D CONTROL (flours, starches and meals)

D CONTROL (flours, starches and meals)

Summary

Significant hazards

r Mycotoxins as for grains. r Salmonella.

Control measures

Initial level (H 0 ) r Use grain harvested from areas with minimal crop stress to control

mycotoxins. r Test for mycotoxins as appropriate (refer to section in grains).

Increase (ΣI) r Maintain grain and flour at <12% moisture for mycotoxin control. r Maintain processing facilities dry condition with a minimal use of water. r Use dry cleaning methods for machinery.

Reduction (ΣR) r Tempering grain in chlorinated water before milling may slightly reduce

hazard levels. r Some decrease in mycotoxins occurs during processing.

Testing

r Visual observation for fungal growth, product damage and insect

infestation in incoming grain. r Ultraviolet screening of maize.

r Test for mycotoxins in incoming grain where appropriate. r Environmental monitoring for salmonellae. r Coliforms are not a useful an indicator. r Spore-forming bacteria when used in canned products.

Spoilage

r Control measures that prevent mycotoxin production control most spoilage

fungi and bacteria.

Control measures. The most important control method in flour manufacture is the control of moisture in the grain, in the equipment and in the processing environment. Properly dried grain (<14%) effectively inhibits the growth of bacteria and fungi, which can produce mycotoxins. There are no processing steps that effectively eliminate biological hazards in the production of flour and meal, however, the following procedures should be implemented to reduce the prevalence of potential hazards in this raw commodity.

Tempering of grains for flour manufacture may be carried out in chlorinated water if particularly low levels of microorganisms are desired. This has minimal effect because chlorine is readily inactivated by the organic material present. Milling machinery should be cleaned regularly to avoid accumulation of static material, where fungi and insects thrive. Cleaning of all dry product areas should be done without using water. The flour should contain no more than 15%, and preferably no more than 14% water, in order to reduce fungal growth. Mills should have a program of rodent and insect control and should avoid condensation of moisture where it can drop back into the product or accumulate on the sides of bins, hoppers, conveyors, etc.

After boots and elevators in the flour system have been fumigated, they should be cleaned immediately to remove the insects, which otherwise will decompose and contribute large numbers of microorganisms to the flour.

413 Testing. Visual observation for fungal growth, product damage and insect infestation in incoming

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grain can identify conditions that contribute to formation of mycotoxins. Ultraviolet screening of maize is a particularly useful tool for identification of pockets of fungal growth. Mycotoxin tests of incoming grain may be appropriate in regions with persistent mycotoxin problems or in years when conditions are likely to contribute to mycotoxin formation.

Salmonellae are capable of becoming established in wet or moist locations in flour or grain processing facilities. Manufacturing environmental monitoring is useful to prevent establishment of harborage sites for salmonellae. The focus of environmental sampling should be in wet or moist locations, such as tempering areas and condensation, and accumulated static material in equipment.

Use of coliforms as an indicator is of little value because of natural variation in the incoming materials and lack of processing steps to reduce levels. Starches that are used in canned products require low levels of spores to prevent spoilage after processing.

V Dough

A Effect of processing on microorganism Dough is a stiff mixture of flour, liquid, and/or fat and other ingredients used to make a wide variety of

baked, boiled or fried products. Dough is made primarily from wheat flour, however, flour, and meal from other grains are often used around the world. Rice is a notable example used in Asian cultures. Other starchy, non-cereal commodities such as potato, cassava, and soy may also be used to prepare dough. Subsequent sections on breads, pasta, and pastry describe unique features of specific dough products in greater detail. This section summarizes common features of dough.

The addition of water to dried flour or meal provides a substrate that readily supports microbial growth. Yeasts are used to leaven dough, but the addition of water to flour and meal may also provide an opportunity for spoilage and pathogen growth if controls are not implemented. Temperature, water activity and competitive exclusion are the primary controlling factors.

