Plain language summary
Fermented foods are growing in popularity in the West due to their unique flavour and nutritional value. This review investigates the fermentation processes, health-associated bioactive components and underlying mechanisms of the popular fermented soy products Natto, fermented soy milk, Tempeh and soy sauce. Each fermented soy product is summarised based on functional activities. The existing literature points to an overall positive effect on bone health and immune activities. Interestingly, each fermented soy food exhibits different profiles of bioactive components and therefore different mechanisms of action. Based on this review, the authors conclude there is a need for further in-depth human studies with large sample sizes and long-term follow up to better understand these foods benefits and potential toxicity.
Abstract
For centuries, fermented soy foods have been dietary staples in Asia and, now, in response to consumer demand, they are available throughout the world. Fermentation bestows unique flavors, boosts nutritional values and increases or adds new functional properties. In this review, we describe the functional properties and underlying action mechanisms of soy-based fermented foods such as Natto, fermented soy milk, Tempeh and soy sauce. When possible, the contribution of specific bioactive components is highlighted. While numerous studies with in vitro and animal models have hinted at the functionality of fermented soy foods, ascribing health benefits requires well-designed, often complex human studies with analysis of diet, lifestyle, family and medical history combined with long-term follow-ups for each subject. In addition, the contribution of the microbiome to the bioactivities of fermented soy foods, possibly mediated through direct action or bioactive metabolites, needs to be studied. Potential synergy or other interactions among the microorganisms carrying out the fermentation and the host's microbial community may also contribute to food functionality, but the details still require elucidation. Finally, safety evaluation of fermented soy foods has been limited, but is essential in order to provide guidelines for consumption and confirm lack of toxicity.
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