Comparison of sensory quality between subjective evaluation and instrument detection for cucumber juice with high pressure processing and heat treatment

Abstract: High pressure processing is an alternative technique for thermal treatment of foods for sterilization, enzyme inactivation, protection of sensory quality and so on. Many studies have showed that there were different effects of high pressure processing on sensory quality for different kinds of juice. This study was focus on two aspects. One is to study the sensory quality protective capability of high pressure processing for cucumber juice. The other is to study the difference of artificial and instrument evaluation on sensory quality and confirm the reliability of instrument evaluation.The Cucumber juice samples were obtained after cleaning, squeezing and centrifugation in sterile conditions. Then the juice was treated with high pressure at 500 MPa for 2 min or 600 MPa for 2 min, and with heat at 60℃ for 2 min. After treatment, the samples were stored at 10, 25 and 37℃ for 15 d, 64 h and 24 h respectively. And the sensory quality evaluations were carried on at 0, 1, 3, 7, 10 and 15 d for 10℃ storage, every 8 h for 25℃ storage and every 4 h for 37℃ storage. The instrument evaluation include chromatic meter combined with ΔE (color evaluated), centrifugal settling quality (precipitation evaluated) and characteristic smells content analysis (with GC-MS for smell evaluate). The artificial evaluation was conducted by a panel of 6 experts trained before formal evaluated. The Pearson correlation analysis was used for confirm the reliability of instrument evaluation.The results showed that there was no obvious difference among the cucumber juice with different treatments on the value of color and smell. During the storage, the total color difference (ΔE) was increased with the time of storage at three store temperatures, and the increasing extent and the final value were similar for the two treatments. The same results obtained in mass fraction of trans-2-cis-6-Nonadienal, acetaldehyde and trans-2-Hexenal. During the storage at 10℃, the centrifugal settling quality of the sample with high pressure treatment was significant lower than that of sample with heat treatment, and this advantage was not significant with the increasing store temperature. Thus, the 10℃ was suitable for cucumber juice store.The correlation analysis on artificial and instrument evaluation showed that there was significant correlation between chromatic meter combined with ΔE and artificial evaluation. This instrument evaluation for color was available for the samples stored at 10, 25 and 37℃. There was significant correlation between centrifugal settling quality and its artificial evaluation for the samples stored at 25 and 37℃, but this instrument evaluation for settling quality wasn't available for the samples stored at 10℃. There was significant correlation between trans-2-cis-6-Nonadienal and trans-2-Hexenal and their artificial evaluations for the samples stored at 10℃, and this instrument evaluation for smell was available for 10℃ storage.