A packaged product formed by enclosing a content material, such as food or
beverage, sanitary products or medical products, within a packaging
material including at least a layer of hydrophilic resin, is heat-treated
with hot water for, e.g., boil sterilization or retort sterilization. The
hot water is caused to contain a water-soluble compound in an amount
substantially exceeding a level contained in tap water, whereby it
becomes possible to suppress the opalescence of the packaging material
causing inferior appearance or transparency and leading to a lowering in
gas-barrier property, which has been problematic in the conventional boil
or retort hot water treatment.
