Comparing methods to produce fibrous material from zein

https://doi.org/10.1016/j.foodres.2019.108804Get rights and content

Highlights

  • Zein fibres can be produced using economical, food grade methods.

  • Electrospun zein nanofibres do not currently offer an economical solution.

  • Antisolvent precipitation depends on the Marangoni effect for fibre formation.

  • Easily oriented mechanically elongated fibres yield chicken-like texture properties.

Abstract

Three methods to produce fibrous material from zein, either as fibrous networks or individual protein fibres, were identified and developed for the purpose of providing a fibrous structure to whole-tissue meat analogues. These methods are: electrospinning, antisolvent precipitation of zein from ethanol using water and mechanical elongation of self-assembled zein networks. Analysis of the fibres was carried out using scanning electron microscopy, as well as texture profile analysis, moisture content and water holding capacity of the fibres within model meat analogue, tofu-style soy gels. Different advantages were identified for each of the three methods. Electrospinning produces individual fibres of the smallest scale, however the process used here was found to have a low throughput and be extremely inefficient. Antisolvent precipitation was the most rapid method, producing a web-like network, however the fibre formation was uncontrolled in terms of size and orientation. Finally, mechanical elongation allowed for great control over the formation of an oriented fibrous network, however advanced techniques to incorporate individual fibres into a matrix must be established. When incorporated into model meat analogue soy protein isolate gels, fibre quantity and orientation appeared to be the most determinant factors in creating statistically similar textures to chicken. The choice between fibre forming methods will ultimately depend on processing requirements and formulation of the eventual meat analogue product.

Introduction

The prevalence of veganism and vegetarianism is continuously increasing, and one major reason for this is because the meat industry is far from sustainable. The excessive amount of resources required for raising cattle, including land and water, and the associated emissions of greenhouse gases, make this practise unsustainable. In comparison, production of plant protein requires a fraction of the land space and water, and the issue of excess greenhouse gas emissions is diminished (Scarborough et al., 2014). Shifting to the increased consumption of plant proteins is therefore intriguing due to the beneficial environmental impact while still providing the needed source of protein in the diet. While consuming a plant-based diet, many now turn to meat analogues: innovative products that strive to mimic the sensory qualities of meat. In a life cycle assessment of a recently popular meat analogue (Beyond Meat’s Beyond Burger) it was determined that there are no situations or conditions where the environmental impact of the meat analogue would be worse than beef farmed in the U.S., in terms of greenhouse gas emissions, use of non-renewable energy, impact on water scarcity, and impact on land use (Heller & Keoleian, 2018).

Meat analogues currently available are primarily composed of coagulated, texturized or extruded proteins, limiting the possible size of pieces produced. In addition accurately mimicking meat’s characteristic oriented, fibrillar structure has proven difficult, further restricting meat analogue products primarily to ground meat applications, such as burgers and sausages. Some of these products have managed to garner significant popularity, however there is still a large gap in the market for meat analogues that more closely mimic whole muscle tissues, such as a chicken breast or a steak. Of the currently available meat analogue products, those that have the most meat-like structures are produced through high moisture extrusion of protein mixtures (Liu and Hsieh, 2008, Pietsch et al., 2019, Yao et al., 2004). Anisotropic, meat-like structures have also be achieved through high temperature shearing of protein mixtures in a wide gap couette shear cell (Dekkers et al., 2016, Krintiras et al., 2015). Fibrous structures are formed through the orientation process that occurs as screws convey the material within the barrel of the extruder. In the case of shear cells, the structures are formed through the process of shear banding, where shear-induced concentration fluctuations cause layered structures to form and orient in the direction of the shear flow (Manski, van der Goot, & Boom, 2007). However, there are some key disadvantages to extrusion and other high shear methods. This includes limitations to the size of the end product based on the size of the equipment obtained, the expensive investment required for the equipment, and the high energy input required (Liang, Huff, & Hsieh, 2002). Having such a high energy input can negate some of the environmental benefits associated with plant-based proteins. Therefore, the production of whole tissue meat analogues relies on the development of methods to create fibrous material from plant-based proteins using inexpensive, less energy intensive methods.

