Arabinoxylans: A new class of food ingredients arising from synergies with biorefining, and illustrating the nature of biorefinery engineering

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Highlights

  • Arabinoxylans offer a new class of food ingredients through synergy with biorefining.

  • The opportunity to produce AX arises from integration with bioethanol production.

  • AX fractions extracted from sugarcane bagasse show potential as a bread ingredient.

  • Co-producing AX fractions can enhance economics through bioethanol pinch analysis.

  • AX integrated with bioethanol illustrates the required skills of the biorefinery engineer.

Abstract

Arabinoxylans (AX) are hemicellulose polysaccharides comprising a linear backbone of xylose sugars with arabinose residues attached along the chain. They offer interesting functional properties that could have application as a new class of food ingredients or for non-food applications. The emergence in recent decades of biorefineries gives a context in which commercial production of a portfolio of AX products could be feasible, through integration with bioethanol production, using ethanol to precipitate the AX. Extending the concept, AX fractions of different functionality can be precipitated at different ethanol concentrations, giving further scope for efficiencies through bioethanol pinch analysis, while producing a portfolio of products with different potential markets and end uses. The current work demonstrates the potential of AX fractions extracted from sugarcane bagasse as bread ingredients. Bagasse AX fractions increased the water absorption in dough formulations, by more than double their own weight for fractions larger than 10 kDa, and increased dough development time in a Chopin Mixolab. As well as promising in their own right, AX also illustrate the more general opportunity for synergies between biorefining and the food industry, with the rise of biorefineries giving opportunities to provide the food industry with new ingredients not currently available.

Introduction

Biorefineries have emerged in recent decades in response to urgent imperatives to address global issues of oil depletion, national energy security, rural development and climate change (Peck et al., 2009; Cherubini, 2010; Tomei and Helliwell, 2016). The embryonic biorefinery industry has had, however, an uneven and uncertain reception in terms of public perception, political support and commercial viability (Bissett-Amess, 2007; Peck et al., 2009; Campbell et al., 2009; Rosillo-Calle, 2012; Mousdale, 2018; Hinson et al., 2019). Biorefineries suffer from numerous technical, commercial, political and even philosophical and moral challenges. On the one hand, it is recognised at a broad conceptual level that biorefineries have a part to play in alleviating pressure on oil and mitigating climate change, alongside benefits of national fuel security and resilience and support for agricultural communities. On the other hand, the challenges of biorefineries are uniquely specific in terms of technical implementation and economic viability within the particular local, national and international political and regulatory contexts. Entering into the biorefinery business is fraught with uncertainty, both in relation to how best to design and operate this biorefinery in this local and national context, and in relation to the likely stability of political support and associated incentives. Thus, in the UK for example, the histories of plants such as Ensus and Vivergo have been punctuated by frequent and disruptive closures in response to changing contexts that impact the marginal commercial viability of biorefineries (see, for example, Hughes, 2017; Hinson et al., 2019; Sapp, 2021).

Philosophically, the perception of biorefineries has been damaged by understandable but sometimes simplistic concerns over “food versus fuel” and whether, in a hungry world, it is ethically and morally acceptable to be diverting food resources into production of bioethanol and biodiesel for transportation fuel (Pimentel et al., 2009; Graham-Rowe, 2011; Rosillo-Calle, 2012; Tomei and Helliwell, 2016; Mousdale, 2018), with UN rapporteur Jean Ziegler famously declaring biofuels as “a crime against humanity” (Mathews, 2008; Campbell et al., 2009; Peck et al., 2009). These moral concerns have been combined with technical concerns claiming that the net energy delivered by biofuels is in some circumstances marginal or even negative (Pimentel et al., 2009), exacerbated by indirect land-use change (Searchinger et al., 2008).

In response to the first concern, the great hope has been to move to a situation in which lignocellulosic biorefineries, which use feedstocks that do not divert resources from the food chain, become technically and economically feasible, while the second concern has been largely alleviated by increasingly detailed technoeconomic and life cycle analyses (Zilberman, 2017) as well as broader perspectives that note, for example, the benefits biorefining might bring to agriculture in places like Africa (Mathews, 2008). Nevertheless, these objections have caused policy changes, such as the European Union’s abandonment of support for first generation biofuels, that have hindered the emergence of biorefineries (Mousdale, 2018). They have also hindered biorefinery research efforts that have any connection with food, for fear of falling foul of this moral and political objection to possible adverse effects of biorefineries on food prices.

