| 摘要: | 本實驗藉由薄層系統的熱風乾燥(40 及 50℃)來部分模擬噴霧乾燥的過程，以瞭解乾燥過程中揮發性物質的保留機制。以麥芽糊精 (40% 及60%)和脫脂奶粉 (40%)兩種物質作為揮發性物質的攜帶者。 實驗初期在麥芽糊精中加入5000ppm的三種揮發性物質(戊醇、苯甲醛、檸檬精油)進行熱風乾燥，後續的實驗中其他三種揮發性物質(乙酸丁酯、乙酸戊酯、2,5-二甲基吡嗪)亦加到麥芽糊精和脫脂奶粉中，進行進一步的研究，但是濃度較低，為50ppm。揮發性成分的保留率測量是先以Liken-Nickerson同時蒸餾及濃縮法萃取樣品中的揮發性成分，再以GC-MS測量其濃度。
結果顯示，在40℃乾燥時，加入40%麥芽糊精中的揮發性成分在最初的80分鐘內嚴重的損失，只有約一半的揮發性成分被保留下來；但之後檸檬精油的保留率就維持恆定不再損失，但是戊醇及苯甲醛的保留率仍持續降低，經過了9個小時後，幾乎損失殆盡。在50℃乾燥時也有類似的情況。另外就40%的脫脂奶粉溶液而言，除了D-limonene之外，其他5種揮發性物質在緩慢的乾燥過程中皆會損失。在40%麥芽糊精的乾燥過程中，乾燥速率大都維持在恆率乾燥期，香氣成分在此時期產生了很大的損失。然而當麥芽糊精的濃度提高到60%時，幾乎所有的六種香氣成分都沒有明顯的損失，這可能是選擇性的擴散在一開始就發揮作用，此時乾燥速率已進入减率乾燥期。從研究結果可知，揮發性物質的選擇性擴散理論無法完全應用在薄層系統的乾燥。
Experiments were designed and conducted to simulate volatiles retention
partially during a drying process by creating a thin layer feed system and drying it by hot-air at 40 and 50℃. Volatiles carriers used were maltodextrin (40 and 60%, WWB)and skim milk (40%). A mixture of volatile compounds made up of pentanol,benzaldehyde, D-limonene, was added to the carriers in the beginning at a higher concentration of 5000 ppm and in some cases three more volatiles were used,including butyl acetate, pentyl acetate and 2,5-dimethyl pyrazine, each at a concentration of 50 ppm. The volatile contents of the feed materials just before and after drying was determined by Liken-Nickerson simultaneous distillation and concentration followed by GC-MS analysis.The results showed that volatiles were seriously lost during the first 80 min at 40℃ for all three volatiles in a 40% maltodextrin feed, after that, as drying continued,D-limonene seemed to cease loss but pentanol and benzaldehyde lost continuously.The same situation was observed at 50℃ drying but with the volatiles retention lower than that of at 40℃ drying. For the 40% skim milk feed, with the exception of D-limonene (presented the highest retention), volatiles loss occurred during the slow drying process. During the whole drying trial of 40% maltodextrin, drying was maintained in the constant rate period of drying and most of the volatiles showed a great loss in this period. However, when 60% of maltodextrin was applied, no distinct
volatiles loss was observed for all of the 6 volatiles, because the selective diffusion mechanism was effective at the concentration from very beginning, which is corresponding to the falling rate period of drying. It was concluded that, the selective diffusion mechanism is not completely applicable during the drying process of a thin layer feed system in terms of volatile retention. |
