Safe and Efficient Cryogenic Grinding of Food Samples

摘要

Most sample materials can be ground to the required analytical fineness at room temperature. However, there are limits, for example when even a small temperature increase affects the sample in a negative way; or when the material is very elastic and will only be deformed. Moreover, food samples which are fatty or sticky may block the mill. Therefore, cryogenic grinding is the best way to pulverise food samples like cheese, raisins, wine gum or marzipan which simply clump together when ground at room temperature. Another important aspect is the preservation of volatile sample components. The heat which is generated during the grinding process would cause volatiles like alcohol or residues of softeners from plastic wrappings to escape. This effect is prevented by using grinding aids like liquid nitrogen (LN_2; -196°C) or dry ice (solid CO_2; -78°C) which also embrittle the sample and make it break more easily. In the following, the special requirements for cryogenic grinding in different mills will be discussed as well as which other aspects need to be taken into consideration (Table 1).