How to use loading text

I'm loading AssetBundle from server and the bundle size is large. So, i tried to use loading text for this. But the loading text is not working.

 public GUIText loadingText;
     IEnumerator GetAssetBundle(ImageTargetBehaviour itbModel ) {
                 while(!Caching.ready)
                 yield return null;
         
             string bundleURL = AssetModelString;
             
             Debug.Log (bundleURL);
             using (WWW www = WWW .LoadFromCacheOrDownload(bundleURL, Version)) {
                 yield return www;
                 Debug.Log (Version);
                 
                 if (www .error != null)
                     throw new UnityException("WWW Download had an error: " + www .error);
                 
                 AssetBundle bundle = www .assetBundle;
                 if (AssetName == "") {
                     Debug.Log ("null");
                       
                     
                    mBundleInstance = Instantiate (bundle.mainAsset) as GameObject;
     
                       while (!mBundleInstance .isDone) {
                     
                     loadingText.text = "Loading... " + (mBundleInstance .progress*100).ToString("f0") + "%";
                     yield return loadingText.text;
                 }
                 
                 loadingText.enabled = false;
                     mBundleInstance.transform.localPosition = new Vector3(0.0f, 0.15f, 0.0f);
                     mBundleInstance.transform.gameObject.SetActive(true);
                     assetbundle_load_hide=true;
                     bundle.Unload(false);
                 }
                 else {
                     Debug.Log ("not null");
                     mBundleInstance = Instantiate(bundle.Load (AssetName)) as GameObject;
                 }
             }
         }