Identifying pre-defined key words from text input.

Question

Hello, basically, i currently have some open source code for text to speech translation (Type some text into a box and the software will have the computer say it back to you).

I need to tweak this code so that the system recognises certain key words (for example 'Fitness', 'Strength', 'Stamina', etc) in the input and then returns some pre-defined voice output.

For example if the key word in the input stage was 'Strength', the software would give "To improve general strength use weights in the gym.".

Does anyone have any idea how i'd go about this? Thanks.