D CONTROL (canned fruits)

Summary Signiﬁcant hazards a r If product has a pH > 4.5, then Cl. botulinum must be considered.

r Patulin in apple juice (Byss. nivea)

Control measures

Initial level (H 0 ) r Control of raw materials through approved supplier programme. r Apply GMP throughout the handling and processing chain. r Bacterial spoilage of correctly processed products only occurs when

initial spore numbers are exceptionally high. r Adequate cleaning of process lines and equipment should prevent such

occurrences.

Reduction (ΣR) r Application of HACCP principles for canning of low acid and acidiﬁed

fruits.

Increase (ΣI) r Holding canned products at elevated temperatures and observing for swells

before release.

Testing

r Testing suspected cans to identify cause of spoilage. r Monitoring levels of thermopiles in raw material and ingredients is

useful if products are likely to be held at elevated temperatures.

Spoilage

r Cl. pasteurianum, B. coagulans, heat resistant fungi r Control of spoilage of canned pears by Cl. pasteurianum relies on a

combination of adjusting the pH to 3.8–4.0, reducing a w to 0.97–0.98 by use of sugar syrup, and an appropriate heat treatment (Jakobsen and Jensen, 1975).

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

Control measures Fungi. Some types of fruit, e.g. berries, pineapple, mango, and passionfruit, may become contam-

inated with soil and hence with heat resistant fungal ascospores. It is usually not practical to increase pasteurisation processes to a level where heat resistant fungal spores can be destroyed, because the organoleptic properties of the fruit will be impaired. For the fruits mentioned, control requires the monitoring of juices used as raw materials for the presence of heat resistant ascospores. Speciﬁcations for raw materials are often set as low as one heat resistant ascospore per 100 ml. Raw materials not meeting such speciﬁcations, are either rejected or usedjin alternative ways such as in frozen products (Cartwright and Hocking, 1984; Hocking and Pitt, 1984).

C for 30 min, then incubating the samples, with or without the addition of an agar medium, for up to 4 weeks. Heat resistant

Monitoring raw materials for heat resistant fungi involves heating samples at 75 ◦

345 spoilage fungi, such as Byssochlamys, Talaromyces, Neosartorya, and Eupenicillium species can be

FRUITS AND FRUIT PRODUCTS

selectively detected in this manner. Culture methods were outlined by Beuchat and Rice (1979). Two methods are recommended: a plating method, ﬁrst described by Murdock and Hatcher (1978) adapted for larger samples (Pitt and Hocking, 1997) and the second, a direct incubation method (Hocking and Pitt, 1984; Pitt and Hocking, 1997).

VII Dried fruits

A Effects of processing on microorganisms Sulphured tree and vine fruits. Some types of fruits, e.g. peaches, apricots, pears, and bananas, are

treated with high levels of sulphur dioxide before drying, which is essential to preserve fruit appearance by preventing browning from the Maillard reaction The SO 2 also completely eliminates the microﬂora, even during prolonged storage. Rehydration to produce moist packs usually does not change this situation. Such products have no microbiology and will not be considered further. However, some “natural” fruits of these types are dried without sulphur dioxide and the remarks in the following sec- tions apply. Such fruits are identiﬁable by a general brown colouration due to products of the Maillard reaction.

Unsulphured fruits. Fruits that are not treated with SO 2 include prunes, dates, figs, and vine fruits. The microbiology of processing these fruits is described below. Fruits are often washed before processing and some types are treated with alkaline detergent solutions to strip surface wax and speed water removal. The subsequent dehydration process used influences the microflora of the dried product. Sun drying, used extensively for certain fruits throughout the world, is subjected to the vagaries of the weather. Strong sunlight will greatly reduce initial microflora. Only black spored Aspergillus species are capable of survival, with consequent potential for ochratoxin A production. However poor drying conditions can cause proliferation of yeasts and filamentous fungi, especially Penicillium species.

Mechanical dehydration reduces the total microbial load, but the extent of the reduction depends both on the type of fruit and the severity of the process. For example, low temperature drying of ﬁgs, at

C, reduced but did not eliminate yeasts (Natarajan et al., 1948). In contrast, prunes are dried at 70 ◦ C–80 ◦

54 ◦ C–60 ◦

C, a process that results in commercial sterility (Miller et al., 1963). However prunes are readily recontaminated during subsequent handling (Pitt and Christian, 1968; Pitt and Hocking, 1997). Figs are usually sun dried, often on the ground where they fall, allowing ample time for growth of fungi. Aspergillus flavus is important, as aflatoxins are readily produced in figs. Inoculation of firm, ripe figs with spores of Asp. flavus produced fungal growth and aflatoxin formation within two days (Boudra et al., 1994).

Moist packs. To satisfy consumer demands for more palatable ready-to-eat foods, dried fruits are often rehydrated to 0.85–0.90 a w , before packing. The dried fruits are reprocessed in hot or boiling water baths, which effectively destroys the microﬂora. Sulphured fruits will usually retain enough SO 2

to remain stable, if well packed. However, dates, ﬁgs, and prunes processed without SO 2 are prone to recontamination after cooking. Many countries now permit the addition of weak acid preservatives such as sorbic or benzoic acid to such packs to ensure microbial stability.

