Discussion On The Reason Of The Formation Of Bitter And Spicy Taste Of Jujube During Drying Process

Fresh Hami jujube was chosen as the experimental materials to be dried by natural drying and hot air drying methods with different technology parameter. The forming mechanism of peppery and bitter taste was discussed through the changing rule of physical character, nutrients and some of the physiological & biochemical indictors. The conclusions followed as:1. The texture and taste can be measured by shearing force. The shearing force would increase whether the drying temperature was too high or too low, and the taste of jujube would be impacted. The shearing force was closely related to the moisture. In this experimental condition, the jujube had the lowest shearing force, the softer texture and the best taste under 45℃.2. The drying technology had greater impact to the flavor of jujube. The long-time-low-temperature drying and short-time-high-temperature drying were negative to the flavor forming of jujube, especially jujube dried by natural drying had conspicuous peppery, bitter and burnt taste, poor sweet. The forming of the peppery and bitter taste could be evitable by using lower temperature hot air drying. In this experimental condition, the peppery and bitter taste was the lightest under 40℃.3. During the drying process, the fructose and glucose content of different drying technologies was increasing, but the sucrose was decreasing. The significant change between fructose & glucose and sucrose happened in the initial stage of drying. In the hot air drying condition, the higher the temperature was, the faster the sucrose degraded; in the natural drying condition, the sucrose content of jujube dried through yin heavenly terms declined faster. Reducing sugar content and anxious burnt taste was significant positive correlative(P<0.05), sucrose content was significantly negatively correlated with anxious burnt taste(P< 0.05); sugar content did not directly related to sweet, bitter, spicy taste.4. Drying processing made great effect on total acid. Total acid content of the jujubes dried at 65℃was higher than fresh ones, and was always higher than other drying process, and the sugar and acid ratio was always the lowest; total acid content of the jujubes dried under other process was higher than fresh ones. The total acid content positively related to sour taste(P<0.05). The sugar and acid ratio significant positively related to sweet taste(P<0.05), but negatively correlated with spicy taste(P<0.05) and bitter taste.5. The content of soluble protein decreased during the drying process. In the initial stage of drying, the higher the drying temperature was, the more quickly the soluble protein content decreaced. The consequence indicated that the content of soluble protein had a certain positive correlation with the bitter taste(R=0.62).6. Drying processing made great effect on VC content, which exhibit a sharp decline in the early time of drying process, and maintain at a lower value. The Vc content did not show direct relationship with flavor.7. Activity of anaerobic respiration metabolic enzyme, substrate and product all first increased and then decreased, activity of alcohol dehydrogenase showed the same change with acetaldehyde content, pyruvate decarboxylase activity was positively correlated with accumulation of acetaldehyde, at the early time of drying process, acetaldehyde content was in synchronization with the change of pyruvate concentration. the accumulation of pyruvate and acetaldehyde showed no significant correlation with sour, sweet, bitter and spicy. 8.β-glucosidase activity was first increased and then decreased during the drying processing. Effect of drying process on the activity and the duration ofβ-glucosidase was as follows:activity ofβ-glucosidase were low when it was dried at low temperature, but the duration was longer; the activity ofβ-glucosidase was higher and the duration was longer (40h-48h)when the jujubes were dried at 40℃and 45℃, and the bitter peppery did not performance in sensory evaluation, in contrast, the flavor was pleasure.9. Total phenols and flavonoids content all showed increasing trend during drying process. Change of browning value was relative to moisture content and total phenol content, except the browning value of the jujubes dried at 45℃showed negatively correlative, browning value was significantly positively relative to total phenol content in other drying process(P<0.01), and showed negatively correlative with moisture content(P<0.01).10. It was significantly positive correlated among peppery, bitter and burnt taste; but it was exceedingly negatively correlated between sweet and peppery, bitter and burnt taste; besides, the sour taste had little direct correlation with other tastes. Affacted syntheticly by drying condition, sugar and acid ratio, soluble protein,β-glucosidase and so on, the peppery and bitter taste emerged.