PURPOSE: A liquid protein food product is combined with juice of fruit or vegetables whose pH is adjusted to a higher level than its isoelectric point to produce good-taste mixed beverage with stabilized properties causing no coagulation or precipitation.

CONSTITUTION: A liquid protein food product such as cow milk or soybean milk is combined with a fruit juice or vegetable juice that is treated with an anion-exchange resin so that its pH becomes higher than the isoelectric point of the protein food product, preferably 5.0W7.0.