Sourdough Fermented Breads are More Digestible than Those Started with Baker's Yeast Alone: An In Vivo Challenge Dissecting Distinct Gastrointestinal Responses

Abstract

As a staple food, bread digestibility deserves a marked nutritional interest. Combining wide-spectrum characterization of breads, in vitro nutritional indices, and in vivo postprandial markers of gastrointestinal function, we aimed at comparing the digestibility of sourdough and baker's yeast breads. Microbiological and biochemical data showed the representativeness of the baker´s yeast bread (BYB) and the two sourdough breads (SB and t-SB, mainly differing for the time of fermentation) manufactured at semi-industrial level. All in vitro nutritional indices had the highest scores for sourdough breads. Thirty-six healthy volunteers underwent an in vivo challenge in response to bread ingestion, while monitoring gallbladder, stomach, and oro-cecal motility. SB, made with moderate sourdough acidification, stimulated more appetite and induced lower satiety. t-SB, having the most intense acidic taste, induced the highest fullness perception in the shortest time. Gallbladder response did not differ among breads, while gastric emptying was faster with sourdough breads. Oro-cecal transit was prolonged for BYB and faster for sourdough breads, especially when made with traditional and long-time fermentation (t-SB), whose transit lasted ca. 20 min less than BYB. Differences in carbohydrate digestibility and absorption determined different post-prandial glycaemia responses. Sourdough breads had the lowest values. After ingesting sourdough breads, which had a concentration of total free amino acids markedly higher than that of BYB, the levels in blood plasma were maintained at constantly high levels for extended time.

Keywords: gallbladder emptying; hydrogen breath test; orocecal transit time; stomach emptying; test meal; ultrasonography.

Conflict of interest statement

The authors declare no competing financial and non-financial interests.

Figures

Figure 1

Sensory analysis of the three types of bread. BYB, baker´s yeast bread leavened with baker’s yeast (1.5%, w/w) for 90 min at 30 °C; SB, sourdough bread leavened with S4 (20%, w/w) and baker’s yeast (1.5%, w/w) for 90 min at 30 °C; t-SB, sourdough bread leavened with S24 (20%, w/w) for 4 h at 30°C. (A) spider web chart of the perception scores (semi-quantitative scale 0–3); (B) degree of pleasantness (visual analogue scale, VAS, 0–100 mm). a–c Within the same parameter, values with different superscript letters differ significantly (p < 0.05).

Figure 2

Perception of appetite and satiety (A), and gastrointestinal symptoms (nausea and fullness) (B) in response to ingestion of the test meals. Time-dependent changes were scored with Visual Analogic Scale (VAS, 0–100 mm), and represented as mean ± SEM (Standard Error of the Mean) and area under curve (AUC). BYB, baker´s yeast bread leavened with baker’s yeast (1.5%, w/w) for 90 min at 30 °C; SB, sourdough bread leavened with S4 (20%, w/w) and baker’s yeast (1.5%, w/w) for 90 min at 30 °C; t-SB, sourdough bread leavened with S24 (20%, w/w) for 4 h at 30 °C. NU, Nutridrink used as the reference. a–c Within the same parameter, values with different superscript letters differ significantly (p < 0.05).

Figure 3

Gastric (A) and gallbladder (B) emptying curves in response to the ingestion of the test meals (isovolumetric). Time-dependent changes of antral area (cm2) are represented as mean ± SEM (Standard Error of the Mean) and area under curve (AUC). Time-dependent changes of gallbladder volume (mL) are represented as mean ± SEM and area under curve (AUC). BYB, baker´s yeast bread leavened with baker’s yeast (1.5%, w/w) for 90 min at 30 °C; SB, sourdough bread leavened with S4 (20%, w/w) and baker’s yeast (1.5%, w/w) for 90 min at 30 °C; t-SB, sourdough bread leavened with S24 (20%, w/w) for 4 h at 30 °C. NU, Nutridrink used as the reference. a–b Within the same parameter, values with different superscript letters differ significantly (p < 0.05).

Figure 4

Oro-cecal transit time (OCTT) in response to the ingestion of test meals. (A) time-dependent curves of H2 concentration (ppm) in exhaled air, expressed as mean ± SEM (Standard Error of the Mean); (B) OCTT (min); (C) H2 peak. BYB, baker´s yeast bread leavened with baker’s yeast (1.5%, w/w) for 90 min at 30 °C; SB, sourdough bread leavened with S4 (20%, w/w) and baker’s yeast (1.5%, w/w) for 90 min at 30 °C; t-SB, sourdough bread leavened with S24 (20%, w/w) for 4 h at 30 °C. NU, Nutridrink used as the reference. a–c Within the same parameter, values with different superscript letters differ significantly (p < 0.05).

Figure 5

Serum glucose concentration in response to the ingestion of the test meals. (A) time-dependent curves of serum glucose (mg/dL) and (B) area under curve (AUC). Data are expressed as mean ± SEM (Standard Error of the Mean). BYB, baker´s yeast bread leavened with baker’s yeast (1.5%, w/w) for 90 min at 30 °C; SB, sourdough bread leavened with S4 (20%, w/w) and baker’s yeast (1.5%, w/w) for 90 min at 30 °C; t-SB, sourdough bread leavened with S24 (20%, w/w) for 4 h at 30 °C. a–c Values with different superscript letters differ significantly (p < 0.05).

Figure 6

Serum total free amino acids (FAA) concentration in response to the ingestion of test meals. Aggregated data are represented in box-plots: (A) total FAA concentration at 60 min after ingestion; (B) total FAA concentration at 120 min after ingestion. BYB, baker´s yeast bread leavened with baker’s yeast (1.5%, w/w) for 90 min at 30 °C; SB, sourdough bread leavened with S4 (20%, w/w) and baker’s yeast (1.5%, w/w) for 90 min at 30 °C; t-SB, sourdough bread leavened with S24 (20%, w/w) for 4 h at 30 °C.