Coffee: Volume 1: Chemistry

ISBN-13: 9789401086936 / Angielski / Miękka / 2011 / 306 str.

R. J. Clarke

Opis

The term 'coffee' comprises not only the consumable beverage obtained by extracting roasted coffee with hot water, but also a whole range of intermediate products starting from the freshly harvested coffee cherries. Green coffee beans are, however, the main item of international trade (believed second in importance only to oiI), for processing into roasted coffee, instant coffee and other coffee products, prepared for local consumers. The scientific and technical study of coffee in its entirety therefore involves a wide range of scientific disciplines and practical skills. It is evident that green coffee is a natural product of great compositional complexity, and this is even more true for coffee products deriving from the roasting of coffee. The present volume on the chemistry of coffee seeks to provide the re ader with a full and detailed synopsis of present knowledge on the chemical aspects of green, roasted and instant coffee, in a way which has not been attempted before, that is, within the confines of a single volume solely devoted to the subject. Each chapter is directed towards a separate generic group of constituents known to be present, ranging individually over carbohydrate, nitrogenous and lipid components, not forgetting the important aroma components of roasted coffee, nor the water present and its significance, together with groups of other important components.

Spis treści

1 Introduction.- 1. Origins.- 2. The Coffee Plant.- 2.1. Species and varieties.- 3. Producing Countries.- 3.1. North/Central America.- 3.2. South America.- 3.3. Africa.- 3.4. Asia.- 3.5. Oceania.- 4. Agricultural Practices.- 5. Processing at Origin.- 5.1. Wet processing.- 5.2. Dry processing.- 5.3. Finishing processes.- 6. Roasted Coffee.- 7. Soluble (Instant) Coffee.- 8. Decaffeination.- 9. Composition.- 10. Physiological Effects.- 11. Coffee Quality.- 12. Coffee Substitutes.- References.- 2 Water and Mineral Contents.- 1. Introduction.- 2. Water Content of Green Coffee.- 2.1. Oven methods of determination.- 2.2. Entrainment distillation.- 2.3. Karl Fischer determination.- 2.4. Non-destructive methods.- 2.5. Sorption isotherms.- 3. Water Content of Parchment Coffee.- 4. Water Content of Roasted Coffee.- 4.1. Sorption isotherms.- 5. Water Content of Instant Coffee.- 5.1. Methods of determination.- 5.2. Sorption isotherms.- 5.3. Fusion and collapse temperature.- 6. Water Content of Coffee Extracts.- 6.1. Water activity.- 6.2. Direct determination of solubles content.- 6.3. Specific gravity and refractive index of extracts.- 6.4. Viscosity.- 6.5. Diffusivity.- 6.6. Freezing point depression.- 7. Mineral Content of Green and Roasted Coffee.- 8. Mineral Content of Instant Coffee.- 9. Trace Elements in Coffees.- References.- 3 Carbohydrates.- 1. Carbohydrates of Green Coffee.- 1.1. Low molecular weight sugars.- 1.2. Polysaccharides.- 1.3. Pectins and lignin.- 2. Carbohydrates of Roasted Coffee.- 2.1. Low molecular weight sugars.- 2.2. Polysaccharides.- 2.3. Carbohydrate conversion products.- 3. Carbohydrates of Coffee Brews, Extracts and Instant Coffee.- 3.1. Low molecular weight sugars.- 3.2. Polysaccharides.- 3.3. Carbohydrate conversion products.- 4. Some Physical Properties of Coffee Carbohydrates.- 5. Determination of Carbohydrates.- References.- 4 Nitrogenous Components.- 1. Introduction.