Adding the main-category to product meta title

[Gomlers]

I want to add the name for the product's main category to the products meta title.

So if I have category: Garden Equipment and Product Waterhose

I want to have this result for the product meta title: Waterhose | Garden Equipment

Can I use only smarty, by adding something like this to the header.tpl:

{if $page_name == 'product'} get the product's main category and add this to the product meta title {/if}

?

Edited October 25, 2017 by Gomlers (see edit history)

[Gomlers]

I hate this, and sorry - but I really want to fix this, so bump 

[Gomlers]

No one can tell me how I can change the product meta-titles to show like "Product name | Parent category" ?