Hard Beans—A Problem for Growers, Processors, and Consumers

Abstract

<jats:p>Hard-to-cook and hard-shell are two textural defects associated with storage of legumes, as typified by the common bean. These defects can lead to failure to germinate, extended cooking times, reduced nutritional value, and economic loss throughout the food chain. Although these losses are predominate in tropical climates, beans stored in temperate areas also will harden eventually, depending on temperature and humidity. Hardened beans also often darken, causing further quality losses. Structurally, hard-shell is associated with the seedcoat and failure of water absorption, while hard-to-cook affects the cotyledons, rendering the cells unable to separate during cooking. Hardening of seedcoats during storage has been reported, and a mechanism based on oxidation and polymerization of phenolic compounds is suspected as being responsible, but few details of the hard-shell defect are known. The traditional theory used to explain the hard-to-cook defect is based on enzymatic hydrolysis of phytate, rendering it unable to chelate divalent cations that then migrate to the middle lamella and participate in crosslinking reactions with demethylated pectins. More recent evidence points to a multiple mechanism of bean hardening, with metabolism of phenolic compounds and membrane deterioration also involved. Control of bean hardening has been attempted at all levels of bean production, processing, and consumption. At present, control of storage conditions, manipulation of agronomic factors, and improved cooking techniques seem to be the best strategies to reduce bean hardening.</jats:p>

Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening

“…Storage of faba bean after flushing with N 2 retards, whereas flushing with O 2 accelerates reduction in phenolic contents, including tannins and proanthocyanidins (Nasar-Abbas et al, 2007). Colour darkening in beans during storage accompanied by seed hardening is probably caused by air-and lightcatalysed oxidation of leucoanthocyanidins, a group of phenolic compounds (Stanley, 1992a). Oxidation of phenolic compounds may directly affect permeability and cookability of seeds.…”

Hard‐to‐cook phenomenon in beans: Changes in antinutrient factors and nitrogenous compounds during storage

“…This is an irreversible phenomenon classified as 'hard-to-cook' (HTC) (Stanley and Aguilera 1985; Hentges ef a1 1991). HTC beans have depressed economic value because of the increased energy requirements for cooking, poor palatability and reduced quality of the protein (Stanley 1992). The rate of HTC development depends on the temperature relative humidity and time of storage.…”

Managing the hard-to-cook (HTC) phenomenon in bambara groundnut (Vigna subterranea (L.) Verdc.) processing for resource limited communities in Zimbabwe

“…Legumes are grown, harvested, dried and then stored until consumption [131,165]. Storage under hot and humid conditions, as encountered in many subtropical and tropical African countries, renders legumes prone to a hardening phenomenon characterized by extended cooking time to ensure adequate softening during cooking [47,131,135,[166][167][168].…”

“…Storage under hot and humid conditions, as encountered in many subtropical and tropical African countries, renders legumes prone to a hardening phenomenon characterized by extended cooking time to ensure adequate softening during cooking [47,131,135,[166][167][168]. HTC in legumes is associated mainly with modifications that occur in the cotyledons and seed coats [131,[169][170][171]. Several intricate factors, external and internal to the tissue, simultaneously contribute to events leading to the HTC phenomenon [172].…”

“…The HTC problem may not seem serious for people living in the developed worlds, who have energy resources and state-of-the-art techniques to utilize HTC legumes. However, in Zimbabwe boiling HTC bambara groundnuts is challenging, especially for those of lower socioeconomic status, who rely on firewood to provide energy for cooking and heating [131,132]. According to [76] a longer cooking time and high energy consumption are important factors limiting bean preparation and consumption.…”