Inactivation of Aspergillus niger in Mango Nectar by High-Pressure Homogenization Combined with Heat Shock

ABSTRACT:  This research evaluated the inactivation of a heat-resistant  Aspergillus niger  conidia in mango nectar by high-pressure homogenization (HPH) combined with heat shock.  A.niger  were inoculated in mango nectar (10⁶ conidia mL⁻¹) and subjected to HPH (300 to 100 MPa) and heat shock (80 °C for 5 to 20 min) before or after HPH. Processes were evaluated according to number of decimal reductions reached by each isolated or combined process. Scanning electron microscopy was performed to observe conidia wall after pressure treatment. Pressures below 150 MPa did not inactivate  A. niger  while pressures of 200 and 300 MPa resulted in 2 and more than 6 log reductions, respectively. D_{80 °C} of  A. niger  was determined as 5.03 min. A heat shock of 80 °C/15 min, reaching 3 decimal conidia reductions, was applied before or after a 200 MPa pressure treatment to improve the decimal reduction to 5 log cycles. Results indicated that HPH inactivated  A. niger  in mango nectar at 300 MPa (>6.24 log cycles) and that, with pressure (200 MPa) combined with post heat shock, it was possible to obtain the same decimal reduction, showing a synergistic effect. On the other hand, pre heat shock associated with HPH resulted in an additive effect. The observation of  A. niger  conidia treated by HPH at 100 and 200 MPa by scanning electron microscopy indicated that HPH promoted intense cell wall damage, which can sensitize the conidia to post heat shock and possibly explain the synergistic effect observed.
Practical Application : The results obtained in this paper are relevant to elucidate the mechanism of conidia inactivation in order to develop the application of HPH as an alternative pasteurization process for the fruit nectar industry.