MICROBIOLOGICAL SPOILAGE IN PHARMACEUTICALS AND COSMETICS 725 formulations contaminants may be seen as a sediment, turbidity or a pellicle while on more solid preparations colonies, often coloured, of bacteria, yeasts or moulds may form. Colour changes Sometimes visible spoilage is more striking, particularly if a colour change is involved. Colour changes due to alterations in the components of a product may result from pH, redox or other changes caused by the metabolic activities of an organism, or to pigment production by the con- taminants themselves. Members of the Pseudomonas genus are often implicated in spoilage of this type. These organisms metabolize a very broad range of compounds, and can also produce soluble pigments ranging in colour from blue-green to brown. In addition, they can render conditions suitable for less adaptable spoilage organisms for example they can create conditions favouring the growth of anaerobes. Similarly, in an acidic product, oxidative yeasts can cause a rise in pH by utilizing organic acids and this will encourage bacterial growth. Gas production If microbial metabolism produces gas in a sufficient amount to exceed its solubility in a product, visible bubbles, frothing and other manifestations of an increase in pressure occur. Products containing carbohydrates or other fermentable substrates are particularly susceptible to this type of spoilage. Of the latter, glycerol, an essential ingredient in many cosmetic preparations, is fermented particularly readily by some common waterborne organisms. Other changes Microbial metabolism can result in the composition of a homogeneous product becoming visibly heterogeneous. Emulsions, for instance, are notoriously susceptible to changes in physicochemical conditions hydro- lysis of the oil phase or changes in the pH of the aqueous phase will upset the equilibrium and thus cause visible changes. In liquid products changes of viscosity can be seen to occur when contaminants have broken down large molecules, utilized sugars or caused the aggregation of particles in suspension. Olfactory effects It has long been known that many micro-organisms produce character- istic odours and as early as 1923 a variety of aroma-producing bacteria had been listed (9). These aromas include the highly characteristic ones of sulphur-containing metabolites such as hydrogen sulphide, the sickly

726 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS smells of the fatty acids, the 'fishy' odours of the amines and the astringency of ammonia. Often these are combined to produce the 'off' odours of a spoiled product. Changes in the aroma of a product due to contaminants vary from the production of a nauseating smell to a slight change in the bouquet but all can be disastrous, particularly to cosmetic and toiletry preparations which depend so much upon their specific perfumes. One of the most common olfactory warnings of spoilage is the typical smell of mould. The responsible aromatic elements have not been clearly identified but some actinomycetes which taint water with undesirable earthy odours have recently been shown to produce geosmin, a strongly earth-smelling, neutral oil (10). An alcoholic odour, produced from fermentable substrates, is typical of spoilage by yeasts. Taste Reports that products taste 'peculiar' are often the first indications that they may be spoiled. The sense of taste varies widely between individuals and these reports do not invariably indicate microbial contamination. For this reason, and because of the hazards involved, taste is not a practicable control procedure with which to detect spoilage at an early stage. Never- theless, the combined senses of smell and taste are highly perceptive to changes in flavour, particularly in bland, unflavoured, preparations where the presence of microbial metabolites is not masked. Margalith and Schwartz (11) have listed over 100 organic compounds involved in the pro- duction of flavour by micro-organisms. These consist mainly of alcohols, aldehydes, ketones, acetals, acids, amines, esters and phenols. Texture The feel of topical preparations, particularly cosmetic and toiletry ones, is vital to their acceptability but texture may be marred by contaminants. For instance, creams can become lumpy or 'gritty' and changes in viscosity of liquid preparations, which can be detected when applied to the skin, may occur. Audible effects Apart from immediate manifestations of toxicity, which happily appear to be rare, audible manifestations of spoilage are the most dramatic. If visible effects of spoilage are obscured by the pack, an explosion can be the