Effect of high hydrostatic pressure and high-pressure homogenisation on Lactobacillus plantarum inactivation kinetics and quality parameters of mandarin juice

The inactivation kinetics of Lactobacillus plantarum in a mandarin juice treated by thermal treatment (45-90 A degrees C), high-pressure homogenisation (HPH) (30-120 MPa at 15 and 30 A degrees C) and high-pressure processing (HPP) (150-450 MPa at 15, 30 and 45 A degrees C) were fitted to different Weibullian equations. A synergic effect between pressure and temperature was observed in HPH and HPP treatments achieving 2.38 log cycles after 120 MPa at 30 A degrees C for 10 s (final T of 45 A degrees C) and 6.12 log cycles after 400 MPa at 45 A degrees C for 1 min (final T of 60 A degrees C), respectively. A combined treatment of 100 MPa at 15 A degrees C for 10 s and 300 MPa at 15-30 A degrees C for 1 min in HPH and HPP, respectively, was needed to the first logarithm microbial population decline. Weibull model accurately predicted microorganism inactivation kinetics after HPH and HPP processing when displaying single shoulder or tail in the survivor curves, whereas when a more complex trend was observed after thermal treatment, the double-Weibull equation was found more appropriate to explain such behaviour. Equivalent treatments that achieved the same degree of microbial inactivation (77 A degrees C-10 s in thermal processing, 120 MPa-10 s at 30 A degrees C in HPH processing and 375 MPa-1 min at 30 A degrees C in HPP) were selected to study the effects on quality parameters. The application of dynamic pressure led to a decrease in sedimentable pulp, transmittance and juice redness, thus stabilising the opaqueness and cloudiness of mandarin juice. Pectin methyl esterase (PME) was found to be highly baroresistant to static and dynamic pressure. Carotenoid content remained unaffected by any treatment. This study shows the potential of high-pressure homogenisation as an alternative for fruit-juice pasteurisation.