Prepackaged fresh-cut fruits that have been peeled or cut in a raw state, ready-to-eat, and unpasteur- ized fresh juices are one category of minimally pro- cessed foods. Among problems that limit the shelf life and commercial development of fresh-cut fruit are browning, softening, flaccidity (loss of water), microbial decay, and safety (King and Bolin, 1989; Rajkowski and Baldwin, 2003).
The pH of many fruits is lower than 4.0. This low pH, combined with the presence of organic acids, generally prevents the growth of pathogenic bac- teria. Therefore, incidents of outbreaks and cases of fruit-borne microbiological diseases are low as compared to those of other foods (Beuchat, 1996). However, changes are taking place in agricultural practices: greater use of animal waste and munici- pal waste on land; an increasing use of fruits grown in and transported from all parts of the world. All these changes including development of novel types
7 Minimally Processed Fruits and Fruit Products and Their Safety 121
Table 7.2. Suggested Parameters for MAP of Fruits Regarding Their Temperature Sensitivity
(Gorris, 2000)
Type of Product Temperature (◦C) RH (%) O2(%) CO2(%)
Fruit (cool ripened)
Apple 1–4 90–95 1–3 0–6
Pear 0–1 90–95 2–3 0–2
Fruit (cool ripened)
Apricot 0–1 90 2–5 0–2 Blackberry 0–2 90 Cherry 0–2 85–90 Currant red 0–1 90 5–10 Grape 1–2 90 Kiwi 0–2 85–90 3–5 Peach 0–2 85–90 1–2 5 Plum 0–1 85–90 2 2–5 Raspberry 0–1 85–90 Strawberry 0–1 90
Fruit (warm ripened)
Avocado 12–13 90 2–3 4–7
Banana 12–14 85–95 2–3 8
Fruit (warm ripened)
Mango 8–12 90 2–5
Pineapple 11–13 85–90 2–4 5–10
Fruit (cool-ripened citrus product)
Grapefruits 10–16 90 5–10 0–1
Lemon 3–5 85–90 5–10 0–1
Mandarin 1–4 85–90 5–10 0–1
Orange 1–6 85–90 5–10 0–1
of product may give rise to new problems (Lund and Snowdon, 2000; Beuchat, 2002; Rajkowski and Baldwin, 2003). Conditions during the growth of fruits and their handling influence contamination and affect the microbiological safety of fruits and fruit products. Major sources of microbiological contam- ination are animal feces, biosolids, or contaminated water used (Beuchat, 1996; Ait and Hassani, 1999). Fruits should not be collected from orchard grounds used for grazing. Following production, the processes of harvesting, washing, cutting, slicing, packaging, and shipping can create additional conditions where contamination can occur.
The formation of a mycotoxin, patulin, by the mold Penicillium expansum in rots occurring in apples is a major problem in the production of apple juice (Stratford et al., 2000).
If acidic fruits and fruit products are contaminated with certain pathogenic bacteria, then they may sur- vive for a sufficient time to cause disease (Miller and Kasper, 1994; Parish, 1997). Unpasteurized juices
from apple and citrus have been commercially avail- able for many years and have a record of safety problems (Rajkowski and Baldwin, 2003). Contam- ination of apples with manure from grazing cattle was probably the cause of outbreaks of infection with Salmonella, Escherichia coli O157, and Cryp- tosporidium parvum, a parasitic protozoon, associ- ated with unpasteurized apple juice and apple cider (Besser et al., 1993; McLellan and Splittstoesser, 1996; Centers for Disease Control and Prevention, 1997). Similarly, oranges that have fallen to the ground and contaminated with Salmonella and have been processed without adequate washing were sus- pected as the cause of infection associated with un- pasteurized orange juice. Consumers, particularly the young, elderly, or immunocompromised for any rea- son, are now warned by government advisories that drinking unpasteurized fruit drinks can make them ill (Tauxe et al., 1997).
Escherichia coli O157:H7 appears to have ac- quired a Shigella-like toxin gene and is capable of
causing illness from a very low infective dose. Infec- tions can cause death from hemorrhagic colitis and hemolytic uremic syndrome. The bacterium has been associated with animal feces from many sources, in- cluding cattle. Escherichia coli O157:H7 is acid tol- erant, and its viability may remain for weeks in apple cider (Zhao et al., 1993). The bacterium is heat sen- sitive; its D value in apple juice proved to be 18 min at 52◦C (Splittstoesser et al., 1995).
