ORIGINAL PAPER Selection of Process Conditions for High Pressure Pasteurization of Sea Buckthorn Juice Retaining High Antioxidant Activity Zacharias Alexandrakis & Konstantina Kyriakopoulou & George Katsaros & Magdalini Krokida & Petros Taoukis Received: 22 November 2013 /Accepted: 12 March 2014 # Springer Science+Business Media New York 2014 Abstract Sea buckthorn berries juice is a nutritious beverage, rich in vitamin C and carotenoids with high antioxidant activ- ity. The main requirements for a freshly squeezed sea buck- thorn juice production are the cloud stability and antioxidant activity retention after processing. Appropriate process tech- nologies and conditions have to be applied in order to inacti- vate pectin methyl esterase (PME), responsible for cloud loss, while maintaining the nutritional characteristics and antioxi- dant activity of the juice. The objectives of the present work were to study and model the effect of thermal treatment and high pressure (HP) processing on the inactivation kinetics of endogenous PME and on total antioxidant activity alteration. Thermal treatment significantly affected PME inactivation and residual antioxidant activity. Processing even at mild process conditions (60 °C for 1 min) resulted in 2.5-fold antioxidant activity reduction and 50 % PME inactivation compared to untreated sample. Pressure and temperature acted synergistically for PME inactivation that followed first-order kinetics with a residual PME activity at all pressure–temper- ature combinations used (200–600 MPa and 25–35 °C). The effect of temperature and pressure on the inactivation rate constants was expressed through the activation energy and activation volume, respectively. Values of 163 kJ/mol and -17 mL/mol at reference pressure of 600 MPa and ref- erence temperature of 35 °C were estimated, respective- ly. Antioxidant activity of the samples was expressed through the determination of the effective concentration (EC 50 ). A slight increase in sea buckthorn antioxidant activity when applying pressures (200–600 MPa) at ambient temperature (25 °C) was observed compared to the corresponding value of untreated juice. Processing at higher temperatures did not significantly alter the total antioxidant activity of sea buck- thorn juice. For sample treated at 600 MPa–35 °C for 5 min, a 5 % reduction of total antioxidant activity was observed. These conditions are proposed as effective process conditions for sea buckthorn juice cold pasteurization, based on the higher antioxidant activity retention and simultaneous PME inactivation. Keywords High pressure processing . Hippophae rhamnoides L. . PME activity . Antioxidantactivity . Extended shelf life Introduction Sea buckthorn (Hippophae rhamnoides L.) (Elaeagnaceae) has become a fruit of interest for consumers, the health food market, and the food processing industry. Due to its high nutritive value, the interest for commercialization of sea buck- thorn berries is increasing in Europe and North America (Guliyev et al. 2004). Products containing sea buckthorn berries are continuously introduced in the market (such as extracted oil rich in antioxidants, juice, and as supplement to candies, jellies, cosmetics, and shampoos). Although sea buckthorn trees are significantly tolerant to extreme cold and drought conditions and may be cultivated in Z. Alexandrakis : K. Kyriakopoulou : G. Katsaros : M. Krokida (*) : P. Taoukis School of Chemical Engineering, National Technical University of Athens, Zografou Campus, 9 Iroon Polytechneiou, Athens 15780, Greece e-mail: mkrok@central.ntua.gr Z. Alexandrakis e-mail: zalexand@chemeng.ntua.gr K. Kyriakopoulou e-mail: kkyriakop@central.ntua.gr G. Katsaros e-mail: gkats@chemeng.ntua.gr P. Taoukis e-mail: taoukis@chemeng.ntua.gr Food Bioprocess Technol DOI 10.1007/s11947-014-1299-5