Changes in antioxidant activity of miso by variety, cooking and added spices

Abstract

Changes in antioxidant activity of miso by variety, cooking method and added spices were investigated. Antioxidant activity of miso increased in proportion to brightness of color and content of total isoflavones and their aglycones. The order of increasing antioxidant activity by variety was soybean-koji miso, dark yellow rice-koji miso, barley-koji miso, light yellow rice-koji miso and sweet rice-koji miso. In increasing order, boiling, frying, broiling or canning of miso enhanced browning and antioxidant activity of miso, while total isoflavones and aglycones contents were decreased. When miso was cooked by microwave, browning and degradation of isoflavone aglycones were decreased. The antioxidant activities of miso cooked with spices did not correlate with their polyphenol compound content. When miso was cooked with ginger, the isoflavone aglycone content decreased, while antioxidant activity and polyphenol compound content increased. When miso was cooked with garlic, mustard, red pepper or sesame, antioxidant activity and browning of miso were remarkably decreased while isoflavone aglycone content was unchanged. These results suggested that antioxidant activity of miso was more affected by melanoidin content formed during cooking more than isoflavone and polyphenol compound content. Based on the above results, ginger may enhance the antioxidant activity of miso by addition of its strong antioxidant compounds, while garlic, mustard, red pepper and sesame may depress miso antioxidant activity by suppressing melanoidin formation during cooking. We expect that cooking miso with spices increases its useful health benefits compared to unseasoned miso.