laravel: Access [original:protected] array, of eloquent collection

model:

return $this->belongsToMany('App\Models\OrgStructure', 'OrgStructurePost', 'post_id', 'node_id')
        ->withPivot('org_struct_post_id');

here is print_r() of returned collection object named as $postNodes:

[0] => ...... Object
(
    [attributes:protected] => Array
    (
        [id] => 24
        [name] => Finance
    )

    [original:protected] => Array
    (
        [id] => 24
        [name] => Finance
        [pivot_post_id] => 1
        [pivot_node_id] => 1
        [pivot_org_struct_post_id] => 1
    )
)
[1] => ...... Object
(
    [attributes:protected] => Array
    (
        [id] => 25
        [name] => Admin
    )

    [original:protected] => Array
    (
        [id] => 25
        [name] => Admin
        [pivot_post_id] => 1
        [pivot_node_id] => 2
        [pivot_org_struct_post_id] => 2
    )
)

I m trying to filter this collection using 'where()' method as shown below:

$currentRecord = $postNodes->where('pivot_org_struct_post_id','1')->first();

But could not access 'original:protected' array, using 'where()' method.

So how to filter above collection by key 'pivot_org_struct_post_id'?

via Chebli Mohamed