THE ROLE OF HARD TO COOK DEVELOPMENT AND SUBSEQUENT PROCESSING ON NUTRIENT DIGESTIBILITY AND OVERALL ACCEPTABILITY OF COMMON BEANS (Phaseolus vulgaris L.)
Food insecurity and malnutrition strongly limits achievement of sustainable development and hunger and poverty reduction which is one of the 2030 Sustainable Development Goals. Protein, energy and micronutrient deficiencies are usually the common causes of widespread malnutrition. Incorporation of legumes in diets, especially in developing countries, could help in eradicating protein energy malnutrition. Legumes serve as a major source of dietary proteins as they are relatively cheap compared to meat sources of proteins. Legumes also provide complex carbohydrates, dietary fibre, unsaturated fats, vitamins and essential minerals to the human diets. Despite their nutritional relevance towards ensuring food security, legumes in general when stored at conditions of high temperatures and high relative humidity, which are the conditions experienced in tropical regions, have been shown to develop hard to cook. This is a phenomenon characterized by prolonged cooking time for the legumes to achieve the desired softening. The long cooking times required for the hard to cook legumes has been shown to limit their utilization due to the high fuel costs incurred. It has also been hypothesized in literature that hard to cook development could have an influence on the digestibility of nutrients. Moreover, a factor such as convenience has become an important driver of food choice and therefore legumes that require prolonged cooking times do not come as first choice hence limiting consumer acceptability. Although the mechanisms of the hard to cook phenomenon in legumes have been widely explored, a few studies have investigated the development of the hard to cook phenomenon in relation to the digestibility of these nutrients in a systematic way. It is therefore the aim of this project to determine how storage induced hard to cook defect and processing influences the digestibility and bio-accessibility of nutrients and how this affects the overall acceptability of these common beans by consumers. This overall objective translates in five specific objectives: In the first specific objective the role of variety and hard to cook phenomenon on texture kinetics will be evaluated and this will be coupled with microstructural characterization of the samples. Different common bean varieties shall be stored at 35°C and 80% relative humidity for a period of 4 months from which samples with different levels of hardness will be selected. Texture analysis will be done on the selected samples from which cooking profiles will be obtained. Microstructural characterization of the samples will also be done using a light microscope. In the second specific objective, the role of variety and hard to cook on influencing starch digestibility shall be evaluated. For this objective samples selected as in objective one shall be subjected to in vitro digestion protocol from which products of starch hydrolysis shall be analyzed to determine the starch digestibility for the different samples. Additionally, fluorescently labelled α-amylase and proteases enzymes shall be used to microscopically visualize how these enzymes take action and whether they act synergistically to aid in in vitro digestion. In the third specific objective the role of variety and hard to cook phenomenon on influencing mineral bio accessibility will be investigated. For this objective samples will be subjected to in vitro digestion protocol from which the digests will be analyzed for minerals content. Minerals bio accessibility will be expressed as a fraction of minerals content in the digests to mineral content in the original sample. The fourth specific objective will involve evaluation of the role of variety and hard to cook on volatile flavors. Sample analysis will be conducted using an untargeted fingerprinting approach and a headspace-solid phase micro extraction-gas chromatography-mass spectrometry (HS-SPME-GC–MS) system will be used to profile the volatiles. The fifth and final specific objective will involve evaluating how flavor and palatability affects consumer acceptability of common beans. For this objective, a sensory analysis will be conducted using 9-point hedonic scale. With the focus on postharvest storage and processing, this project aims to foster understanding of the utilization of legumes such as common beans to improve consumer acceptability. More specifically, the insight obtained on nutrient digestibility and bio-accessibility coupled with aroma chemistry of cooked legumes will be helpful towards developing convenient legume products of high nutritional value.