A method for the investigation of free and protein-bound N-nitrosoproline in beer

Hydrolysis of beer peptides and proteins by both mild enzymatic and vigorous alkaline conditions has established that peptide-bound N-nitrosoproline residues are not present in beer in significant quantities. Free N-nitrosoproline remains the single most abundant identified N-nitroso compound, and this accounts for up to 10% of the apparent total N-nitroso compounds (ATNC). Both hydrolysis and extractability studies strongly indicate that the majority of the ATNC are not associated with beer peptides, but rather are likely to be low molecular weight possessing in some cases an acidic functional group.