Sentence:  Root and stem tumors from sweet clover plants infected with WTV were <WSD>quick-frozen</WSD> in liquid nitrogen , embedded in ice , and cut at 3 - 6 | m in a cryostat maintained at - 16 ` to - 20 ` . 
Meaning of the word marked with <WSD> tags:  (used of foods) preserved by freezing sufficiently rapidly to retain flavor and nutritional value