Microalgae as a safe food source for animals: nutritional characteristics of the acidophilic microalga Coccomyxa onubensis

Abstract

Background: Edible microalgae are marine or fresh water mesophilic species. Although the harvesting of microalgae offers an abundance of opportunities to the food and pharmaceutical industries, the possibility to use extremophilic microalgae as a food source for animals is not well-documented.

Objective: We studied the effects of dietary supplementation of a powdered form of the acidophilic microalga Coccomyxa onubensis on growth and health parameters of laboratory rats.

Method: Four randomly organized groups of rats (n=6) were fed a standard diet (Diet 1, control) or with a diet in which 0.4% (Diet 2), 1.25% (Diet 3), or 6.25% (Diet 4) (w/w) of the standard diet weight was substituted with dried microalgae powder, respectively. The four groups of animals were provided ad libitum access to feed for 45 days.

Results: C. onubensis biomass is rich in protein (44.60% of dry weight) and dietary fiber (15.73%), and has a moderate carbohydrate content (24.8%) and a low lipid content (5.4%) in which polyunsaturated fatty acids represent 65% of the total fatty acid. Nucleic acids are present at 4.8%. No significant difference was found in growth rates or feed efficiency ratios of the four groups of rats. Histological studies of liver and kidney tissue revealed healthy organs in control and C. onubensis-fed animals, while plasma hematological and biochemical parameters were within healthy ranges for all animals. Furthermore, animals fed a microalgae-enriched diet exhibited a statistically significant decrease in both blood cholesterol and triglyceride levels. The blood triglyceride content and very low density lipoprotein-cholesterol levels decreased by about 50% in rats fed Diet 4.

Conclusions: These data suggest that C. onubensis may be useful as a food supplement for laboratory animals and may also serve as a nutraceutical in functional foods. In addition, microalgae powder-supplemented diets exerted a significant hypocholesterolemic and hypotriglyceridemic effect in animals.

Keywords: Coccomyxa onubensis; hypolipidemic induction; nutraceuticals; rats; safe food.

Fig. 1

Hematoxylin and eosin stained sections of rat liver and kidney from experimental rats. Liver: a,b. Hepatocyte architecture in parenchyma (P) and central vein (cv). c,d: Higher magnification of hepatic sections where the portal triad it can be observed: normal portal vein (v), artery (a), and bile duct (b) without occlusions. d. Black arrow heads indicate hepatocyte nuclei. Kidney: e-h. Sections of the cortex (black dot) and convoluted proximal (x) and distal (asterisks) tubules are shown in e,f. g,h: Medulla. Longitudinal section of tubule epithelium (black arrows).

Fig. 2

Enzyme activities in plasma from rats fed diets supplemented with C. onubensis biomass. Experimental conditions are described in the Materials and Methods. GOT, glutamate-oxaloacetate transaminase; GPT, glutamate-pyruvate transaminase. Each value is expressed as the mean±SD (n=6 per group). Results were statistically analyzed with Kruskal–Wallis test. None of the diets (Diet 2, Diet 3, and Diet 4) showed significant differences at the p<0.05 level with respect to each other, or relative to the control (Diet 1).

Fig. 3

Lipid profiles of rats fed with diets supplemented with C. onubensis biomass. Experimental conditions are described in the Materials and Methods section. Each value is expressed as the mean±SD (n=6 per group). Results were statistically analyzed with Kruskal–Wallis test. *p<0.05 compared with the control group. None of the diets (Diet 2, Diet 3, and Diet 4) showed significant differences at the p<0.05 level with respect to each other. HDL=High density lipoprotein. VLDL=Very low density lipoprotein.