It, therefore, is necessary to stop frequently and sanitize low - temperature evaporators, and where sterile concentrated food are required, to resort to an additional preservation. 

It 是形式主语，两个不定式to stop frequently and sanitize low - temperature evaporators, and wheresterile concentrated food are required和to resort to an additional preservation是真正的主语？and where sterile concentrated food are required是做什么成分？起什么作用？整个句子怎么翻译？