Basic protein isolate from lobster shell

Abstract

Some structural characteristics of the basic protein concentrate isolated from the lobster shell were determined. The influence of the NaOH concentration, temperature and treatment time on the concentrate characteristics were also analyzed. An adequate combination of treatment time and alkaline copcentration allowed to obtain similar protein yields with closer analogies in their structural characteristics, but the lower alteration and higher molecular weight are produced with the longest treatment time and the lowest alkaline concentration.The simultaneous isolation of chitin and protein from crustacean waste is an important research line in those countries that, like ours, have a significant capture volume of these species.The chitinous structure of the branchial lobster shell is formed by glycoproteins and only 20 % of the total protein content is soluble in water [l, 21. The protein yield does not increase either by heating the water mixture or by the use of Ca(OH), during the extraction [3]. On the other hand acid treatments are not adequate, but the use of dilute NaOH solutions allows good protein extraction. Taking into account that the use of basic treatment could provoke detectable changes over the protein, we decide to analyze the effect of this procedure over the concentrate characteristics. Materials and methodsShells from lobsters captured in 1981 in the zone of Batabano Gulf (in the southern part of Cuba) were used. They were cleaned, dried and ground. The protein extractions were carried out with 0.5, 1 and 2 : ; , NaOH stirring dviring different times 141. After centrifugation, the supernatants were neutralized and freeze-dried. The protein concentrates were analyzed on Sephadex G-100. The content of free amine groups was determined using the method reported by COCKING [5].The solubility was determined with 0.5 g of protein dissolved in 25 ml of water. It was stirred during 30 min.After centrifugation at 3000 rpm the protein concentration was determined by the KJELDAHL method [6]. The in vitro digestibility (relative to milk powder) was determined with 0.05 g of protein, adding 1.5 mg pepsin i -15 ml of 0.1 N HCI during 3 h at 37 "C. Then the pH was adjusted at 8.2 and 25 mg of pancreatine in a,HPO, buffer was added and the solution was batched during 15 h at 37 "C. To 0.5 ml of the solution were added 9 ml ethanol and after centrifugation the amine content in the supernatant was determined.The I R spectra were obtained in a UR 20 equipment using KBr, while the derivatograms were obtained in a Derivatograph MOM with a heating rate of 5 "C/min and a sample size of 80 mg.The LAL formation was calculated as DOWRSCHAK (Personal communication) taking into consideration the lys, cys, ser and tre contents of the shell protein. The amino-acid composition was determined in a Hitachi Kla 5 autoanalyzer.