Hi Manoj
Chances are that it's the delay between the spider bot crawling the website and the index being updated.
When (most) bots crawl a page, they take a cache (spiders' copy) of the page and process that copy at a later time. Thus there is a delay between when a spider crawls a page and the search results being updated.
You may find at times that the meta description isn't the same as the one you've written anyhows, Google does sometimes create it's own description to display in the search results, based upon some of the actual page content.
I'd suggest resubmitting your updated sitemap.xml and waiting a while longer, chances are all will be sorted shortly.
Regards
Simon
