Evaluating the influence of germination as a post-harvest treatment on green and roasted South African coffee beans (Coffea arabica)
Date
2021-12
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Coffee is popular worldwide for its diversity in flavour as well as its beneficial
health factors. The coffee bean is produced from Coffea species, of which there are 103 different
species. The chosen method for post-harvest processing plays an essential role in the
development of the coffee bean’s flavour and aroma. Aside from the hybrid “semi-washed” process,
no other processing has been commercially established in the last few decades.
Germination has been proposed as a novel, post-harvest treatment for coffee
bean processing, specifically for South African coffee beans. Although research has
focused on germination and its effects in terms of sprouting seeds, no research has
been conducted regarding intentional germination during coffee processing.
In this research, liquid chromatography coupled to a mass spectrometer (LCMS) was used to
analyze the various chemical components of South African coffee beans (C. arabica, Catuai). For the
first study, caffeine, chlorogenic acid, trigonelline, and nicotinic acid were identified as key
compounds that play a role in coffee’s flavour profile. These compounds were therefore
evaluated to determine if germination influenced their concentration levels. Analysis of Variance
(ANOVA) results revealed that the interaction effect of production stage and treatment
were not significant (p < 0.05) for all the compounds studied. The main effect of
treatment also did not reveal significant differences (p < 0.05) for all the compounds
(caffeine (p = 0.48), chlorogenic acid (p = 0.27), trigonelline (p = 0.28), and
nicotinic acid (p = 0.44)). The low p-values of chlorogenic acid and trigonelline suggest that
perhaps some significance could be observed. However, further sampling a second
population would be required to support this since the current research had a sampling
size of 24 and only one coffee variety. The influence of germination on the key compounds was not
observed for either green or roasted coffees and therefore it is assumed that the flavour profile
would remain the same between control and germinated coffee.
The second study focused on the entire phenolic profile of the coffee beans
to determine if other compounds were being influenced. Principal Component Analysis (PCA) and
Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) were the chosen
chemometric techniques to analyze the data matrices. Normalization, pareto scaling, and
automated minor peak-shift alignments were applied as pre-processing techniques to
eliminate unwanted variations. However, neither PCA nor OPLS-DA could distinguish
significant differences (p < 0.05) between the control and germinated coffee samples.
Although the sampling size was sufficient for statistical analysis, the small sample set, from only
two harvest years, impacted the reproducibility of the multivariate data analysis.
Thus, it is recommended to gain more samples from different harvest years to determine if
germination influences chemical composition.
The results observed in this study reveal the first evaluation of a South African origin coffee
bean and the first study of germination as novel, post-harvest treatment. Although the results
suggest that germination has no influence on coffee’s flavour profile, more research
should be conducted to include samples from different origins, different species, and different
harvest years.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MScFoodSc)--Stellenbosch University, 2021.
Keywords
Coffee -- Breeding -- Africa Southern, Coffee beans(Coffea Arabica) -- South Africa, Coffee -- Postharvest technology, Germination -- Effect of temperature on, UCTD