Using a specific fungus (Monascus) to process the soybeans, researchers from Chung-Hsing University and Shih Chien University produced Monascus-fermented soybeans (MFS) with more beneficial components.
When tested at the milligram scale, the MFS-extracts were found to compare favourably with vitamin C for antioxidant activity, as well as with synthetic preservatives like butylhydroxyanisole (BHA). Indeed, cold water extracts exhibited strong antioxidant activity of up to 70 per cent, report the researchers in the journal Food Chemistry.
"Based on the results obtained, MFS-31499, MFS-31527 and soybeans were relatively effective in the antioxidant properties assayed and might be potential antioxidants for application in food products," they wrote.
The use of natural alternatives to synthetic preservatives, such as like BHA and butylhydroxytoluene (BHT), to slow down the oxidative deterioration of food is gaining interest.
According to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts, tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by easier consumer acceptance and legal requirements for market access.
This natural antioxidant range could potentially include the polyphenol-rich extract from fermented soybeans, suggest the researchers, led by Jeng-Leun Mau.
The researchers compared hot and cold water extracts from Monascus-fermented soybeans. A five milligram per millilitre cold water extract from MFS was found to have an antioxidant activity of 70.5 per cent, which compared favourably with a one mg/ml extract from unfermented soybean (55 per cent antioxidant activity), and 64 per cent for 20 mg/ml of ascorbic acid.
Hot water extracts had slightly lower antioxidant activity, they report, suggesting that hot water may cause the thermal destruction of certain compounds with antioxidant activity.
However, antioxidant activities for BHA and vitamin E (alpha-tocopherol) were 88.4 and 87.4 per cent, respectively, at the 0.01 mg/ml level.
The extracts also performed well with respect to the reducing power and scavenging ability on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals.
While further research is ongoing concerning the nature of the antioxidant compounds, the researchers indicated that polyphenols were the major naturally occurring antioxidant components in both fermented and unfermented soybeans.
Mau and co-workers note that, while the results suggest that BHA and vitamin E were more efficient antioxidants in terms of concentrations needed, they note that these are limited to the milligram level in food.
"Both water extracts of [MFS] and soybeans could be used in grams or hundreds of gram levels as a soymilk or food processing products such as tofu," they stated.
"Therefore, fermented soybeans in human diets might supply a new alternative for health protection to help humans reduce oxidative damage daily."
Source: Food Chemistry (Elsevier)
Volume 106, Pages 1128-1137
"Antioxidant properties of water extracts from Monascus fermented soybeans"
Authors: Y.-L. Lee, J.-H. Yang, J.-L. Mau