Whole Potato Tubers (Solanum tuberosum L.) Provide a Protective Matrix Effect That Stabilizes Antiproliferative Inhibitory Metabolites from Thermal Degradation, and Retains Inhibitory Properties Against HT-29 Colon Cancer Cells In Vitro, Poster Board #048

Our previous research revealed that two solid pigmented skin and flesh selections, a red selection (POTR) and a purple selection (POTP) inhibited HT-29 colon cancer cells in culture when harvested as immature tubers. Potentially bioactive classes of metabolites have been found in potato by others, to induce antiproliferative activity in cancer cells in vivo and/or in vitro. Included are dietary fiber, resistant starch, vitamin C, glycoalkaloids, flavonoids and polyphenolic acids. A primary objective of this study was to assess if heating degraded inhibition of HT-29 colon cancer cells in culture following extraction from raw immature tubers compared to heated aqueous extracts. Raw immature tubers, and extracts from immature tubers, were exposed to 22–24 °C, 37 °C, 45 °C, 55–60 °C, 72 °C ,and 96°C (boiling) for 20 minutes in a water bath. CellTiter 96 Aqueous Non-Radioactive Cell Proliferation Assay by Promega was used to measure the number of viable HT-29 colon cancer cells in all cell culture assays. The goal was to gain insight into what class of metabolites may be responsible for inhibitory activity and to evaluate if the tuber matrix serves to protect these inhibitory metabolites. Most significant differences in temperature sensitivity were detected at a 24% extract concentration in cell cultures. Heating purple pigmented POTP whole tubers had minimal impact on inhibitory properties, indeed heating to 60 °C increased inhibitory properties compared to heated tubers at room temperature. On the other hand, boiling red pigmented tubers of POTR, decreased antiproliferative activity by half compared to heated tubers at 45 and 60 °C. Heated extracts of POTP had weak antiproliferative activity and no significant differences upon exposure to six different temperatures at any extract concentration. Red pigmented heated extracts of POTR completely lost antiproliferative activity upon exposure to 72 °C and boiling. Higher antiproliferative activity was found in heated tubers when compared to heated extracts at all temperatures in POTP and at 45 °C, 55–60 °C, and 72 °C in POTR at 24%. Immature tubers stored at 4 °C for six months retained their inhibitory properties. Full to partial inhibitory activity retained at high temperatures may be a result of heat stable glycoalkaloids. The tuber matrix itself may also have served to protect and conserve additional heat sensitive inhibitory metabolites from thermal degradation whereas inhibitory metabolites alone in heated extracts did not have a tuber matrix to protect heat sensitive activity.