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Bran-Enriched Extruded Snacks
The incorporation of milling by-products, in particular bran, into starch-based extruded snacks allows manufacturers to address two consumer demands at once, i.e., those for goods that are more sustainably produced and of higher nutritional value. However, the higher fiber content in bran than in refined cereal flours poses a limit to the amount that can be included without compromising the quality of extruded snacks, which crucially depends on expansion. Thus, several studies have focused on the effect of bran on the physicochemical characteristics of extruded snacks, leading to the need to review the recent findings in this area. Opportunities and potential solutions of bran-enriched snacks are addressed, and several current knowledge gaps are highlighted.
The global extruded snacks market was valued at USD 51.59 billion in 2019 and is expected to grow by more than 4% until 2026 as a result of changes in the eating habits of consumers and the growing demand for ready-to-eat foods . Extruded snacks are convenience products and their low moisture content (around 4–6%) makes them shelf-stable. The versatility of their manufacturing process facilitates innovation in this product category, allowing the use of various ingredients and/or nutrient-rich constituents to make attractive products.
Cereal-based snack foods cover a wide range of ready-to-eat products, such as popcorn, pretzels, breakfast cereals, and expanded products. The structure and texture of such snack foods are the results of their respective manufacturing processes, which can involve operations like baking, deep-frying, or the topic of this review, extrusion cooking. This technology can be tailored to yield various products: direct-expanded (or second-generation) snacks, semi-finished product pellets (or third-generation snacks), or co-extruded products .
As these products are specifically formulated to allow for maximum expansion and thus starch gelatinization, extruded snacks have often been criticized for their poor nutritional profile (i.e., high starch content and glycemic index [3,4]). At the same time, extruded snack products are usually low in protein, vitamins, minerals, and dietary fiber . Recently, efforts to produce extruded snacks to address these nutritional shortcomings have increased, and breakfast cereals and snacks are anticipated to be among the fastest-growing segments in the global dietary fiber market . An increase in the dietary fiber content can be achieved via using: (1) Wholemeal instead of refined flours; (2) Feed mixes containing flours with high dietary fiber contents such as barley, oat, pseudocereals or pulses; (3) Bran as an ingredient; or (4) Commercial sources of purified dietary fiber preparations, typically soluble fibers such as inulin, pectin, or psyllium. The latter approach makes it possible to achieve label claims of the product being a “source of fiber” or “high in fiber” (3 versus 6 g of dietary fiber per 100 g of serving)  with minimal changes in formulation and product quality. The use of whole grains and/or their milling fractions (especially bran) has a positive effect on the nutrient composition by increasing the contents of protein as well as fiber and other bioactives . In a recent survey of breakfast cereals available in Italy, bran-containing products were significantly higher in protein but lower in energy content than all other categories . In addition, formulating foods to contain by-products addresses the crucial need for a more sustainable food production. In this context, several recent articles have highlighted compositional and functional aspects of extruded snacks formulated with by-products [9,10,11], or summarized the effects of cereal fiber on microstructural, technological, and sensory attributes of products either extruded at low (pasta) or high (snacks) temperature . If a manufacturer was aiming to develop a novel bran-enriched extruded product with the help of a multidisciplinary team, a debate between nutritionists and food technologists might emerge on how much bran should be included. On the one hand, more added bran maximizes the nutritional benefits, but on the other hand, the negative impact of fiber on physicochemical features of snacks and consumer acceptability is usually evident even at low percentages. Almost a decade ago, Robin et al.  pointed out the challenges of using fiber in extrusion and discussed some approaches for suitably processing the fibers to facilitate their inclusion. Since then, several studies have explored the opportunity to include fibers either as isolated compounds or in the form of bran in extruded snacks. Researchers have expanded the range of used raw materials, such as through the inclusion of legume bran (i.e., the hulls) as well as bran pre-treatments.The focus of this review revolves around the challenges of producing bran-enriched snacks and potential solutions to assure product quality (Figure 1). This work aims to provide an overview of recent approaches for improving the features of bran-enriched snacks involving bran pre-treatment or processing optimization. It will conclude with a discussion on crucial research needs to better understand the relationship between structural attributes of the raw materials, processing conditions and product quality, so that results from different studies are easier to compare.
2. Strategies to Enhance the Quality of Bran-Enriched Snacks
Bran enrichment can increase the content of protein, fiber and other bioactive compounds in snacks whose main component is starch. However, the enhanced nutritional properties come at the expense of inferior physical features of the final product (Figure 1). A balance between nutritional and technological quality might be achieved by adopting two approaches. On the one hand, several treatments can be used to modify the dietary fibers—mainly the insoluble fraction—prior to using the bran in food. These treatments involve mechanical, chemical and biotechnological processes. On the other hand, when a new ingredient is included in a recipe, both enrichment level and processing conditions can be optimized. While there is broad consensus among studies about the improvement of certain factors, there is also a knowledge gap (Figure 2).
2.1. Bran Pre-Treatments
2.1.1. Particle Size Reduction
2.1.2. Chemical Approaches
2.1.3. Bio-Technological Approaches
3. Knowledge Gaps and Future Perspectives
The entry is from 10.3390/foods10092024
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