Remove [caption] from wp_trim_words

I use Twenty Twelve 1.5 and WordPress 4.0. I created child theme.

I edit content.php to make my entry showing excerpt 40 words for normal post and 65 words for sticky post. So I use wp_trim_words

This is the code,

<div class="entry-summary">
<?php
$content = get_the_content();
$trimmed_content = wp_trim_words( $content, 40, '...<div class="readmoretag"><a href="'. get_permalink() .'">continue reading</a></div>' );
echo $trimmed_content;
?>
</div><!-- .entry-summary -->

But now my website is showing [caption] because in my post, I put image with caption in the first paragraph.

How can I remove the caption and only show text paragraph on the excerpt?