Useful Microorganisms

                                      Lactobacillius

                                                     

Lactobacillus is the largest genus within the group of lactic acid bacteria. They are mainly used in the manufacture of fermented dairy, sourdough, meat and vegetable foods or used as probiotics. The general utility of the Lactobacillus species is related to their GRAS (Generally Recognized as Safe) status and it will be dependent on the availability of cost-effective methods for production and delivery of viable cultures. In dairy products such as fermented milks and cheeses, the lactobacilli have multiple effects depending on the species, strain, manufacturing conditions and product. The two most obvious beneficial roles of lactobacilli are as starter cultures (to produce acid rapidly) and as probiotic cultures. However, they may also synthesize bacteriocins and exopolysaccharides, and contribute to flavor of different dairy products. In some circumstances, lactobacilli may also cause flavor and texture defects.

Lactobacillus spp. are members of the family Lactobacillaceae. They are psychrophilic, non-spore forming, rod shaped, non-motile, Gram positive and facultative anaerobic. Lactobacillus spp. do not contain the enzyme catalase. Homofermentative Lactobacillus spp. ferment sugars predominantly into lactic acid (more than 90%) and do not produce gas. Heterofermentative species, on the other hand, ferment sugar (glucose) into lactic acid besides other substances such as acetic acid and produce CO2. The production of gas is regularly the cause for food spoilage. At a pH value below 5.0 in a meat product, the conditions are more suitable for growth of heterofermentative Lactobacillus spp. than homofermentative Lactobacillus spp. Most Lactobacillus spp. require an Aw above 0.95 to ferment substances such as sugars. An Aw below 0.95 severely restricts growth while growth stops altogether at an Aw below 0.92. A pH above 3.2 is required for growth.

Lactobacillus spp. are members of the family Lactobacillaceae. They are psychrophilic, non-spore forming, rod shaped, non-motile, Gram positive and facultative anaerobic. Lactobacillus spp. do not contain the enzyme catalase. Homofermentative Lactobacillus spp. ferment sugars predominantly into lactic acid (more than 90%) and do not produce gas. Heterofermentative species, on the other hand, ferment sugar (glucose) into lactic acid besides other substances such as acetic acid and produce CO2. The production of gas is regularly the cause for food spoilage. At a pH value below 5.0 in a meat product, the conditions are more suitable for growth of heterofermentative Lactobacillus spp. than homofermentative Lactobacillus spp. Most Lactobacillus spp. require an Aw above 0.95 to ferment substances such as sugars. An Aw below 0.95 severely restricts growth while growth stops altogether at an Aw below 0.92. A pH above 3.2 is required for growth.

Lactobacillus is the largest genus within the group of lactic acid bacteria. Based on the 16S rRNA sequences, lactobacilli are phylogenetically distributed in seven groups: Lb. buchneri (bu), Lb. casei (ca), Lb. delbrueckii (de), Lb. plantarum (pl), Lb. reuteri (re), Lb. sakei (sa), and Lb. salivarius (sl). Traditionally, the genus is split into three groups based on the carbohydrate fermentation pathways: (1) obligate homofermentative, (2) facultative heterofermentative, and (3) obligate heterofermentative lactobacilli. The two most obvious beneficial roles of lactobacilli are as starter cultures (to produce acid rapidly) and as probiotic cultures. Lactobacilli are one of the few contaminant bacteria that are able to grow in cheese after manufacture (as nonstarter lactic acid bacteria (NSLAB)). Lactobacilli as starters and as NSLAB may play different roles in the metabolism of lactose, lactate, and citrate, and in proteolysis and lipolysis, which are considered the primary events during cheese ripening.