Moringa leaf protein as a substitute for fishmeal in aquaculture diets

The importance of aquaculture products in the global supply of fish is steadily increasing and their human consumption has exceeded that of wild fish since 2014. However, many farmed animals are fed with feed containing fishmeal from wild-caught fish. Due to overfishing of the oceans, this is not a sustainable situation. The leaves of the (sub-)tropical plant Moringa oleifera have a nutrient profile that makes them suitable as a potential source of protein for use as animal feed. The “FIMBA” project, funded by the Fraunhofer Gesellschaft, aimed to obtain high-quality plant proteins from easy-to-process Moringa leaf material that are suitable for reducing the proportion of fishmeal in aquaculture diets.

Extraction of a high-quality protein fraction from Moringa leaves

As part of the project, a moringa culture was established at Fraunhofer IME site in Aachen. Several harvests were carried out and good yields were achieved with the plants cultivated in the greenhouse (Figure 1). The production of leaf mass in the greenhouse provided the basis for a comprehensive process development for protein fractionation. During the development of the fractionation process, the focus was on the simplicity of the process, the optimization of the material yield and the quality of the fraction obtained in order to be able to provide high-quality substances at low cost. As a result of the process development at the IME site in Aachen under the direction of Prof. Dr. Dr. Johannes Buyel (now BOKU Vienna), a simple process for protein fractionation was defined, which was used in the project to obtain a larger quantity of Moringa protein extract (MPE) to be used in a fish feeding study.

Characterization of Moringa protein extract

The MPE samples obtained during process optimization were tested in Schmallenberg for the total protein content (Bradford and Kjeldahl method), the content of phenolic substances, flavonoids (e.g. quercetin and kaempferol) and antinutritive substances (e.g. saponins) as well as the antioxidant potential (FRAP assay, DPPH assay) of the individual matrices. The crude protein content of the MPE obtained with the optimized process was approx. 48 % in the dry matter and thus around 18 % higher than in the reference leaf material. A significant enrichment of leaf protein was therefore achieved with the extraction method developed. However, the MPE obtained in the project also contained a not inconsiderable proportion of flavonoids, which means that in addition to a high total protein content, the extract can also be attributed as an antioxidant effect. The content of antinutritive substances in the leaf extract could be reduced by the developed extraction process compared to the reference leaf material. However, a complete reduction of these substances (e.g. saponins) is not possible.

Fish feeding study

The MPE produced in the project was used to produce a fish feed with different supplementation rates (replacement of fishmeal). The fishmeal used in the study, which is usually used in aquaculture diets, had a higher protein content of around 60% witch is higher compared to the MPE. The experimental diets were fed to the Nile tilapia (Oreochromis niloticus L.) in a feeding study. During the test phase, the growth of the juvenile fish in the treatment groups and the feed conversion rate for the individual test diets were determined. The results show that up to 10 % of the protein content in tilapia aquaculture diets can be replaced by MPE without impairing the growth of the fish compared to the control diet. Higher proportions of MPE in the feed (>20%) led to a reduction in the growth of the test fish in the study. Prof. Dr. Christian Schlechtriem, who led the studies in Schmallenberg, explains that the effects observed in the higher supplementation levels were probably caused by the content of antinutritional substances in the MPE, even though this could be significantly reduced by the extraction process compared to the original leaf material. Further optimization of the extraction process would therefore be necessary to enable higher levels of MPE in aquaculture diets.

The project was carried out in cooperation with Prof. Dr. Klaus Becker (University of Hohenheim) and Dr. Heinrich Heinrichs (Africrops).