A review on β-carboline alkaloids and their distribution in foodstuffs: A class of potential functional components or not?

•β-Carboline alkaloids (βCs) are a class of pharmacologically active compounds.•Foodstuffs are rich in βCs, especially norharman, harman and tetrahydro-β-carbolines (THβCs).•The highest levels of norharman and harman are found in coffee.•Smoked foods seem to contain the highest concentrations of THβCs.•Long-term consumption of foodstuffs rich in βCs may be beneficial or noxious to human.