Zein, the primary storage protein from corn, is an uncommon food ingredient primarily due to the deficiency of certain essential amino acids and the lack of widespread availability (Boye et al., 2012, Shukla and Cheryan, 2001). However, this protein presents a unique advantage in this area as fibrous structures from zein have been visualized at different scales for some time. Lawton (1992) presented SEM images of zein fibres structures that naturally formed within zein-starch doughs after mixing and kneading (Lawton, 1992). Zein fibres can also be formed by simply extruding thin strips or ribbons of zein-ethanol solutions, followed by air drying to remove the ethanol. This concept is applied when extruding the solutions through syringes by hand (Reddy, Li, & Yang, 2009), or using the more sophisticated process of electrospinning (Moomand and Lim, 2015, Selling et al., 2007, Torres-Giner et al., 2008). Anisotropic material has been produced from zein and starch blends using high shear flow (Habeych, Dekkers, van der Goot, & Boom, 2008) and it has been shown that zein can withstand a number of passes through an extruder, opening up additional possibilities if extrusion becomes a more economical option in the future (Selling and Utt, 2013, Selling, 2010). While fibrous structures have been observed or produced for various reasons, no studies up to this point have investigated the production of zein fibres for the specific application of structuring of whole tissue meat analogues. Further, the natural propensity of zein to form fibrous structures is also promising in terms of producing fibres using food grade methods that require minimal equipment and energy.

The objective of this research was to identify and develop different methods of producing fibrous material from zein for the intended use of structuring whole tissue meat analogues. The methods included electrospinning (ES), antisolvent precipitation (AS) of zein from ethanol using water, and mechanical elongation (ME). The resultant fibres from each method were compared in terms of feasibility (energy, cost, scalability and time requirements), the ability and ease of orienting the fibres, and the contribution to texture in model meat analogue systems of tofu-like soy protein isolate (SPI) gels containing the different types of fibres. The model composite gels were analyzed to define the physical properties and compare them with the properties of commercially available tofu and pre-cooked chicken and beef strips.

Section snippets

Materials

Zein from maize was obtained from Flo Chemical Corp (Ashburnham, MA). and soy protein isolate (SPI) (>90% protein) was obtained from Myprotein (Cheshire, UK). Calcium sulphate was obtained from Fisher Scientific (Hampton, NH). Pre-cooked chicken strips, pre-cooked beef strips and tofu were purchased from a local supermarket.

Electrospinning

The electrospinning procedure used was modified from the methods described by Moomand and Lim (2015), with the conditions optimized to produce zein fibres of uniform width

Structure

Though it is obtained in the form of small particles (Fig. 1a), when zein was hydrated and stored at 40 °C, it self-assembled into a characteristic network. At larger length scales, the network structure formed appeared as an agglomerate of zein nuggets (Fig. 1b). The surface of the network was quite smooth and continuous, consistent with previous observations of the surface of cast zein films (Khalil et al., 2015, Lai and Padua, 1997, Pan and Zhong, 2016). At smaller length scales, it was be

Conclusions

This work has demonstrated that there can be economically feasible methods to produce fibrous material from zein for use as a food ingredient, and that the use of fibrous zein to structure meat analogue type products has proven promising. ME zein displayed the greatest potential in structuring whole-tissue meat analogues, as it produced a statistically similar texture to chicken meat (determined by TPA) and was the most promising in terms of economic and functional feasibility. From this

Acknowledgements

The authors would like to acknowledge the Natural Science and Engineering Research Council of Canada for providing financial support for this project (Grant number 05715-2015).

Declaration of Competing Interest

The authors declare there are no conflicts of interest.

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