The loud fears regarding antagonism between the food supply chain and biorefineries have obscured the opportunities for synergistic benefits between the food industry and the emerging biorefinery industry. In fact, complete divorce from the food industry has become an expedient policy for biorefineries. Mousdale (2018) notes this development: “A defining feature of a biorefinery…is production of market-ready chemicals from non-food resources”, a policy that sounds innocuous and indeed positively desirable. However, this political and social imperative to be seen to be distancing biorefineries from the food supply chain is a mistake, as it precludes seeking or even acknowledging the substantial synergistic benefits that could be realised through bringing these two sectors, that share so much similarity, more closely together.

The key insight that is missing from much of the debate is that genuine, formal process integration has the power to make the difference to the economics of marginal industries such as food and biorefining. Process integration also reduces energy and resource usage, enhancing environmental benefits as well as economics. The power of process integration tools such as heat and water pinch analysis requires certain conditions, not least a degree of complexity arising from numerous processes operating simultaneously, giving scope for integrating material and energy flows. However, much of the biorefinery literature, while using the terminology of integration, does so in ways that miss the importance and power of this concept and its relevance to synergies between food processing and biorefining.

Sheppard et al. (2019) highlight the process integration synergies that could arise through co-location of biorefineries and food and drink manufacturing facilities, such that scope for material and energy flows between the two facilities could increase integration opportunities, thereby reducing both costs and emissions. Thus, for example, a biorefinery could take the wastes from the food facility as its feedstocks, with co-location eliminating transportation costs and emissions, while heat and water usage between the co-located facilities could be exploited and integrated more efficiently than within either facility on its own. Recent research has highlighted that distance is one of the key technical barriers in the implementation of circular business models based on reuse of solid resources (Angelis-Dimakis et al., 2021), encouraging the intentional co-location of complementary facilities. The similarities of biomass materials handled in food processing and in biorefining, along with similarities of temperatures in thermal processes and potential synergies in relation to water usage, and similarly tight profit margins, make the identification of well-matched facilities a promising basis for enhancing the environmental credentials and economic viability of both food processing and biorefining.

Even in the absence of co-location, the rise of biorefineries offers further synergistic benefits for the food industry. There are numerous components of plants that, if they could be extracted economically, would be useful as high value food ingredients of specific and targeted functionality. For example, one of the current authors was involved in a project on oat fractionation, motivated in part by the identification of an oat glycolipid emulsifier that had specific promise in chocolate, but for which the economics of extraction on its own would not have been viable; hence the project investigated integrated processing that focussed on the major components of oats, starch and bran, in order to give a context in which extraction of that emulsifier might be technically and economically viable (South et al., 1999). Showing that biorefineries can offer ingredients not currently available to the food industry could help to enhance their “cognitive and sociopolitical legitimacy” (Peck et al., 2009).

The opportunity presented to the food industry by biorefineries is this: some components of biomass of particular interest as food ingredients, but not currently economical to produce, might be feasible in the integrated context of a biorefinery. Such an integrated context could allow these novel components to be introduced as commercial products, offering new functional ingredients into the food industry (and also for animal feed and non-food applications). This is an exciting possibility arising from the new processing contexts offered by biorefineries.

Arabinoxylans (AX) serve as an interesting and promising illustration of this general point: that biorefineries can offer to the food industry new ingredients not currently available, made feasible through process integration, while the food industry offers markets for biorefinery products that could help establish their commercial viability and the associated environmental and social benefits. The specific opportunity to produce arabinoxylans at commercial scale has arisen from the emergence of bioethanol plants, as one approach for producing arabinoxylans uses ethanol to precipitate the AX (Hollmann and Lindhauer, 2005; Swennen et al., 2005, 2006; Peng et al., 2009, 2012; Deutschmann and Dekker, 2012; Zhang et al., 2014; Solier et al., 2020), such that in the context of a bioethanol plant in which the ethanol can be recovered, it is possible that AX production could be economic (Sadhukhan et al., 2008; Misalidis et al., 2009). Co-production of AX with bioethanol, optimised through formal process integration, could contribute positively to the biorefinery’s profits, while delivering new healthy and functional ingredients to the food industry (Martinez-Hernandez et al., 2018). AX also has potential for non-food products including film forming, emulsifiers and stabilisers in the pharmaceutical and cosmetic industries (Deutschmann and Dekker, 2012; Aguedo et al., 2015; Zhang et al., 2014; Jacquemin et al., 2015; Izydorczyk, 2021).

