**Abstract**

The sustainability of the food supply chain is gaining increasing attention in the quest to balance economic, environmental, and social dimensions. A key opportunity to enhance food system sustainability is by addressing food waste through upcycling strategies to generate higher value, functional foods. Extrusion is a food manufacturing technology that is emerging as a promising option for the incorporation of various types of biomass by-products, such as fruit and vegetable pomace, brewer's spent grain, bagasse, and oil press cake. In this chapter, we present an overview of the latest research conducted on incorporating biomass by-products into extruded food products, with an emphasis on the challenges and opportunities associated with this approach. A meta-analysis study was conducted regarding a key challenge for product quality when incorporating by-products, which is the reduction in radial expansion index of expanded snack and breakfast cereal products. To highlight future opportunities, two case studies illustrate successful examples of by-product incorporation for commercial extruded food products, while emerging protein sources from wasteconsuming insects were also explored. Overcoming these challenges and leveraging opportunities can contribute to a more sustainable food system through the integration of by-products into value-added extruded foods.

**Keywords:** extrusion, by-products, food waste, upcycling, radial expansion index, optimisation, quality

## **1. Introduction**

#### **1.1 Chapter overview: from biomass to sustainable food products**

There are a myriad of specialty biobased products that can be generated from biomass across the broad subject areas of biofuel, biochemical, biomaterial, pharmaceutical, food, and feed production. While biobased products have been around for centuries, recent advancements in technology have allowed for more efficient and cost-effective production, improving their functionality and economic viability. The focus of this chapter will be on the production of sustainable food products using

biomass by-products, specifically manufactured through extrusion technology. It is clear from **Figure 1** that extrusion technology is linked to sustainability through the processing of food by-products into functional foods, in the effort to fight food waste. Biomass by-products that have been incorporated into extruded products include fruit and vegetable pomace, bagasse, oil press cake, brewer's spent grain (BSG), crop byproducts such as bran or husks, and general food waste that forms the feed material for insect-based protein. The chapter outlines the latest research into by-products incorporated into extruded foods, detailing the major challenges facing this topic and sharing a couple of case studies of commercial ventures incorporating by-products into extruded food. This chapter forms a resource for researchers to study when developing a research questions and hypotheses within this field, and for industrials to consult when investigating opportunities to up-cycle biomass by-products into extruded foods across a range of applications including snack foods, breakfast cereals, and plant-based meats.