- 2. Alkaloids (Caffeine).- 2.1. Caffeine content of green, roasted and instant coffees.- 2.2. Physiological effects of caffeine.- 2.3. Determination of caffeine.- 3. Trigonelline.- 3.1. Determination of trigonelline.- 4. Nicotinic Acid.- 4.1. Levels in green, roasted and instant coffee.- 4.2. Nutritional significance of nicotinic acid in coffee.- 4.3. Determination of nicotinic acid.- 5. Proteins and Free Amino Acids.- 5.1. Proteins.- 5.2. Enzymes.- 5.3. Pigments.- 5.4. Free amino acids.- References.- 5 Chlorogenic Acids.- 1. Introduction and Brief History.- 2. Chlorogenic Acids Nomenclature.- 3. Chemical Synthesis.- 3.1. Preparation of the protected acyl chloride.- 3.2. Preparation of the protected quinic acid.- 3.3. Esterification reactions.- 3.4. Acyl migration as a synthetic method.- 4. Physical Properties.- 4.1. Solubility and partition coefficients.- 4.2. Dissociation constant.- 4.3. Crystal form and melting points.- 4.4. Polarimetric data.- 4.5. Infrared spectra.- 4.6. Mass spectra.- 4.7. Nuclear magnetic resonance spectroscopy.- 4.8. Ultraviolet spectroscopy.- 5. Origin and Function.- 5.1. Biosynthesis.- 5.2. Function.- 6. Chlorogenic Acids Extraction and Analysis.- 6.1. Size reduction.- 6.2. Extraction.- 6.3. Possible artefacts.- 6.4. Chlorogenic acids analysis.- 7. Chlorogenic Acids Content in Green Coffee Beans.- 7.1. Normal commercial coffee beans.- 7.2. Green beans from immature fruit.- 7.3. Discoloured green beans.- 7.4. Stored green beans.- 8. Chlorogenic Acids Content of Roasted Beans and Soluble Powders.- 8.1. Relative loss per gram dry matter loss.- 8.2. Relative loss per unit time.- 8.3. Loss in absolute terms.- 8.4. Fate of the chlorogenic acids.- 9. Organoleptic Properties.- 9.1. Model system studies and structure-activity relationships.- 9.2. Relevance to the acceptability of coffee products and coffee beverage.- 9.3. Chlorogenic acids as predictors and determinants of beverage quality.- References.- 6 Lipids.- 1. Introduction.- 2. Coffee Oil.- 2.1. Determination of total oil content.- 2.2. Isolation of coffee oil for detailed analysis.- 2.3. Free and total fatty acids.- 2.4. Triglycerides.- 2.5. Diterpenes.- 2.6. Sterols.- 2.7. Tocopherols.- 2.8. Other compounds.- 3. Coffee Wax.- 3.1. Determination of the content of C-5-HT in green and roasted coffee.- References.- 7 Volatile Components.- 1. Preamble.- 2. Methodology.- 2.1. Introduction.- 2.2. Headspace methods.- 2.3. Distillation techniqueS.- 2.4. Other techniques.- 2.5. Summary.- 3. The Nature of the Volatile Components of Coffee.- 3.1. Introduction.- 3.2. Green coffee.- 3.3. The roasting process.- 3.4. Roasted coffee.- 3.5. Effect of species on coffee aroma composition.- 3.6. Coffee processing and its effect on volatile composition.- 3.7. Quantitative assessment of coffee volatiles.- 3.8. Summary.- References.- 8 Carboxylic Acids.- 1. The Role of Acids in Infusions.- 1.1. The importance of acidity to taste and flavour.- 1.2. Relationship between pH and acid content.- 2. The Acid Content of Green Coffee.- 3. The Acid Content of Roasted Coffee.- 3.1. Identified acids.- 3.2. Quantitative data.- 3.3. Changes on roasting.- 3.4. Changes on storage.- 3.5. Relationships to perceived acidity.- 4. The Acid Content of Dried Coffee Extracts (Instant Coffees).- 5. Determination of Acids.- 5.1. pH and titratable acidity.- 5.2. Individual acids.- 6. The Origins of Acids Found in Coffee Infusions.- References.