[Problem] To provide a freshness-maintaining agent having reduced off-flavor containing monomenthyl glutarate. [Solution] Disclosed is a composition containing high-purity monomenthyl glutarate having a content of dimenthyl glutarate of 5 mass% or lower in a freshness-maintaining agent comprising monomenthyl glutarate and dimenthyl glutarate. Such a composition can be obtained efficiently by a preparation method including a step for extracting monomenthyl glutarate as an alkali salt from a composition containing monomenthyl glutarate and dimenthyl glutarate in which the latter is present in an amount exceeding 5%.
