Realce o texto de pesquisa na pesquisa do mysql php

<?php
 //$keyword -> keyword to be search in string.
 //$field   -> string contain value to be seach
 // Returns HTML content with highlighted text
function makeHighlighter($keyword, $field) {
    $i = strripos($field, $keyword);
    if ($i !== false) {
        $keyword = str_ireplace($keyword, substr($field, $i, (strlen($keyword))), $keyword);
    } else {
        return $field;
    }
    $as_unm_split = explode($keyword, $field);
    $string_hig = "";
    for ($i = 0; $i < count($as_unm_split); $i++) {
        if ($i < count($as_unm_split) - 1)
            $string_hig.=$as_unm_split[$i] . "<span style=\"color: red\">" . $keyword . "</span>";
        else
            $string_hig.=$as_unm_split[$i];
    }
    unset($as_unm_split, $keyword, $i);
    return $string_hig;
}

echo makeHighlighter("keyword","this is keyword to be match...");
?>