Soy fractionation pathways for food applications
The market for plant-based alternatives for meat products is growing for about a decade now (Ismail et al., 2020). Initially, traditional soy-foods were consumed for thousands of years, and still remain popular in Eastern diets nowadays also as alternative to meat. More recent though, the versatile properties, health benefits and relatively low price of soy has made it a source for the production of protein ingredients, which in their turn have stimulated the innovation of soy-based products, especially meat analogues, for broad markets (Thrane et al., 2017). As a results, novel soy-foods are mainly developed based in the use of soy protein ingredients, but the current forms of commercially available soy protein ingredients are not optimized for these products. Specifically, current fractionation processes of soy protein focuses on achieving high protein purity, or specific protein functionality to fit broad applications as functional ingredients at low addition levels. Unfortunately, resource- and energy-intensive processing steps are involved in the process of making soy protein ingredients. Therefore, it was deemed important to investigate more effective fractionation pathways to produce functional soy protein ingredients aimed at use as bulk ingredient in novel food applications such as meat analogue.The current aqueous fractionation process of soy protein includes sequential oil extraction, alkaline solubilization, acid precipitation and intensive washing steps to remove oil, insoluble carbohydrate and soluble carbohydrate in the soybean, respectively. This process leads to ingredients with a protein content over 85%. The oil extraction and intensive washing steps require the use of organic solvent (such as hexane) and large amount water respectively, which is undesired from an environmental point of view for soy fractionation. Therefore, we explored the effects of simplification of current process by omitting these steps. The majority of oil was successfully removed from full-fat soy flour (FFSF) by centrifugation, and the protein content of soy protein-rich fractions (SPFs) was enriched to around 75%. Further, since high protein solubility may not be essential for developing novel soy-foods, such as meat analogues, we explored a pH adjustment step (Chapter 2) or a moisture heating treatment (Chapter 3) to produce the SPFs. We concluded that the change of processing pH or heating temperature markedly altered the functional behaviors of obtained SPFs without influencing their compositions.Next to the simplified aqueous fractionation developed in Chapter 2, we simplified the process further by removing the acid precipitation step (Chapter 4). The protein content of SPF was reduced after additional simplification but still comparable to the purity of commercial SPC. During the aqueous fractionation, NaOH is regularly used as the basic solution for pH shifts in the alkaline solubilization and neutralization step, which introduced extra Na content to the soy ingredient. With the use of Ca(OH)2 as an alternative, the pH shifts provided the chance for Na reduction, as well as Ca enrichment. We found that the use of Ca(OH)2 in the alkaline solubilization step enhanced the protein content of SPF. The Ca content of the SPF was almost completely determined through the use of Ca(OH)2 in the neutralization step. That lowered the Na content as well. However, complete replacement of NaOH by Ca(OH)2 altered the functionality of SPF drastically, especially the reduction of protein solubility, in such a way that the SPF became less suitable for application as ingredient in meat analogue applications.Therefore, in Chapter 5 we continued to explore the use of Ca(OH)2 in the neutralization step to gain more in-depth understanding on how the Ca enrichment affects the soy protein. Instead of completely replacing NaOH by Ca(OH)2, combinations of NaOH and Ca(OH)2 in different ratios were applied to neutralize the protein-rich dispersions, and the effects of Ca enrichment on the conformation and functionalities of soy protein were discussed. No separation step was performed after the neutralization step, so the Ca and Na content in the SPF could be precisely controlled by adjusting the ratios. The functional changes of SPF were impacted mainly by the difference on Ca content. However, we observed a critical Ca concentration (6.5 mg Ca/g protein), below which the structural and functional properties of soy protein were not changed significantly. Therefore, the Ca content in the SPF can be enriched to a certain level without strongly impacting the applicability of SPF.Chapter 6 we focused on using aqueous ethanol washing process to produce SPF. Cold-pressed de-fat soy meal (DFSM) was used as the starting material. It was observed that the washing process was limited in enrichment of the protein content because the insoluble carbohydrate fraction of the soy meal was hardly removed. The SPFs obtained in this chapter generally had lower protein content than the aqueous fractionated SPFs described above However, washing with 40-80% ethanol led to SPFs with relatively high protein yield and low oil oxidation level. The fractions obtained after washing has a certain range of functional properties, controlled by both protein and non-protein components that might be relevant for food application.To conclude, we explored the potential of using simplified fractionation and washing process to make novel soy ingredients. The production of less refined ingredients usually involves fewer processing steps, which may reduce energy consumption and increase resource use efficiency. The residual oil in the ingredients can possibly decrease the use level of refined oil in meat analogue formulations. However, the sustainability of the proposed fractionation pathways needs to be further quantified to be able to select the more sustainable process for novel soy-foods like meat analogue. A further step is to extend this research to other oilseeds or legumes.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
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Wageningen University
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| Subjects: | Life Science, |
| Online Access: | https://research.wur.nl/en/publications/soy-fractionation-pathways-for-food-applications |
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