Mammalian and avian species quantification in homogenized foods: real time PCR and digital PCR as tools for label compliance controls

Abstract

Currently food fraud and authenticity of products composition are topics of great concern; ingredients quantification could allow to identify small amounts of contaminats or voluntary addition of improper components. Many molecular methods are available for species identification in foodstuffs but, for a better application, they should not be affected by the interference of other ingredients. The main purpose of this work was to verify the Real Time PCR and the Digital PCR (dPCR) quantification performances on baby food samples, specifically selected for their high miscibility to limit variability; chicken was selected as target to verify the performance of quantification of methods after having spiked the same quantity in different baby foods. The other aims were: (1) to verify a constant genome copies ratio existence between mammalian and avian species (2) to verify the dPCR performance, set up on housekeeping, to quantify mammalian and avian species in commercial products. Digital PCR showed fewer differences respect to Real Time PCR, at the same 15% w/w chicken spiking level. Despite the constant difference between mammalian and avian genome copies, in samples with the same spiking weight, the confidence intervals increasing towards the extreme values, made impossible to use genome copies ratio as a sort of correction factor between species. Finally, the dPCR system using the myostatin housekeeping gene to determine the chicken content seemed reliable to verify the labelling compliance in meat-based commercial products.

Figure 1

Boxplots of chicken DNA concentration in food samples spiked at 15% chicken (three runs with three replicates for each food were analysed); (1A) data obtained vs 100% chicken muscle standard curve (1B) data obtained vs 30% chicken baby food standard curve. Legend: veal meat baby food (A), soft cheese (B), organic soy mayonnaise (C), mixed vegetables baby food (D), mixed fruits baby food (E), Yogurt (F), Beef (G). Y axis: DNA concentration.

Figure 2

Boxplots of genome copies data obtained by dPCR from different food samples spiked at 15% (three replicates for three runs were analysed). Legend: veal meat baby food (A), soft cheese (B), organic soy mayonnaise (C), mixed vegetables baby food (D), mixed fruits baby food (E), Yogurt (F), Beef (G). Y axis: genome copies.

Figure 3

Estimation of the correction factor for species concentration (from 1 to 100%); graphic representation of avian/mammalian ratio and confidence intervals.