title: Presence and dehydration of ikaite, calcium carbonate hexahydrate, in frozen shrimp shell.
abstract: Ikaite, calcium carbonate hexahydrate, has by means of X-ray diffraction analyses of frozen samples been identified as the mineral component of the white spots formed in the shell of frozen shrimp during storage. When the shrimp thaw and the shell material is dried and kept at room temperature, ikaite rapidly transforms into a mixture of anhydrous calcium carbonate forms. X-ray diffraction analyses and Raman spectra of synthetic ikaite as well as the dehydration product confirm the assignments, and the rate constant for dehydration is approximately 7 x 10(-)(4) s(-)(1) at ambient temperature. Differential scanning calorimetry showed that dehydration of synthetic ikaite is an entropy-driven, athermal process and confirms that a single first-order reaction is rate-determining. Ikaite is found to be stable in aqueous solution at temperatures below 5 degrees C and in the shell of frozen shrimps but decomposes on thawing to form anhydrous calcium carbonates.
authors.affiliation: Department of Dairy and Food Science, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Mikkelsen
authors.forename: A B
authors.initials: AB
authors.lastname: Andersen
authors.forename: S B
authors.initials: SB
authors.lastname: Engelsen
authors.forename: H C
authors.initials: HC
authors.lastname: Hansen
authors.forename: O
authors.initials: O
authors.lastname: Larsen
authors.forename: L H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D000818:Animals; D002119:Calcium Carbonate / Q000032:analysis*; D002152:Calorimetry, Differential Scanning; D033364:Decapoda / Q000737:chemistry*; D003890:Desiccation; D005628:Frozen Foods / Q000032:analysis*; D012758:Shellfish / Q000032:analysis*; D013816:Thermodynamics
chemical_list: D002119:Calcium Carbonate