Croatian Society of Food Technologists, Biotechnologists and Nutritionists
Abstract
Bakterije mliječne kiseline su auksotrofni industrijski mikroorganizmi i uzgajaju se u hranjivim podlogama kompleksnog sastava. Između
ostalih sastojaka, u hranjive podloge u kojima se uzgajaju ove bakterije potrebno je dodati i određene aminokiseline. Aminokiseline s razgranatim bočnim lancem, leucin, izoleucin i valin, moraju se dodati u podloge u kojima rastu bakterije mliječne kiseline. Potreba za preostalim aminokiselinama zavisi o vrsti i soju bakterije pomoću koje se provodi određeni bioproces. Tijekom transporta aminokiselina u stanice bakterija mliječne kiseline i razgradnje ovih izvora dušika i ugljika formira se elektrokemijski gradijent, pridobiva se metabolička energija, regeneriraju kofaktori enzima, ublažava se učinak proizvodnje mliječne kiseline tj. snižavanja pH vrijednosti, stanice se prilagođavaju osmotskom šoku kao i uvjetima okoline u stacionarnoj fazi rasta. Aminokiseline i/ili (među)spojevi nastali tijekom katabolizma ovih supstrata ishodišni su spojevi za proizvodnju: drugih aminokiselina i masnih kiselina, koje se ugrađuju u membrane; α-keto kiselina i α-hidroksi kiselina, koje mogu imati i ulogu siderofora; laktona; nukleinskih kiselina; proteina; lipida i poliamina. Katabolizam aminokiselina u stanicama bakterija mliječne kiseline nedovoljno je poznat i uglavnom se istražuje u cilju smanjenja koncentracije nepoželjnih amina u fermentiranim proizvodima.Lactic acid bacteria are auxotrophic industrial microorganisms usually cultivated in complex growth media. Among other ingredients, in the media for cultivation of the bacteria, particular amino acids need to be added. Branched-chain amino acids, leucine, isoleucine and valine, have to be added in the media in which lactic acid bacteria are expected to grow. Requirement for the rest of amino acids depends on the species and strain of the bacteria that have been used in defi ned bioprocess. During transport of amino acids in the lactic acid bacteria cells and degradation of this nitrogen and carbon sources, electrochemical gradient is formed, metabolic energy is yielded, enzyme cofactors are regenerated, effect of
produced lactic acid i.e. reduction of pH value is moderated, the cells are adapted to osmotic shock as well as to stationary growth phase conditions. Amino acids and/or (intermediate) compounds generated during their catabolism represent precursors for production of: other aminoacids and fatty acids, which can be incorporated in membranes; α-keto acids and α-hydroxy acids, which can also act as siderophores; lactones; nucleic acids; lypides and polyamines. Amino acids catabolism in lactic acid bacteria cells is not known enough and it is mainly investigated in order to reduce concentration of undesired amines in fermented food
