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, 7 (1), 624

Sourdough Authentication: Quantitative PCR to Detect the Lactic Acid Bacterial Microbiota in Breads

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Sourdough Authentication: Quantitative PCR to Detect the Lactic Acid Bacterial Microbiota in Breads

Erica Pontonio et al. Sci Rep.

Abstract

No national legislation anywhere in the world regulates and protects traditional/typical sourdough breads. Sourdough fermentation is firmly associated with a century-old tradition, and with sensory and nutritional quality of breads. A well-defined cell density of lactic acid bacteria has to be reached at the end of fermentation, and be indirectly detectable in baked breads. A Quantitative PCR (qPCR) method was developed to discriminate between breads made with and without sourdoughs. Universal primers targeting an approximately 178-bp fragment of the 16S rRNA-encoding gene of lactic acid bacteria were designed, covering the known diversity of sourdough lactic acid bacteria and excluding commonly encountered flour bacterial contaminants. A total of 191 breads either made with traditional type I and dried sourdough and baker's yeast, or by a chemical leavening method were shown to be accurately discriminated by means of qPCR. Discriminating values of gene copy number were only weakly correlated with pH values, and with lactate and acetate concentration, thus questioning the validity of these latter indirect indices. The use of sourdough has to be guaranteed to meet both bakery and consumer expectations, and to fulfil legal requirements; our work presents a reliable authentication method providing a suitable tool to satisfy such requirements.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Scatterplot based on gene copy number as determined from laboratory breads. Scatterplot based on gene copy numbers of traditional and dried sourdough or baker’s yeast breads made under pilot scale/laboratory conditions. Mean (+), median (red line), and cut-off (dashed line) values are shown. Dried sourdough breads coded as P1, P10, P13, and P16 were made using 2.2% [wt/wt] of dried sourdough. The ingredients and technology parameters used for bread made at the pilot plant scale (laboratory) are reported in Table 2.
Figure 2
Figure 2
Scatterplot based on gene copy number obtained from bakery breads. Scatterplot based on gene copy numbers of sourdough or baker’s yeast breads collected from various bakeries. Mean (+), median (red line), and cut-off (dashed line) values are shown. Breads coded as A18, A24, A37, and A43 were claimed as sourdough breads. Information on the commercial breads collected from bakeries is reported in Supplementary Table S6.
Figure 3
Figure 3
Principal Component Analysis. Score and loading plots of first and second principal components after principal component analysis based on values of gene copy, pH, TTA (ml NaOH 0.1 N) and concentration of lactic and acetic acids (mmol/kg) of breads made under pilot plant conditions (laboratory). Traditional and dried sourdough and baker’s yeast breads are delineated by blue and red line ovals, respectively. The ingredients and technology parameters used for bread made at the pilot plant scale (laboratory) are reported in Table 2.
Figure 4
Figure 4
Principal Component Analysis. Score and loading plots of first and second principal components after principal component analysis based on values of gene copy, pH, TTA (ml NaOH 0.1 N) and concentration of lactic and acetic acids (mmol/kg) of breads collected from bakeries. Sourdough and baker’s yeast breads are delimited by blue and red line circles, respectively. Information on the commercial breads collected from bakeries is reported in Supplementary Table S6.

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