Extraction and downstream processing of pungency principles and pigments of Capsicum

Post-harvest features

Provitamin-A carotenoids of Capsicum, namely /3-carotene and /3-cryptoxanthin, are reduced during the processing of paprika. Esterified carotenoids, which are found as ketocarotenoids, cap-santhin and capsorubin, are more stable than zeaxanthin (free, monoesterified and diesterified forms), /3-cyrptoxanthin (free and mono-esterified form) and /3-carotene (free form) (Howard, 2001). Loss of provitamin-A activity of 67% and 81% has been reported for paprika varieties Agridulce and Bola, respectively. (Minguez-Mosquera and Horneo-Mindez, 1994). The natural antioxidants present in the fruit prevent the degradation of colour (Kanner et al., 1979). Tocoferol acts as an oxidation barrier, while ascorbic acid is useful for tocoferol regeneration and carotenoids prevent lipid oxidation (Esterbauer, 1991). Though there are reports of a decrease of capsaicinoid upon food processing, the pungency factor is generally not affected under the conditions of oleo-resin preparation. However, prolonged storage of pasteurized yellow wax pepper for a period of four months has caused a reduction in capsaicin and dihydrocapsaicin by 30% and 10%, respectively (Lee and Howard, 1999). Thus, characteristic features of raw materials need to be considered for the processing and extraction of the constituents for pungency or colour components.

Extraction and down stream processing

The oleoresin is oil-soluble, but when emulsified becomes water-dispersible. Oleoresins are extracted by percolation with hexane and hexane/acetone/alcohol isopropyl (3:2:1) at ambient temperature, with the paprika/solvent ratio being 1:4.

Light shows a strong degradative effect on the colour of all oleoresins. The oleoresin extracted with hexane/acetone/isopropyl alcohol (3:2:1) has the least stability, especially in the presence of air. In darkness and in the presence of air, an induction period became evident for all oleoresins and the oleoresin extracted with hexane/acetone/ isopropyl alcohol (3:2:1) showed a colour degradation rate constant 1.8 times higher than the others. The commercial oleoresin needs to be made more stable by the addition of antioxidant to facilitate storage.

The stability of paprika oleoresin is strongly dependent on light and on the type of solvent used for its extraction. Balakrishnan and Verghese (1997) reported that after hexane extraction, it was possible to reduce pungency in oleoresin by fractionation with 70% alcohol v/v methanol solutions, recovering 87% of carotenoids and 83% of capsaicinoids after separation. Amaya Guerra et al. (1997) reported the extraction of oleoresin from dried Guajillo pepper with the four solvents ethanol, acetone, ethyl acetate and hexane. Selective extraction of capsaicinoids and carotenoids from chilli guajillo "puya" flour was studied by Santamaria et al. (2000) (Figure 6.3). They reported that when ethanol was used as a solvent 80% of capsaicinoids and 73% of carotenoids were extracted, representing an interesting alternative for the substitution of hexane in industrial processes. Additionally, when the flour was pretreated with cellulases and pecti-nases and extracted in ethanol, the yield increased to 11% and 7% for carotenoid and capsaicinoid, respectively. They have also proposed selective two-stage extraction process after the treatment with enzymes. The first step uses 230% (v/v) ethanol and releases up to 60% of the initial capsaicinoids, and the extraction step with industrial ethanol permits the recovery of 83% of carotenoids present in the flour.

Manuel Jaren-Galan et al. (1999) reported the extraction of oleoresins from paprika (C. annuum) with supercritical carbon dioxide. They have reported that higher extraction volumes,

Figure 6.3 A protocol for extraction of capsaicinoids and carotenoids by using three extraction options: water, industrial alcohol, ethanol (30% v/v).

Source: Santamaria et al. (2000).

Figure 6.3 A protocol for extraction of capsaicinoids and carotenoids by using three extraction options: water, industrial alcohol, ethanol (30% v/v).

Source: Santamaria et al. (2000).

increasing extraction pressures and the use of co-solvents, such as 1% ethanol or acetone, resulted in higher pigment yields. Pigments isolated at lower pressures consisted of (3-carotene exclusively and at higher pressures resulted in more proportions of red carotenoids and smaller amounts of /3-carotene. Kiss et al. (2000) have used the microwave-assisted extraction of pigments from paprika powders.

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