Some less acidic fruit products may even permit the growth of certain pathogens and may be thereby a potential source of microbiological disease of the consumer (Zhuang et al., 2003). The pH of can- taloupe and honeydew melons is between 6.2 and 6.7 and that of watermelons and papaya is between 5.8 and 6.0 and between pH 4.5 and 6.0, respectively (Splittstoesser, 1996). Because melons are grown on the ground, it is difficult to prevent contamination with microorganisms. If melons with a contaminated rind are cut, then the edible part may be contami- nated by the cutting knife and maintenance of the cut melon at ambient temperature can also result in the growth of pathogenic bacteria. Salmonella spp. and Shigella spp. have been shown to multiply on the cut surface of these produce at 23◦C (Escartin et al., 1989; Golden et al., 1993). Escherichia coli O157:H7 multiplied on cubes of cantaloupe and wa- termelon at 25◦C and high humidity (Del Rosario and Beuchat, 1995). Even Campylobacter jejuni was re- ported to survive on sliced watermelon and papaya for sufficient time to present a risk to the consumer (Castillo and Escartin, 1994). When fresh-cut mel- ons were inoculated with C. botulinum, then treated with UV light to inactivate vegetative microorgan- isms, and packaged using passive MAP, storage re- sulted in marginal spoilage and botulinal toxin for- mation (Larson and Johnson, 1999).
The growth of C. botulinum was also demonstrated in fresh tomatoes with metabolic association of fungi Fusarium, Alternaria, and Rhizoctonia (Draughon et al., 1988). Transfer of Salmonella Montevideo into the inner tissue of tomato by cutting has also been demonstrated (Lin and Wei, 1997). Salmonella spp. have been reported to multiply at 22–25◦C on the cut surface of tomatoes with a pH between 3.99 and 4.37 (Asplund and Nurmi, 1991; Wei et al., 1995). L. monocytogenes was able to maintain its original population density numbers in chopped tomatoes for up to 2 weeks of storage at 10 or 21◦C (Beuchat and Brackett, 1991). All these observations also reflect the importance of cold temperature chain manage- ment.
The possible use of certain plant volatiles to pre- vent microbial growth, thereby improving the shelf life and safety of minimally processed fruits, have been widely investigated recently in response to con- sumer pressure to eliminate chemically synthesized additives. Literature data (Lanciotti et al., 2004) in- dicate that aroma compounds and their combination with other hurdles such as CO2, mild heat treatment, pH reduction, etc., can represent useful tools to in- crease shelf life and safety of specific minimally pro- cessed fruits. The in vitro efficacy of a number of plant volatiles has been demonstrated, e.g., Utama et al. (2002); however, their application potential may also be limited by their eventual phytotoxicity and human toxicity.
Using certain lactic acid bacteria to improve the microbial safety of minimally processed refrigerated fruits and vegetables, e.g., fruit-based salads through competitive inhibition of pathogenic bacteria, also in combination with other hurdles, seems to be a promising research field (Breidt and Fleming, 1997). Due to the above-mentioned problems, prevention of microbial contamination of fresh fruits is impor- tant to control microbiological safety of them or of their products. To minimize these hazards, growers, packers, and shippers should use good agricultural and management practice (FDA, 1998). In 1998, the FDA issued guides, which describe good agri- cultural and manufacturing practices for fresh fruits and vegetables covering water quality, manure man- agement, worker training, field and facility sanita- tion, and transportation (FDA, 2001). Kvenberg et al. (2000) developed a generic hazard analysis critical control points (HACCP) plan mandated for the pro- duction of fruit and vegetable juices.
Antimicrobial Agents in Wash Water
Washing with water can reduce the number of mi- croorganisms on the produce. However, when an- timicrobial agents such as chlorine are used in wash water in usual concentrations (e.g., 100 mg free chlo- rine per liter at pH 6.5–7.0 for 20 min), the reduction may only be of the order of 10- to 100-fold (Beuchat, 1998; Beuchat et al., 1998; FDA, 1998). The antibac- terial activity of chlorine solutions is mainly due to hypochlorous acid and it is influenced strongly by the pH of the solution. A pH of 6.5–7.0 is suitable. Be- low a pH of 6.0, the hypochlorite solutions become too unstable for use. In addition to chlorine, treat- ments with chlorine dioxide, trisodium phosphate, organic acids, hydrogen peroxide, and ozone have
7 Minimally Processed Fruits and Fruit Products and Their Safety 123 also been investigated as alternative antimicrobial
chemicals; however, none of them appears to be more effective than chlorine for decontamination of fruits (Lund and Snowdon, 2000; Sapers, 2003). This role of chlorine is mainly to prevent the spread of bac- teria in the wash water rather than to kill them on the surface of the fruit. Golden et al. (1993) showed that chlorinated water reduced but did not eliminate Salmonella contamination once it was on the rind of melon. They concluded that chlorine was only a risk reduction factor, and other preventive measures were needed to further reduce the risk of Salmonella on melon rind. Novel means of applying sanitizing agents such as vacuum infiltration, vapor-phase dis- infection, or surface pasteurization with hot water washing show promise for more powerful antimicro- bial effects; however, they are not yet fully developed (Sapers, 2003).
Considering the relatively poor efficacy of chemi- cal sanitizers, it is a challenge for further research to understand the competitive inhibition of pathogens by naturally occurring microorganisms on produce in fresh-cut packages during storage.