How can I improve DNA yields from very tough tissues using the DNeasy Blood & Tissue Kit or the QIAamp DNA Mini Kit?
FAQ ID -374

Efficient DNA isolation requires thorough sample disruption and digestion.

Although the QIAamp and DNeasy procedures requires no mechanical disruption of the tissue sample, the lysis time will be reduced if the sample is ground in liquid nitrogen or mechanically homogenized in advance. For mechanical homogenization, a rotor–stator homogenizer, such as the QIAGEN TissueRuptor, or a bead mill, such as the QIAGEN TissueLyser, can be used.

To improve digestion of tough tissue samples, Proteinase K incubation at 56°C can be performed overnight. DNA yields may be improved by increasing the amount of Proteinase K or by adding additional proteinase K after several hours of digestion.