How to give name to topics created using LDA? I have categorized 800,000 documents into 500 categories using the Mahout topic modelling.

Instead of representing the topic using the top 5/10 words for each topics, I want to infer a generic name for the group using any existing algorithm.
For the time being, I have used the following algorithm to arrive at the name for the topic:

For each topic


Take all the documents belonging to the topic (using the document-topic distribution output)
Run python nltk to get the noun phrases
Create the TF file from the output
name for the topic is the phrase (limited towards max 5 words)


Please suggest a approach to arrive at more relevant name for the topics.
I can suggest several papers on this topic:


Automatic Labelling of Topic Models
Automatic Labeling Hierarchical Topics
Representing Topics Labels for Exploring Digital Libraries


You can find more by looking at their citations.