4.4. Chemical composition

A summary of the chemical composition of water hyacinths (fresh, dried and composted) from different geographic regions of the world is presented in Table 4.2. Like most other aquatic macrophytes, water hyacinths have very high moisture content; the dry matter generally varies between 5-9 percent. Table 4.2 indicates that there is little variation in proximate composition in relation to geographic location. Variation, however, does exist between the proximate composition of whole plants and leaves.

The crude protein content of the whole plant is about 12-20 percent DM, although a level as low as 9 percent was reported in studies. Gohl (1981) reported that the crude protein of fresh green part of water hyacinths from India and the Philippines was 12.8-13.1 percent DM. The crude protein content of leaf meal appears to be higher than the whole plant and varies between 20-23 percent.
Like most other aquatic macrophytes, the crude lipid content of water hyacinths is usually low and varies between 2-4 percent on dry matter basis regardless of whole plant or leaves. The ash content of whole plants varies between 15-34 percent while it is between 10-18 percent for leaves. Crude fibre content is usually high in water hyacinths and ranges between 17-32 percent, irrespective of whole plant or leaves. Some information on the amino acid content of various aquatic macrophytes is contained in Annex 1.

Gunnarsson and Petersen (2007), in a review that covered water hyacinths collected from various sources, also reported levels of some other components: hemicellulose 22-43.4 percent; cellulose 17.8-31 percent; lignin 7-26.36 percent; and magnesium 0.17 percent. Matai and Bagchi (1980) provided some additional component levels for fresh water hyacinths, namely that the ash contained 28.7 percent K2O, 1.8 percent Na2O and 21 percent Cl.