Hola mleonsoft
Prueba de esta manera ..
<?php
$book = “'<books>'
'<book>'
'<author>'Jack Herrington'</author>'
'<title>'PHP Hacks'</title>'
'<publisher>'O'Reilly'</publisher>'
'</book>'
'<book>'
'<author>'Jack Herrington'</author>'
'<title>'Podcasting Hacks'</title>'
'<publisher>'O'Reilly'</publisher>'
'</book>'
'</books>'”;
$doc = new DOMDocument('1.0', 'iso-8859-1');
$element = $doc->createElement('test', $book );
$doc->appendChild($element);
echo $doc->saveXML();
///luego tu ciclo..el foreach( )
?>