D CONTROL (mushrooms)
D CONTROL (mushrooms)
Summary
Significant hazards
r Cl. botulinum. r Staph. aureus enterotoxin (canned mushrooms). r Enteric bacterial pathogens.
Control measures
Initial level (H 0 )
r Pasteurize compost for mushroom growing beds. r Monitor environment for pathogens.
Increase (ΣI) r Maintain aerobic packaging for fresh mushrooms (Cl. botulinum). r Prohibit or chill (<10 ◦
C) brine for mushroom harvest (Staph. aureus). r Train food handlers on importance of personal hygiene.
r Control hydration time for dried mushrooms. Reduction (ΣR)
r Use appropriate canning procedures for canned mushrooms. r Use in cooked applications if source does not control for pathogens.
Testing
E. coli may be an indicator of fecal contamination for fresh. r No other microbiological tests are recommended for routine surveillance.
Spoilage
r Controls used for pathogens effectively control spoilage organisms, especially pasteurization of compost growing beds.
General considerations. Correct preparation of the growing bed through proper fermentation and heat treatment to pasteurize the compost is essential to prevent crop loss from mushroom pathogens. During mushroom growth, steps should be taken to prevent access of flies, mites, and rodents to the compost bed. At the end of the growing cycle, the entire growing structure should be disinfected using live steam, to eliminate viruses and other mushroom pathogens.
When harvesting, personal hygiene must be practiced by pickers to prevent transfer of human pathogens. Mushrooms must be handled carefully at all stages to prevent bruising. Where brine is used to preserve fresh mushrooms until they reach canning collection stations, it should be chilled (<10 ◦
C) to prevent growth of Staph. aureus. Only clean washing water should be used at collection stations. Frequent cleaning and disinfection of tables, conveyors, and screens are essential to prevent the build-up of debris and spread of spoilage microorganisms.
An acid vacuum-chelation process is claimed to improve color and texture of canned mushrooms by permitting a slightly reduced process, without risk of botulinal survival and toxigenesis. It involves acidification of vacuum-hydrated mushrooms by blanching in 0.05 M citric acid solution (pH 3.5)
and the addition of the equivalent of 200 ppm CaNa 2 -EDTA to the canning brine (Okereke et al., 1990).
MICROORGANISMS IN FOODS 6
Testing. If fresh mushrooms are to be used without cooking, tests for E. coli as an indicator of fecal contamination may be appropriate. No other microbiological tests are recommended for routine surveillance of fresh, dried, marinated, or canned mushrooms.
Spoilage. Controls used for pathogens effectively control spoilage organisms, especially pasteurization of compost growing beds.
XI Cassava
Cassava (tapioca) is a staple food in many countries and there are many recipes for its use, including fresh cassava, beiju (fermented), sour cassava starch, chips, and gari.
Cassava processing is generally done under conditions where the application of sophisticated control technologies is impractical. Gari goes through fermentation and other processing steps before drying (Steinkraus, 1989a). In Zaire, cassava tubers are dug, peeled, retted (rotted in water), drained, pounded and pulped, transported for defibering, and made into bread (chikwangue) by kneading, precooking, kneading again, wrapping in leaves, and cooking for up to 120 min (Regez et al., 1987). Another fermented product made from cassava is “Tapai ubi” (Malaysia) or “Tape ketella” (Indonesia). This is produced using cassava as the substrate with a starter culture (“ragi”). Another substrate commonly used is glutinous rice (Steinkraus (1983, 1989b).
A Effects of harvesting, transportation, processing, and storage on microorganisms Sampling of the cassava processing from three regions of Zaire revealed average aerobic colony popu-
lation of 2 × l0 8 cfu/g at the retted tuber stage, diminishing to <1 × l0 2 cfu/g for fresh bread, and rising to 1 × l0 9 cfu/g after 7 days of storage. During retting, the population of Bacillus spp., lactic bacteria (Leuconostoc spp. and Lactobacillus spp.), and Corynebacterium spp. reached levels of 1 × l0 9 cfu/g, almost disappeared on cooking, and then rose slowly to about 5 × l0 4 cfu/g after 3 days of storage (Okafor et al., 1984). Microorganisms play an important role in the texture and flavor of traditional cassava products; therefore, high levels of aerobic and lactic bacteria during processing are not viewed as a sign of bad processing or a health risk (Okafor et al., 1984). Lactic acid bacteria predominate, al- though yeasts and clostridia are observed (Brauman et al., 1996). The lactic acid fermentation generated ethanol and lactic acid (Brauman et al., 1996).
Leaves used for wrapping the dough are often dirty, and are an obvious source of contamination. Up to 4 × 10 5 cfu/mL coliforms (Klebsiella spp.) were detected in all samples of water used for retting, and up to 8 × l0 3 cfu/g in cassava pulp, but not in fresh or stored bread. This is not unusual because coliforms occur naturally in plant material and baking reaches temperatures that destroy vegetative microbes.
8 The high fungal population in retted tubers (3 × l0 2 cfu/g) fell below 1 × l0 cfu/g after cooking, but rose to 3 × 10 7 cfu/g after 7 days of storage. Molds are the main factor limiting the shelf life of cassava products, but there is also the risk of the production of mycotoxins.
In Tanzania, use of a Lb. plantarum starter culture for fermentation of cassava flour resulted in a higher quality product and reduced levels of Enterobacteriaceae, yeast, and molds during fermentation, when compared with the use of 5% inoculum from the previous spontaneous fermentation (Kimaryo et al., 2000). Starter culture usage may provide more consistent control in the production of cassava flour.
Aflatoxins have been reported in various cassava products (Masimango and Kalengayi, 1982), but these and other reported detection of aflatoxins appear to be artifacts of the analytical method.
VEGETABLES AND VEGETABLE PRODUCTS