Bacterial Stressors in Minimally Processed Food

Stress responses are of particular importance to microorganisms, because their habitats are subjected to continual changes in temperature, osmotic pressure, and nutrients availability. Stressors (and stress factors), may be of chemical, physical, or biological nature. While stress to microorganisms is frequently caused by the surrounding environment, the growth of microbial cells on its own may also result in induction of some kinds of stress such as starvation and acidity. During production of fresh-cut produce, cumulative mild processing steps are employed, to control the growth of microorganisms. Pathogens on plant surfaces are already stressed and stress may be increased during the multiple mild processing steps, potentially leading to very hardy bacteria geared towards enhanced survival. Cross-protection can occur because the overlapping stress responses enable bacteria exposed to one stress to become resistant to another stress. A number of stresses have been shown to induce cross protection, including heat, cold, acid and osmotic stress. Among other factors, adaptation to heat stress appears to provide bacterial cells with more pronounced cross protection against several other stresses. Understanding how pathogens sense and respond to mild stresses is essential in order to design safe and effective minimal processing regimes

Lactic acid bacteria as starter cultures: An update in their metabolism and genetics

Lactic acid bacteria (LAB) are members of an heterogenous group of bacteria which plays a significant role in a variety of fermentation processes. The general description of the bacteria included in the group is gram-positive, non-sporing, non-respiring cocci or rods. An overview of the genetics of lactococci, Streptococcus thermophilus, lactobacilli, pediococci, leuconostocs, enterococci and oenococciis presented with special reference to their metabolic traits. The three main pathways in which LAB are involved in the manufacture of fermented foods and the development of their flavour, are (a) glycolysis (fermentation of sugars), (b) lipolysis (degradation of fat) and (c) proteolysis (degradation of proteins). Although the major metabolic action is the production of lactic acid from the fermentation of carbohydrates, that is, the acidification of the food, LAB are involved in the production of many beneficial compounds such as organic acids, polyols, exopolysaccharides and antimicrobial compounds, and thus have a great number of applications in the food industry (i.e. starter cultures). With the advances in the genetics, molecular biology, physiology, and biochemistry and the reveal and publication of the complete genome sequence of a great number of LAB, new insights and applications for these bacteria have appeared and a variety of commercial starter, functional, bio-protective and probiotic cultures with desirable properties have marketed

Microbial pollution and food safety

Microbial pollution is a serious food safety issue because it can lead to a wide range of foodborne diseases. A great number of foodborne diseases and outbreaks are reported in which contamination of fresh produce and animal products occurs from polluted sources with pathogenic bacteria, viruses and protozoa and such outbreaks are reviewed and the sources are revealed. Investigations of foodborne outbreaks involved meat production and fresh produce, namely, that occurred at the early stages of the food chain have shown certain sources of contamination. Domesticated food animals, as well as wild animals, flies and rodents can serve as a source of contamination of nearby produce-growing fields and can lead to human infection through direct contact at farms and, mostly, mail order hatcheries. The most of the fresh produce associated outbreaks have followed wildlife intrusion into growing fields or fecal contamination from nearly animal production facilities that likely led to produce contamination, polluted water used for irrigation and improper manure. Preventive measures, as part of implemented good agricultural practice systems are described. Controlling and minimizing pre-harvest contamination may be one of the key aspects of food safety

Microbiological quality of white-brined cheeses: A review

White-brined cheeses are widely produced in the North-east Mediterranean area and the Balkans. Traditionally, they were manufactured as artisanal cheeses, and nowadays they are manufactured on an industrial scale, and rigorous control of the production and maturation processes is essential. Aspects of the microbiology of white-brined cheeses and their significance with respect to the quality and safety of the final products are discussed in this revie

Cheese from Non-Bovine Milk

Non-bovine milk cheeses, although mainly produced in the Mediterranean basin, are widely accepted and enjoyed worldwide. This chapter discusses the importance of non-bovine milk cheeses for local economies, cultural heritage and the role in preserving biodiversity. The special characteristics, composition, as well important parameters, such as animal feeding regimes/farming systems, and cheese-making technologies are presented. The diversity is clearly reflected in the organoleptic profile of every cheese in the relevant category i.e., soft, semi-hard, hard, mold surface-ripened, blue pasta-filata, blue-veined, whey or white-brined, making non-bovine milk cheeses unique

A study of the effects of adjunct cultures on the aroma compounds of Feta-type cheese

The influence of adjunct brine cultures on the volatile compounds in Feta-type cheeses made from bovine milk was studied. Four batches of brine were produced: one with no added adjuncts, a second containing Lactobacillus paracasei subsp. paracasei, a third containing Lb. paracasei subsp. paracasei plus Debaryomyces hansenii and a fourth with Lb. paracasei subsp. paracasei plus Yarrowia lipolytica. All the cultures were isolated from commercial Feta brines. Aroma compounds were analysed by dynamic headspace analysis, on-line coupled with GC/MS. The most important volatile compounds were quantified in the experimental cheeses; it was concluded that the use of Lb. paracasei subsp. paracasei and D. hansenii as adjuncts in the manufacture of Feta-type cheeses contribute to the formation of a richer pattern of aroma compounds, namely alcohols, aldehydes and esters. The inclusion of Y. lipolytica resulted in the production of undesirable aroma compounds that are not part of the usual volatile profile of high quality Feta cheeses. (C) 2004 Elsevier Ltd. All rights reserved

The Evolution of Fermented Milks, from Artisanal to Industrial Products: A Critical Review

The manufacture of fermented milk products has a long history, and these products were initially produced either from spontaneous fermentation or using a batch of previously produced product, that is, back-slopping. Milk of different mammal species has traditionally been used for the manufacture of fermented milk products. Cow’s milk is the basis for most dairy fermented products around the world. Milk from other mammals, including sheep, goat, camel, mare, buffalo, and yak may have been historically more important and remain so in certain regions. The milks from different species have differences in chemical composition and in certain, vital for the fermentation, components. The diversity of fermented milk products is further influenced by the wide variety of manufacturing practices. A great number of fermented dairy products have been traditionally produced worldwide, and many of them are still produced either following the same traditional process or manufactured industrially, using standardized processes under controlled conditions with specified starter cultures. The evolution from traditional to industrial production, their specific regional differences, their special characteristics, and the microbiological aspects of fermented dairy products are discussed. Throughout the evolution of fermented milk products, functional and therapeutic properties have been attributed to certain components and thus, yogurts and fermented milks have gained a significant market share. These products have gained wide global recognition as they meet consumers’ expectations for health-promoting and functional foods. The exploitation of microbiological methods based on DNA (or RNA) extraction and recently high-throughput techniques allowed for the accurate identification of the microbiota of fermented milk products. These techniques have revealed the significance of the properties of the autochthonous microbes and provided novel insights into the role of the microbiota in the functional and organoleptic properties of many fermented milk products

Microbiological quality of white-brined cheeses: A review

White-brined cheeses are widely produced in the North-east Mediterranean area and the Balkans. Traditionally, they were manufactured as artisanal cheeses, and nowadays they are manufactured on an industrial scale, and rigorous control of the production and maturation processes is essential. Aspects of the microbiology of white-brined cheeses and their significance with respect to the quality and safety of the final products are discussed in this revie