Optimizing mechanical, moisture-based, and enzymatic pretreatments to improve dehulling outcomes and nutritional quality in four U.S. dry bean market classes

Authors: GRAHAM, WINTER - Michigan State University; Cichy, Karen; SWADA, JEFFERY - Michigan State University

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2026
Publication Date: 8/19/2026
Citation: Graham, W., Cichy, K.A., Swada, J. 2026. Optimizing mechanical, moisture-based, and enzymatic pretreatments to improve dehulling outcomes and nutritional quality in four U.S. dry bean market classes. Journal of Food Science. 91(8). Article 8:e71342. https://doi.org/10.1111/1750-3841.71342.
DOI: https://doi.org/10.1111/1750-3841.71342

Interpretive Summary: Dry beans are globally important sources of plant protein, fiber, minerals, and bioactive compounds, contributing significantly to dietary quality and food security in both high- and low-income regions. Despite their nutritional value and sustainability advantages relative to other protein crops, dry beans remain underutilized as functional food ingredients compared to other pulses such as soy, chickpea, or pea. This ingredient gap is driven largely by technological barriers in processing, particularly those associated with dehulling inefficiency and seed-coat adhesion. This study aimed to identify pretreatment strategies that enhance dry bean dehulling performance and support value-added utilization of resulting fractions. Specifically, the objectives were to: (1) determine the optimal combination of pretreatment variables—moisture level, enzyme concentration, mechanical disruption, and drying conditions—to maximize dehulling efficiency and cotyledon yield in black beans, and (2) evaluate the scalability of these optimized pretreatments across four major U.S. dry bean market classes (black, pinto, navy, and great northern) while assessing the nutritional quality of recovered hull and cotyledon fractions to inform their potential use as functional ingredients. Nutritional analyses demonstrated that optimized dehulling did not compromise cotyledon quality. Small-scale screening identified moisture adjustment to 40% followed by bran-cracking as the primary drivers of efficient hull detachment, while enzymatic application provided a modest but consistent additional benefit under optimized conditions. In contrast, roasting following soaking reduced dehulling performance, underscoring the importance of maintaining adequate moisture during hull-loosening steps. Larger, scaled-up trials supported the industrial potential of these pretreatments. Protein remained concentrated within the cotyledon fraction, while hulls retained high levels of dietary fiber. This work provides industry-ready enzymatic and mechanical pretreatment strategies that significantly improve dry bean dehulling and reduce processing inefficiencies. By recovering seed coat fractions with high fiber content processors can generate new clean-label functional ingredients and reduce waste in future pulse-processing operations.

Technical Abstract: Dry beans (Phaseolus vulgaris L.) are a nutrient-dense and sustainable protein source, with potential for use as a food ingredient, but strong adhesion between the seed coat and cotyledon limits processing efficiency. This study optimized physical and enzymatic pretreatments to improve dehulling performance across four major U.S. market classes (black, pinto, navy, and great northern) and evaluated the nutritional quality of cotyledon and hull fractions. Small- and large-scale trials examined the effects of moisture level and enzyme application on dehulling efficiency (DE), degree of dehulling (DD), and dehulling index (DI). Small-scale trials showed that both mechanical and enzymatic pretreatments significantly enhanced black bean dehulling. At 40% moisture, combined bran-cracking and low-enzyme pretreatment achieved DE = 82.4 ± 2.1%, DD = 95.4 ± 1.2%, and DI = 0.94 ± 0.01, confirming effective weakening of hull–cotyledon adhesion. Bran-cracking alone produced DE = 76.2 ± 2.5%, DD = 92.8 ± 1.9%, and DI = 0.88 ± 0.02, demonstrating a viable enzyme-free alternative. Scaled-up validation across all market classes confirmed reproducibility, with treatments achieving approximately 80–85% DE, 95–99% DD, and 0.90–0.96 DI depending on variety. Enzyme-free treatments were most successful on a larger scale. Compositional analysis showed that hulls contained 33.2 ± 1.5% crude fiber and 6–16% protein while cotyledons contained 12.4 ± 3.5% crude fiber and 19-24% protein, supporting their use as functional food ingredients. These findings demonstrate a scalable framework for enhancing dry bean dehulling while supporting value-added utilization of hulls as functional, fiber-rich ingredients.