Understanding the cooking behavior of common beans: linking texture and flavor evolution during cooking with state diagrams and storage conditions

The quality of plant-derived foods is rooted on composition and cellular structure of the food matrix. Quality attributes of critical importance in food include colour, flavour and texture. In plant-based foods, cellular structure is mostly dependent on polysaccharides that make up the cell wall and middle lamella. Modifications of these polysaccharides during pre-process storage, processing and/or post-process storage due to enzymatic and/or non-enzymatic reactions may lead to drastic changes in quality. Therefore, a lot of research has been done on preservation of quality of plant-based foods before, during and after processing using thermal and non-thermal processing technologies. However, success of such measures demands a full understanding of the possible changes that can cause quality deterioration. Legumes are one of the foods that exhibit deterioration of quality during pre-processing storage. During storage under tropical conditions, they develop a textural defect termed as hard-to-cook (HTC). In this current study, the focus will be on the widely cultivated and consumed legume, common beans (Phaseolus vulgaris), which has been branded as a model food legume. Over the years, there have been attempts on elucidation of mechanisms of HTC development in common beans but the defect is still poorly understood. The extent of HTC development has been shown to be variety dependent and this has led to classification of common beans as either easy-to-cook (ETC) or HTC. Several biomolecules in common beans have been implicated in HTC development, chief among them polysaccharides in the cell wall and middle lamella, which have been shown to undergo modifications during storage. Such modifications include pectin crosslinking, lignin formation, complex formation between proteins and phenolics, and lipid oxidation. The influence of HTC on bean-cooking behaviour and consequently on nutrients and visual and texture appeal of cooked common beans has been investigated. HTC significantly increases cooking time of beans, leading to loss of thermolabile nutrients. It reduces digestibility of starch and proteins as well as bioavailability of the latter. However, there are still knowledge gaps and unaddressed issues that may provide more insights into this defect and its consequences. The objective of the proposed research is to enhance the current knowledge and mechanistic insight in the development of HTC and its consequence in preparing (cooking) legumes. It is well known that for long-term storage and stability of foodstuffs, they should be stored below their glass transition temperatures (Tg). This hypothesis has so far not been evaluated in the context of HTC development of legumes and creates the starting point for the first part of the research. The appropriate storage conditions for prevention of HTC development in common beans have not been defined. It is in this light that the Tg of common beans will be determined in the current study. Since modifications of components of the cell wall and middle lamella occur simultaneously during storage of beans, independent investigations on individual components will not allow a comprehensive understanding of this phenomenon. To achieve this, in the second part of the research an integrated approach that considers the major hypotheses simultaneously and the independent contribution of cotyledons and seed coats to HTC development is vital. A thorough review of literature revealed that this is lacking. Therefore, it is the focus of this study to use an integrated approach in investigating HTC development. To gain more insight into biomolecular changes during cooking of beans, it is imperative to analyse these biomolecules along the cooking profile of beans rather than before and after cooking. A few studies have been done on volatiles from beans but neither along the cooking profile nor with consideration of the influence of HTC. Through analysis of volatiles along the cooking profile, the types of reactions taking place during cooking can be better understood and any volatiles produced due to HTC development can be noted. This approach of analyses along the cooking profile of beans will give a better understanding of the texture-microstructure-biomolecular-flavour relations during cooking.

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