The red-, orange-, and yellow-pigmented fruit in Capsicum spp. is the result of accumulation of carotenoids, both carotenes and xanthophylls, in the pericarp (Wall et al., 2001). These pigments have beneficial nutritional value as precursors for vitamin A and as antioxidants (Clevidence et al., 2000; Fraser and Bramley, 2004; Simonne et al., 1997). In addition to their nutritional value, the red pigments in particular are important as sources of non-toxic red dyes (Sun, 1985). These red pigments are added to many processed foods and to some cosmetics to enhance their appearance (Wall and Bosland, 1998). The xanthophylls extracted from Capsicum fruit have become an important economical source of red pigments that can replace carcinogenic synthetic red dyes.
Typically, dried red fruit are extracted as a mash in a large heated volume of hexane; the extracted liquid is recovered and the hexane is evaporated or distilled from the sample leaving an oleoresin. Capsaicinoids, the compounds that are responsible for the heat or pungency of the Capsicum fruit, are also readily soluble in hexane. So to produce an oleoresin with no pungency, only mild or non-pungent red-pigmented fruit can be extracted. Breeding programs to develop varieties of Capsicum for higher yields of red pigmentation need to also breed in a non-pungent or mild Capsicum background (Hornero-Méndez et al., 2002; Walker et al., 2004). In New Mexico, the economic value of a chile (C. annuum, L.) crop includes the value of the fruit harvested as a fresh green product and a dried red product often harvested at a later time in the season. Using current extraction processes, red pigment can only be recovered from American paprika varieties or other mild cultivars. If the extraction of the red pigments could be achieved separate from the capsaicinoids, then a wider range of red-fruited cultivars could be used, including ones with important values also as a fresh green crop.
Disposal of hazardous waste generated by industrial processes is expensive and becoming unpopular because water sources are accidentally contaminated with improper disposal. If alternative and environmentally sound, so-called “green” extraction protocols could be developed to replace the use of hexane as a solvent for oleoresin production, this would improve the environmental risks for the isolation of red pigments from Capsicum fruit. Supercritical fluid extractions (SFE) using CO2 as the solvent is one such green extraction method that is especially suited for the extraction of non-polar analytes (King and Hopper, 1992). Methods for the extraction of capsaicinoids by SFE have been described (Peusch et al., 1997; Sato et al., 1999). Several groups have described SFE methods for the extraction of pigments from Capsicum. In some cases, the authors have used paprika types of Capsicum, which are non-pungent, so interference of capsaicinoids coextracting with the pigments was avoided (Ambrogi et al., 2002; Jaren-Galan et al., 1999). In a few cases (Gnayfeed, et al., 2001; Perva-Uzunalic et al., 2004; Uquicke et al., 2004), pungent Capsicum samples were used in the extraction of pigments; however, in those cases, extraction conditions were designed for the recovery of both the pigments and the capsaicinoids. Paprika oleoresins, typically prepared by hexane extraction, are generated for their pigment concentrations. They also need to have reduced capsaicinoid levels, no more than 0.5% or less than 25 ppm. These oleoresins are generated by extracting paprika types of chile fruit, those with less than 700 Scoville heat units capsaicinoids (Walker et al., 2004). To date, no SFE methods have been reported that allow for the preferential extraction of carotenoid pigments from pungent Capsicum fruit.
In this report, we describe a green chemical method that generates an oleoresin from dried Capsicum fruit with virtually the same carotene and xanthophyll composition as a hexane extraction method. Furthermore, this method includes a step that separates the pigments from the capsaicinoids. This last feature increases the flexibility of the process to allow a variety of red Capsicum fruit, pungent and non-pungent, to be used easily for pigment production.
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