Okara-Enriched Gluten-Free Bread: Nutritional, Antioxidant and Sensory Properties

Abstract

The aim of this study was to produce an eco-innovative gluten-free bread with a pleasant taste and a unique formulation that includes the highest quality grains and pseudocereals (buckwheat; rice; and millet); and okara; a by-product of soy milk production. The mixture of pseudocereal and cereal flour contained buckwheat flour 45%, rice flour 33%, and millet flour 22%. Three gluten-free breads; each containing different contents of gluten-free flour (90%, 80%, and 70%, respectively); okara (10%, 20%, and 30%, respectively); and a control sample (without okara); were prepared and subjected to sensory evaluation. The okara-enriched gluten-free bread with the highest sensory score was selected for further analysis of physico-chemical (total proteins; total carbohydrates; insoluble fiber; soluble fiber; sugars; total lipids; saturated fatty acids; and salt) and functional properties (total phenolic content and antioxidant properties). The highest sensory scores were obtained for 30% okara-enriched gluten-free bread including taste; shape; odor; chewiness; and cross-section properties; classifying this bread in the category of very good quality and excellent quality (mean score 4.30 by trained evaluators and 4.59 by consumers). This bread was characterized by a high content of dietary fiber (14%), the absence of sugar; low content of saturated fatty acids (0.8%), rich source of proteins (8.8%) and certain minerals (e.g.,; iron; zinc); and low energy value (136.37 kcal/100g DW). Total phenolic content was 133.75 mgGAE/100g FW; whereas ferric reducing power; ABTS radical cation; and DPPH radical scavenging activity were 119.25 mgAA/100g FW; 86.80 mgTrolox/100g FW; and 49.92 mgTrolox/100g FW; respectively. Okara addition in gluten-free bread production enables the formulation of high-nutritive; good antioxidative; low-energy bread; and better soy milk waste management.

Plant-Based Antioxidants in Gluten-Free Bread Production: Sources, Technological and Sensory Aspects, Enhancing Strategies and Constraints

“…as phenolic acids, flavonoids (predominantly anthocyanins), and tannins are the most frequently present in GF cereal, pseudocereal, and legume flours, alongside carotenoids (β-carotene) and vitamins which exert antioxidant activity (tocopherols, tocotrienols). In addition to the aforementioned GF flours, and in line with the sustainable development goals, food industry by-products (pomace, peel, leaves, husk) (Table 1) are new rising sources of antioxidant compounds for direct application in GFB production [34,35,48,51,66,[69][70][71]78] and will be discussed in more detail in Section 5.2. Antioxidant compounds are frequently accompanying compounds of other plant components such as dietary fibers and proteins [37,84,85].…”

“…The unique composition of millet and, consequently, derived milled flour, in terms of biologically active components such as antioxidant compounds (tannins, flavonoids, phenolic acids, and β-carotene), vitamins (B1, B2, B3, and E), and minerals (K, Ca, P, Mg, Fe, and Zn) followed by a high content of dietary fiber (13.1%) [71], implies the potential of millet flour inclusion in GFB production [32,55,60,71]. In addition, other types of phytochemicals such as γ-amino butyric acid were detected in millet varieties (foxtail and barnyard), specifically in their germinated grains [87] (pp.…”

“…Depending on the chosen sensory methodology, the sensory evaluation of antioxidant-enriched GFB samples was most frequently assessed by a sensory panel with up to 10 panelists [34,54,67] or a population enveloping approximately 30, 50, or 70 respondents [35,38,45,49]. Nevertheless, a larger population of more than a hundred respondents was also engaged in studies for corresponding product evaluation (116 and 150 respondents) [43,71].…”

“…Still, there is a noticeable predominance in terms of the number of female respondents who participated in the assessment, particularly when small groups of up to 10 members were evaluators (expert panelists) [34,42]. Larger population groups were mostly balanced regarding the number of male and female participants [49,62,71].…”

“…The use of FRAP coupled with other methods to measure radical scavenging ability is considered significant for the determination of the dominant reaction mechanism exhibited by antioxidant compounds [31]. Concerning GFB, results were dominantly reported as TE [35,39,48,50,60,72], but also as Fe 2+ equivalents [37,41,45,55] and ascorbic acid equivalents [71,75]. Variations regarding applied wavelengths were also noticed; however, the majority of the readings were performed at 593 nm [34,35,50,63,72,75] over 595 nm [37,60].…”