What are the comprehensive utilization methods for fish processing by-products?

The fish heads, tails, minced meat, scales, skin, viscera, bones, and gall bladders left over from fish processing contain large amounts of protein, amino acids, trace elements, and vitamins. Using these protein resources, various deeply processed products can be made, including soluble edible fish protein powder, liquid fish protein feed, fish scale glue, fish skin glue, bone paste, fish protein calcium candy, bile pigment calcium salt, and bile salts. Comprehensive utilization of fish processing by-products can lower the cost of main products and increase the added value of aquatic products; it can also protect the environment, reduce wastewater and waste emissions, and achieve higher economic, ecological, and social benefits. The above several products are described separately below.

I. Soluble edible fish protein powder. Soluble edible fish protein powder is rich in nutrients, has good water solubility, and is easy to digest and absorb. It can be used as a base material for amino acid-fortified foods and as a substitute for milk powder; it can also be used to develop products such as nutritional soups, seasonings, and fish protein beverages. It is an effective medicine for treating diarrhea in children caused by indigestion, and can also serve as a protein source in liquid foods for cancer patients or postoperative patients who have difficulty eating. There are many methods for preparing this product, such as enzymatic hydrolysis, acid hydrolysis, alkali hydrolysis, and alcohol extraction degreasing. Enzymatic preparation is especially preferred, as it not only preserves the inherent nutritional components of fish but also has good taste and is easy to dissolve. It is a new technology developed abroad in recent years.

1. Process flow: raw material treatment -> enzymatic hydrolysis -> centrifugal filtration -> fish protein hydrolysate -> decolorization -> vacuum drying -> grinding -> finished product.

2. Process. Use fish minced meat, fish heads, and fish tails from processing by-products as raw materials, wash them, add water, and mash them. Take the mashed fish paste into a reaction pot, add water to adjust the pH to 6.5-7.5, and make the solid-to-liquid ratio 5:8, add 1%-2% protease, react at 45°C-60°C for 2 hours to 4 hours, heat and boil for 10 minutes to inactivate the enzyme, then centrifuge and filter. The filter residue is discarded (used as fertilizer or feed) to obtain fish protein hydrolysate. Use 10 grams of activated carbon per liter to decolorize at 65°C for 30 minutes, vacuum dry at 50°C-55°C, grind with a ball mill, and pass through a 200-mesh copper sieve to obtain soluble edible fish protein powder.

II. Liquid fish protein feed. Liquid fish protein feed is not only rich in nutrients, but its protein exists in the form of polypeptides and amino acids, making it more conducive to animal digestion and absorption. Methods for preparing this feed include the molasses fermentation method (using by-products from sugarcane sugar production), the acidification method, and the alkalization method. The production method of the acidification method is as follows.

1. Process flow: raw material treatment -> acidification -> liquefaction -> finished product -> storage.

2. Process. Liquid fish protein feed uses spoiled fish that have lost edible value, low-quality small miscellaneous fish, fish heads, viscera, etc. as raw materials. They are mashed with a hammer mill, and the mashed raw materials are placed in an acid-resistant container. Formic acid with a volume concentration of 85% is added in an amount of 3.5% of the raw material weight. The pH value of the acidified raw material must be lower than 4. The acidified raw material is placed in an acid-resistant liquefaction tank for liquefaction. The liquefaction time varies depending on temperature and raw materials, and generally one to two days at room temperature of 30°C-35°C is sufficient. The liquefied fish protein feed is stored in an acid-resistant covered container, with a storage period of 1 year to 2 years at room temperature.

III. Fish scale glue and fish skin glue. Use the discarded skin, scales, etc. from fish processing to extract animal glue, replacing pig skin, cowhide, mule skin, and turtle and soft-shelled turtle shells for glue making. Fish skin accounts for about 5% of the fish body, and fish scales account for about 2.5%-4%. Therefore, not utilizing fish scales and fish skin is a great waste. Practice has proved that making glue from fish scales and fish skin is one of the best raw materials among animals. Fish scale and fish skin glue can provide the same effects as turtle shell glue and donkey-hide gelatin in nourishing yin and stopping bleeding, and has unique effects in moistening the lungs and tonifying the lungs.