D CONTROL (frozen fruits)

Summary

Signiﬁcant hazards a r No major hazards.

Control measures

Initial level (H 0 ) r Microbial populations on fruits to be frozen are best controlled by: adequate washing, removal of obviously diseased fruit, careful handling

to prevent bruises, frequent cleaning and sanitation of handling and conveying equipment and prompt freezing of the prepared fruit.

Reduction (ΣR)

r Sulphuring is of limited effectiveness.

Increase (ΣI)

r Frozen storage below −10 ◦

C will prevent all microbial growth, but does not necessarily lead to inactivation of microorganisms. r Time/temperature control needed before, during and after preparation,

and during transportation, storage and sale.

Testing

r Routine microbiological testing of fruit is not recommended. r Aerobic colony count and/or coliforms may be used to monitor process

control or to monitor potential temperature abuse. r Environmental testing for L. monocytogenes or indicators monitors the

potential for contamination. r Monitor equipment hygiene using tests such as ATP.

Spoilage

r No problems with microbial spoilage.

a Under particular circumstances, some hazards need to be considered.

VI Canned fruits

A Effects of processing on microorganisms Pasteurising heat processes are used for nearly all fruit products. Care is needed with low acid fruits

such as tomatoes, which in some countries are acidiﬁed to ensure a pH below 4.5 before processing (Lopez, 1971; Schoenemann and Lopez, 1975). Fruit products with pH values above 4.6 or a w above

0.85 are subjected to the sterilization process for low acid canned food, to kill spores of Cl. botulinum.

FRUITS AND FRUIT PRODUCTS

B Spoilage Bacteria. The saprophytic bacterial ﬂora of canned fruits is made up of mesophilic and thermoduric

spores, as vegetative cells have been destroyed by pasteurisation. Bacterial spoilage of canned fruits is rare, and due to butyric or thermophilic anaerobes. Butyric anaerobes such as Cl. pasteurianum can grow at pH 3.8 in syrups, and cause spoilage of pears by production of butyric acid, hydrogen, and carbon dioxide (Jakobsen and Jensen, 1975).

Underprocessing of tomato products can result in growth of thermoduric facultative anaerobes such as Bacillus coagulans, leading to ﬂat sour spoilage. Spoilage of tomato juice by B. coagulans is ac- companied by pH reduction, but not gas production and the taste of such spoiled products has been described as “medicinal”, “phenolic”, and “fruity” (Pederson and Becker, 1949). B. coagulans is common in soil and readily contaminates tomato processing lines. There is a direct relationship between the concentration of soil particles and number of B. coagulans spores in tank water used to wash tomatoes. This species can multiply in washing equipment, if introduction of cold water is insufﬁcient causing water temperatures to rise to 27 ◦ C–32 ◦

C (Fields, 1970; Segmiller and Evancho, 1992). The vegetative cells of some strains of B. coagulans can grow in tomato juices of pH 4.2, although heat-treated spores can only germinate and grow if juice pH is above 4.3 (Pederson and Becker, 1949).

Occasionally, heat tolerant lactobacilli have caused spoilage of canned tomato products (Gould, 1974).

Heat resistant fungi. Traditionally, mild heat processes have been used for acid foods such as fruits and fruit products. Pasteurisation at temperatures of 70 ◦ C–75 ◦

C is effective, as it inactivates most enzymes, yeasts and the spores of common contaminant fungi. However, fungi that produce ascospores are capable of surviving such processes and causing spoilage.

In practice, only a few species of heat resistant fungi have been isolated from fruit products after a heat process, and still fewer have been recorded as causing spoilage. Byssochlamys fulva and Bys. nivea head the list of species that spoil strawberries in cans or bottles (Hull, 1939; Put and Kruiswijk, 1964; Richardson, 1965), blended juices that contain passionfruit, and fruit gel baby foods (Hocking and Pitt, 1984). Neosartorya ﬁscheri has also been repeatedly isolated from strawberries (Kavanagh et al., 1963; McEvoy and Stuart, 1970) and other products, but has rarely been reported to cause spoilage. Talaromyces ﬂavus, Tal. Bacillisporus, and Eupenicillium species are other potential causes of spoilage in heat processed products (Hocking and Pitt, 1984).

The source of heat resistant fungal ascospores is soil. Juices particularly at risk from heat resistant fungi, are those made from pineapples, passionfruit and berries, where fruit frequently come in contact with soil before or during harvest (Cartwright and Hocking, 1984).

C Pathogens Canned fruits are among the safest processed foods. However, outbreaks of botulism have been

recorded from home canned fruits including pears, apricots, peaches, and tomatoes (Odlaug and Pﬂug, 1978). The usual underlying cause is an initial fruit pH above 4.5 coupled with under-processing. However, some instances of botulism from home canned fruits have resulted from growth of other microorganisms causing an increase in pH permitting Cl. botulinum to grow (Odlaug and Pﬂug, 1978). In commercial operations, pH is controlled to ensure a safe heat process and prevent such problems.

Although tomatoes are not a good substrate for growth of L. monocytogenes, cells inoculated into com- mercially processed tomato juice remained viable for periods exceeding the normal shelf-life (Beuchat and Brackett, 1991).

MICROORGANISMS IN FOODS 6

The presence of mycotoxins in canned fruit products is largely conﬁned to the formation of patulin in apple juice by Bys. nivea (Roland and Beuchat, 1984). Byssochlamys species have been reported to produce patulin in spoiled canned fruit, but only at very low levels. Tomato products can potentially become toxic due to tenuazonic acid from growth of Alternaria species, but such occurrences have not been well documented.

D CONTROL (frozen fruits)