Capsicum peppers are known by a variety of common names (chilli, paprika, pimiento, sweet, red, cayenne, and bird), which are more closely connected with their uses as foods and spices than with any taxanomic differences (). However, the main division may be drawn between the sweet peppers, which are forms of Capsicum annuum and are eaten as a vegetable (), and the more pungent peppers, which can be Capsicum annuum, Capsicum frutescens, Capsicum baccatum, Capsicum pubescens or Capsicum chinense, and are generally used as spices (). The pungency of Capsicum peppers is derived mainly from the compound capsaicin (), one of the most pungent compounds known, which is detectable on the palate at dilutions of from 1 to 15 million (). It is with the pungent varieties of Capsicum, rather than the vegetable varieties, that the spice industry is concerned and the following figures are with reference to these varieties.
The commercial cultivation of Capsicum spp. is widespread, with major producers including India, Pakistan, China, East Africa, the USA, and Mexico (). It has been estimated by the International Trade Centre (1982) that during the period 1976-1980, average imports of Capsicum ranged from 40000 to 44000 t/a, with a value of $67 million. They are, therefore, the second most important commodity in the international spice trade, after Piper pepper species. The main use of Capsicum fruits is for culinary purposes and seasoning, although extracted capsaicin does have a pharmaceutical role, internally as a powerful stimulant and externally as a counter-irritant in the treatment of such diseases as rheumatism. In western Europe and North America some two-thirds of Capsicum is processed by the food industry, going into products such as processed meats, spice mixes, curry powders, soups and a wide range of other prepared foods ().
Capsicum seeds are generally sown in a nursery bed or greenhouse, and plants are grown for 6-8 weeks before transplanting. Approximately 1 kg of seed should provide sufficient plants for 1 ha (), with around 17 500 plants/ha (), depending on cultivar. Harvesting takes place between 17-24 weeks after sowing ().
After harvesting, the dried spice is prepared from the fruit by reducing the water content from 65-80% down to approximately 10% (). In all areas except the USA this is generally carried out by sun-drying, without any special preparation of the fruit. In the USA artificial drying takes place, with the fruit being exposed to a flow of air at 50-60 °C. Artificial drying gives a more consistent quality crop in a shorter time. The dried fruit may be stored whole or sliced, or as a ground spice powder.
An alternative to the ground spice, of increasing importance in industrial applications, is the oleoresin preparation. The bulk of oleoresin produced is used in the food industry and a small proportion (10-15% in the FRG, less in the USA and UK) is used by the pharmaceutical industry (). Oleoresins are prepared from highly pungent Capsicum species, dried down to 7-8% water content. These are ground and then extracted with a solvent such as acetone or ether. The solvent is finally removed from the crude oleoresin by distillation ().
The use of immobilized C.frutescens cultures in production medium, in combination with continuous extraction, has given specific production rates of capsaicin, of 0.1 mg/g dry weight per day (), which compare well with those in ripening fruit, of 0.5 mg/g dry weight per day (). However, many problems remain to be solved before the commercial production of capsaicin from tissue culture becomes feasible. Quoted levels of capsaicin are generally produced by selected high yielding cell lines, which are invariably unstable. The fluctuations of product levels in the culture media also requires further investigation, as do oxygen and nutrient stressing effects. Some initial work on a scale-up of the stirred immobilization bioreactor has been carried out at this laboratory, but further work is required on this, and on downstream processing and process integration.
Selections from the book: “Medicinal and Aromatic Plants IV”, 1993.