Symfony3 dump() in JSON response

<?php
    use Symfony\Component\HttpFoundation\Response;

    /* INSIDE THE CONTROLLER */    

    // the varaibles you want to dump out
    $var1 = 'bar_1;
    $var2 = 'bar_2;

    // create the twig template
    $template = $this->get('twig')->createTemplate('{{ dump(foo) }} {{ dump(foo2) }}');

    // render the template
    $res = $template->render(['foo'=>$va1, 'foo2'=>$var2]);

    // return a simple response and set the content with the rendered Twig template
    $response = new Response();
    $response->setContent($_res);
    $response->setStatusCode(Response::HTTP_OK);
    return $response;