Let's clear something first.
This line of yours
text_field_words = 'Orange','Mango','banana'
Should be
$text_field_words = 'Orange, Mango, banana';
If you're storing this string into wp_option table you can get those values using
$text_field_words = get_option( 'your_option_key', '' );
Now to your question you can get string into array as follows: (You've $text_field_words and it has your string "Orange", ... )
$text_field_words_array = explode(",", $text_field_words);
print_r($text_field_words_array);
Output:
Array
(
[0] => Orange
[1] => Mango
[2] => banana
)