Glac´e fruits. Glac´e fruits are produced by infusing blanched fruit with increasingly concentrated glucose syrups that contain SO 2 as a preservative. After this treatment, fruits are usually given a low

MICROORGANISMS IN FOODS 6

temperature dehydration process to reduce a w to about 0.85. The initial microﬂora is largely destroyed by this process.

B Spoilage Unsulphured fruits. Fruits that are not treated with SO 2 , are susceptible to spoilage by xerophilic

fungi. However, if fruits are properly dried and stored, the extent of damage should be slight. Australian vine fruits that are sun dried and not preserved with SO 2 are usually contaminated with Asp. niger and closely related species, which may grow to some extent during drying (King et al., 1981, Leong et al., 2004). Other fungi are much less common. Californian vine fruits are also dried in the sun, but without the elevated drying racks used in Australia as a protection against rain and surface water. Losses in the occasional rainy drying season in inland California can be catastrophic.

Poor factory hygienic conditions may result in contamination of dried fruits, during packaging. In particular, the extreme xerophile Xeromyces bisporus, which is able to grow quite rapidly at 0.70–

0.75 a w , may build up on conveyers and other equipment, be transferred to the fruits and then cause spoilage of products, which is safe from all other fungi (Pitt and Hocking, 1982, 1997). Mature ﬁgs are always contaminated in the seed cavity by yeasts (Miller and Phaff, 1962). Spoilage of dried ﬁgs sometimes occurs, if these contaminant yeasts include xerophilic species.

Ready to eat packs. Nearly every known xerophilic fungus was isolated from Australian dried and high moisture prunes by Pitt and Christian (1968). At that time, microbial stability of this product relied on hot ﬁlling into packages. The most common fungi isolated were Eurotium species, especially Eur. herbariorum, Xer. bisporus, and xerophilic Chrysosporium species. Moistened ready-to-eat prunes and dates are now commonly preserved with benzoic or sorbic acids, which prevent fungal growth.

Glacé fruits. Sulphur dioxide used as a preservative in the glacé fruit process, is only partially effective, as free SO 2 is rapidly bound by glucose. Partially prepared glacé pineapple may spoil due to the growth of the yeast Schizosaccharomyces pombe. This species apparently possesses a unique combination of resistance to SO 2 and ability to grow at reduced a w , enabling it to grow at a particular point in the infusion process (Pitt and Hocking, 1997).

C Pathogens Bacterial pathogens. Survival of pathogenic bacteria on dried fruits is usually poor, and limited to a

few weeks. Relatively long storage periods before sale, normal for such products, further minimises risks. However, E. coli O157:non-H7 has been isolated from one sample of conventionally grown imported raisin and one sample of organically grown imported apricot (Johannessen et al. 1999).

Mycotoxins. The possibility of mycotoxin production in high moisture unsulphured dried fruit (above

0.85 a w ) exists, but has not been reported to be signiﬁcant. Growth of Asp. carbonarius, a black Aspergillus species, on grapes before or during drying, can lead to production of ochratoxin A. Formation of ochratoxin A by Asp. carbonarius (and a few isolates of the closely related species Asp. niger) was discovered only recently (Abarca et al., 1994; T´eren et al., 1996; Heenan et al., 1998). Infection of grapes by black Aspergillus species occurs in the vineyard as the result of insect or mechanical penetration, splitting due to rain before harvest, or infection by pathogenic fungi such as Botrytis or Rhizopus ( Snowdon, 1990; Leong et al., 2004).

Aflatoxins have been a cause for concern in dried figs for a number of years, because the fungus carried in by insects, is able to penetrate the fruits before harvest (Buchanan et al., 1975). Unacceptable levels have been reported in dried figs from Turkey and Greece (Masson and Meier, 1988; Reichert et al.,

347 1988; Boyacioglu and Gonul, 1990; ¨ Ozay and Alperden, 1991; Sharman et al., 1991) and Syria (Haydar

FRUITS AND FRUIT PRODUCTS

et al., 1990), but not Pakistan (Shah and Hamid, 1989). As with peanuts, aflatoxins are not uniformly distributed, usually being present in a low proportion of the figs. Percentages containing significant levels (usually 10 ug/kg or more) were reported as 1% (Steiner et al., 1988), 2–4% (Boyacioglu and Gonul, 1990), or sometimes higher, 7% (Masson and Meier, 1988), 24% (Sharman et al., 1991), or 29%

(¨ Ozay and Alperden, 1991). The highest levels of aﬂatoxin B 1 found in individual fruit ranged from

12 µg/kg (Haydar et al., 1990) to 63 µg/kg ( ¨Ozay and Alperden, 1991), 112 µg/kg (Boyacioglu and Gonul, 1990) and 165 µg/kg (Sharman et al., 1991). Figs can also be contaminated by ochratoxin A. Figs with “ﬁg smut”, which have been infected with black Aspergillus species, including Asp. carbonarius, sometimes contain unacceptable levels of this toxin ( ¨ Ozay and Alperden, 1991; Doster et al., 1996).

D CONTROL (canned fruits)