The kit is intended for the isolation of intact mitochondria. It was not developed for cytoplasma collection. Nevertheless, reviewing the protocol, it can be assumed that the cytoplasmic fraction should be in the supernatant after the second centrifugation (point 8 of the Preparation of mitochondria from soft tissues protocol). Please keep in mind that this is not tested for suitability for cytoplasmic fraction.
Please see product MIT1000 Mitochondria/Cytosol Fractionation Kit for efficient isolation of intact mitochondria from cultured cells. This kit can be used for tissue samples as long as the tissue is first homogenized into a single cell suspension. It may be helpful to use the same protocol that is recommended for cells following homogenization of the tissue into a single cell suspension in the supplied Isotonic Mitochondrial Buffer containing protease inhibitors, then follow the kits protocol for cells: https://www.sigmaaldrich.com/product/mm/mit1000.