Two-step demineralization of shrimp (Pandalus Borealis) shells using citric acid: an environmentally friendly, safe and cost-effective alternative to the traditional approach

Removal of minerals from crustacean shells during chitin extraction is traditionally achieved using hydrochloric acid. However, the environmental, health and safety concerns of hydrochloric acid have led to investigation of potential alternatives for this application. In most previously reported studies using other acids, the residual ash content in the demineralized shells could not be reduced to below 1%, which is required for high-grade applications of chitin. In the present study, near-complete demineralization of Pandalus Borealis shells was achieved using citric acid through one-step and two-step processes within 2 hours at room temperature. Fresh shrimp shells were pretreated by thorough grinding and washing. In the one-step demineralization, a residual ash content of 0.59% was obtained by treating the shells with twice the stoichiometric amount of citric acid for 2 h. The residual ash content was further reduced to 0.19% with implementation of a two-step process, in which the majority of minerals in the shells were first dissolved within 35 min using 1.5 times the stoichiometric amount of citric acid, followed by the second demineralization using 8 times the stoichiometric amount of citric acid for 60 min. The two-step process consumed a lower amount of citric acid in comparison to the one-step process (approx. 13.8% less 50% citric acid for every 1000 kg of fresh shrimp shells processed). The low residual mineral content achieved was comparable to the conventional process using hydrochloric acid, indicating the potential of using citric acid for demineralization of shrimp shells to produce premium-quality chitin.