Heat Sterilization of Buckwheat Flour with Low-Oxygen Gas at High Temperature

Abstract

　We investigated a heat sterilization method for powdered foods such as buckwheat (soba) flour and used a low-oxygen gas heat sterilizer to extend the quality retention period of raw buckwheat noodles. The sterilization instrument incorporated closed circuit flow in which high-temperature, low-oxygen gas (N₂ and water vapor from buckwheat flour) circulated as a heating medium. The low-oxygen gas sterilized the buckwheat flour in a short period without deterioration of the flour quality. Open circuit flow and high temperature air sterilization were also performed using a conventional method. Low-oxygen gas heat treatment significantly reduced bacterial counts, although some characteristics (moisture content, color, flavor, etc.) were altered by the treatment; however, retention of these qualities was better than with the hot-air sterilization treatment. We prepared raw buckwheat noodles from buckwheat flour sterilized with low-oxygen gas and investigated the quality retention period. The bacterial counts of sterilized buckwheat noodles were lower than the prescribed reference value at 10 days. In addition, low-oxygen gas sterilization had little effect on some characteristics (moisture content, water activity, flavor, color, and food texture) or on a sensory evaluation of the buckwheat noodles.