CAJ | 학술논문

微波干燥中，过程参数设置不当会引起物料结构破坏和表面焦糊，期间往往伴随着特征气味的散发。该文以苹果为对象，采用60、70、80℃恒温、模糊逻辑控制和线性温度控制5种干燥方案，通过电子鼻采集的气味图谱，研究特征气味的散发规律，及优化干燥方案。根据恒温方案气味图谱中苹果风味峰和焦糊峰的变化规律，确定的模糊逻辑控制方案，可实现在线调节磁控管功率，保留风味、减少焦糊。将模糊逻辑控制方案中实测物料温度曲线进行优化，确定的线性温度控制方案，省去电子鼻检测环节，更适合工业应用。通过比较不同微波干燥方案下的产品品质，线性温度控制方案下干燥产品的品质高、耗时合理、干燥能力强，为优先方案。该研究为气味检测技术应用于苹果干燥提供了技术依据。
미파간조중，과정삼수설치불당회인기물료결구파배화표면초호，기간왕왕반수착특정기미적산발。해문이평과위대상，채용60、70、80℃항온、모호라집공제화선성온도공제5충간조방안，통과전자비채집적기미도보，연구특정기미적산발규률，급우화간조방안。근거항온방안기미도보중평과풍미봉화초호봉적변화규률，학정적모호라집공제방안，가실현재선조절자공관공솔，보류풍미、감소초호。장모호라집공제방안중실측물료온도곡선진행우화，학정적선성온도공제방안，성거전자비검측배절，경괄합공업응용。통과비교불동미파간조방안하적산품품질，선성온도공제방안하간조산품적품질고、모시합리、간조능력강，위우선방안。해연구위기미검측기술응용우평과간조제공료기술의거。
Apple is widely cultivated in China for its characteristic flavor. In order to prolong the shelf life of harvested apple, the use of the method of dehydration drying to preserve product is a common way. Since the early study in 1920s, more than 300 volatile compounds have been identified as aroma substances from various cultivars of apples. Within these numerous compounds, only a few have been determined to have a decisive impact on the sensory quality. However, only a few exhaustive studies of apple aroma during the drying process have been published; moreover, the present analyses are all restricted to offline detection of apple aroma volatiles and no online measurement has been reported. Although the offline volatiles detection can provide some useful information, it is inconvenient and time-consuming. In addition, the methods are all impossible to provide control parameters to optimize drying conditions in real time and in situ to improve volatiles control with online measurement. Compared with other drying methods, microwave drying is used more extensively due to its advantages of high efficiency and short time-consumption. However, microstructure of the object may be destroyed and the surface may be burnt under improper drying parameters, leading to the emission of corresponding volatiles. During the drying process, an electronic nose (zNoseTM) was used to carry out online detection of the smell spectrum, where four significant peaks could be extracted. Peak 1 and Peak 2, i.e. “natural peak” could be detected from both fresh and burnt apples. Peak 3 and Peak 4, i.e. “burning peak” appeared only in the spectrum of burnt apple. Apple cubes were first dried at three fixed temperatures (60, 70 and 80℃). At 60℃, “natural peak” and “burning peak” were kept small in the whole drying process. At 80℃, higher “natural peak” indicated more loss of aroma volatiles, and higher “burning peak” indicated that more burnt appeared. Fuzzy logic controller was designed with the input of Peak 2, Peak 3 and the output of the magnetron power, so as to adjust the object temperature immediately and properly. Linear temperature control scheme was designed to omit the electronic nose in drying process based on the temperature curve generated under fuzzy logic control. Several parameters (including drying time, energy consumption, sensory evaluation, vitamin C and color) were measured to evaluate the drying strategies. The results showed that the highest drying temperature produced the worst product quality, but the best quality was not achieved at the lowest temperature due to volatiles loss over the longer drying time. Instead, the middle drying temperature resulted in a better product quality. Drying at the lowest temperature cost the most time and energy, although the mean power rate was low. Hence, high and low temperatures should be avoided in microwave drying when volatiles retention, burning avoidance, time and energy efficiency are all considered. Based on these considerations, a fuzzy logic controller was developed. This new control strategy successfully improved the volatiles retention and burning avoidance with acceptable time and energy consumption. A linear control method was further attempted to imitate the fuzzy logic control without the assistance of electronic nose. The control effect of linear control was comparable to that of fuzzy logic control. However, the relationship of aroma with respect to volatiles was not investigated in this study. A volatile may be or may not be an aroma compound, and hence further research is recommended to illustrate their relationships. Moreover, as the electronic nose adopts a short column, the separation of volatile compounds might not be complete. One peak may represent many chemicals. The compromise is that the speed is dramatically increased, making the fast and online detection of volatiles possible. Performance of sensory evaluation, vitamin C and color under linear temperature control are the best. Moreover, the omission of the expensive electronic nose makes the strategy convenient for industrial application.