What makes the beans ( Phaseolus vulgaris L.) soft: insights into the delayed cooking and hard to cook trait

Cooking quality has recently piqued the interest of bean researchers due to its implications for energy, nutrition, and gender equity and carbon footprints. Cooking imparts unique sensory characteristics, improves digestibility, reduces anti-nutritional factors, and boosts nutritional and biological value in beans. Delayed and hard to cook (HTC) traits result in extended cooking time to confer desired texture. Cooking has a complex mechanistic basis ranging from water imbibition to complex micro and macro structural (impermeable seed coat) and biochemical mechanisms (pectin-cations, lignification, phenols, starch and protein alterations, lipid polymerization, non-starch polysaccharides) that result in hard to cook trait. The mechanistic events leading to water uptake and seed softening may be a useful high throughput assay for genotypic screening for delayed cooking and HTC trait. Cooking time is largely under additive genetic control with high heritability and fast cooking is dominant over slow cooking trait. Use of molecular and genomics approaches has led to identification of various genomic regions on chromosome 1, 2, 3, 5, 6, 7 and 9 associated with cooking time, coding for various cooking related genes such as cystatin/monellin superfamily protein, tonoplast dicarboxylate transporter, acyl-CoA sterol acyl transferase and polygalacturonase. This review discusses, mechanistic insights, genetics and genomics information about delayed cooking and hard to cook trait, that will help breeders to improve cooking quality in beans using effective surrogate traits based on seed physical, biochemical, water absorption and microstructural parameters.