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However, the polyphenolic compounds (tannins) found in bean seed coats adversely impact nutritional bioavailability (Salunkhe et al. 1990; Hart et al. 2019; Rousseau et al. 2020). These compounds are reactive and will bind with soluble proteins and reduce their bioavailability and interfere with protein digestibility (Elias et al. 1979; Aw and Swanson 1985). Seed coat tannins leached into the soak and cook water are particularly important in subsistence feeding programs because of the detrimental effect they have on overall nutrient bioavailability. This negative impact is dramatic if the tannin‐rich bean broth is used as a component of weaning foods.

ssss1 General classification of phenolic compounds.

Source: Adapted from Luthria and Pastor‐Corrales (2006).

In recent years, interest in the antioxidant capacity of plant foods and specifically the phenolic content of dry beans (Wu et al. 2004; Xu and Chang 2009; Giusti et al. 2019) has intensified. There is increasing evidence that flavonoids consumed in native foods convey health benefits in human diets through their antioxidant activity (Frankel et al. 1993; Hertog et al. 1993). Condensed and hydrolyzable tannins of high molecular weight also have been shown to be effective antioxidants with even greater activity than simple phenolics (e.g., flavonoid monomers) (Hagerman et al. 1998). Although exceptionally high levels of antioxidant capacity have been reported in raw dry beans (Wu et al. 2004), further work on the retention of these properties in prepared (cooked or canned) beans is warranted.