Domestic Research Progress Of Collagen Casing

In the 1980s, Wuzhou, Guangxi, built my country's first factory for the production of collagen casings, and it has made great progress in the 1990s. The invention patents of Huang Binghua and Zhou Yaxian of Wuzhou Protein Casing Factory in Guangxi introduced the following preparation method: take 100kg of the second or third layer of cowhide, wash it, cut into 5mm×60mm leather strips with a peeler, first use 5% NaOH solution Soak for 1 hour, and then soak with 0.1mol/L HCl solution for 6 hours. When it becomes a translucent strip, wash it with water to about pH 4.5.

Chop the leather strips, grind them into a slurry in a colloid mill, adjust with water to a solid content of 4% to 6%, put them in a vacuum mixer, add lactic acid (according to 100kg of glue, add 0.5kg of lactic acid and 3kg of edible cellulose , 6kg polyvinyl acetal solution), stir well and degas.

Pass the above glue into a screw extruder, spray a 20mm tubular film through a rotating nozzle, then immerse it in a saturated ammonium sulfate solution for dehydration and shape, cut it off, inflate it, and dry it once in an electric heating box at 50°C.

Wash the once-dried casing with water to remove ammonium sulfate, soak it in a mixed solution of 5% glycerin, 0.2% glyoxal and 0.1% sorbic acid for 20 minutes, then quickly spray it with clean water once, and air dry until the water content is 10%. 20% of the product. After folding or shrinking, packaging, the finished product is obtained. The tensile strength reaches 28MPa and the elongation at break is 29.4%.

The supply of cowhide in our country is tight and there are more pigskins, so you can use two layers of pigskins, soak them in lime milk for 2-3 days, and then soak them in 0.1mol/L HCl solution for 6h after washing. When they become translucent strips, wash them with water The above operation can be performed when the pH is about 4.5.

However, the above-mentioned use of polyvinyl acetal solution as internal crosslinking agent and glyoxal as external crosslinking agent seems improper. Polyvinyl acetal cannot be used in food. Glyoxal is more toxic, and glutaraldehyde, which is allowed to be used in food, should be used instead. In the subsequent invention patents, they have already used glutaraldehyde.

Since the pH value of the glue entering the extrusion molding machine is generally controlled at 2 to 4, which is acidic and will cause corrosion to the equipment, the production equipment uses stainless steel materials. For this reason, Wuzhou Protein Casing Factory invented alkaline collagen to make casings. The technique is to wash pigskins and cowhides with clean water, soak them in 5%-lo% lime water to soften them for 10-20 days, then divide, wash, pickle, and cut into small pieces, strips, and wash until neutral. Then wash 2 to 3 times with a dilute acid solution of pH 2 to 3, rinse with water to neutrality, then mince with a meat grinder, and soak in 0.2-0.3mol/L sodium hydroxide or sodium carbonate to maintain the pH of the solution 13一14. After the leather becomes translucent, wash off the alkali with water to make the pH value 11.5-13. At this time, it can be pressed into thin slices with a tablet press, add water and carboxymethyl cellulose, and stir evenly. Keep adding alkali to keep the pH value of the mortar at 11.5-13. Filter to remove coarse particles to form an extrudable mucilage. Its protein content should be 3% to 7%, cellulose 0.1% to 0.5%, and water about 93% to 97%. After extrusion, the coagulation bath is saturated with table salt, and the pH is adjusted to 3.0-5.0 with hydrochloric acid. The solidified tube is dried in a tunnel dryer at 40-50℃, and sprayed with clean water once for the next drying. After 2 to 3 times, use 0.1%-0.5% glutaraldehyde, 2.0-4.0% Spray a mixed solution of glycerin, 0.08%-0.1% preservative, then dry, wash, dry, collect and shrink, treat at 70-85℃, relative humidity 80%-95% for 30h, package, and then leave the factory.

Whether it is cowhide or pigskin, the epidermis cannot be used, otherwise there will be small fibrous pieces in the made glue, which will cause the casing film to crack during enema or cooking. The appearance of small fiber clumps is also related to the fat content in the pulp. If there is more or less fat, fiber clumps may appear. Generally, it is controlled at about 8%. The added fat needs to be partially hydrolyzed in advance to generate monoglycerides, A mixture of diglycerides and triglycerides, including hydrolyzed fatty acids.

Adding a certain amount of cellulose (such as methyl cellulose, carboxymethyl cellulose, etc.) to the collagen can improve the properties of the casing, especially the strength, and the addition of sodium alginate can also improve the properties of the casing. Glutaraldehyde cross-linking at pH 3.5, the casing made of casing has higher strength, because the cross-linking reaction is relatively slow at this time, glutaraldehyde molecules can enter the collagen membrane to react, and the degree of cross-linking inside and outside is compared balance.

Some people in China have studied the use of tanning scraps (before tanning) to make collagen casings. The tanning scraps have been soaked in alkaline medium and sodium sulfide solution to swell and shed hair. Not only most of the fat is removed, but the keratin and other soluble proteins in the hair and epidermal layer are also removed, although they can no longer pass through the skin. Method to obtain the dermis, but after all, most of it is collagen, and the cortex is also loose, which is good for beating. However, since the collagen may have been degraded during alkaline immersion and hair removal, the strength of the casing produced in this way is lower and can be improved by secondary crosslinking.