Over the years, further development of the process for FPC for human consumption has paralleled the development of other processes to ensure that all portions of a fish are totally utilized for profitable products. For many years programs have been carried out to utilize better these secondary raw materials currently being discarded or made into products that do not maximize the nutritional value. Tryptic digestive enzymes, pepsin hydroly- sis, papain, and many other enzymatic processes were tried in an effort to produce a highly functional protein concentrate.
The use of enzymes to hydrolyze fish flesh has been studied extensively for preparation of a highly functional protein powder that can be used in products for human consumption (Tarky and Pigott 1973: Pigottet al.1976).
However, this entails adding an enzyme, which significantly increases the cost of production, since there are no concentrations of natural enzymes in the flesh. The basic process consists of adding an enzyme to homogenized flesh, controlling the pH, temperature, and other processing conditions, and then allowing the digestion of proteins in the flesh to take place.
In general, acid pepsin digestion with continuous pH control has proven to be one of the best procedures for producing a high-quality, low-cost hydrolyzate that can be used as an animal or fish feed supplement (Tarky and Pigott 1973). Fish waste, containing the visceral portion, has endoge- nous enzymes that can be controlled to produce a hydrolyzed product. The primary enzyme in the viscera of a fish is pepsin, the same enzyme that pre- vails in the human stomach for digesting meats and other protein products.
Pepsin requires an acid environment to be active so that, by controlling the pH of a homogenized fish waste, natural enzyme digestion will take place.
This eliminates the requirement for adding expensive purified enzymes.
Research has shown that the resulting products from natural enzyme diges- tion can be valuable for animal feed supplements and foliage spray fertilizers (Pigott 1999a,b).
In many fish processing plants the volume of fish waste does not warrant the investment of a fish meal facility for converting the waste to animal feed. Furthermore, meal made from fish waste does not have the nutritional value of conventional meal, which is normally made from whole industrial fish. Because fish meal is nonfunctional due to its having been heated to a high temperature during cooking and drying, it cannot be solubilized in a water solution. The knowledge gained from previous studies on fish protein hydrolyzate for human foods was used to develop a process for converting fish waste into a most effective hydrolyzed fish protein (HFP) for animal feed and fish fertilizer. Used as a foliage spray, this product has
proven to be a superior fertilizer for a wide variety of crops. Research has only recently begun to concentrate on this high-quality protein for fish diets (Pigott 1999c).
11.3.3.2. Animal Feed and Fertilizer
Numerous projects are being directed toward developing highly nutri- tional feed supplements for animals and well-balanced fertilizers for a wide variety of agriculture crops. Successfully reaching these goals would elimi- nate the environmental concerns of waste discharge and improve the overall economics of commercial fish processing as well as reducing the damaging runoff from petrochemical fertilizers.
A wide variety of products can be prepared from the normally wasted portion of processed fish. These include high-quality proteins for animal and fish feed. Raw material for production of high-quality products include
(1) discarded by-catch from present fisheries,
(2) industrial fish of high nutritional value but currently being reduced to fish meal and oil,
(3) waste from primary and secondary fish processing operations, and (4) species not being commercially exploited at the present time.
Acid enzyme hydrolysis not only provides highly functional protein but also includes important macro- and micronutrients that are often lost in other processes carried out at high temperatures or in a neutral or basic en- vironment that does not remove these compounds from bones and cartilage.
There are particular advantages to reclaiming normally wasted portions from aquaculture fish (Fig. 11.1). The fish can be processed shortly after harvest and this prevents the mechanical breakdown and spoilage products found in commercially caught fish that have been held for varying periods of time. This is also true of the minced flesh removed from aquaculture fish for human food products. In fact, the requirement for rapid processing is the reason much of the surimi manufactured from pollock, hake, and other species is processed on high-seas processing vessels. However, the economics of processing aquaculture fish on-site (Fig. 11.2) or in nearby plants is a major advantage over high-seas processing. Also, the utilization of unwashed minced flesh in finished products greatly improves the yield and reduces the cost compared to those prepared from washed flesh (Nielsen and Pigott 1996). A wide variety of products can be prepared from the normally wasted portions of processed fish. The high quality of reclaimed meat from aquaculture fish used in value-added products can significantly increase the profitability of the industry.
For the past several decades there have been active research programs designed to utilize totally the raw materials from the marine and freshwater
Flow diagram for on-site processing.
FIG. 11.2 Flow diagram for processing at the central plant.
bodies of the world. This work has covered a wide spectrum of processing technology applicable to aquaculture fish as well as those harvested from wild stocks. The waste from processing operations includes edible flesh, visceral portions, and bones and cartilage. A wide spectrum of products has been developed and studied, including human and animal foods, superior- quality fertilizer, and nonfood commercial products. Of particular interest is processing aquaculture waste and then recycling the superior high-quality proteins in on-site feed manufacturing. Hence, not only is total utilization of the fish accomplished but also there is a tremendous economic advantage in such a concept.
Recent research has demonstrated that HFP can be substituted for fish meal in high-quality fish diets (Pigott 1999c). Initial results indicate that the functional proteins in HFP are more efficient and reduce the cost of feed.