GTIN on packing slip

Need to include gtin on the packing slip.

was including <td><?php echo $item['gtin']; ?></td>
and also try with <td><?php echo $product['gtin']; ?></td>

but no succés, any one that know the answer?

/Nick
tim
Try <?php echo reference::product($item[’product_id’])->gtin; ?>.  Be aware my mobile keyboard only shows apostrophe for single-quote so I’m not sure how it comes out.
Adjusting your keyboard error  <td><?php echo reference::product($item['product_id'])->gtin; ?></td>

Thanks for your help.
What file is this statement put in and where is the file found?
Where in the file do you insert the statement??
tim
includes/templates/default.catalog/pages/printable_packing_slip.inc.php
Thanks. Litecart is a great system as it's simple and has a lot of flexibility.