Abstract
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.
Highlights
Coffee belongs to the global mainstream drinks [1,2]
The values of 19.32 ± 1.23, 19.56 ± 1.25, 16.13 ± 1.03, 13.47 ± 0.86, and 5.91 ± 0.38 nmol/mg protein were obtained for de-pulped coffee beans, initial and final fermentation, washed, and green coffee beans, respectively
The values of 7.65 ± 0.13 and 4.57 ± 0.076 nmol/mg protein were obtained for green coffee beans in Santa Sofia and Rio Colorado Company, respectively
Summary
Coffee belongs to the global mainstream drinks [1,2]. The demand for coffee beverages is growing, and only crude oil has a larger trade volume [3]. The dried husk composed of coffee pulp, mucilage, and parchment layer is removed subsequently by machine [6]. Coffee processed by the dry method is cherished for its fruity note and silky mouthfeel It is one of the most difficult methods to produce high-quality coffee [4]. There are some hybrid forms of processing, namely the semi-wet and the semi-dry method, as well as monsooning. They differ in their method of mucilage removal. In the semi-washed method, the mucilage layer is removed after 1 day of sun-drying, whereas in the semi-dry, beans are placed to dry directly after removal of coffee pulp and are often referred to as “pulped natural” coffees [4]. The “monsoon” approach should not be considered as a direct processing technique, but represents more of a post-processing method that is added after a natural dry process at the coast of Malabar
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