New advances in extending the shelf-life of fresh-cut fruits: a review

Minimally processed fresh (MPF) fruits and vegetables are good media for growth of microorganisms. They have been involved in outbreaks because of the consumption of products contaminated by pathogens. They are also sensitive to various spoilage microorganisms such as pectinolytic bacteria, saprophytic Gram-negative bacteria, lactic acid bacteria, and yeasts. Contamination of MPF fruits and vegetables occurs at every stage of the food chain, from cultivation to processing. Polluted environments during cultivation or poor hygienic conditions in processing increase the risk of contamination with foodborne pathogens. Although MPF fruits and vegetables may harbor psychrotrophic microorganisms such as fluorescent pseudomonads or Listeria monocytogenes, good control of refrigeration temperature limits growth of spoilage and pathogenic microorganisms. Modified atmospheres are often efficient to maintain or improve visual organoleptic quality of MPF fruits and vegetables, but their effects on microorganisms are inconsistent. Chemical disinfection can partially reduce the initial bacterial contamination; irradiation seems to be more efficient. The applications of legislations and quality assurance systems to control contamination, survival, and growth of foodborne pathogens in MPF fruits and vegetables are discussed.

Modified-atmosphere packaged (MAP) foods have become increasingly more common in North America, as food manufacturers have attempted to meet consumer demands for fresh, refrigerated foods with extended shelf life. Although much information exists in the general area of MAP technology, research on the microbiological safety of these foods is still lacking. The great vulnerability of MAP foods from a safety standpoint is that with many modified atmospheres containing moderate to high levels of carbon dioxide, the aerobic spoilage organisms which usually warn consumers of spoilage are inhibited, while the growth of pathogens may be allowed or even stimulated. In the past, the major concerns have been the anaerobic pathogens, especially the psychrotrophic, nonproteolytic clostridia. However, because of the emergence of psychrotrophic pathogens such as Listeria monocytogenes , Aeromonas hydrophila , and Yersinia enterocolitica , new safety issues have been raised. This stems mainly from the fact that the extended shelf life of many MAP products may allow extra time for these pathogens to reach dangerously high levels in a food. This review focuses on the effects of MAP on the growth and survival of foodborne pathogens. Considered are the major psychrotrophic pathogens, the mesophiles such as the salmonellae and staphylococci, as well as the microaerophilic Campylobacter jejuni . The use of MAP in various food commodities such as beef, chicken, fish, and sandwiches is also discussed. Examples of various foods currently being packaged under MAP in North America are given, along with the specific atmospheres employed for the various food groups. Major safety concerns that still need to be addressed include the potential for growth and toxin production of Clostridium botulinum type E in MAP fish products, the growth of L. monocytogenes and A. hydrophila under modified atmospheres in various food commodities, and the enhanced survival of anaerobic spores and C. jejuni under certain gas atmospheres. Additional research with MAP foods is needed to ensure the microbiological safety of the numerous MAP products that will be available to the consumer in the next decade and beyond.

The preparation and distribution of fresh-cut produce is a rapidly developing industry that provides the consumer with convenient and nutritious food. However, fresh-cut fruits and vegetables may represent an increased food safety concern because of the absence or damage of peel and rind, which normally help reduce colonization of uncut produce with pathogenic bacteria. In this study, we found that Salmonella Enteritidis populations can (i) survive on fresh-cut melons and apples stored at 5 degrees C, (ii) increase up to 2 log units on fresh-cut fruits stored at 10 degrees C, and (iii) increase up to 5 log units at 20 degrees C during a storage period of 168 h. In addition, we examined the effect of lytic, Salmonella-specific phages on reducing Salmonella numbers in experimentally contaminated fresh-cut melons and apples stored at various temperatures. We found that the phage mixture reduced Salmonella populations by approximately 3.5 logs on honeydew melon slices stored at 5 and 10 degrees C and by approximately 2.5 logs on slices stored at 20 degrees C, which is greater than the maximal amount achieved using chemical sanitizers. However, the phages did not significantly reduce Salmonella populations on the apple slices at any of the three temperatures. The titer of the phage preparation remained relatively stable on melon slices, whereas on apple slices the titer decreased to nondetectable levels in 48 h at all temperatures tested. Inactivation of phages, possibly by the acidic pH of apple slices (pH 4.2 versus pH 5.8 for melon slices), may have contributed to their inability to reduce Salmonella contamination in the apple slices. Higher phage concentrations and/or the use of low-pH-tolerant phage mutants may be required to increase the efficacy of the phage treatment in reducing Salmonella contamination of fresh-cut produce with a low pH.