How to update additional value in cart?

Question

opencart

Hello, there was a need to transfer an additional value to the basket. No problem adding
$this->request->post['price_custom']

$this->cart->add($this->request->post['product_id'], $quantity, $this->request->post['price_custom'], $option, $recurring_id);

Everything is perfectly transmitted and displayed.
Here at updating there was a question how to thrust this field here.

if (!empty($this->request->post['quantity'])) {
            foreach ($this->request->post['quantity'] as $key => $value) {
                $this->cart->update($key, $value);
            }

I hope I explained ... Thanks in advance for the answers