Laravel 5 - Extract ID from Object

I have an object in laravel 5.5 $categories that looks like this...

Illuminate\Database\Eloquent\Collection Object
(
    [items:protected] => Array
        (
            [0] => App\Category Object
                (
                    [table:protected] => categories
                    [primaryKey] => id
                    [attributes:protected] => Array
                        (
                            [id] => 22
                            [title] => Fruit
                            [slug] => fruit
                        )

                    [original:protected] => Array
                        (
                            [id] => 22
                            [title] => Fruit
                            [slug] => fruit
                        )
                )
         )

)

How can I get the id from this object? I have tried both of these...

But they are not working, how should I be extracting this value?

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