Improvement of robusta coffee aroma quality
Publication Date
July 17, 2019
Creator
Abstract
In this thesis, two main novel pre-treatment approaches were developed, with the aim to change the chemical reaction pathways during thermal treatment (roasting) and thereby regulate aroma formation during coffee roasting. The objective for this study is to up-value Robusta coffee beans with overall aim of increasing aroma chemistry similarities between Robusta and Arabica coffees.
Green Robusta beans were subjected to pre-treatment with the aim of reducing the perceived aroma difference between Arabica and Robusta coffee. The first approach was a short soaking procedure before roasting with varying concentrations of acetic acid (up to 5%). Samples were subjected to thermal treatment (roasted) and ground to a standardised particle size distribution. Aroma compounds were evaluated by headspace analysis using Solid Phase Micro Extraction - Gas Chromatograph Mass Spectrometry. Acetic acid pre-treatment significantly affected aroma formation during roasting and resulted in a modified level of pyrazines, furanic compounds and sulphur-containing compounds (p ˂ 0.05). Principal Component Analysis (PCA) illustrated that the aroma profile of the acetic acid treated Robusta coffee was closer to the target Arabica coffee after roasting. Sensory results confirmed that the aroma of the 2% acetic acid pre-treated Robusta brew was similar to Arabica and the maximum inclusion level of Robusta coffee in a blend could be increased from 20% to 80%.
A second approach was attempted to improve Robusta sensory properties based on modification of the beans chemical composition before roasting. Building on the first approach, which modified bean pH through acid pre-treatment, sugar solutions (glucose, fructose and sucrose) were used to pre-treat Robusta coffee beans with the aim to modify the concentration/availability of these aroma precursors. The treatment significantly affected aroma generation during roasting and lead to an altered level of pyrazines, furans, ketones, organic acid and heterocyclic nitrogen-containing compounds (p < 0.05). The optimum treatment was 15 % fructose. 80% treated Robusta could be blended with Arabica in coffee brew without significant aroma differences being perceived when compared to 100% Arabica brew.
The stability of volatile compounds found in Arabica and Robusta coffee beans were also investigated after roasting over six weeks of accelerated shelf-life storage (ASL) (5˚C, 25˚C and 35˚C, up to 6 weeks). As previously demonstrated, coffee bean pre-treatment technology enhances Robusta aroma by pre-soaking the beans in either acetic acid (2%) or 15 % fructose prior to roasting and the impact on aroma loss over shelf-life was also evaluated for these samples. Results indicated that Arabica coffee lost the greatest amount of volatile compounds during storage. Surprisingly, Robusta coffee treated with 2% acetic acid was the most stable over storage. Although the 15% fructose treated Robusta showed less aroma stability than non-treated Robusta during 6 weeks storage, the aroma of 15% fructose treated Robusta was still more stable compared with Arabica.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Biosciences (UK)
eprints ID
55850
UoN Repository URI
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Improvement of Robusta Coffee Aroma Quality_Chujiao Liu.pdf
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