It seems to me both sentences follow the same pattern in that all the adjectives to 'male volunteers' but the last one are followed by a comma ; which would be the expected punctuation in my opinion. 'healthy, non-smoking, caucasian male volunteers' 'healthy, non-smoking male volunteers' Personally they both look and sound good to me... And same for the following one : 'healthy, non-smoking, caucasian, professional male volunteers' Now it would be a different story if you were to say : 'healthy, non-smoking, caucasian, young urban professional male volunteers'.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.