Studies on the practical use of soybean peptides for oral health promotion in the elderly

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In order to investigate the hypothesis that dietary consumption of soybean peptides may be beneficial for oral health promotion in the elderly, we studied their effects on growth of oral pathogenic microorganisms. The soybean peptides "Hinute-R" (average chain length 3-4) inhibited the growth of Aggregatibacter actinomycetemcomitans, an etiologic agent of periodontitis. It also inhibited the growth in early stage of Candida albicans and Candida glabrata, which can cause opportunistic oral infections. Two fractions were obtained from Hinute-R by gel filtration chromatography. The fraction I, showing a molecular weight of approximately 10,000 daltons, was remarkably effective in inhibiting the growth of C. glabrata when compared to Hinute-R and fraction II having a molecular weight of approximately 2,000 daltons. The presence of LLPHH, anti-oxidative peptide isolated from digests of a soybean protein, at 2.5 and 12.5 mg/ml reduced the growth of C. glabrata by 23% and 42%, respectively. No toxicity of soybean peptides was observed against human cells. These results support the potential of soybean peptides for elderly subjects with poor resistance to infections.In the second part of the project, we showed that the suction method is useful to obtain information regarding the salivary protein profiles in aged subjects who cannot eat or spit saliva easily. As preliminary studies for our clinical trials, we investigated the relationship between salivary components and oral conditions in the elderly requiring care. Among components investigated, the substance P, an endogenous substance causing cough reflex and involved in swallowing function, was positively correlatedwith the number of teeth present. This information may be useful for further clinical trials using the soybean peptides.