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Comparative assessment of NaOH and NH4OH in alkaline extraction of lentil and chickpea sidestream proteins: impacts on protein quality and process sustainability
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DOI：10.1007/s00217-026-05246-x.png)
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Abstract
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Preservation of protein quality is critical in food technology because it influences product functionality and consumer acceptance. To our knowledge, this study provides the first systematic comparison of ammonium hydroxide (NH4OH) and conventional sodium hydroxide (NaOH) as alkaline extraction agents for recovering proteins from broken chickpea and lentil seeds, a pulse-processing sidestream. The extraction methods were evaluated with respect to protein recovery, structural preservation, colloidal stability, visual quality, and process sustainability. Following compositional characterisation of the biomass, extraction trials revealed that NH4OH produced comparable protein yields (65–69%) to NaOH (62–73%). However, NH4OH extraction significantly reduced alkali-induced browning (browning index, NH4OH vs. NaOH: lentil, 21.9 ± 3.9 vs. 41.3 ± 4.5; chickpea, 16.7 ± 1.5 vs. 24.8 ± 4.0), protein aggregation, and the degree of hydrolysis (free amino groups, NH4OH vs. NaOH: 41–61 mM vs. 69–75 mM glycine equivalents). Dynamic light scattering confirmed smaller aggregate sizes in NH4OH extracts, while SDS-PAGE and FTIR demonstrated improved structural preservation. Additionally, the buffering capacity of NH4OH yielded smoother suspensions during low-pH precipitation, resulting in lighter-coloured, more uniform dried protein concentrates. From a process sustainability perspective, literature proposes thermal NH4OH recovery via evaporation; however, acidification during protein precipitation converts the base into non-volatile ammonium chloride (NH4Cl), rendering recycling impractical. Nonetheless, the resulting NH4Cl stream may present opportunities for future valorisation as a nitrogen-rich agricultural fertiliser, subject to further agronomic and techno-economic evaluation. NH4OH-extracted proteins, with their better-preserved structure and lighter colour, may benefit applications such as pale plant-based beverages, edible films and selected food or biomaterial formulations, pending further validation and regulatory approval.
Keywords:
NaOH
NH4OH
Alkaline-extraction
Protein stability
Sustainability
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