Emulsifying properties of lentil protein preparations obtained by dry fractionation

Matthias Funke,Remko Boom,Jochen Weiss,Caspar Winkelmeyer,Mareike Krayer,Myriam Loeffler

doi:10.1007/s00217-021-03883-y

Matthias Funke, Remko Boom + Show 4 more

Open Access

https://doi.org/10.1007/s00217-021-03883-y

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Abstract

Dry fractionated legume protein ingredients are gaining attention as alternatives to conventional solvent extracted legume proteins, being more resource efficient and often exhibiting novel functional properties. However, lack of knowledge about the relationship between composition and functionality limit a more wide-spread use of dry-fractionated legume protein in applications. In this study, lentil fractions of different degrees of refinement were prepared using air classification having protein and starch contents of 16–59% and 4–64%, respectively. The dry fractionated lentil fractions could emulsify and stabilize 10 wt% oil-in-water emulsions, while a conventional lentil protein isolate used for comparison was not able to form stable emulsions. The latter had significantly larger mean droplet diameters (around 20 µm) due to droplet flocculation than emulsions made with the different lentil fractions ranging between 0.3 and 5.5 µm. Similar surface charges (between −22 and −31 mV) indicated that the discrepancy could be ascribed to differences in steric repulsion and mechanical strength of the interfacial layers between conventionally and dry fractionated lentil. Storage stability tests of emulsions stabilized with dry fractionated samples resulted in separation into a low and higher density phase with the individual droplets being stable against coalescence in both phases. The phase separation was attributed to gravimetrical sedimentation of larger insoluble components accumulating in the denser phase, which was impacted by the degree of refinement by air classification. The results highlight the potential of dry fractionation for the production of sustainable ingredients with unique composition and functionality.

Highlights

The increasing world-wide demand for protein is one of the major challenges for the global food system [1]
lentil flour fractions (LFF) was initially able to stabilize emulsions, while Lentil protein isolate (LPI) was not, but LFF-stabilized emulsions phase separated after storage, which could not be ascribed to classical destabilization mechanisms
We attributed the destabilization to gravimetric sedimentation of larger particles and aggregates, dragging some the associated oil droplets with it

Summary

Introduction

The increasing world-wide demand for protein is one of the major challenges for the global food system [1]. It is generally accepted that this demand can only be satisfied with a high proportion of plant-based proteins. European Food Research and Technology (2022) 248:381–391 these structures are liberated by a milling process yielding a finely milled flour that can be separated in a proteinrich and a starch-rich fraction by air classification. Wet fractionation yields protein fractions that have characteristic solubility curves with low solubilities around the isoelectric point of the extracted proteins. This is because the extraction often uses precipitation at the isoelectric point to form protein sediments that is separated by filtration. Wet fractionated protein ingredients may contain high amounts of insoluble protein aggregates due to dehydration processes like spray or drum drying. During drying, proteins may be exposed to high product temperatures that can cause changes in the state of proteins, i.e., a loss of nativity, which in turn affects their functional properties [6, 7]

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