Design of novel oven-baked sweet potato snack enhanced with brewery byproduct: the effect on sensory and nutritional content

Abstract

This doctoral thesis investigates the potential of converting sweet potatoes into flour and analyzes how different drying techniques affect the preservation of bioactive compounds. It also assesses the role of ultrasound as a pretreatment strategy to improve the content of these compounds during processing. The obtained flour was subsequently used on the design of a novel baked snack enriched with brewer's spent grain (BSG), a by-product of the brewing industry, to evaluate the effects of this enrichment on its sensory and nutritional attributes. The main motivation lies in the growing demand for more nutritious snacks and the valorization of agro-industrial by-products. The general objective was to apply and evaluate the effects of ultrasound, storage, and drying methods in the processing of sweet potato to obtain flour with increased phenolic and carotene content, and to use it as an ingredient in an oven-baked snack enriched with BSG, aiming to achieve improved nutritional properties and acceptable sensory characteristics. The methodology included the production of sweet potato flour (SPF), evaluation of the effect of ultrasound treatment, different storage times (0, 24, 48, 72, and 96 h), and drying methods (dehydration and freeze-drying) on the content of bioactive compounds (phenolics and carotenoids), and physicochemical properties. Subsequently, a base snack was formulated using the produced sweet potato flour with corn flour and wheat flour, and the proportions were optimized through mixture design, based on sensory evaluation, and texture analysis. Finally, different proportions of ground BSG (6.25%, 12.5%, 18.75%, and 25%) were added to the base snack to evaluate its impact on sensory properties, color, texture, nutritional composition (moisture, fat, protein, fiber, ash, starch), and content of bioactive compounds (phenolics, carotenoids, and antioxidant activity). The results showed that ultrasound treatment significantly affected the polyphenol content of sweet potato flour, increasing it by 93%, highlighting the effectiveness of US as an abiotic elicitor for the accumulation of phenolic compounds even in processed foods. The drying method influenced the carotenoid content, achieving 65% more content when the samples were freeze-dried. In addition, the b* and L* values were affected by these two factors, resulting in higher values for both parameters. The processing methodology was defined as the use of US-pretreatment, storage for 48 h and dehydration, and the produced flour was used to develop a novel oven-baked snack with nixtamalized corn (CF) and wheat flour (WH). The optimal formulation consisted of 28.29% SPF, 41.45% CF, and 30.3% WF, achieving satisfactory overall acceptability with a score of 7.05±0.22 ("moderate liking"). The addition of BSG (up to 25%) to the optimized formula significantly modified the color by reducing the a* and b* values, and texture by increasing the hardness, gumminess, and chewiness of the snack. However, the overall sensory acceptance according to the hedonic scale remained at acceptable levels with scores above 6, defined as like slightly, even with the addition of up to 25% BSG. Nutritional analysis showed that adding BSG significantly increased 1.6 more times of dietary fiber and double the ash content, as well as three times more in the phenolic content and 33% more in antioxidant activity of the snack. The formulation containing 6.25% BSG proved to be the best final formula, offering the greatest balance between improved nutritional properties and favorable sensory attributes, with the highest overall acceptability score. Overall, this work brings together two main contributions: first, it proposes a novel processing strategy for sweet potato that combines ultrasound, cold storage, and dehydration, which resulted in a flour with enhanced bioactive content. Rather than limiting the contribution to improved flour, the study extends this development into an oven-baked snack that aligns with consumer demand for more nutritious foods. The combination of the produced sweet potato flour with corn, wheat, and brewer’s spent grain represents a mixture that has been scarcely explored, and working with it provided new information on how they can improve the nutritional profile of an oven-baked snack. These findings not only offer a promising direction for new added-value snack products but also respond to current trends in health-focused eating and sustainable food development. By valorizing an agro-industrial by-product and incorporating plant-based ingredients, the final product contributes to more responsible and forward-looking food systems.