Valorizing Carasau Bread Residue Through Sourdough Fermentation: From Bread Waste to Bread Taste

Abstract

Surplus bread accounts for a significant proportion of food waste in many countries. The focus of this study was twofold: firstly, to investigate the use of carasau bread residue as a sourdough substrate, and secondly, to reuse this sourdough into a new carasau baking process. Selected lactic acid bacteria (Lactiplantibacillus plantarum) and yeast strains (Saccharomyces cerevisiae and Wickerhamomyces anomalus) were used to inoculate three substrates: bread residue (S1), bread residue supplemented with durum wheat middlings (S2), and semolina (S3). Sourdoughs were refreshed for five days by backslopping, and microbiological and physicochemical analyses were performed. Results indicated that incorporating wheat middlings into bread residue enhanced microbial performance, as evidence by a decrease in pH from 6.0 to around 4.5 compared to using bread residue alone as a substrate. Carasau bread produced with the sourdough derived from bread residue and wheat middlings exhibited comparable physicochemical properties to commercial baker's yeast carasau bread, but had better sensory properties, scoring a mean acceptability of 7.0 versus 6.0 for baker's yeast bread. These results show that bread residue supplemented with wheat middlings can serve as a sourdough substrate, allowing its reuse in the baking process to produce high-quality carasau bread and promote the circular economy.

Keywords: Lactiplantibacillus plantarum; Saccharomyces cerevisiae; Wickerhamomyces anomalus; carasau bread; circular economy; semolina; wheat middlings.

Figure 1

Changes in pH (solid lines) and total titratable acidity (TTA) values (dotted lines) in sourdough samples (S1, S2, S3) after inoculation (T0) and daily refreshments (R1–R5). TTA is reported as mL of NaOH 0.1 N in 10 g of sample. Bars indicate standard deviation.

Figure 2

Cell density (log₁₀ CFU g⁻¹) of presumptive L. plantarum (A), S. cerevisiae (B), and W. anomalus (C) in sourdough samples (S1, S2, S3) after daily refreshment. T0 refers to the cell density after inoculation of microbial starter. Bars indicate standard deviation. Different uppercase letters indicate significant differences among samples within each refreshment time (Tukey’s test at p < 0.05). Different lowercase letters indicate significant differences for each sample among refreshments (Tukey’s test at p < 0.05). Not significant = ns/NS.

Figure 3

Amount of lactic acid (A) and acetic acid (B) in sourdough samples (S1, S2, S3) refreshed for 5 days. Bars indicate standard deviation. Different uppercase letters indicate significant differences among samples within each refreshment time (Tukey’s test at p < 0.05). Different lowercase letters indicate significant differences for each sample among refreshments (Tukey’s test at p < 0.05).

Figure 4

Content of glucose (A), fructose (B), and maltose (C) in sourdough samples (S1, S2, S3) refreshed for 5 days. Bars indicate standard deviation. Different uppercase letters indicate significant differences among samples within each refreshment time (Tukey’s test at p < 0.05). Different lowercase letters indicate significant differences for each sample among refreshments (Tukey’s test at p < 0.05). Not significant = NS.

Figure 5

Ethanol concentration in sourdough samples (S1, S2, S3) refreshed for 5 days. Bars indicate standard deviation. Different uppercase letters indicate significant differences among samples within each refreshment time (Tukey’s test at p < 0.05). Different lowercase letters indicate significant differences for each sample among refreshments (Tukey’s test at p < 0.05).

Figure 6

Increase in volume in doughs inoculated with 5%, 10%, and 20% of S2 (A) and S3 (B) sourdoughs. Values are in mL, calculated as differences between values at each time and at time zero. Bars indicate standard deviation.

Figure 7

Evolution of CO₂ production in doughs inoculated with different percentages of S2 (A) and S3 (B). Bars indicate standard deviation.

Figure 8

Box plot showing the distribution of liking scores for carasau bread samples. The median (horizontal line) and the mean value (+) are highlighted within each box. The box limits indicate the range of the central 50% of the data. The whiskers indicate minimum and maximum values. Outliers are represented as points () beyond the whiskers.