D CONTROL (fermented and acidified fruits)

D CONTROL (fermented and acidified fruits)

Summary Significant hazards a r Foodborne illness from correctly fermented or acidified fruits is

extremely rare. r Formation of mycotoxins has not been reported.

Control measures

Initial level (H 0 )

r Does not apply.

Reduction (ΣR)

r Does not apply.

Increase (ΣI)

r Does not apply.

Testing

r Does not apply.

Spoilage

r Microbial spoilage can occur in some products and control depends on

appropriate processing techniques.

a Under particular circumstances, other hazards may need to be considered.

351 Control measures. Many of the control measures are similar to the good manufacturing practices used

FRUITS AND FRUIT PRODUCTS

for vegetables and the reader should consult the chapter on vegetables. Olives. Control of spoilage in fermented green olive production, depends initially on effective alkali

treatment followed by its complete removal. This is necessary to ensure adequate acid generation by lactic acid bacteria in low salt brines. Proper fermentation is also dependent on the controlled availability of a fermentable carbohydrate source. Proper brine concentrations and fermentation temperatures are needed to get the correct end-products of the fermentation. Maintenance of anaerobic conditions is essential to prevent growth of oxidative yeasts.

Cucumbers. Control of spoilage depends on correct brine concentrations, acidification, and pure starter cultures. Pasteurisation treatments need to be adequate and controlled. Clean handling is nec- essary to prevent excessive numbers of unwanted bacteria and yeasts that may overload the desirable fermentative bacteria and lead to spoilage. Preservative-resistant yeasts pose a special problem in unpas- teurised products; scrupulous cleanliness in the packing plant is the only effective control. Bloating is

controlled through the purging of fermentation vats to remove CO 2 and to introduce O 2 into the interior of the cucumber, as a means of accelerating gas exchange and thus increasing the rate of fermentation (Daeschel and Fleming, 1981; 1983).

IX Canned Tomato products

The main tomato products are canned foods such as canned tomatoes (whole, peeled or diced) with or without added juice, or packed in tomato pur´ee; tomato concentrates including tomato juice and tomato pastes; tomato powder; and formulated products such as salsa, tomato sauce (catsup or ketchup), soup and chili sauce.

A Effects of processing on microorganisms The tomato is considered to be an acidic raw material with a pH value generally 4.6 or less and so a rel-

atively mild heat treatment should render tomato products commercially sterile. The acid content of the products to prevent growth of bacterial spores, including those of Cl. botulinum. However, the acidity of tomatoes has decreased in recent decades and mechanical harvesting results in a higher load of microor- ganisms than in handpicked fruit. If spoilage is to be prevented, tomatoes would have to be processed sufficiently such that adverse quality changes will result. Acidification of canned tomato products has proved a practical solution to this problem (Lopez, 1971; Schoenemann and Lopez, 1975; Powers, 1976).

For processing of tomato juice various methods are employed including: retorting of packaged product under pressure, atmospheric processing under agitation or in still conditions, and hot filling followed by atmospheric processing in a steam tunnel (Gould, 1974). Agitating product and processing under pressure results in shorter process times. Atmospheric processing destroys microorganisms with low heat resistance, but is inadequate to destroy heat resistant flat sour bacterial spores. Bulk sterilisation,

i.e. use of a flash steriliser followed by hot filling, holding, and water-cooling, is used to destroy flat sour spores. More recently aseptic packing after sterilisation has also been used.

B Spoilage Spoilage of canned tomatoes may occur because of under processing or leakage.

The bacteria usually found on tomatoes are lactobacilli and other relatively heat sensitive genera. Therefore, spoilage due to under processing is caused predominantly by aciduric spore formers such as

MICROORGANISMS IN FOODS 6

The taste of tomato juice spoiled by aciduric flat sour spoilage is described as “medicinal”, “phenolic” or “fruity”, and this taste is usually accompanied by a reduction in pH. Ends of cans of spoiled product remain flat.

Bacillus coagulans is a common soil bacterium. The vegetative cells of some strains can grow in tomato juices of pH 4.15–4.25, however, heated spores could not germinate and grow in tomato juice adjusted to a pH lower than 4.3 (Pederson and Becker, 1949).

A definite relationship exists between the concentration of soil particles and the number of flat sour spores in water from tomato soaking tanks. These bacteria have been found to multiply in equipment for tomato washing where the volume of cold water is insufficient and water temperatures rise to 27 ◦ C

C. Spores have been isolated from various points in tomato canneries (Fields, 1970; Segmiller and Evancho, 1992). “Machinery mould”, Geo. candidum (= Oidium lactis) may be a contaminant in tomato juice plants with poor sanitation and is the dominant mould on tomato processing equipment. Bacillus coagulans may be able to grow and produce spores in tomato juice in which this mould has grown (Fields, 1962).

Less frequently, other types of microbial spoilage occur, in particular swollen cans caused by some heat tolerant species of Lactobacillaceae (Gould, 1974).

C Pathogens The heat treatment of tomato products should be designed to inactivate vegetative and spore forming

bacteria capable of multiplication in the product. With product of pH 4.5 or less, the growth of Cl. botulinum spores will be inhibited. However, aciduric Bacillus species capable of elevating the pH of tomato juice, can sometimes be isolated from soil and natural vegetable materials (Al-Dujaili and Anderson, 1991). Instances of botulism from home canned tomatoes were apparently related to visible mould growth that had caused a pH rise sufficient to permit growth of Cl. botulinum spores.

Tomatoes are not a favourable substrate for growth of L. monocytogenes. Nevertheless, cells of L. monocytogenes inoculated into commercially processed tomato juice and sauce, remained viable for periods exceeding normal product shelf-life (Beuchat and Brackett, 1991).