ABSTRACT
Fermentation of food is a desirable process because of the modication in metabolites generated by certain microorganisms, which impart benecial attributes. For fermentation of milk and its products, lactic acid bacteria (LAB) are considered to be the major workhorses due to their genetic and metabolic properties (Pedersen et al. 2002). LAB are used worldwide in the manufacture of fermented dairy foods, because they facilitate lactic acid and exopolysaccharide (EPS) production, exhibit
5.1 Introduction 109 5.2 Metabolic Pathways of LAB 110
5.2.1 Homofermentative Pathway 111 5.2.2 Heterofermentative Pathway 112
5.3 Metabolic Pathways for Flavor Enhancers 112 5.3.1 Glycolysis and Citrate Metabolism 113 5.3.2 Protein Metabolism 115 5.3.3 Lipid Metabolism 116
5.4 Flavor Compounds in Fermented Milk Products 117 5.4.1 Carbonyl Compounds 120 5.4.2 Acids and Alcoholic Compounds 121 5.4.3 Ester Compounds 122 5.4.4 Sulfur Compounds 123
5.5 Other Miscellaneous Metabolites 124 5.6 Future Perspectives 125 5.7 Conclusions 126 References 127
antimicrobial activity, and enhance avor and texture (Papagianni 2012). Generally, LAB are fastidious in nature and possess limited biosynthetic apparatus due to their small genome size (~2-3 Mb) and their ability to utilize simple sugars for their metabolism. Moreover, LAB carry several plasmids with technological traits, such as ability to utilize carbohydrates (lactose, sucrose, ranose, etc.), citrate metabolism, production of EPS, bacteriocin, and antibiotic resistance, all of which are advantages that can be exploited for metabolic engineering purposes (Ayad 2008; Papagianni 2012).
