Coffee Robusta

B. Comparison of Beverages from Arabica and Robusta Coffees... 

Coffee is grown in countries situated between the Tropics of Capricorn and Cancer. C. arabica is the most widely grown, but regions where temperature and humidity are rather high have been replanted with C. canephora var. robusta. Robusta coffees are thus the major species grown in the less mountainous regions closest to the equator. 

Production of coffee in Brazil was 42% of the world crop in 1960. However, by 1980, although the actual amount was still high, Brazil s proportional contribution to world exports was halved. African Robusta coffees instead now represent over 25% of all coffee used in the U.S. and Europe. 

The dry method produces green coffee beans much less expensively than the wet method. A high proportion of Brazilian Arabica coffee is processed in this way, and almost all Robusta coffees are treated in this way. The final beverage produced from dry-processed coffee has a full flavor that is often described as hard and sometimes is characteristic of a region, for example Rio coffees. 

The diy-processed coffees, especially Robustas, are often selected for the production of instant coffees since they have less-popular powerful flavors that are rendered mild in the production of an instant coffee. There is also economy in the use of Robusta coffees in this way, since they are produced much less expensively than wet-processed Arabicas. Before the instant coffee is marketed, it can be flavored with the coffee oil obtained from a wet-processed Arabica coffee to improve the acceptability of the product. 

In the U.S. the per capita consumption of coffee has declined by one-third since 1960. Parallel with this has been a change in the proportion of Robusta coffees imported into the U.S. In 1950 only 6% of the imported coffees were Robustas whereas by 1975, 35% were Robustas. In the 1950s, Robustas were mainly used for instant coffee now they also constitute a significant part of the roast and ground coffee blends. These Robustas are used to the highest extent in vending machines, restaurants, decaffeinated blends, and instant coffees. 

One of the most significant differences between Arabica and Robusta coffees is in the caffeine content. Robusta coffees contain almost twice the caffeine found in Arabica coffees. There are some other differences recognized thus far Robustas contain almost no sucrose and only very small amounts of the kaurane and furokaurane-type diterpenes they contain higher proportions of phenols, complex carbohydrates (both soluble and hydrolyzable), volatile fatty acids on roasting, and sulfur compounds, all in comparison with Arabicas. References to these distinctions can be found in Chapter 6 of this book. 

Additionally Robusta coffees are frequently used to prepare instant coffees and the result is a distinctly brown beverage Arabicas give a reddish colored beverage. 

Methods for the decaffeination of green coffee beans, mainly with solvents after a steaming, have already been described. Even with the selective adsorption techniques to remove only caffeine, it is unlikely that the full character of the starting beans can be realized in a final decaffeinated beverage the result is that Robusta coffees are generally used to prepare decaffeinated coffee. The cost is kept down and the treatment, anyway, reduces any harsh or bitter flavor that the Robusta coffee may have had. The resulting beverage will be relatively caffeine-free, but Robusta coffee will contribute more soluble carbohydrates, phenols, and volatile fatty acids, and much less of the diterpenes found in Arabica coffees. 

The compounds given off during the roasting of coffee are not necessarily found in the finally roasted bean, and so only a few such compounds are included. In a list of volatile components in foods which is regularly brought up to date4 more than 800 volatile compounds are listed for coffee when it is roasted, and of these 60 to 80 contribute to coffee aroma.5 Comparison of the 14 most potent odorants from roasted Arabica and Robusta coffees, revealed significant differences,6 (see Table 2). 

Compound Concentration in Arabica coffee (mg/kg) Concentration in Robusta coffee (mg/kg)... 

The characteristic earthy and harsh flavor and aroma of roasted Ro-busta coffees is largely attributed to 2-methylisoborneol. Amounts found in green Robusta coffee beans were 0.03 to 0.3 ppb, and this could be completely removed by steam heating or roasting.26 There is approximately ten times as much 2-methylisoborneol in roasted Robusta coffee beans than in similarly treated Arabica coffee.27... 

More recently, a series of 11 chlorogenic acids has been recognized in green Robusta coffee beans.51... 

Robusta coffee has a somewhat higher phenolic content than Arabica (see Table 7). The feruloylquinic and dicaffeoylquinic acid content in Robusta is higher than in Arabica coffee beans.71 72... 

Crossing the boundaries of phenolic compounds and amino acids in coffee, caffeoyl tryptophan, and p-coumaiyl-(L)-tryptophan have both been identified recently in green Robusta coffee beans.51 A... 

Sulfur-containing compounds are significantly more concentrated in Robusta coffees than in Arabicas. This difference can be used to recognize Robusta in coffee blends with Arabica.83... 

Coffee oil is generally described as the petroleum ether-soluble fraction from green coffee beans. Arabica coffees contain 11.1 to 13.6% oil, whereas Robusta coffees contain only 4.4 to 4.8% oil.106 Triglycerides constitute 79% of this oil, terpene esters 17%, and the remaining 4% is contributed by sterols, free terpenes, tocopherols, and as yet unknown... 

Cafestol from robusta coffee as well as kahweol from arabica coffee were both recognized as capable of elevating serum cholesterol levels.124... 

Large amounts of diterpene mono- and di-alcohols have been found in both Arabic and Robusta coffees, including cafestol, kahweol, and 16-O-methylcafestol.126 The characteristic differences can be used to quantify the Robusta content of commercial blends with Arabica.127... 

Roasted Robusta coffee contains 16-O-methylcafestol, mostly in its esterified form 128 and it has been recognized as useful for detecting the addition of Robusta to Arabica coffee because of its stability during roasting.129... 

Determinations of nicotinamide in green and roasted Robusta coffee are indicative of its much increased content in coffee roasted at or below 240°C. The values are 3 and 46 mg/100 g for green and roasted coffee, respectively.183 At least part of this increase is from trigonelline as it decomposes on roasting. 

Robusta coffee has undesirable flavor agents that can be masked by the addition of L-aspartyl-L-phenylalaninemethyl ester.218 The methylxanthine stimulant properties of coffee can be antagonized by spraying freshly roasted coffee beans with nicotinamide and nicotinic acid,219 quinolinic acid, or trigonelline.220... 

Rouge, F., Gretsch, C., Christensen, K., Liardon, R., Thermal stability of 2-methylisoborneol in Robusta coffee. Colloq. Sci. Int. Cafe, 15th(Vol.2), 866, 1993. (CA121 33729q)... 

Belyaya, K. J., Clifford, M. N., Individual chlorogenic acids and caffeine contents in commercial grades of wet and dry processed Indian green robusta coffee, J. Food Sc 1. Technol, 32(2),104, 1995. (CA123 197159w)... 

Correia, A. M. N. G., Leitao, M. C. A., Clifford, M. N., Caffeoyl-tyrosine and Angola II as characteristic markers for Angolan Robusta coffees, Food Chem., 53(3), 309, 1995. (CA123 8347x)... 

Nurok, D., Anderson, J. W., Zlatkis, A., Profiles of sulfur containing compounds obtained from Arabica and Robusta coffees by capillary column gas chromatography, Chromatographia, 11, 188, 1978. (CA89 22468y)... 

To identify further which substance, cafestol or kahweol, or both, was inducing changes in serum cholesterol, the investigators attempted, but failed due to technical limitations, to separate the two chemical compounds. Alternatively, they compared coffee oil from Arabica vs. Robusta coffee beans. Arabica beans contain both cafestol and kahweol, while Robusta beans contain cafestol, but almost no kahweol. The investigators found that Arabica and Robusta oils both increased serum cholesterol and triglyceride levels comparably. They thus concluded that cafestol is, and kahweol might be, a serum cholesterol raising factor. 

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