How to load additional properties of a record?

In short, I need to load additional fields of a record, after it's been selected with the non-complete set of properties.

Consider the following query:

$quotes = Quote::select(['id', 'probability'])->get();

after doing some manipulations with $quotes and choosing one of the quotes - $q, I need to load it's additional properties. How can this be achieved?

via Chebli Mohamed