Pigmented heirloom beans: quality characteristics before and after cooking

This study aimed at characterizing 4 varieties of heirloom beans - Hutterite Soup (HS), Jacob’s Cattle (JC), Koroni’s Purple (KP) and Tiger’s Eye (TE) - for composition [starch, protein, total (TDF), soluble (SDF), and insoluble (IDF) fiber], pasting properties (by Micro-ViscoAmylograph, MVAG), in vitro antioxidant activity (AOX), total phenolic content (TPC), soaking (hydration rate) and cooking (optimal cooking time) properties. Pinto beans (PB) were used as control. Starch and protein amounts ranged from 36.3-40.2% and 22.3-25.9%, respectively. TDF ranged from 27.1% (PB) to 34.9% (KP), with an IDF/SDF ratio of 5.9 and 3.0, respectively. Heirloom beans exhibited lower gelatinization temperatures (72.1-75.2⁰C) compared to PB (77.5⁰C). Moreover, they reached higher values of maximum viscosity (332-468 mPa*s) and setback (352-403 mPa*s) than PB (max viscosity: 301 mPa*s; setback: 295 mPa*s), suggesting higher swelling and retrogradation tendency. Soaking time (defined as time to reach 50% hydration) ranged from 273 min to 319 min for TE and KP, respectively. All heirloom beans required lower soaking time than PB (490 min). Cooking times (determined by tactile method) were very similar (60 and 85 min for PB and HS, respectively). JC and HS showed the highest and lowest AOX activity (49.5 vs 10.5%) and TPC (2.38 vs 1.40 mg GAE/g), respectively. Before cooking, heirloom beans showed lower values for both AOX (13.3-49.5%) and TPC (1.40-1.73 mg GAE/g) compared to PB (AOX: 65.9%; TPC: 2.23 mg GAE/g), with the exception of JC that showed a similar value to PB for TPC (2.38 mg GAE/g). Interestingly, loss of AOX activity during cooking was lower in heirloom beans (8.3-37.6%) compared to PB (49.6%). Moreover, after cooking TE showed higher TPC than PB (4.43 and 3.90 mg GAE/g, respectively). This study improved current knowledge of quality characteristics of heirloom beans.