Comparison of dynamic water distribution and microstructure formation of shiitake mushrooms during hot air and far infrared radiation drying by low-field nuclear magnetic resonance and scanning electron microscopy.

BACKGROUND: An abundance of shiitake mushrooms is consumed in dried form around the world. In the present study, changes in water state, water distribution and microstructure of shiitake mushrooms during hot-air drying (HAD) and far-infrared radiation drying (FIRD) processes were investigated using low-field nuclear magnetic resonance and scanning electron microscopy. Quality attributes of the dried products were compared in terms of drying property, appearance, rehydration behavior, texture and storage stability. RESULTS: Compared with HAD, the rate of water diffusion and evaporation of the shiitake mushrooms dried by FIRD was higher, thus resulting in a shorter drying time (630 min), a lower water content (0.07 g g-1 wet basis) and a higher glass transition temperature (7.88 °C) for dried products. Moreover, a homogenous and porous microstructure with less shrinkage and case hardening was demonstrated by the FIRD samples, indicating a superior texture, including a larger pileus diameter (3.4 cm), a higher rehydration ratio (7.31), a lower hardness (37.93 N) and a higher crispness (1.41 mm) for FIRD shiitake mushrooms. CONCLUSION: High-quality shiitake mushrooms with a desirable texture could be produced by FIRD by enhancing the diffusion of internal water and alleviating the case hardening during a relatively short drying process. © 2018 Society of Chemical Industry.

Understanding the Relations Among the Storage, Soaking, and Cooking Behavior of Pulses: A Scientific Basis for Innovations in Sustainable Foods for the Future.

The world faces challenges that require sustainable solutions: food and nutrition insecurity; replacement of animal-based protein sources; and increasing demand for convenient, nutritious, and health-beneficial foods; as well as functional ingredients. The irrefutable potential of pulses as future sustainable food systems is undermined by the hardening phenomenon that develops upon their storage under adverse conditions of temperature and relative humidity. Occurrence of this phenomenon indicates storage instability. In this review, the application of a material science approach, in particular the glass transition temperature concept, is presented to explain phenomena of storage instability such as the occurrence of hardening and loss of viability under adverse storage conditions. In addition to storage (in)stability, application of this concept during processing of pulses is discussed. The state-of-the-art on how hardening occurs, that is, mechanistic insights, is provided, including a critical evaluation of some of the existing postulations using recent research findings. Moreover, the influence of hardening on the properties and processing of pulses is included. Prevention of hardening and curative actions for pulses affected by the hardening phenomenon are described in addition to the current trends on uses of pulses and pulse-derived products. Based on the knowledge progress presented in this review, suggestions for the future include: first, the need for innovation toward implementation of recommended solutions for the prevention of hardening; second, the optimization of the identified most effective and efficient curative action against hardening; and third, areas to focus on for elucidation of mechanisms of hardening, although existing analytical methods require advancement.

Detailed analysis of seed coat and cotyledon reveals molecular understanding of the hard-to-cook defect of common beans (Phaseolus vulgaris L.).

The hard-to-cook (HTC) defect in legumes is characterized by the inability of cotyledons to soften during the cooking process. Changes in the non-starch polysaccharides of common bean seed coat and cotyledon were studied before and after development of the HTC defect induced by storage at 35°C and 75% humidity for 8months. Distinct differences in the yields of alcohol insoluble residues, degree of methoxylation (DM), sugar composition, and molar mass distribution of non-starch polysaccharides were found between the seeds coat and cotyledons. The non-starch polysaccharide profiles, both for seed coats and cotyledons, significantly differed when comparing HTC and easy-to-cook (ETC) beans. In conclusion, differences in the structure, composition and extractability of non-starch polysaccharides between the ETC and HTC beans confirmed the significant role of pectin polysaccharides in interaction with divalent ions in the HTC development, which consequently affect their cooking behaviors.

Hydration properties and texture fingerprints of easy- and hard-to-cook bean varieties.

The objective of this study was to understand the factors that affect the hydration and cooking profiles of different bean varieties. During this study, nine bean varieties were classified as either easy-to-cook (ETC) or hard-to-cook (HTC) based on a subjective finger pressing test and an objective cutting test. Rose coco, Red haricot, and Zebra beans were classified as ETC, while Canadian wonder, Soya fupi, Pinto, non-nodulating, Mwezi moja, Gwaku, and New mwezi moja were HTC. The effect of different soaking (pre)-treatments on the cooking behavior and/or water absorption of whole or dehulled beans was investigated. Dehulling, soaking in high pH and monovalent salt solutions reduced the cooking time of beans, while soaking in low pH and CaCl2 solutions increased the cooking time. Moisture uptake was faster in ETC and dehulled beans. Soaking at high temperatures also increased the hydration rate. The results point to pectin-related aspects and the rate of water uptake as possible factors that influence the cooking rate of beans.

Extraction and characterization of pectic polysaccharides from easy- and hard-to-cook common beans (Phaseolus vulgaris).

The occurrence of the hard-to-cook (HTC) defect in legumes is characterized by the inability of cotyledons to soften during the cooking process. This phenomenon may be influenced by pectin properties. The objective of this study was to characterize the pectic polysaccharides comprised in the alcohol insoluble residue (AIR) extracted from easy-to-cook (Rose coco) and hard-to-cook (Pinto) common beans. This would provide an insight in the relationship between the pectin properties and HTC defect. The AIR was extracted from raw, half-cooked hard, half-cooked soft and fully-cooked bean samples. Subsequently, it was fractionated into water-, chelator- and Na2CO3-soluble pectin fractions and a hemicellulose fraction. For the AIR and the pectin fractions, determination of the galacturonic acid content, neutral sugars, degree of methylesterfication (DM), degree of acetylation (DAc) and molar mass (MM) distribution was performed. Results on the pectin fractions, MM distribution and pectin content profile, revealed that Rose coco pectin generally showed higher pectin solubility than Pinto. Neutral sugar profiles indicated that Pinto contained higher amounts of branched pectin (i.e. arabinans) than Rose coco. There was no difference between the DM of Pinto and Rose coco, however, the DAc was higher in Rose coco. In conclusion, the differences in pectin structure and solubility properties between easy- and hard-to-cook common beans might contribute to the differences in their cooking behavior.