Effect of High Pressure Processing (HPP) Combined with Low and Moderate Temperature Treatments on the Color and Enzyme Inactivation in Freshly Squeezed Lychee Juice
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Abstract:
In order to investigate the effects of high pressure processing (HPP) on the activities of peroxidase (POD) and polyphenol oxidase (PPO) in the freshly squeezed lychee juice, HPP (300~450 MPa, 10~40 min) alone and treatments of HPP (450 MPa, 20 min) combined with low (10 ℃) and moderate temperatures (40~70 ℃) were conducted on fresh lychee juice, respectively. Physicochemical properties and sensory quality of lychee juice were measured to explore the combination of HPP and temperature on the quality of lychee juice. The results showed that POD was activated only when HPP was carried out under pressure between 300~450 MPa at 25 ℃ for 20 min. The POD activity reached the maximal level after 300 MPa treatment. Below the aforementioned pressure range, the PPO activity decreased with increasing pressure. PPO was less pressure-resistant than POD. At the pressure of 450 MPa, the activities of POD and PPO decreased with increasing pressure-holding time. HPP combined with low and moderate temperatures had a certain degree of synergistic effect on the POD and PPO inactivation. In the moderate temperature range (40~70 ℃), the synergistic inhibitory effect was more significant with higher temperatures. Upon combining the treatment of HPP with moderate temperature, the L* value of lychee juice was significantly increased and the brightness of the juice was enhanced. However, with increasing temperature in the HPP and temperature combined treatment, the total color difference ?E* value and the change in color of the juice gradually increased.
