A student investigated the effect of temperature on the rate of starch breakdown by the enzyme amylase. The starch was mixed with amylase at different temperatures, and the time taken for starch to be completely broken down was recorded.
| Temperature (∘C^{\circ}\text{C}∘C) | Time taken for starch to be completely broken down (minutes) |
|---|---|
| 20 | 10 |
| 35 | 4 |
| 50 | 8 |
| 70 | Starch was still present after 15 minutes |
Explain why the starch was not broken down in the investigation at 70∘C70^{\circ}\text{C}70∘C.