Effect of High Pressure Processing on Functional Ingredient and Quality of Heat-sensitive Juice

Lemon juice and apple juice are popular beverages in Taiwan, but after conventional heat processing, it will destroy its nutrients and affect the appearance and quality that reduce consumer willingness to buy. Polyphenol oxidase (PPO), peroxidase (POD) and Pectin methyl esterase (PME) can cause browning of fruit juices and turbid apple juice as affecting the appearance quality of the key enzymes. PPO、POD and PME are key enzymes, which can cause fruit juices to be browning and reduce its appearance quality or make it cloudy. In this study, we utilize the high-pressure processing technique to destroy the enzymes activity and maintain the nutrients. First, the lemon juice and apple juice are divided into three groups: untreated (Control), traditional heat treatment (Thermal processing, TP ; 65°C /30 min), and high pressure processing (HPP) with three conditions: 200 MPa (10、20、30min)、300 MPa (10、20、30min)、400 MPa (5、10、20 min). Furthermore, the lemon juice and the apple juice have no significant change on TP and HPP. Although the total microorganisms may not be completely sterilized like a conventional heat sterilization; however, both juices can reach the safety standard with 100 MPa for 10 minutes processing. Associated with the increase of the total processing time and pressure plate count decreases, and Escherichia coli coliform is not detected; i.e., negative. PPO and POD, the key enzymes effecting appearance quality of lemon and apple juices, do not significantly decrease. PME activity in apple juice reduces at 300 MPa 10 and 20 minutes treatment，0.17 ± 0.012 ~0.19 ± 0.026 [ΔOD min-1 (g of fw)] in 400 MPa PME activity reduce at 20 minutes treatment and from the results we can know that in 300 MPa short time treatment can reduce PME activity in apple juice, however no significant influence on lemon juice. That is to say, the high-pressure treatment has effect on apple juice’s PME active destruction to some extent. For nutrients, the lemon juice can reach the equival vitamin C 211.9 mg / L content, the same to the control group with the 300 MPa for 10 minutes treatment, and apple juice can reach the equival vitamin C 145.9 mg / L content, the same to the control group 200 MPa for 10 minutes treatment. On the other hand, as for soluble proteins affecting turbidity, that in lemon juice reduces to a minimum at 300 MPa for 30 minutes treatment and that in apple juice reduces when treated with 200, 400 MPa pressure treatment and longer time. The heat-sensitive apple juice with high-pressure treatment can achieve the same sterilization effect to conventional heat treatment, and is better than the traditional thermal processing in maintaining the nutritional value and appearance quality. Besides, after the apple juices are treated with the optimum conditions of 200, 300, 400, and 600 MPa for 20 minutes, it was stored at 4°C in two weeks. The results show that the thermal processing and pressure treatment for 300 MPa or higher has sterilization effect. In addition, the pH, soluble solids, titratable acidity after storage do not have significant changes, meaning that different processing does not change the physical properties; however, nutrients decreases with increasing storage time. The use of high-pressure treatment offers better retention effect when compared with the control group the heating group. Finally, it also shows that enzyme content of PPO has no significant differences among the treatments, but content of POD enzymeaa with 200 MPa treatment declines, PME increased at 300 MPa. Based on the above results, lemon juice and apple juice can achieve sterilization effect with 100 MPa or higher treatment, but 300 MPa or higher pressure for storage. The high-pressure treatment not only does not affect the physical ingredient juice, but also reserves better nutrients compared to the heat treatment.