Bromelain, a proteolytic enzyme extracted from the stem of the pineapple plant, is capable of digesting protein when eaten directly after a meal. It has also been used in sinusitis as an anti-inflammatory and mucolytic agent when taken an empty stomach between mealtimes. It appears to thin nasal secretions and reduce inflammation of the nasal mucosa.
Helms S, Miller A (2006). Natural treatment of chronic rhinosinusitis. Alternative Medicine Review. 11(3):196-207