Food Research International xxx (xxxx) xxx Please cite this article as: Clare Kyomugasho, Food Research International, https://doi.org/10.1016/j.foodres.2020.109794 Available online 16 October 2020 0963-9969/© 2020 Elsevier Ltd. All rights reserved. Evaluation of storage stability of low moisture whole common beans and their fractions through the use of state diagrams Clare Kyomugasho * , Paul G. Kamau, Shruti Aravindakshan, Marc E. Hendrickx KU Leuven, Department of Microbial and Molecular Systems (M 2 S), Laboratory of Food Technology, Kasteelpark Arenberg 22, Box 2457, 3001 Leuven, Belgium A R T I C L E INFO Keywords: Common beans Glass transition temperature State diagrams Storage stability Hard-to-cook Cotyledon Cell wall ABSTRACT A material science approach was explored towards understanding storage stability of common dry bean seeds. State diagrams of powders from distinct bean varieties were generated through determination of their glass transition temperatures (Tgs) using differential scanning calorimetry. Confronting the state diagrams with dry matter-temperature combinations during storage facilitated establishing the link between the relative position of the bean storage conditions along the Tg line and extent of hard-to-cook (HTC) development. Generally, Tg increases with dry matter content of the bean powders implying stability at increasingly higher temperatures attributed to the reduced plasticizing effect of water. Whereas Tg lines of powders of the different bean varieties were very similar, distinct differences were observed for the powders of bean substructures. At a given moisture content, the Tg of the cotyledon material was lower than that of the seed coat material and the Tg values of the whole bean powders were dominated by the cotyledon material. Cooking time analysis showed that whole beans stored above their Tg developed the HTC defect, this extent being correlated with the difference between storage temperature and Tg value. Considering the HTC development rate, (R-value, rate of change in cooking time with storage time over a period of 0–4 months or at 0 months of storage) the higher the difference between the storage temperature and the Tg value, the faster the change in cooking time during storage. Exploring the role of the major polymer components of bean cotyledon revealed that at a given moisture content, the cell wall material showed the lowest Tg values compared to the protein and starch isolates (Tg cell wall < Tg protein < Tg starch isolate). Confronting these values with the HTC development rates (change of cooking time with storage time) supports involvement of the cell wall material and probably protein changes in the development of this defect. 1. Introduction Legumes are widely grown and consumed throughout the year in developing countries, and have in the recent years gained renewed in- terest in developed countries due to their suggested nutritional and health associated benefts as well as environmental sustainability (Uebersax, 2006; Willett et al., 2019). Generally, legumes are dried after harvest to facilitate transportation and storability as well as to prolong their shelf life (Njoroge et al., 2016). However, their storage presents a great challenge, particularly in (sub)tropical countries where conditions of high temperature (>25 ◦ C) and high humidity (->65%) prevail. Under these conditions, legumes develop the ‘hard-to-cook’ (HTC) defect, a physiological defect that results in legumes exhibiting pro- longed cooking time to soften and achieve desired palatable texture (Liu & Bourne, 1995; Shiga, Cordenunsi, & Lajolo, 2009), a situation that reduces the convenience and limits utilization of legumes, promoting their postharvest loss (Mubaiwa, Fogliano, Chidewe, & Linnemann, 2017; Njoroge et al., 2016). Although research dedicated to understanding the HTC defect dates back to the 1940 ′ s and several solutions including appropriate storage have been proposed in order to prevent development of this phenome- non (Reyes-Moreno, Paredes-Lopez, & Gonzalez, 1993), there is a lack of mechanistic understanding both from a (bio)chemical reaction point of view and the material science point of view (molecular mobility). It is however clear that it is important to control the factors that promote the (bio)chemical changes implicated in the several hypotheses explaining the development of the HTC defect including the pectin-cation-phytate, the protein-starch, the lignifcation like and the membrane damage by lipid oxidation hypotheses (and combinations thereof) (Liu & Bourne, 1995; Reyes-Moreno et al., 1993). Of particular interest is understanding the conditions of moisture content of the legumes linked to relative humidity of the storage unit, temperature and storage time, which * Corresponding author. E-mail address: clare.kyomugasho@kuleuven.be (C. Kyomugasho). Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres https://doi.org/10.1016/j.foodres.2020.109794 Received 30 July 2020; Received in revised form 3 October 2020; Accepted 5 October 2020