パンくずリストを構造化付きデータごとレンダリングさせるカスタムビルダ breadcrumbs_on_railsがベース(https://github.com/weppos/breadcrumbs_on_rails)

breadcrumb_helper.rb

module BreadcrumbHelper
  def render_breadcrumbs
    super(builder: CustomBreadcrumbsBuilder)
  end
end

class CustomBreadcrumbsBuilder < BreadcrumbsOnRails::Breadcrumbs::SimpleBuilder
  def initialize(context, elements, options = {})
    super
    @options[:separator] = ' > '
  end

  def render
    if @elements.present?
      @context.content_tag(:ol, class: 'breadcrumb', itemscope: true, itemtype: "http://schema.org/BreadcrumbList") do
        @elements.map.with_index do |element, index|
          separator = @options[:separator]
          separator = "" if @elements.size == index + 1
          render_element(element, index) + separator
        end.join.html_safe
      end
    else
      ''
    end
  end

  def render_element(element, index)
    # truncate page title
    # if element.name !~ /^</ && element.name.to_s.length > 20
    #   trunc = element.name[0..19].to_s
    #   element.name = trunc + '...'
    # end
    # with microdata
    # NOTE: https://productforums.google.com/d/msg/webmaster-ja/61INP019tKA/1hm-Tg4XhVkJ
    content = @context.content_tag(:span, compute_name(element), itemprop: "name")
    unless element.path.nil?
      content = @context.link_to_unless_current(
        content,
        compute_path(element), itemprop: "item")
    end
    position = index + 1
    content << @context.content_tag(:meta, nil, itemprop: "position", content: position)
    @context.content_tag(:li, content.html_safe, itemprop: "itemListElement",
                                                 itemscope: true, itemtype: "http://schema.org/ListItem")
  end
end