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Received Aug 6, 2017; Accepted Dec 3, 2017
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1. Introduction
Prunus mume, also known as Mei or green plum in China, mume or Japanese apricot in Japan, and Maesil in Korea, is a deciduous tree of the Rosaceae family [1]. The fruit of P. mume, weighing 12.0–30.0 g freshly, green in immature and yellow in mature stage as well as rich in organic acids, edible fibre, minerals, and phenolic compounds, is known to have good medicinal effects on stomach and intestine disorders [2]. Unlike many other fruits which are mainly consumed freshly, most P. mume fruits should be processed before consumption, due to presence of cyanoglycoside, prunasin, and amygdalin and very high organic acid content [3].
Traditionally, P. mume fruit was firstly pickled with salt or smoked to dry and then processed to preserved fruit or used as medicinal material [4]. For example, the pickled P. mume fruit (named umeboshi in Japan) has been widely used as a food garnish, sauce, juice, and liquor in China, Japan, Korea, and other Southeast Asian countries. Besides, smoked and dried immature P. mume fruit, Fructus mume (Chinese name “Wu Mei”), has been traditionally used as a medical alternative for its antitussive, expectoration, antiemetic, antidiarrheal, anthelmintic, and antipyretic actions [5]. In addition, in many other Asian countries, mainly in Japan, a few of these processed products of P. mume fruit, such as umeboshi and bainiku ekisu (concentrated juice of P. mume fruit), had been used as a folk remedy for fatigue, diarrhea, and fever [6].
Even though a growing number of new technologies have been developed, salt-pickling remains the dominant method for P. mume fruit processing. During pickling of P. mume with salt, a large amount of liquid named Meilu in China and umezu in Japan is produced. Owing to its extreme salty and sour taste, umezu is mostly disposed as sewage, causing environment pollution. Umezu, composed of salt and liquid from P. mume fruit, is a natural source with great potential application. To realize the industrial utilization of umezu, its nutritional values, functional properties, and potential...