Study of changes of antioxidant activity during fermentation of various types of legumes as a possible functional food ingredient

Abstract

Background: Diacylglycerol (DAG) oil is a natural component of various edible oils. DAG has been reported to prevent obesity through a variety of potential mechanisms in comparison with triacylglycerol (TAG) in humans. An increase in postprandial energy expenditure (EE) is proposed to be one of the mechanisms underlying this effect of DAG. Up-regulated mRNA expressions associated with EE by DAG in the small intestine may explain increased postprandial EE. The small intestine seems to contribute to changes in EE by DAG. We previously studied plasma serotonin, which is mostly present in the small intestine and mediates sympathetic thermogenesis. We found that DAG ingestion increases plasma serotonin levels by approximately 50% compared to TAG ingestion.

Objective: To understand the molecular mechanisms for DAG-induced increase in serotonin and EE, we investigated effects of DAG on serotonin release and expressions of genes associated with EE, using the human intestinal cell line.

Methods: The intestinal cell line, the Caco-2 cells, was incubated with medium containing 1-monoacylglycerol (1-monooleyglycerol [1-MOG]) and 2-monoacylglycerol (2-monooleylglycerol [2-MOG]), distinctive digestive products of DAG and TAG, respectively. We measured serotonin release from the Caco-2 cells using a newly developed high-performance liquid chromatography. Further, we studied effects of 1-MOG, 2-MOG, and serotonin on expressions of mRNA associated with EE (acyl-CoA oxidase [ACO], medium-chain acyl-CoA dehydrogenase [MCAD], fatty acid translocase [FAT], and uncoupling protein-2 [UCP-2]), by the Real-Time quantitative RT-PCR system.

Results: 100 mM 1-MOG significantly increased serotonin release from the Caco-2 cells compared with the same concentration of 2-MOG by approximately 37% (P<0.001). Expressions of mRNA of ACO, FAT, and UCP-2 were significantly higher in 100 mM 1-MOG-treated Caco-2 cells than 100 mM 2-MOG-treaed cells by approximately 13%, 24%, and 35%, respectively. Expressions of mRNA of ACO, MCAD, FAT, and UCP-2 were significantly increased in 400 nM serotonin-treated Caco-2 cells as compared with the Caco-2 cells incubated without serotonin by approximately 29%, 30%, and 39%, respectively.

Conclusion: Our study demonstrated that a hydrolytic product of DAG increases serotonin release from the intestinal cells and enhances expressions of genes associated with b-oxidation (ACO, MCAD), thermogenesis (UCP-2) and fatty acids metabolism (FAT). Furthermore, this study revealed that serotonin also enhances expression of these genes, proposing a new molecular biological mechanism for DAG-mediated anti-obesity effect. Serotonin may play an important role in DAG-mediated prevention of obesity.

Keywords: Fabaceae functional food, sustainable food, fermentation, antioxidant activity, osteoporosis prevention, obesity prevention, B vitamins, natto, vegetable protein.