Extract XML element value from a RSS feed

I have a RSS feed and I need to extract the latest pubDate element from it for my test. What is the best way to do the same ?

RSS Feed link: http://ift.tt/1vwvBLu

Sample XML:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<rss version="2.0" xmlns:atom="http://ift.tt/r5ut6F">
    <channel>
        <atom:link href="http://ift.tt/1vwvBLu" rel="self" type="application/rss+xml" />
        <link>http://ift.tt/1ujT3VN;
        <title>Hyper-Reach Automated Test Account alerts feed "Automated RSS Test"</title>
        <description>Constant feed of alerts from Automated Test Account via hyper-reach.com</description>
        <lastBuildDate>Fri, 21 Nov 2014 00:56:15 -0500</lastBuildDate>
        <language>null</language>
        <ttl>5</ttl>
        <item>
            <title>Alert (2014-11-21)</title>
            <pubDate>Fri, 21 Nov 2014 00:56:15 -0500</pubDate>
            <description>This is a test message.</description>
            <link>http://ift.tt/1vwweom;
            <guid isPermaLink="false">http://ift.tt/1ujT2Bi;
        </item>
        <item>...</item>
        <item>...</item>
</channel>
</rss>

What I am doing:

checkRSSFeed = function() {
    //first I navigate to a certain page in my website
    var href = '';

    casper.then(function() {
        this.test.assertExists(x('//a[contains(@href, "SUBSTRING OF URL")]'), 'the element exists');
        href = casper.getElementAttribute(x('//a[contains(@href, "SUBSTRING OF URL")]'), 'href');
     }).then(function() {
        this.open(href);
     }).then(function() {
        this.echo(this.getCurrentUrl());

        var pubDate = '';
        this.getPageContent();
        pubDate = this._utils_.getElementByXPath('.//pubDate');
     });
};  

The error I am getting is

uncaughtError: TypeError: 'undefined' is not an object (evaluating 'this._utils_.getElementByXPath')