Protractor: Checking data is sorted by date

I need to check the data returned is sorted by date. This is how I'm writing it:

it('should be sorted by date', function() {
    element.all(by.repeater('users in group.users')).then(
        function(users) {
            var lastUser = users[0].element(by.id('birth-date')).getText();
            for (var i = 1; i < users.length; ++i) {
                var currentUser = users[i].element(by.id('birth-date')).getText();
                expect(moment(currentApplication).format('MMM d, YYYY HH:mm')).toBeGreaterThan(moment(lastApplication).format('MMM d, YYYY HH:mm'));
                lastUser = currentUser;
            }
        }
    )
})

This returns:

Expected 'Jan 1, 2015 00:00' to be greater than 'Jan 1, 2015 00:00'.

What am I doing wrong? currentUser and lastUser seem to be objects instead of text...but I'm not sure why.