The dry bean (Phaseolus vulgaris L.) is an important grain legume that is used for human consumption worldwide. In Africa and other parts of the World, legume diets contribute tremendously to protein and energy requirements of consumers. Dry beans provide about 16- 33% protein, dietary fibre (between 14 and 19%), starch, minerals and vitamins. Dry beans have a long storage life and can be cooked as whole grains, fried or dehulled and splitted for production of dhal and salads. There is a tremendous variability in the dry bean varieties. It is believed that consumer preferences for dry beans are influenced by factors such as seed size, seed colour, cooking time and flavour. Although, substantial research has been done on physicochemical properties, description of sensory properties that differentiate bean varieties specifically in terms of liked or disliked flavours was lacking. Sensory evaluation is one of the methods used for evaluating product quality and it can be used to describe the sensory properties of a product (i.e. descriptive sensory evaluation) and determines its acceptability by consumers (i.e. consumer acceptability or preferences). Physicochemical properties and descriptive sensory evaluation of six dry bean varieties (Jenny, Kranskop, PAN 148, AC Calmont, PAN 150 and Mkuzi) from Mpumalanga (MP) and Free State (FS) locations of South Africa were determined. Significant (p<0.05) variety, location as well as location x variety interaction effects were found for both physicochemical and sensory properties of beans. Of the six bean varieties, Jenny (FS), Mkuzi and PAN 148 (MP) beans had relatively long cooking times (>60 min) using a Mattson Bean Cooker. PAN 150 beans from both locations were described as bitter, soapy and metallic with a raw bean flavour. Mkuzi beans were mostly described as having a soapy mouthfeel. Jenny (MP), Kranskop (MP&FS) were sweet, soft and with a cooked bean flavour. Consumer sensory evaluation revealed that beans with sweet, soft and cooked bean flavours were the most preferred. Beans that took long to cook and those that were described as bitter, soapy and metallic in the mouth, received low consumer ratings on a 9-point hedonic scale. The total polyphenol content of PAN 150 (MP), along with Jenny and AC Calmont from MP was determined to find out whether the bitterness was associated with its polyphenol concentration. PAN 150 beans had the lowest concentration of total polyphenols compared to the two other varieties, suggesting that factors other than total polyphenol content caused the bitterness of these beans. A follow up investigation of mineral profiles in whole bean flour of all six bean varieties from the two locations was done to find out whether differences in mineral content e.g. iron (Fe) contributed to bitterness and metallic mouthfeel of certain beans. Results showed significant (p< 0.05) variety differences for phosphorous (P) and significant (p< 0.05) location differences for magnesium (Mn) only. Fe and copper (Cu) contents did not contribute to bitterness or metallic mouthfeel of PAN 150 beans. For maximum consumer acceptability, farmers should concentrate on the production of beans that have characteristics similar to Kranskop (MP&FS), PAN 148 (FS) and Jenny (MP) beans. As bean hardening was suspected in Jenny (FS), PAN 148 (MP) and Mkuzi (MP), the importance of storing beans at proper temperatures (e.g. less than 35ºC) and relative humidity (e.g. < 75 %) should be emphasized to minimize the development of the hard-to-cook defect over long storage periods.
Dissertation (MSc(Agric))--University of Pretoria, 2008.