PRIMARY FACTORS

As indicated in Chapter 11, air-dry drugs contain about 10–12% of moisture, and in some instances (e.g. digitalis) this may be sufficient to activate enzymes present in the leaves and bring about decomposition of the glycosides. Other drugs, such as powdered squill, which contain mucilage quickly absorb moisture and become a sticky mass. The containerized shipment of drugs which is now common practice can lead to spoilage due to excessive condensation of moisture on the inner metal walls. It is a particular problem with cargoes in transit from humid moist climates to temperate regions. An increase in temperature, in combination with moisture, may accelerate enzyme activity; a large temperature rise will obviously lead to a loss of volatile constituents (e.g. essential oils from dried plant material) and in the case of absorbent cotton-wool cause a reorientation of the small amount of fatty material present leading to non-absorbency or lower absorbency. Direct sunlight can cause decomposition of certain constituents (e.g. vitamins in cod-liver oil) as well as producing a bleaching of leaves and flowers. Oxygen assists in the resinification of volatile oils and in the rancidification of fixed oils.

MOULD AND BACTERIAL ATTACK

The moulds found in deteriorating drugs are usually the same as those associated with poorly stored food products. Species of Rhizopus, Mucor, Penicillium and Eurotium are common. Their presence is indicated by a mass of hyphae which bind the particles of drug and by a characteristic smell. Deterioration of drugs is only one aspect of the importance of moulds in pharmacognosy—see Chapter 30. Bacterial attack of crude drugs is less obvious unless chromogenic species are involved or effects produced such as dustiness in cotton-wool by attack on the fibres. Although not a cause of deterioration, certain pathogenic bacteria such as salmonellae and Escherichia coli are tested for in some crude drugs taken internally (digitalis, sterculia, tragacanth, gelatin). Also, as plant materials which have been dried under normal conditions contain viable bacteria and mould spores in variable amounts, the pharmacopoeias set limits for the total viable aerobic count per gram of drug (see Quality Control, Chapter 16).

COLEOPTERA OR BEETLES

Beetles are insects and constitute the largest order of the animal kingdom, comprising some 250 000 species, of which about 600 have been found associated with stored food products or drugs. Not all of these utilize the stored product itself but may be found in the wood of packing-cases or living predaciously. Beetles have a body which is divided into head, thorax and abdomen. To the lower side of the thorax are attached three pairs of legs, while the upper surface usually bears two membranous hind-wings which are folded beneath horny elytra (forewings). They show complete metamorphosis of egg, larval, pupal and adult stages, and those which constitute pests in stored products cause damage both as adults and as larvae. Among the characters which distinguish the larvae of most species which attack foodstuffs and vegetable drugs are the well-developed biting mouth-parts and a head which is darker in colour than the rest of the body. Table 15.1 lists beetles commonly found in stored drugs; for illustrations see Fig. 15.1.

Table 15.1 Beetles commonly found in stored drugs.

Fig. 15.1 Insect pests found in crude drugs. A, Calandra granaria; B, Ptinus spp; C, Gibbium spp.: (all × 10). D, Stegobium paniceum (× 12).

(Photos: Dr M. E. Brown)