Making fibrous plant meat with less refined, starch-rich crops

The reduction of meat consumption is considered an effective way to increase the sustainability of one’s diet. Meat analogues can help consumers to eat less meat and more plant-based foods. It is suggested that meat analogues should mimic the texture and taste of real meat as much as possible. The texture, specifically the fibrous structure of meat, can be re-created from plant-based ingredients in thermo-mechanical processes such as High Moisture Extrusion (HME) or High Temperature Shear Cell (HTSC). Currently, mainly proteins from soy, wheat and to a lesser extent pea are used in meat analogues, which are obtained after intense fractionation processes. However, it is now recognized that new and less processed ingredients have to be incorporated to prevent monocultures and to increase the sustainability of meat analogues. In this dissertation, we aim to explore the potential of faba beans as a new ingredient for fibrous meat analogues and unveil the effect of using less refined ingredients. The latter introduces more starch to the final product.

In Chapter 2, we described the suitability of Faba bean Protein Isolate (FPI) as an ingredient in gluten-containing fibrous meat analogues and compared it to Soy Protein Isolate (SPI) and Pea Protein Isolate (PPI). Swelling experiments revealed a universal interaction of gluten and the legume proteins, where the gluten formed a continuous network and exerted a pressure on the legume phase, which prevented it from swelling. Furthermore, we found that gluten formed fibrous structures on its own, while SPI, PPI and FPI did not. We concluded that gluten was responsible for the formation of fibrous structures and the non-gluten protein acted as a filler. A gluten content of 50% (d.b.) was necessary to form fibrous structures, which confirmed that gluten needs to form a continuous network to form a fibrous structure.

To increase sustainability of the ingredients, we moved from isolates to concentrates. However, less refined raw ingredients sometimes lack the alleged functional properties for making fibrous food products. A high water holding capacity (WHC) is considered one of the functional properties relevant for fiber formation in the HTSC. In Chapter 3, we therefore studied the WHC of Faba bean Protein Concentrate (FPC), a mildly refined faba bean product. We found that the WHC of FPC was lower than that of Soy Protein Concentrate, but could be increased via a dry heat treatment. The dry heat treatment partially denatured the native protein in FPC and thereby increased the hydrophobicity of the protein. This led to aggregation, a lower protein solubility in water and finally an increased WHC of FPC.

Faba beans contain a significant amount of starch. In Chapter 4 we reviewed the literature on the use of starch in meat and meat analogues. We discovered that purified starch is used as a functional ingredient in meat and meat analogues, often in modified form. We called this exogenous starch, because it is added to the recipe. Starch that is endogenously present in the original matrix of less refined or whole crop ingredients is rarely added deliberately, minimizing the reviewable literature findings in this regard. We proposed a new approach in which endogenous starch can be modified ‘in-situ”, using conventional starch modification processes as a route to obtain functional ingredients. The effect of starch on textural properties such as hardness and springiness of fibrous products has been investigated empirically, while deductive studies on the effect of starch on the mechanism of fibre formation are still lacking.

This gap in the literature was taken as motivation for the work described in Chapter 5, where we explored the effect of starch on the formation of fibrous structures in the HTSC when mixed with gluten. We found that low amylose content starch (Amioca Starch - AS) disrupted fibre formation due to its inability to form a gel, while intermediate amylose content starch (Maize Starch – MS) and high amylose content starch (Hylon VII) could be applied in the same way as protein isolates. Pre-gelatinizing MS improved its structuring potential and resulted in remarkable textural properties, most notably a large anisotropy of the Young’s modulus that was previously not seen with protein ingredients.

Chapters 2, 3 & 5 revealed that the interaction of the ingredients with water played a large role in the formation of fibrous structures. In Chapter 6 we therefore quantified the water content of the protein and the starch phase of doughs at room temperature and gels at high temperatures. The samples were made from air-classified faba bean fractions, but we modelled the water content of the individual starch and protein water phases. For the doughs, data for modelling was extracted from the partial sorption isotherms of doughs containing different amounts of starch, protein and water. The water content of the protein phase in the gels was modelled using the denaturation temperature of legumin. We found that starch takes up less water than protein at room temperature. The often described swelling of starch before initial gelatinization did not increase the water content of the starch. However, upon protein gelation, the starch had absorbed more water, thereby lowering the water content in the protein. We concluded that the water had migrated from the protein to the starch phase after the initial gelatinization of starch but before or during the gelation of protein.

The dissertation was concluded with a general discussion of the results in Chapter 7. We reviewed the role of gluten as an agent of the formation of fibrous structures and revealed new insights regarding zein as a possible alternative. We discussed the use of faba beans as novel ingredient, as well as the opportunities and challenges that stem from using less refined ingredients. A list of ingredient requirements for fillers in fibrous structures was presented, along with a list of desirable properties. We highlighted the importance of water distribution in protein-starch blends and suggested thermal pre-treatments as a tool to improve the functionality of ingredients. To round out the dissertation, a new approach in the search for suitable new ingredients for fiber formation was proposed.