Enrichment of Rice Flour with Almond Bagasse Powder: The Impact on the Physicochemical and Functional Properties of Gluten-Free Bread

Abstract

Almond bagasse, a by-product of almond milk production, is rich in fibre, protein, polyunsaturated fatty acids, and bioactive compounds. Its incorporation into food products provides a sustainable approach to reducing food waste while improving nutritional quality. This study explored the impact of enriching rice flour with almond bagasse powders-either hot air-dried (HAD60) or lyophilised (LYO)-at substitution levels of 5%, 10%, 15%, 20%, 25%, and 30% (w/w), to assess effects on gluten-free bread quality. The resulting flour blends were analysed for their physicochemical, techno-functional, rheological, and antioxidant properties. Gluten-free breads were then prepared using these blends and evaluated fresh and after seven days of refrigerated storage. The addition of almond bagasse powders reduced moisture and water absorption capacities, while also darkening the bread colour, particularly in HAD60, due to browning from thermal drying. The LYO powder led to softer bread by disrupting the starch structure more than HAD60. All breads hardened after storage due to starch retrogradation. The incorporation of almond bagasse powder reduced the pasting behaviour-particularly at substitution levels of ≥ 25%-as well as the viscoelastic moduli of the flour blends, due to fibre competing for water and thereby limiting starch gelatinisation. Antioxidant capacity was significantly enhanced in HAD60 breads, particularly in the crust and at higher substitution levels, due to Maillard reactions. Furthermore, antioxidant degradation over time was less pronounced in formulations with higher substitution levels, with HAD60 proving more stable than LYO. Overall, almond bagasse powder improves the antioxidant profile and shelf-life of gluten-free bread, highlighting its value as a functional and sustainable ingredient.

Keywords: almond bagasse powder; antioxidant properties; bread; flour; food waste; hot air-drying; lyophilised; rheological properties; storage; techno-functional properties.

Figure 1

Pasting curves, pasting temperature, and the pasting behaviour of rice flour (control) and flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) or lyophilised (LYO), at substitution levels of 5–30%. PV: peak viscosity; TV: trough viscosity; BV: breakdown viscosity; FV: final viscosity; SV: setback viscosity. (A) Treatment; (B) replacement percentage. The results represent the mean of three repetitions. Different lowercase letters indicate significant differences (p ≤ 0.05) among the different flours.

Figure 2

Elastic modulus (G′) and viscous modulus (G″) of rice flour (control) and of flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) (a) or lyophilised (LYO) (b), at substitution levels of 5–30%. The results represent the mean of three repetitions. Different lowercase letters indicate significant differences (p ≤ 0.05) among the different flours.

Figure 3

Gel hardness (N) of samples prepared from rice flour (control) and from flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) or lyophilised (LYO), at substitution levels of 5–30%. All samples were hydrated, heated, and cooled to allow gel formation prior to analysis. The results represent the mean of three repetitions. Different lowercase letters indicate significant differences (p ≤ 0.05) among the different flours.

Figure 4

Hardness (N) of fresh (a) and 7-day stored (b) bread made from rice flour (control) and flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) or lyophilised (LYO), at substitution levels of 5–30%. The results represent the mean of three repetitions. Different lowercase letters in each compression indicate significant differences (p ≤ 0.05) among the different bread formulations.

Figure 5

Antioxidant activity determined by (a) DPPH and (b) FRAP methods; (c) total phenol content; and (d) reducing sugars in samples prepared from rice flour (control) and from flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) or lyophilised (LYO), at substitution levels of 5–30%. The results represent the mean of three repetitions. Different lowercase letters indicate significant differences (p ≤ 0.05) among the different flours.

Figure 6

Antioxidant activity determined by (a) DPPH and (b) FRAP methods; (c) total phenol content; and (d) reducing sugars in the crumb and crust of fresh bread made from rice flour (control) and flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) or lyophilised (LYO), at substitution levels of 5–30%. The results represent the mean of three repetitions. Different lowercase letters within each bread fraction (crumb or crust) indicate significant differences (p ≤ 0.05) among the different bread formulations.

Figure 7

Antioxidant activity determined by (a) DPPH and (b) FRAP methods; (c) total phenol content; and (d) reducing sugars in the crumb and crust of 7-day stored bread made from rice flour (control) and flour blends in which rice flour was partially replaced with almond bagasse powder, hot air-dried at 60 °C (HAD60) or lyophilised (LYO), at substitution levels of 5–30%. The results represent the mean of three repetitions. Different lowercase letters within each bread fraction (crumb or crust) indicate significant differences (p ≤ 0.05) among the different bread formulations.