Display custom product field in order confirmation

[pette]

Hi,
I added a custom field in product. I follow the step in the this guide Adding a new field to products in Prestashop 1.6 
So I have add a field in the database, override the informations.tpl and all works.
So I try to display this field , in product template I can retrieve it with

{$product->second_reference}

in the order confirmation email but it doesn't work.
I try to add in PaymentModule.php this in the loop

$data_disponibilita = $this->context->second_reference;

$product_var_tpl = array(

							'data_disponibilita' => $data_disponibilita,
							'data_disponibilita_b' => $product['second_reference'],
							'data_disponibiita_c' => $product->second_reference,

						);

but I cannot retrieve the value

Can you help me?
Thanks