The co-production of AX with ethanol also illustrates the distinctive feature of true biorefineries, that they gain their status as biorefineries (as opposed to mere bioprocesses) through formal integration to exploit synergies, in order to achieve commercial viability through a combination of an efficient process and a portfolio of revenue streams that are well chosen to create integration opportunities (Campbell et al., 2018). Biorefineries are by nature marginal in their economic viability, such that small gains in profits, through process efficiency or through new revenue streams, have large effects on commercial viability. However, these are two distinct and separate elements of biorefinery economics, albeit interacting ones: (i) a portfolio of products to generate several revenue streams; and (ii) an integrated process that reduces both costs and emissions. Frequently the emphasis in the biorefinery literature has been on the first of these – identifying possible products and their contributions to the business’s revenues is easy and obvious. By contrast, identifying and exploiting integration opportunities, and product combinations that might create such opportunities, is harder, requiring a way of thinking and a set of tools that distinguish “the biorefinery engineer”.

Section 2 of the current paper examines how the usage of the term “biorefinery” frequently overlooks the integration element that is the key to unlocking the potential of biorefineries, including the opportunity to introduce a new class of ingredients based on arabinoxylans. Section 3 then introduces arabinoxylans in more detail, including their integrated production with bioethanol and their potential as food ingredients and for non-food applications. Section 4 describes recent work to evaluate AX extracts as possible bread ingredients, then identifies the scope of research required to introduce this new class of ingredients as a commercial reality. Section 5 then stands back to consider the nature of biorefinery engineering as a discipline and the skills and educational needs of the biorefinery engineer.

Section snippets

Inadequate and confusing views of the biorefinery concept

Since its inception, many have sought to define “the biorefinery concept”. In many cases, and certainly in the early days, while integration may be mentioned or even highlighted in such definitions and associated discussions, it has often been obscured by a more prominent emphasis on the multiple products of a biorefinery. Thus for example, Cherubini et al. (2009) and Cherubini, (2010) considered the “most exhaustive” definition to be that of the IEA Bioenergy Task 42 (Biorefining):

Arabinoxylans as co-products of bioethanol production

This section introduces the key features of arabinoxylans that underpin their potential as food ingredient and as co-products of bioethanol production. It emphasises that different fractions (precipitated at different ethanol concentrations) will have different functionalities and markets, and that their co-production allows economic savings through bioethanol pinch analysis, as well as giving a portfolio of revenue streams.

Arabinoxylans as a potential bread ingredient

Like the historical development of the oil industry, the creation of a new class of AX-based food ingredients from biorefineries is likely to start with some initial products that begin to establish markets and give a basis for ever greater refinement of products and identification of new markets. The obvious first ingredient would be into the bread industry, for four reasons:

  • i)

    most of the current knowledge of AX has been developed in relation to wheat AX and its behaviour in bread systems

Arabinoxylans as an example of biorefinery integration

The identification of AX as a potential new class of food ingredients arising from the emergence of biorefineries was sparked by the realisation that the use of ethanol in the AX extraction process gives a natural process integration opportunity. AX co-produced with bioethanol serves as an illustration of the knowledge and skills required by the biorefinery engineer, whose task is to design biorefineries that can operate profitably within tight economic margins while delivering products of

Conclusions

The vision and promise of arabinoxylan co-production with bioethanol constitute an “arabinoxylan manifesto” that illustrates several distinct lessons, opportunities, needs and benefits, both specific and general:

  • i)

    The emergence of bioethanol production gives a context in which AX could be economically feasible, as ethanol is used to precipitate the AX;

  • ii)

    Revenue streams from AX would enhance marginal biorefinery economics and facilitate the sustained commercial viability of biorefineries;

  • iii)

    The

Data availability

Data will be made available on request.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors gratefully acknowledge Nell Masey O’Neill of AB Agri and Mike Bedford and Gemma Gonzalez-Ortiz of AB Vista, whose long-standing support of our research has given a context in which the ideas presented in the current paper have been able to flourish. Support is also gratefully acknowledged for earlier work from the Home-Grown Cereals Authority (HGCA), the National Council of Science and Technology (CONACYT) of Mexico, the BBSRC Plants to Products Network in Industrial Biotechnology

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