Processing temperature has a major impact on the handling characteristics of dough, and also on the potential for microbial growth. Soft, pliable, moist doughs, and high fat doughs are frequently handled at cool temperatures (ca. 15 ◦ C). Conversely, stiff dry dough may be handled at warmer temperature (30 ◦ –40 ◦

C) for functional purposes, e.g. yeast dough is held at these warmer temperatures to stimulate yeast activity. Bacterial pathogens are not a hazard of concern in yeast-leavened dough because of competitive exclusion. Although Staphylococcus aureus is rarely isolated from wheat flour (Richter et al., 1993), it is a potential concern in dough processed at warmer temperatures without yeasts if the water activity is favorable for growth.

A modern development is the baking of bread in specialist retail bread shops. Bread doughs mixed in

a central facility are frozen and distributed to retail outlets, where they may be held frozen or defrosted, proofed, and baked immediately. Such frozen doughs may also be sold direct to consumers, in which case they contain high yeast populations to permit a frozen storage life as long as 18 weeks while maintaining adequate fermentative activity (Kulp, 1991). In many western countries, chilled raw or partially baked doughs designed to be finished by the consumer have also become popular. The products are mostly breads and rolls, cookies, pizza, and baking powder biscuits, primarily packaged in hermetically sealed cardboard, plastic film and metal containers. All chilled doughs are chemically leavened, usually by sodium acid pyrophosphate and sodium bicarbonate. Yeast action may continue during storage and burst the containers (Lannuier and Matz, 1967; Lamprech, 1968). Whereas most doughs are baked

MICROORGANISMS IN FOODS 6

immediately, chilled doughs are sometimes held for prolonged periods at temperatures suitable for fungal growth. Water activity of chilled dough ranges from <0.80 in cookie dough to ca. 0.94–0.95 in roll and biscuit dough. Fungal and bacterial counts in the doughs are low unless ingredients are highly contaminated or microbial growth occurs during temperature abuse of higher a w dough. Sources of contamination can be the flour, dry milk, eggs, sugar, spices, water, flavors and the dough-making equipment (Deibel and Swanson, 2000). Usually the fungal flora of the dough is a reflection of that of the flour (Graves and Hesseltine, 1966). Bacterial levels in fresh dough products vary widely, from

10 3 /g in dinner rolls to l0 8 /g (lactic acid bacteria) in buttermilk biscuits. All fresh doughs contain wild yeasts (Hesseltine et al., 1969).

B Spoilage Spoilage is not an issue for dough used immediately after preparation. Doughs in cool storage owe their

stability to the following factors (Lannuier and Matz, 1967; Lamprech, 1968). r Conditions are anaerobic, thus inhibiting the growth of filamentous fungi and aerobic bacteria.

r The leavening agent produces CO 2 .

r Formulations are designed to attain a low a w . r Refrigeration slows microbial and enzyme activity. r Manufacturers have strict microbiological specifications for ingredients and maintain faultless sani-

tation in the manufacturing operation. If well controlled, the lactic acid bacteria in doughs produce quality sourdough breads. On the other

hand, if they are permitted to multiply excessively in refrigerated doughs, packages may split open or burst owing to gas pressure, revealing dough with undesirable odor and flavor (Lannuier and Matz, 1967; Hesseltine et al., 1969). Spoiled doughs contain the kinds of flora listed in Table 8.10.

Fungi are rarely involved in the spoilage of refrigerated doughs, even after 6–7 months of storage. Fungal counts usually remain at similar levels in stored doughs as those in freshly prepared doughs (Graves and Hesseltine, 1966).

C Pathogens and toxins Refrigerated doughs may contain Salmonella species if ingredients such as eggs are contaminated. Dried

yeast preparations also sometimes contain salmonellae. B. cereus is a fairly common contaminant of refrigerated doughs (Rogers, 1978), but there appear to be no reports of food poisoning attributable to this source. Mycotoxins present in the original flour will probably persist. Temperatures required to set the dough structure of baked dough products inactivate vegetative pathogens. The low levels of

B. cereus found in flour are also likely to be inactivated during baking (Kaur, 1986).

Table 8.10 Bacteria isolated from spoiled doughs Species

Percentage Leuconostoc mesenteroides

No. of isolates

Leuc. dextranicum

Lactobacillus spp.

Streptococcus spp.

Bacillus spp.

Micrococcus spp.

Gram-negative rods

From Hesseltine et al. (1969).

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