Lactic acid bacteria as agents to improve sensorial and hygenic quality of meat and meat products

Abstract

Lactic acid bacteria (LAB) constitute a heterogeneous group of microorganisms that produce lactic acid from the fermentation of sugars as the main metabolic product. LAB are Gram (+), non-spore forming cocci, coccobacilli or rods with a DNA-base composition of less than 53 mol% G+C. They generally are non respiratory organisms and lack catalase, fermenting glucose primarily to lactic acid, or to lactic acid, CO2 and ethanol. All LAB grow anaerobically, but unlike most anaerobes they grow in the presence of O2 as "aerotolerant anaerobes". Although most of them lack catalase, they possess superoxide dismutase and have alternative means to detoxify peroxide radicals, generally through peroxidase enzymes (Carr et al. 2002). The genera currently included in the LAB group are Lactobacillus, Lactococcus, Streptococcus, Pediococcus, Weisella, Carnobacterium, Leuconostoc, Enterococcus, Tetragenococcus, Oenococcus and Vagococcus (Holzapfel et al. 2001). Although most of LAB members are non pathogenic being Generally Recognized as Safe (GRAS) organisms, only a few of them are pathogenic, most notably some members of the genus Streptococcus. In addition, LAB are heterotrophic and generally have complex nutritional requirements because they lack many biosynthetic capabilities; most species have multiple requirements for amino acids and vitamins. Because of these nutritional exigencies, they are generally abundant in environments where these requirements can be provided. They are often associated with animal and human oral cavities and intestines (eg. Streptococcus mutans, Enterococcus faecalis), plants (Lactobacillus, Leuconostoc) and in decaying plant materials. Also they can be found in other nutrient rich environments including milk and dairy products, cereals, meat and meat products. Due to the described characteristics, LAB are among the most important group of microorganisms involved in food fermentations in which they are either present as contaminants or deliberately added as starters cultures to guarantee the optimal fermentation process. They contribute to the taste and texture of fermented products and inhibit food spoilage bacteria by producing growth-inhibiting substances and large amounts of lactic acid. They are involved in making yogurt, cheese, cultured butter, sour cream, sausages, cucumber pickles, olives and sauerkraut among others, but some species may spoil beer, wine and processed meats. Moreover, LAB are also considered the most important microorganisms responsible for the health-promoting effects of fermented foods, such as immunomodulation, intestinal integrity and pathogen resistance (Vaughan et al. 2005). Indeed, strains of some species have traditionally been used as probiotics and added as functional bacteria in various food commodities (Ljungh and Wädstrom 2006). Due to the huge economic significance of industrial application of LAB as starters, biopreservatives and probiotics, a research emphasis on their metabolism, genetic and applications has been placed in the last 25 years (Gasson and de Vos 2004). This chapter addresses recent data about LAB as the main protagonists of quality in meat and meat products, acting both as starter and biopreservatives cultures improving sensory and safety. The role of LAB in peptides generation from meat protein hydrolysis in fermented sausages with impact on flavor as well as the proteomic approach as a means to select highly competitive meat-borne LAB strains for quality improvement and the production of antimicrobial peptides as a strategy for safety assurance of meat products are here discussed.