Bleached cardamom is creamy white or golden yellow in colour. Bleaching can be done either with dried cardamom capsules or freshly harvested capsules as starting material.
Fresh capsules soaked for 1 h in 20 per cent potassium metabisulphite solution containing 1 per cent hydrogen peroxide solution degrade the chlorophyll. Drying of these capsules yield golden yellow colour.
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216 T. John Zachariah and VS. Korikanthimath 3.3.2 Bleaching of dry capsules
(a) Sulphur bleaching: It involves sulphur fumigation with alternate periods of soaking and drying. Capsules are soaked in 2 per cent bleaching powder (20 g/l of water) for 1 h and spread on wooden trays, which are arranged inside air-tight chambers. Sulphur dioxide is produced by burning sulphur (15 g/kg of capsules) and made to pass over the trays. The process of soaking and drying is repeated 3—4 times depending upon the intensity of white colour required.
(b) Potassium metabisulphite bleaching: In this method capsules are treated with 2 per cent potassium metabisulphite containing 1 per cent hydrochloric acid for 30 min. Further they are transferred to 4 per cent hydrogen peroxide solution for 6 h.
(c) Hydrogen peroxide bleaching: Hydrogen peroxide at low concentration (4—6 per cent, pH4) can bleach capsules in 6—8 h of soaking. These capsules are then dried to moisture content of 10—12 per cent. Bleached capsules contain sulphur which protect cardamom from pests. However it was found that bleaching lead to loss of volatile oil.
(d) Conventional bleaching: In Karnataka state of India, bleaching of cardamom is carried out by steeping the dried capsules in soap nut water. The fruits of soap nut (Sapindus saponaria) are mixed with water in a large vessel and stirred vigourously to produce plenty of lather. Dried cardamom capsules are then steeped in this water with occasional stirring. After an hour or so the fruits are collected in wicker baskets, water is allowed to be completely drained off and then spread out in mats for drying. Clean water is occasionally sprinkled over the cardamom capsules. The process of sprinkling water and drying is continued for a couple of days till a good quality bleached product is obtained.
In general, bleaching of dried capsules lead to loss of volatile oil probably because the bleaching process makes the husk brittle. However, bleached cardamom has white appearance and is resistant to weevil infestation due to sulphur dioxide content (Krishnamoorthy and Natarajan, 1976; Govindarajan etal., 1982).
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