Soybean germination limits the role of cell wall integrity in controlling protein physicochemical changes during cooking and improves protein digestibility

Mostafa Zahir,Vincenzo Fogliano,Edoardo Capuano

doi:10.1016/j.foodres.2021.110254

Mostafa Zahir, Vincenzo Fogliano + Show 1 more

Open Access

https://doi.org/10.1016/j.foodres.2021.110254

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Abstract

Previous studies showed that in vitro digestibility of proteins in cooked beans is modulated by heat treatment and that the effect may be different whether proteins are heated in intact cotyledon or in a bean flour. In this study, germinated and non-germinated soybean cotyledons and flour were boiled at 100 °C for varying times (30, 90, or 180 min). After grinding, the level of trypsin inhibitors, protein aggregation, surface hydrophobicity, the secondary structure, and in vitro digestibility were studied. The presence of an intact cell wall during cooking increased protein denaturation temperature by about 10% and reduced the denaturation of trypsin inhibitors, and induced distinct changes in protein surface hydrophobicity and secondary structure. These physicochemical properties translated into an increment in protein degree of hydrolysis (DH, 72%) of protein cooked for 30 min as flour compared to proteins cooked in intact soybean tissues (64%). Increase in cooking times (90 and 180 min) resulted in limited improvement in the protein digestibility and changes in protein physicochemical properties for both boiled cotyledons and flour. Soybean germination resulted in distinct changes in protein physicochemical properties and higher protein DH% of raw soybean (61%) compared to non-germinated raw soybean (36%). An increase in protein digestibility of germinated soybean was also observed after boiling for both cotyledon and flour. However, significant differences in DH% were not observed between proteins boiled in intact cotyledon and in a flour. This work provides extra knowledge of the role of cellular integrity on protein properties in plant foods and suggests that germination or grinding before cooking may increase protein digestibility.

Highlights

The consumption of plant-based proteins has gained popularity in recent decades due to the increasing demand for sustain able and healthy foods
We provided evidence that protein digestibility is higher in soybean particles that have been produced by milling soybean before boiling compared to particles produced after boiling (Zahir, Fogliano, & Capuano, 2018) This was explained by the higher fraction of broken cells produced when milling is applied before boiling compared to the fraction of broken cells produced when milling is applied after boiling
Investigation of the role played by cellular integrity on proteins physicochemical changes during cooking is of particular interest since it might provide useful information on the improvement of soybean pro tein digestibility

Summary

Introduction

The consumption of plant-based proteins has gained popularity in recent decades due to the increasing demand for sustain able and healthy foods. We demonstrated that protein digestibility in soybean particles obtained by first milling and boiling was higher than protein digestibility of soybean particles of the same size that were first boiled and milled This difference is mainly driven by a different degree of tissue integrity being the fraction of broken cells higher when the soybean was first milled and boiled. Another recent study has indicated that the protein conformational change of bean proteins is different according to whether they are heated inside intact cells (i.e. in the crowded bean intracellular environment) or in a flour (i.e. open environment due to the loss of cellular integrity) (Rovalino-Cordova, Fogliano, & Capuano, 2019). That study showed that differences in protein secondary struc ture may, at least partially, explain the higher digestibility of bean proteins heated in flour

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