The yoghurts were produced in our dairy technology pilot plant. Raw milk (cow, goat and sheep milk, collected in the summer from conventional farms in the Czech Republic) was heat treated using a discontinuous method with three temperature regimes (85, 90 and 95 °C for 10 min). Three types of commercial yoghurt starter cultures containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus were used, namely culture A (Milcom a.s., Prague, Czech Republic), culture B (Danisco, Paris, France) and culture C (Chr. Hansen, Hørsholm, Denmark), as these are the starters used in key dairies in the Czech Republic. All inoculated samples were incubated at 40 °C for 4–7 h with continuous pH measurement until they reached a pH of 4.5. The finished yoghurts were then stored for 3 weeks in two different temperature-controlled refrigerators with temperatures set at 2 and 8 °C. To determine the benzoic acid content, samples were taken from each batch starting the morning after yoghurt production and then repeated every 3–4 days. Seven samples were taken for each yoghurt batch during storage, as can be seen from the x-axis description in Figure 1. For each type of milk, 3 batches of yoghurts were produced, thus we analysed a total of 1134 yoghurt samples.

Changes in benzoic acid content in cow, goat and sheep yoghurts during storage. Different letters (a–e) for each type of yoghurt indicate a statistically significant difference (p < 0.01).

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