Оберните ваши узлы в CDATA:
def wrap_in_cdata(node)
# Using Nokogiri::XML::Node#content instead of #inner_html (which
# escapes HTML entities) so nested nodes will not work
node.inner_html = node.document.create_cdata(node.content)
node
end
Nokogiri::XML::Node#inner_html
экранирует сущности HTML, за исключением разделов CDATA.
fragment = Nokogiri::HTML.fragment "<div>Here is an unescaped string: <span>Turn left > right > straight & reach your destination.</span></div>"
puts fragment.inner_html
# <div>Here is an unescaped string: <span>Turn left > right > straight & reach your destination.</span></div>
fragment.xpath(".//span").each {|node| node.inner_html = node.document.create_cdata(node.content) }
fragment.inner_html
# <div>Here is an unescaped string: <span>Turn left > right > straight & reach your destination.</span>\n</div>