ABSTRACT
Vegetable Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 14.3 Fermented Vegetables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
14.3.1 Fermentation Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 14.4 Acidified Vegetables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
14.4.1 Definitions and Regulations for Acid and Acidified Foods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
14.4.2 Pathogenic Bacteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 14.5 Organic Acids and Destruction of Pathogens . . . . . . . . . . . . . . . . . . . . . 322
14.5.1 Specific Effects of Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 14.5.2 Genetic Regulation of Acid Resistance . . . . . . . . . . . . . . . . . . . 325
14.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
Food fermentation technology likely originated sometime between 8,000 to 12,000 years ago as plants and animals were being domesticated in the Middle East, Africa, and Asia [1-3]. The development of primitive pottery technology likely led to early fermentation experiments, either planned or unplanned. Cheese, bread, and alcoholic beverages may have resulted from the fermentation of milk, grains, fruits, and vegetables stored in ceramic jars or pots. If these ‘‘spoiled’’ or fermented products were found to have desirable sensory properties, they may have been developed as the first processed or fermented foods [2]. An important characteristic of fermentation was the increase in the storage lifetime during which foods could be safely eaten. The microbial nature of food fermentation or foodborne illnesses was not understood, however, until the advent of the science of microbiology in the late 19th century. The fermentation of vegetables by lactic acid bacteria (LAB) is now well understood as an effective means of preserving and ensuring the safety of foods [4,5]. LAB are being considered for use in nonfermented vegetable products as a means of ensuring safety and preventing spoilage [6-8]. Fermented and acidified vegetable products, such as sauerkraut, kimchi, olives, and cucumber pickles, not only have desirable sensory qualities, but also have an excellent safety record with no known reported cases of foodborne illness.
The microflora on fresh fruits, grains, and vegetables can range from as low as 102 to 109 colony forming units (CFU) per gram [9,10]. On pickling cucumbers, for example, the aerobic microflora is typically between 104 to 106CFU/ml for fresh fruit, with LAB less than 101CFU/g [11]. In the absence of processing, degradative aerobic spoilage of plant material by mesophylic microorganisms occurs, with Pseudomonas spp., Enterobacter spp., and Erwinia spp. initiating the process [10]. A variety of pathogens, including Salmonella spp., Shigella spp., Aeromonas hydrophylia, Yersinia enterocolitica, Staphylococcus aureus, Campylobacter, Listeria monocytogenes, Escherichia coli, and others, may be present on fresh vegetable products [12-15]. Pathogens on fruits and vegetables may also include enteric, hepatitis, or polio viruses [16]. A variety of sources may contribute to the occurrence of pathogenic bacteria on fruit and vegetable crops, including exposure of plants to untreated manure or contaminated water, the presence of insects or birds, personal hygiene practices of farm workers, postharvest washing or hydrocooling water, and conditions of storage during distribution [12,14]. A study comparing the use of organic fertilizer (composted manure) and inorganic fertilizer from farms in Minnesota showed significantly higher coliform counts on the organically grown vegetables [17]. However, in this and related studies [18,19], pathogens, including E. coli O157:H7, were not detected.
