脫水冷凍蔬菜之試製（二）脫水冷凍菠菜、芥藍及青江菜品質之影響

Preliminary Report on the Dehydrofreezing of Vegetables (Ⅱ) Effect of Dehydrofreezing Methods on the Quality of Frozen Spinach, Chinese Kale and Chin-Kung Tsai

由於綠色葉菜類合水份特高、軟弱之質地及較多葉綠素含量，故至今尚未發展商業化之冷凍加工製品。本試驗即以改善此泠凍綠色葉菜透過一連串之殺菁、脫水及冷凍過程而在冷凍前試以脫去部份水分以達到改進品質之目的。1.改善產品之外觀品質以1.2%食鹽水在90～95°C經過數分鐘之殺菁顯示獲得較高之營養分如全可溶性固形物、胡蘿蔔素及維生素丙等以及較高之官能品評記分。2.殺菁時為了避免不安定之葉綠素受高溫之影響，結果發現以90～95°C之熱水（含1.2%食鹽）殺菁較用蒸汽為有利。3.綠色葉菜可於60～70°C而在30分鐘內用任何熱風循環脫水機直接脫去部份水分（約40%），為了獲得產品之較佳衛生條件，在冷凍前部份脫水後之蔬菜以高溫蒸汽作半分鐘噴射處理即可。4.綠色葉菜類如菠菜、芥藍或青江菜不適合用個別跳凍凍結，用接觸凍結方法，雖可使蔬菜緊包於紙匣內，但其品質往往較差，因為蔬菜凍結時通過結凍帶之時間過長，因此較大之冰晶形成，致滴水損失多而品質低。故應用-40°C之急風吹凍於30分鐘內完成泠凍則可達到預期之效果。5.綠色葉菜如青江菜在凍結前做四種不同脫水程度之處理，結果發現以脫水40%者所得之冷凍品質最佳。6.本研究亦提出一綠色葉菜類之脫水冷凍加工程序，以為進一步研究及不久將來從事於此綠色葉菜冷凍加工生產上之參考。

Due to the rather high moisture content, soft texture and abundance of chlorophyll presented in the green leaf vegetables, so far it is difficult to make them into commercial frozen product. In this experiment, a series of test includipg blanching, dehydration and freezing methods with partial dehydration prior to freezing is carried out in order to improve the quality of frozen green vegetables. It is found that dehydrofrozen vegetables revealed better appearance and quality together with higher nutrition contents as total soluble solids, β-carotene, ascorbic acid and higher organoleptic evaluation scores. Scalding at 90~95°C hot brine shows better result for avoiding the unstable chlorophyll changes in high temperature during blanching than that by steam blanching, Partial moisture of green leaf vegetables can be directly dehydrated (about 40%) at 60~70°C within 30 minutes in any hot air circulation dehydrator. The better sanitary condition can be obtained by spraying the partial dehydrated vegetables with steam for half minute and then freeze. Green leaf spinach, Chinese kale or ching-kung tsai is not suitable for freezing by the individual quick freezing method. Although vegetables frozen by the contact freezing method can stay together during being packed in carton but their qualities are no good due to a need of longer time to pass them through the freezing zones in the contact freezing chamber. Thus more and larger ice crystals cause poor quality such as higher in dripping loss are found. Vegetables frozen in-40°C air-blast room within 30 minutes are able to keep better quality than the other two freezing methods. A proposed scheme for the dehydrofreezing of green leaf vegetables is presented in this paper as a reference of further advanced study or for the commercial production of frozen green leaf vegetables in the future.