Coffee extract

Coffee bioconversions through enzymatic hydrolysis have been used to modify green coffee and improve the finished product (60). Similarly, enzymes have been reported which increase yield and improve flavor of instant coffee (61). Fermentation of green coffee extracts to produce diacetyl [431 -03-8] a coffee flavor compound, has also been demonstrated (62). 

A French Standard, which corresponds to ISO 10095 issued in 1992, specifies a method for determination of caffeine in green or roasted coffee or in coffee extracts (decaffeinated or not).33 Caffeine is extracted with water at 90°C in the presence of MgO. The extract is filtered, then cleaned-up on a mini-column packed with a silica phenyl group derivative, and analyzed by HPLC on a C18 column with a methanol/water (30 70) mobile phase and a UV detector operating at 254 to 280 nm. 

A method for determining the caffeine content of regular and decaffinated green and roasted coffee beans and of regular and decaffeinated coffee extract powders, using HPLC, is specified in a British Standard Instruction.34 Caffeine is extracted from the sample with water at 90°C in the presence of magnesium oxide. The mixture is filtered and an aliquot purified on a silica microcolumn modified with phenyl groups. The caffeine content is then determined by HPLC with UV detection.35... 

In outline, a percolation process is used to produce an aqueous coffee extract, which in turn is dehydrated to yield water-soluble solids. Instant and soluble coffees are synonymous for these water-soluble coffee extract solids. Usually some of the volatile aroma and flavor compounds, which are lost during the processing, are added back immediately before packaging. 

Roasted and ground coffee is packed into columns and percolated by the passage of hot water under pressure at about 340°F. The use of pressurized boiling water not only brings about the dissolution of the most readily water-soluble coffee extractables, it also causes the solubilization and possibly the hydrolysis of complex carbohydrates. Water-soluble compounds of a smaller molecular weight are produced. The extent of possible... 

One of the most widely used spray-drying techniques for coffee extract involves spraying percolated coffee extract at 40°F into the top of a baffled tower of hot air at 480°F initially. The cooler wet air is removed toward the bottom of the tower and finally a powder of the coffee extract solids leaves the tower at about 90°F. These solids are in the form of hollow beads and contain 3% moisture. 

Kramer, F., Henig, Y. S., Garin, T. A., and Vogel, G. J., Selective adsorption from solutions such as coffee extracts, UK Pat. Appl. 2,027,576, 1980. (CA93 69060g)... 

Polyphenoloxidase, produced by Alternaria or CJadosporium, can be used to improve the brown coloration in a coffee extract.221... 

Takahashi, K., Kondo, Y., Sawano, T., Mori, M., Changes in pH of coffee extract depending on temperature and its quality, Nippon Shokuhin Kogyo Cakkaishi, 26,... 

Thaler, H., The chemistry of coffee extraction in relation to polysaccharides, Food Chem., 4, 13, 1979. (CA90 166719z)... 

Ara, V., Thaler, H., Studies on coffee and coffee substitutes. XIX. Dependence of the quantity of a highly polymeric galactomannan on the degree of extraction of commercially prepared coffee-extracts, Z. Lebensm.-Unters. Forsch., 164, 8, 1977. (CA87 51829f)... 

Fig. 1.53. Freezing and thawing plot of coffee extract with 25 % solids. UFW (g H20/g solids) as a function of temperature (Fig. 2 from [ 1.37])-I, Subcooling 2, collapse temperature.

If the material is granulated, e. g. frozen and granulated coffee extract, having a solid content perhaps of 40 % and a density of 0.6 g/cm3 (Fig. 1.61), Eq. 12 is still applicable, but the product data are different. The heat transfer is through the dried product with a Atr = 8.37 10 2 kJ/m h °C. To make the results better comparable, d = 0.7 cm and rtot have been retained from the earlier example, even if Ttol were normally higher, e. g. 100 °C. 

The freeze drying of coffee extracts has been, and still is, the most frequent application of this process in the food industry. For economic reasons it is best to start with 40 % solid content in the extract. The final product is judged by the following criteria ... 

Fig. 4.6. Distribution of grain size as a function of bulk density of freeze dried coffee extract, which has been gassed with different pressures of C02 before freezing.

Flink [4.17] described the relative retention of volatile components in coffee extracts as a function of the freezing speed and the operation pressure ... 

Coffee extract foam in a soft-ice-machine , and then frozen in 15 layers in resting air down to -40 °C... 

Coffee extract sprayed on a drum freezer at -52 °C with a layer thickness of 3 mm... 

Coffee extract with CO, foamed at +20 °C and than sprayed as in 5). 

Crystallisation by freezing, or freeze crystallisation, is a process in which heat is removed from a solution to form crystals of the solvent rather than of the solute. This is followed by separation of crystals from the concentrated solution, washing the crystals with near-pure solvent, and finally melting the crystals to produce virtually pure solvent. The product of freeze crystallisation can be either the melted crystals, as in water desalination, or the concentrated solution, as in the concentration of fruit juice or coffee extracts. Freeze crystallisation is applicable in principle to a variety of solvents and solutions although, because it is most commonly applied to aqueous systems, the following comments refer exclusively to the freezing of water. 

Future research. From an industrial standpoint, the major requirements of p-mannanases are thermostability and the ability to hydrolyse crystalline and/or amorphous mannan to low DP oligosaccharides. Enzymes with such properties could find application in such processes as coffee extraction and in enzymic treatment of wood pulp. 

Gas-liquid chromatography detects thienothiophenes in crude Qj]204,2oj gjjjj coffee extract. ... 

CA234 Yamaguchi, T. and M. Iki. Inhibitory effect of coffee extract against some mutagens. Agr Biol Chem 1986 50(12) 2983-2988. 

---