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

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.

Limited enzymatic hydrolysis of green coffee protein as a technique for preparing new functional food components

“…The MW of an 11S coffee storage protein is 300–400 kDa and after treatment with non-reducing materials such as SDS or urea can be separated to produce six subunit pairs with MW of 55–60 kDa, each pair being linked by a disulfide bond. The breaking of these disulfide bonds under reducing conditions gives two subunits (α-acidic and β-basic) with MW ~ 33 and 24 kDa, respectively (Ali et al 2012 ; Campos et al 2022 ; Fukshima 2001 ). Polyacrylamide gel electrophoresis under denaturing conditions was performed to study the effect of the pepsin enzyme treatment, at two different pH (1.5 and 3) and for 0, 15 min, 1, and 3 h, on GC protein breakdown.…”

Influence of pre-and post-harvest factors on the organoleptic and physicochemical quality of coffee: a short review

“…After roasting, 20–40% of cell wall storage polysaccharides are degraded, but there is no significant loss in terms of caffeine (Campos et al. 2022 ). Trigonelline changes into N-methylpyridinium and nicotinic acid as its major products, which make them a useful index of the degree of roasting (Li et al.…”

“…After roasting, the grinding of roasted beans allows to balance the humidity and increases the surface area of the roasted beans for the respective extraction. After roasting, 20-40% of cell wall storage polysaccharides are degraded, but there is no significant loss in terms of caffeine (Campos et al 2022). Trigonelline changes into N-methylpyridinium and nicotinic acid as its major products, which make them a useful index of the degree of roasting (Li et al 2021).…”

Processing Effects on Protein Structure and Physicochemical Properties

“…Coffee is an extremely important product and, thereby, also the coffee bean processing. In an extensive and detailed, including development of an MRM method using HPLC-MS/MS for analyzing protein-phenolic modification, study of 14 Coffea arabica samples from various processing methods and countries was conducted (all commercially available samples) [ 1 ]. The proteins are considered to be the most important compounds for the coffee aroma, hence a good cup of coffee.…”

“…In conclusion, larger sample set are needed to prove the observed trends and changes. Moreover, the authors conclude that there is a possibility of using the modified peptides as biomarkers, though with more in-depth analysis, in order to bring them closer to coffee quality [ 1 ].…”