Study On Sensory Evaluation And Kinetics For Litchi Juice Treated With PEF And Freeze Concentration

The change of conductivity, pH, soluble solids, Vc , amino acid, L values and other physical and chemical indicators and the rate of quality degradation are investigated for the untreated litchi juice, heat treatment litchi juice (85℃, 15s), high-voltage pulse (PEF) and PEF combined with freeze concentration litchi juice in refrigerated storage respectively. Then the sensory indicators of color, taste, flavor and turbidity for different treatments litchi juices were evaluated using Triangle different test methods, Wilcoxon Test methods and fuzzy methods respectively. The experimental results are showed as follows:(1) The quality of litchi juices by pulsed electric fields is the best; The effect of enzyme inactivations by heating treatment is better than others, however, its impact on sensory indicators of color, taste and flavor is significant (P<0.05), and in the heating process, nutrient compositions of litchi juices are destroyed badly. The combination of PEF technology and freeze concentration is better than the heating treatment in litchi juices (P> 0.05).(2) During storages, the change of conductivity, pH, soluble solids and other physical and chemical indicators is a little for different treatments litchi juices. However, the change of Vc, amino acid and L value of litchi juices is relatively more, which will be reduced with the extension of storage time. And the relationship between degradation rate and the time can beexpressed as:(3) Six months later, the sensory evaluations of litchi juices after different treatments stored at -20℃were compared with control samples (stored at -70℃). The results were showed that: compared with the control samples, the sensory indicators of the litchi juices' taste and color by heating treatment had significant impact. While the combination of PEF and freeze concentration was so superior to heating treatment, moreover, it was even closer to taste and color of the control samples.(4) Litchi juices data of Vc, amino acid and L value after different treatments stored at different temperatures(0℃, -10℃, -20℃) were analyzed. The relationship between the stored time, temperature , different ways of treatments and litchi juice qualities is established using the Arrhenius equation. Then the kinetics model of litchi juices, taking Vitamine C as a detection indicator, was founded during storages. The model could be described as:(5) The storage time of litchi juices was predicted after different treatments. The results showed that: The storage time of the untreated litchi juice was 45 days at 0℃,86 days at -10℃and 172 days at -20℃respectively; the Heat-treated one was 112 days at 0℃, 175 days at -10℃and 283 days at -20℃respectively; the PEF-treated one was 101days at 0℃, 173 days at -10℃, 310 days at -20℃respectively; and the combination of PEF and freeze concentration one was 134 days at 0℃, 191 days at-10℃and 280 days at -20℃respectively.