Understanding metabolism in live microalgae is crucial for efficient biomaterial engineering, but conventional methods fail to evaluate heterogeneous populations of motile microalgae due to the labelling requirements and limited imaging speeds. Here, we demonstrate label-free video-rate metabolite imaging of live Euglena gracilis and statistical analysis of intracellular metabolite distributions under different culture conditions. Our approach provides further insights into understanding microalgal heterogeneity, optimizing culture methods and screening mutant microalgae.

β-Glucans are a class of polysaccharides consisting of D-glucose units that are polymerized primarily via the β-1,3 glycosidic bonds, in addition to the β-1,4 and/or β-1,6 bonds. They are present in various food products such as cereals, mushrooms, and seaweeds and are known for their numerous effects on the human body, depending on their structures, which are diverse. The major physicochemical properties of β-glucans include their antioxidant property, which is responsible for the scavenging of reactive oxygen species, and their role as dietary fiber for preventing the absorption of cholesterol, for promoting egestion, and for producing short-chain fatty acids in the intestine. Dietary β-glucans also exert immunostimulatory and antitumor effects by activation of cells of the mucosal immune system via β-glucan receptors, such as dectin-1. In this review, we elaborate upon the diversity of the structures and functions of β-glucans present in food, along with discussing their proposed mechanisms of action. In addition to the traditional β-glucan-containing foods, recent progress in the commercial mass cultivation and supply of an algal species, Euglena gracilis, as a food material is briefly described. Mass production has enabled consumption of paramylon, a Euglena-specific novel β-glucan source. The biological effects of paramylon are discussed and compared with those of other β-glucans.

Euglena gracilis Z is a micro-algae that is used as a food or nutritional supplement. Paramylon, the carbohydrate storage substance of Euglena gracilis Z has β-1, 3-glucan structure. Euglena gracilis Z and paramylon are reported to affect the immune system. In this study, we investigated the protective effects of Euglena gracilis Z and paramylon against influenza virus infection in mice. Euglena gracilis Z and paramylon were administered to mice as a 2% dietary mixture ad libitum. At 2 weeks after initiation of dietary administration, mice were infected intranasally with influenza virus A/PR/8/34 (H1N1). Survival rate was monitored 10 days after infection. In addition, we performed virus titer and cytokine profiles in the lung. High survival rates were observed for Euglena gracilis Z and paramylon-treated groups compared to the control group. Significantly lower virus titer in the lung was observed in the Euglena gracilis Z and paramylon-treated groups compared to the control group from day 1 after infection. Higher amount of IL-1β, IL-6, IL-12 (p70), IFN-γ, and IL-10 was observed in the paramylon groups compared to the control group. Our data therefore reveals a novel immunoregulatory role of the Euglena gracilis Z and paramylon which provides protection against influenza virus infection.

In the present study, the effects of Euglena and paramylon on hyperglycemia were examined in Otsuka Long-Evans Tokushima fatty (OLETF; type 2 diabetes mellitus model) rats. OLETF rats were fed an AIN-93 M diet containing cellulose, Euglena, or paramylon for 10 weeks. Long-Evans Tokushima Otsuka (LETO) rats were used as nondiabetic controls. An oral glucose-tolerance test (OGTT) was performed at 0 and 10 weeks. OLETF control rats were obese because of bulimia and showed abdominal fat accumulation and hyperglycemia. Euglena supplementation improved hyperglycemia and decreased food intake, body weight gain, and abdominal fat. However, there were no changes in the paramylon-supplemented group compared to the OLETF control group. Triglyceride concentrations in the serum and liver were lower in Euglena-supplemented rats than in OLETF control rats. There was a correlation between hepatic triglyceride concentration and the area under the curve (AUC) of OGTT at 10 weeks. This suggests that the improvement in glycemic control in the Euglena-supplemented group may depend on substances other than paramylon present in Euglena.

We determined whether the anti-obesity effect provided by the consumption of Euglena gracilis (Euglena), which is rich in insoluble dietary fiber, could be enhanced by the co-consumption of vegetables with an abundance of soluble dietary fiber. Nine-week-old male C57BL/6J mice were divided into five groups as follows: group 1 received a normal diet, group 2 received a high-fat diet, and groups 3, 4, and 5 received high fat diets containing 0.3% paramylon, 1.0% Euglena, or 1.0% Euglena plus 0.3% vegetables (barley leaf, kale, and ashitaba), respectively. Mice were fed ad libitum until 18 weeks of age. Euglena intake significantly reduced visceral fat accumulation in obese mice, and co-consumption of vegetables enhanced this effect. Consumption of Euglena with vegetables reduced adipocyte area, suppressed the expression of genes related to fatty acid synthesis, upregulated genes related to adipocyte lipolysis, and suppressed serum markers of inflammation. Notably, we also observed an increase in the fraction of short-chain fatty acid-producing beneficial bacteria, a reduction in harmful bacteria that cause inflammation, and an increase in short-chain fatty acid production. Therefore, the co-consumption of vegetables enhanced the anti-obesity and anti-inflammatory effects of Euglena, likely by modulating the gut microbiota composition.