By Dave A Higgs, Ian Shand, and Bob Cairns
Pressure on global supplies of fishmeal and oil is driving researchers to find suitable alternatives for aquaculture feeds. (See "Aquafeed: A growth market for grains," World Grain, December, 2002; E-Archive #58784.) To date, most fish nutritionists have directed their research to determining the potential for using rendered animal protein and lipid sources, oilseed protein and lipid products (primarily meals with some focus on concentrates and isolates in the case of the former and crude, partially or fully refined oils in the case of the latter) and highly digestible cereal and grain protein products (notably wheat and corn gluten meals). All of these have shown moderate to excellent promise.
Most oilseed research has been conducted on soybean products with less emphasis on rapeseed/canola, cottonseed, sunflower and flax, with almost no research on hempseed protein and lipid products. None of these lipid sources contain n-3 highly unsaturated fatty acids i.e., eicosapentaenoic acid (EPA) and docahexaenoic acid (DHA), which are characteristically rich in the lipids of fish species in the natural environment, especially those of marine origin.
These latter fatty acids are essential for optimal growth and health of marine fish species. Consequently, the market for conventionally produced vegetable oils could be enhanced if these lipid sources contained these beneficial fatty acids.
The inclusion of n-3 HUFA enriched oilseed lipid sources into the diets of many farmed aquatic finfish species would also elevate the potential nutritional value of their flesh to the consumer.
With this background in mind, we sought to develop a simple and economical process for the preparation of nutritionally upgraded oilseed protein and lipid sources for use not only in aquafeeds but animal feeds as well.
Unlike the conventional practice of processing only oilseeds to yield oil and meal, or fish or fish offals to produce fishmeal and oil, or animal carcasses and/or poultry (whole without feathers or offal) to yield meat and bone meal, poultry by-product meal and hydrolyzed feather meal, we elected to co-process the animal protein sources with the oilseeds to yield a wide array of unique protein and lipid sources for the marketplace as well as other value-added products.
The process itself is simple and first consists of pre-treating the oilseed. For oilseeds that have heat labile antinutritional factors of concern such as the trypsin inhibitors in soy or myrosinase in canola, these enzymes are rapidly inactivated through subjecting the oilseed to infrared energy.
Other forms of rapid heat treatment likely can also be used. The rapid heat treatment also serves to denature the protein and concurrently improves the digestibility of the carbohydrate fraction of the oilseed. Some moisture is lost at this stage, which may improve the efficiency of the next step, which is front-end dehulling.
In the case of soy, canola, hempseed, and sunflower, the process of de-hulling was accomplished by using an impact dehuller together with aspiration of the hulls, and screening (Forsberg Inc., Thief River Falls, Minnesota, U.S.). This process proved to be highly effective and recently has been improved by CSH Innovations Ltd., in the case of canola where the percentage of extensively dehulled meats has been increased well above 50% of the initial micronized seed weight.
It was not possible to extensively dehull flaxseed using this process but a good commercial process is now available for this oilseed (i.e., the process of Natunola Health, Winchester Ontario, Canada).
Sunflower was not subjected to rapid heat treatment but instead was dried and then dehulled.
After dehulling, all of the oilseeds except soy, which is low in oil content relative to the others, were cold pressed to yield high value human-grade oils for the marketplace as well as protein and lipid-rich meals with significantly reduced fiber contents without any appreciable presence of heat labile antinutritional factors except phytic acid. These meals could be used directly in high-energy diets, such as for salmonids, or they can be nutritionally upgraded further through co-processing.
Co-processing, the second and most novel major phase of our process, consists of the following steps.
• Blending the pre-treated particulate oilseed with a ground animal protein source in various combinations, together with antioxidant and some supplemental water, depending upon the proportion of the animal protein source to the oilseed.
• Cooking the mixture to free the bound cellular water in the animal protein source, denature the protein, and wash the oilseed meats to enable the subsequent significant removal of their water soluble antinutritional factors as well as carbohydrates, such as monosaccharides, disaccharides and oligosaccharides.
• Pressing and then centrifuging the cooked mixture to yield stickwater (which contains water soluble nitrogen, minerals, carbohydrates and water soluble antinutritional factors such as glucosinolates and sinapine from canola), and nutritionally upgraded animal feed-grade oil especially if fish or fish offal are used as the source of animal protein (enriches the plant oil with EPA and DHA).
• The final step consists of drying the presscake, or the decanted solids if a decanter is employed, to produce a highly digestible protein concentrate.
Previous attempts by others to co-process animal protein sources with oilseeds have generally involved the co-extrusion of commercial sources of oilseed meals with the animal proteins, the co-drying of oilseed meals with various fish products, such as hydrolysates, or the rendering of animal protein sources with oilseed meals. None of these have satisfactorily removed the water soluble antinutritional factors in the final products since the water was always removed through evaporation. In addition, the fiber and other indigestible carbohydrates present in the oilseed meal were decreased only through their dilution by the dry matter stemming from the animal protein source.
Therefore the new co-processing procedure has distinct advantages over those used previously as it concurrently yields several value-added products instead of potentially one.
The apparent digestibility (bioavail- ability) of protein in all of the protein concentrates produced by our process was found to be high for Atlantic salmon in sea water (generally more than 93% and near 100% in some cases). This was true even when the percentage of oilseed protein in the protein provided by the initial mixture was near 90%. In the future it is hoped to utilize the condensed solubles and hulls as components in high value agricultural fertilizers so that all products stemming from phases 1 and 2 of the process have a value-added purpose.
POTENTIAL FOR NOVEL PRODUCTS
The successful application of this process likely will decrease the production costs of many aquatic and possibly some terrestrial species, channel animal protein sources that are unutilized (fish-by-catch whose global amounts may exceed 40 million tonnes), poorly utilized (spent hens that are presently being directed to composting operations), and inefficiently utilized (waste streams from fish processing) into value-added and environmentally friendly purposes. In addition, the process could: extend limited regional supplies of animal protein sources into the production of value-added protein and lipid products through their co-processing with oilseeds; enhance the profit margins of farmers involved in the production if oilseed crops; increase the revenues of processors involved in the production of agri-commodities and those involved in the manufacture of aquafeeds and animal feeds; and provide new products for agri-commodity brokers and exporters.