Volatile and bioactive compounds in different roast level specialty coffee: doctoral thesis for acquiring a doctor of science (PhD) in food and beverage technologies

Doctoral thesis was developed from 2017 to 2022 in the scientific laboratories of the Department of Food Technology, Latvia University of Life Sciences and Technologies, and Center for Sensory Analysis and Consumer Behavior, Kansas State University (USA). The object of the doctoral thesis is Coffea arabica L. coffee beans at different roast levels. The hypothesis of the doctoral thesis – coffee consumers would prefer specialty coffee due to increased bioactive compound content by adjusted roast level. The hypothesis was confirmed by the following theses. 1. Solid-phase microextraction (SPME) fibre coating affects volatile compound extraction and detection in specialty coffee brew. 2. Specialty coffee origin and roasting parameters impact phenolic compound content and sensory quality. 3. Light roast level has a positive effect on phenolic and volatile compound content in specialty coffee. 4. Initial gas chromatography-olfactometry vocabulary allows to detect and describe aroma-active compounds in specialty coffee. 5. Consumer perception of specialty coffee brews can be affected by sensory attributes and potentially increased bioactive compound content. The aim of the doctoral thesis was to evaluate the impact of the roast level on the composition of bioactive compounds and sensory quality in specialty coffee. To achieve the aim of the doctoral thesis, the following objectives have been established: 1. To evaluate different solid-phase microextraction (SPME) fibre influence on specialty coffee brew volatile compound extraction and detection. 2. To analyse phenolic compound content and cup quality profile in different origin and roast specialty coffees. 3. To determinate roasting process influence on volatile compound profile. 4. To evaluate non-volatile compound content changes during the roasting process. 5. To develop an initial gas chromatography-olfactometry vocabulary for specialty coffee. To assess consumer perception of specialty coffee brews with potentially increased bioactive compound content. The doctoral thesis consists of three chapters. Chapter 1 summaries previous literature about coffee's chemical composition, sensory properties, and possible changes during roasting and brewing processes; provides information about the biologically active compound composition and their impact on health; defines specialty coffee and coffee quality standards. Chapter 2 describes the coffee roasting process and summarises the materials and methods of analysis. Chapter 3 summarises the results obtained in this study with a discussion to achieve the conclusions according to the hypothesis and established objectives. The chapter describes the evaluation of different SPME fibre influence on specialty coffee brew volatile compound extraction and detection; the chemical and sensory profile changes under the influence of roasting process; aroma-active compound perception in coffee by gas chromatography-olfactometry; analysis of consumer perception of specialty coffee brews. The novelty of the doctoral thesis: 1. A complex volatile and biologically active compound comparison has been developed for different roast level specialty coffee. 2. Solid-phase microextraction fibre evaluation for improved volatile compound detection in specialty coffee. 3. Volatile and aroma-active compound profile analysis in different roast level specialty coffee; 4. Developed gas chromatography-olfactometry vocabulary allows to analyse aroma-active compound perception in differently roasted and brewed specialty. The economic significance of the doctoral thesis: the completed analysis about the roast level impact on coffee quality and bioactive compound content in specialty coffee provides the coffee roasters with an opportunity to adjust roast parameters. During the PhD studies, the author had an internship at the Center for Sensory Analysis and Consumer Behavior in Kansas State University (United States of America), where experimental work was done. The internship was provided by the Baltic-American Freedom Foundation (BAFF) and the Council on International Education Exchange (CIEE). The thesis is written in English (United Kingdom); it consists of 108 pages, 27 tables, 16 figures, four appendixes, and 190 bibliographic sources.