The juice of various fruits e.g. citrus fruits, apples, peaches and the like is used for a beverage or for a sarcocarp beverage, and the juice of citrus fruits e.g. citrus junos, citrus sphaerocarpa, citrus limon and the like is used for seasoning. The juice of these fruits is generally used for the fresh juice in the form of a suspension containing fine fibrous elements of the fruits or under the as-extracted condition, though it is sometimes used for limpid juice after the fine fibrous elements of the fruits are removed therefrom.
Since the as-extracted natural fruit juice contains not only the aforementioned fine fibrous elements of the fruits but also pectin and pectin decomposing enzymes, the fine fibrous elements of the fruits are combined with one another due to the function of pectin and form a colloidal suspension. On the other hand, since the as-extracted natural fruit juice contains pectin decomposing enzymes, e.g. pectin esterase, poly galacturonase et al., pectin is gradually decomposed and therefore becomes inactive. Following the progress of this reaction, the colloidal suspension is dissolved into precipitation of the fine fibrous elements of fruits and limpid juice. Incidentally, putrefaction occurs due to the function of microorganisms e.g. molds, yeasts or the like. Therefore, the natural fruit juice can not be stored for a long time.
For the purpose of enabling the natural fruit juice to be stored for a long time, a sterilization process which is conducted at approximately 90 degrees C has been used. In other words, the heating sterilization process has been conducted for two purposes, including extinction of the microorganisms which cause putrefaction and deactivation of the pectin decomposing enzymes which are effective to keep the natural juice in a colloidal situation which is produced by combining fine fibrous elements of the fruits with one another, employing the function of pectin, thereby preventing the colloidal juice from being dissolved into precipitation and limpid juice. This heating sterilization process, however, requires a long time for transmitting heat and is involved with drawbacks wherein the nutritious elements are destroyed, the aromatic elements are dispersed, and the color and the taste are deteriorated due to heating with high temperature, thereby in combination deteriorating the quality of the natural juice.
For the purpose of removing the drawbacks of the heating sterilization process which inevitably deteriorates the quality of the natural juice, a high pressure sterilization process was developed, and various results of the experiments of the high pressure sterilization process wherein the natural juice is compressed with high pressure in excess of 1,000 atm. are published in e.g. "Nippon Nogeikagaku Kaishi (The Journal of the Japanese Association of Agricultural Chemistry)" Vol 63, No. 6 (1989) According to these articles, the microorganisms including molds and yeasts which can propagate and can be a cause of putrefaction, are entirely killed by being compressed with high pressure of 2,000 atm. for 10 minutes, provided the high pressure process is conducted for the acidic natural juice of citrus fruits of which the pH value does not exceed 4.5.
The technology is publicly known wherein enzymes are added to foodstuffs. For example, some of the aforementioned pectin decomposing enzymes have been employed for dissolving the fruit juice into fine fibrous elements of the fruits and limpid juice. Amylase and cellulase have been employed to decrease the molecular weight of the polysaccharides (for saccharification or decomposition of the polysaccharide to convert them into sugar). Proteolytic enzymes have been employed to prevent the alcoholic liquors from clouding, to soften meat, or to solidify cheese. Proteolytic enzymes have seldom been employed to dissolve or deactivate an enzyme which is a type of protein.