Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
After cellulose, chitin is the most widespread biopolymer in nature. Chitin and its derivatives have great economic value because of their biological activities and their industrial and biomedical applications. It can be extracted from three sources, namely crustaceans, insects and microorganisms. However, the main commercial sources of chitin are shells of crustaceans such as shrimps, crabs, lobsters and krill that are supplied in large quantities by the shellfish processing industries. Extraction of chitin involves two steps, demineralisation and deproteinisation, which can be conducted by two methods, chemical or biological. The chemical method requires the use of acids and bases, while the biological method involves microorganisms. Although lactic acid bacteria are mainly applied, other microbial species including proteolytic bacteria have also been successfully implemented, as well as mixed cultures involving lactic acid-producing bacteria and proteolytic microorganisms. The produced lactic acid allows shell demineralisation, since lactic acid reacts with calcium carbonate, the main mineral component, to form calcium lactate.Hitin je, nakon celuloze, najrasprostranjeniji biopolimer u prirodi. Hitin i njegovi derivati imaju veliku ekonomsku vrijednost zbog njihove biološke aktivnosti te moguće primjene u industriji i biomedicini. Može se ekstrahirati iz tri izvora, i to iz rakova, insekata i mikroorganizama. No, glavni komercijalni izvor hitina su oklopi rakova, kao što su škampi, rakovice, jastozi i zooplanktonski (krill) račići, koji u velikim količinama preostaju nakon prerade rakova. Ekstrakcija se hitina odvija u dva koraka: demineralizacija i deproteinizacija, a može se provesti kemijskim ili biološkim putem. Kemijska metoda podrazumijeva uporabu kiselina ili baza, a biološka uključuje primjenu mikroorganizama. Iako se najčešće primjenjuju mliječno-kisele bakterije, dosad su uspješno upotrijebljene i proteolitičke bakterije, te mješovite kulture mliječno-kiselih bakterija i proteolitičkih mikroorganizama. Nastala mliječna kiselina omogućuje daljnju demineralizaciju, jer reagira s kalcijevim karbonatom, glavnim mineralnim sastojkom oklopa, pri čemu nastaje kalcijev laktat
