Antioxidants, nutritional, antinutrients and functional characteristics of black turtle bean (Phaseolus vulgaris): synergistic and antagonistic interrelationship of epigeal germination periods

Abstract

Purpose Black turtle bean has nutritional potentials in the human diet and could provide a significant amount of food in developing countries. Low consumption of black beans has been attributed partly to the hard-to-cook phenomenon which requires a long time of cooking. Germination improves nutritional, functional, bioactive compounds, reduces anti-nutrients and cooking time. Germinated black turtle bean can contribute to efforts geared towards the production of functional foods and the fight against protein malnutrition. This study aims to investigate the changes in the nutritional, antioxidants and functional properties of black turtle bean due to different epigeal germination times to increase its utilization in food systems. Design/methodology/approach Black turtle bean seeds (Phaseolus vulgaris) were cleaned, winnowed, washed, soaked for 16 h, drained and subjected to epigeal germinated at ambient temperature for 0, 24, 48, 72 and 96 h, respectively. The germinated seeds were dried, dehulled, milled and sieved. Proximate, antioxidant properties and activity, anti-nutrients, mineral (calcium, phosphorus, iron, sodium, manganese, copper, potassium, zinc and magnesium) and functional properties (water absorption capacity, oil absorption, bulk density, swelling index, water solubility index and gelling concentration) of the germinated black turtle bean (GTB) flour (0GTB, 24GTB, 48GTB, 72GTB and 96GTB) were determined using standard procedures. Findings The ash, protein, fat and fibre contents of the black turtle bean were significantly increased through germination. Germination resulted in changes in the antioxidant activity of the black turtle bean samples. The mineral content of the black bean samples was improved significantly by germination and as well altered the functional properties (p < 0.01). Oxalate and phytate were significantly reduced with increased germination time (p < 0.01). In total, 96 h germination (96GTB) had better antioxidant activity, mineral and proximate composition with lower anti-nutrients. Originality/value Germination for 96 h proved to be the optimum time for improved mineral content, increased protein, ash, fibre, antioxidant activity and property with reduced antinutrients. Germination represents an attractive, inexpensive means of improving the nutritional profile and enhancing the bio-functionality of the black turtle bean. The epigeal germinated turtle bean could find applied as a functional ingredient in food formulation.