Farmed Jumbo shrimp molts: an ionic liquid strategy to increase chitin yield per animal while controlling molecular weight

Abstract

In pursuit of bioplastics which require a controlled biopolymer molecular weight, consistency, and supply, we have examined the chitin in the molts of farm raised Hybrid (H1) Pacific whiteleg shrimp (Litopenaeus vannamei) by collecting the molts during the shrimp growth cycle, sorting by shrimp average body weight (ABW), and extracting the chitin from the molts using the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]). The amount of available chitin in the molts increases with the age/size of the molting shrimp, 19% in juveniles to 22% in adults. As expected from the biology of molting, the chitin in the final shell peeled from the adult shrimp contained the most chitin (29%). It is neither easier nor harder to extract the chitin from molts or peels, and the extracted chitin was equivalent in purity and degree of acetylation with comparable extraction efficiency (67% for molts, 63% for peels). In addition, the weight average molecular weight (M_W) of the chitin has the potential to be controlled by shrimp age/size. The M_Ws of the chitin in the smaller animals (5–10 and 10–20 g ABW) were comparable at ∼4–5 MDa, while the chitin obtained from the large adult molts (30–40+ g ABW) exhibited a significantly higher M_W of 23 MDa. Thus, by collecting and using the shrimp molts, the industrial viability of chitin can be improved by providing both a larger amount of chitin per shrimp (an ca. 8-fold increase) and by providing the opportunity to extract chitin of a specific M_W.