Simple rotations question

I did look quite hard to find the answer to this other places, including here at Unity Answers, yet nothing seemed to work for my problem.
I’m currently making a similar game to fruit ninja (if you know what that is).
Simple concept, fruit gets thrown up in the air and you have to cut it in half.
The objects I am throwing in the air seem to look a little boring, since they aren’t randomly rotating in the air, they are merely just getting thrown up, and keeping their original rotations.
I want to make something that just rotates them randomly while they are in the air.
I am currently instantiating them as a random rotation (which is perfect), and I want them to fly up from there, with a smooth rotation.
I tried this:

var rotationSpeed = 20;
fruit.gameObject.transform.Rotate(rotateSpeed * Time.deltaTime,rotateSpeed * Time.deltaTime,rotateSpeed * Time.deltaTime);

Yet that didn’t seem to want to work.
Any other suggestions?
Thank you for your help!

You’re probably doing this in the wrong place: Rotate should be called at Update in a fruit script to make it rotate continuously. You could create random angular velocities for each axis at once using Random.insideUnitSphere at Start(), and use them in Update. Add this script to the fruit prefab:

var maxRotationSpeed: float = 60.0; // max 60 degrees per second

private var rotSpeed: Vector3; // this will hold the XYZ velocities

function Start(){
  // create random angular velocities around the 3 axes at once:
  rotSpeed = Random.insideUnitSphere * maxRotationSpeed;

function Update()
  // rotate the object continuously:
  transform.Rotate(rotSpeed * Time.deltaTime);

Thank you both for the answers!
Both work very well, but Aldo’s answer works better for my problem.