MOULD GROWTH

Onions and garlic are susceptible to moist conditions, which encourage mould growth, and are stored at humidities of 65-70%. It is not possible to store these together with other vegetables for more than a very short time. 

R FS. 0.05m Potassium hydrogenphthalate. Dissolve 10.21 g of the solid (dried below 130 °C) in water and dilute to 1 kg. The pH is not affected by atmospheric carbon dioxide the buffer capacity is rather low. The solution should be replaced after 5-6 weeks, or earlier if mould-growth is apparent. 

Mould growth, 25 °C Trichoderma viride Waste paper Yes Yes... 

Fig. 11.4 The effect of pH on the concentration of phenol (pKa 10) and of acetic acid (pJtj 4.7) to inhibit mould growth.

Overhead pipes in all manufaeturing areas should be sited away from equipment to prevent eondensation and possible eontaminants from falling into the produet. Unless negleeted, stainless steel pipes support little mierobial growth, but lagged pipes present a problem and unless they are regularly treated with a disinfectant they will support mould growth. 

Both crumpets and pikelets have high moisture content so mould growth can be a problem. Mould inhibitors or vinegar are sometimes used to counter the problem. 

Drying out can be prevented in one of two ways, either by packaging or by lowering the water activity of the product. Starch retrograda-tion can be inhibited by using a starch complexing emulsifier with or without the addition of fat. Mould growth is inhibited by a low water activity. 

Notably, low water activity only inhibits mould growth. Most bakery products leave the oven in a sterile condition, any mould contamination is subsequent to baking. The effect of a low water activity is that the osmotic pressure is such that no mould spores can reproduce. Thus the product is safe unless the water activity rises locally. 

A few studies have been performed examining the resistance of acetylated wood to mould and stain fungi in a laboratory environment (Wakeling etal., 1991, 1992). These studies found that acetylation reduced the rate of mould growth, but at the end of the test there was no difference in the extent of colonization. Furthermore, samples modified to a WPG of 10 % exhibited a higher rate of colonization for reasons that were not clear. Samples acetylated up to a WPG of 20 % did not exhibit any improvement in performance in terms of mould growth, compared to unmodified samples, when exposed in a field trial. 

Mycotoxins are toxic secondary metabolites produced by fungi growing within or on foods. They can be a serious threat to human and animal health (Nagler el al., 2001). Table 11.4 details mycotoxins associated with soft drinks and fruit juice manufacture and raw materials. Patulin is the most common mycotoxin associated with fruit juice, particular ly apple juice (Pitt Hocking, 1997). It commonly occurs if juice is produced from stored apples. Mould growth in infected apples increases with time, raising levels of patulin. The use of windfall apples for juice is also a factor. Avoidance of windfall apples, filtration of juice and pressing quickly after harvest are all methods to reduce the incidence of patulin in juice. Patulin can be destroyed by fermentation to cider or by the addition of ascorbic acid (Marth, 1992). Within Europe, the European Union has set a limit of 50 ig/kg for patulin in both apple juice and cider. A recent survey of apple products in Chile found that 28% of samples of juice and concentrate exceeded this limit (Canas Aranda, 1996). 

Various Antiseptics.—Arsenic or mercury compounds, carbolic acid, salicylic acid or thymol are sometimes added to inks to prevent fermentation and mould growth. 

Mycotoxins are defined as secondary metabolites of mould growth which are generally believed to be produced in response to stress factors acting on the fungus. Individual moulds, fungi or mycotoxins rarely occur in isolation... 

Equilibrium relative humidity studies have shown that cardamom dried and maintained at or below 10% moisture retains its original colour and avoids mould growth (Govindarajan et al., 1982). If black polyethylene is used, the effect of light is further minimized and safe storage is possible for... 

Lopez-Malo, A., Alzamora, S.M. and Argaiz, A. (1 998) Vanillin and pH synergistic effects on mould growth. Journal of Food Science 63, 143-146. 

Synthetic colours are normally so intense that they must be diluted considerably for them to be readily measured and dispersed into the product. If colour solutions are made up in the factory they have to be made up not more than 24 hours before use to avoid mould spoilage. The pre-prepared colour solutions have a permitted preservative or are made up in glycerine, propylene glycol or propan-2-ol. These non-aqueous solvents inhibit mould growth. 

Figure 9.8 describes a batch process for the production of Japanese soy sauce (koikuchi). Soybeans and defatted soybean meals are cooked in continuous pressure-cookers and mixed with roasted and coarsely broken wheat. The mass is inoculated with Aspergillus spores and incubated in shallow vats with perforated bottoms that allow air to be forced through the mass. After three days of incubation at around 30°C, mould growth covers the entire mass. This mass is called koji. Koji is the essential ingredient of most fermented products of East Asia. It is a concentrated source of enzymes necessary for breaking up the large molecules of the carbohydrates and proteins. 

Schmitz, S., Weidenborner, M. and Kunz, B. 1993. Herbs and spices as selective inhibitors of mould growth. Chem. Mikrobiol. Technol. Lebensm. 15 175-177. 

Marin, S., Guynot, M.E., Neira, R, Bernado, M., Sanchis, V., and Ramos, A.J. 2002. Risk assessment of the use of sub-optimal levels of weak-acid preservatives in the control of mould growth on bakery products. International Journal of Food Microbiology 79 203-211. 

A mould inhibitor in the form of sodium propionate was incorporated into films of cellulose acetate, the films were sandwiched between slices of bread and the sliced bread packed in LDPE bags and stored for 15 days at about 25C. The effect of the mould inhibitor on mould growth on the surface of the bread slices was investigated by means of microbiological analysis and water activity, moisture content and pH analyses. The presence of sodium propionate in the cellulose acetate films was found to have an inhibitoiy effect on microbial growth on the bread. 12 refs. 

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