The effect of hydrogen peroxide on the growth of thermophilic lactic starter and acid gelation of UHT milk

The influence of H 2 O 2 pre-treatment (10–250 mg L −1 ) of ultra-high temperature treated (UHT) milk devoid of lactoperoxidase activity on the growth of thermophilic starter in the process of yoghurt production was studied using isothermal batch microcalorimetry and dynamic rheological measurements. Typical dual-peak power-time curves of diauxic growth of starter bacteria in milk were registered. Even the lowest concentrations of H 2 O 2 added into milk 1 h before inoculation hindered the growth of thermophilic bacteria, retarded the onset of milk gelation, and resulted in formation of weaker gels. UHT milk samples treated with H 2 O 2 and subsequently with catalase showed certain bacteriostatic influence of H 2 O 2 pre-treatment on the second exponential growth phase. However, hardly any difference in gelation and no changes in rheological characteristics of mature gels in milk free of residual H 2 O 2 due to catalase treatment prior to inoculation in comparison with H 2 O 2 -free control samples were observed.