves, fruits collected on the ground, and over-ripe fruits from having access to the fermentation tank and transferring undesirable aromas to coffee beans.

Download Full-text

Comparison of the Antioxidant Activities and Volatile Compounds of Coffee Beans Obtained Using Digestive Bio-Processing (Elephant Dung Coffee) and Commonly Known Processing Methods

Antioxidants ◽

10.3390/antiox9050408 ◽

2020 ◽

Vol 9 (5) ◽

pp. 408

Author(s):

Mesfin Haile ◽

Hyung Min Bae ◽

Won Hee Kang

Keyword(s):

Antioxidant Activity ◽

Volatile Compounds ◽

Green Coffee ◽

Roasted Coffee ◽

Green Beans ◽

Processing Methods ◽

Green Coffee Beans ◽

Coffee Beans ◽

Roasted Coffee Beans ◽

Elephant Dung

There are different types of coffee processing methods. The wet (WP) and dry processing (DP) methods are widely practiced in different parts of coffee-growing countries. There is also a digestive bioprocessing method in which the most expensive coffee is produced. The elephant dung coffee is produced using the digestive bioprocessing method. In the present experiment, the antioxidant activity and volatile compounds of coffee that have been processed using different methods were compared. The antioxidant activity, total phenolic content (TPC), total flavonoid content (TFC), and total tannin content (TTC) of green coffee beans from all treatments were higher as compared to roasted coffee beans. Regarding the green coffee beans, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of elephant dung coffee beans was higher as compared to that of the DP and WP coffee beans. The green coffee beans had higher DPPH activity and ferric reducing antioxidant power (FRAP) value compared to the roasted coffee beans. The green beans of elephant dung coffee had a high TPC than the beans obtained by WP and DP methods. TFC in elephant dung coffee in both green and roasted condition was improved in contrast to the beans processed using dry and wet methods. The elephant dung coffee had an increased TTC in comparison to the DP and WP coffee (green beans). About 37 volatile compounds of acids, alcohols, aldehydes, amide, esters, ethers, furans, furanones, ketones, phenols, pyrazines, pyridines, Heterocyclic N, and pyrroles functional classes have been found. Some of the most abundant volatile compounds detected in all treatments of coffee were 2-furanmethanol, acetic acid, 2-methylpyrazine, 2,6-dimethylpyrazine, pyridine, and 5-methylfurfural. Few volatile compounds have been detected only in elephant dung coffee. The principal component analysis (PCAs) was performed using the percentage of relative peak areas of the volatile compound classes and individual volatile compounds. This study will provide a better understanding of the impacts of processing methods on the antioxidants and volatile compounds of coffee.

Download Full-text