The Use of 3 Natural Red Coloring in the Meat Product

In order to give meat products an ideal color, impart a unique aftertaste, and extend the shelf life, nitrates or nitrites are used as curing agents for meat products at home and abroad. However, excessive intake of nitrites is harmful to the human body, such as nitrite poisoning of human blood, and the residual nitrite in meat products can produce carcinogens [1-2]. Therefore, in recent years, research institutes and manufacturers around the world have been actively seeking a meat-coloring agent that can replace nitrates or nitrites.

Synthetic food colors not only have no nutritional value, but most of them are harmful to the human body and have low safety. Natural pigments, on the other hand, are mainly extracted from animals, plants and microorganisms, and are safer for the human body. In addition, many natural pigments are easily absorbed and have health benefits in themselves, with good preventive effects against some diseases [3]. Therefore, natural pigments have become the preferred coloring agents for meat products among researchers. Among them, the three natural pigments nitrosoporphyrin pigment, red yeast pigment, and sorghum red pigment are considered to be promising alternatives to nitrites.

1 Nitrosoporphyrin pigment

Nitrosyl-hemoglobin pigment is produced by directly combining nitroso with hemoglobin in livestock and poultry blood or heme in pig blood. Nitrosyl-hemoglobin is sensitive to light and Fe2+, easily damaged by peroxide oxidation, has good thermal stability, is highly soluble, and has no special requirements for use [4]. According to Li Qingwen et al. [5], the electrochemical activity of hemoglobin decreases after binding to the NO molecule. Therefore, hemoglobin bound to NO is more difficult to oxidize or reduce than hemoglobin or oxyhemoglobin, and the presence of NO disrupts the inherent physiological function of hemoglobin molecules to carry oxygen. Therefore, the nitroso group binds to the heme iron in hemoglobin to obtain a reddish-pink nitrosohemoglobin and nitrosohemin polypeptide with good stability.

Domestic and foreign researchers have conducted some research on the preparation process of nitrosylhemoglobin pigments. Shahidi et al. [6] used bovine hemoglobin as a raw material, with SrCl2 and CaCl2 as reaction aids, and used the acetate and pyruvate methods to prepare methemoglobin from the blood. and then nitrite hemoglobin was synthesized in the presence of a reducing agent using sodium nitrite (or directly using NO). Kong Baohua et al. [7] used the pigment in pig blood, successively adding Na OH solution, ascorbic acid and sodium nitrite, heating at high temperature for several minutes, cooling to room temperature, adjusting the pH of the solution to acidic, centrifuging and precipitating, and vacuum drying to obtain the cured meat pigment. Wang Dong et al. [8] used hemoglobin solution from pig blood as the raw material, added ascorbic acid and sodium nitrite, and obtained a powdered pigment by heating, cooling, filtering, and vacuum freeze-drying. It is used as a nitrite substitute for curing meat.

Zheng Lihong et al. [9] used fresh pig blood as a raw material, isolated a hemoglobin solution, and then used VC as a reducing agent and sodium nitrite as a color developer to directly prepare semi-dry solid nitrosylhemoglobin. Since nitrosylated hemoglobin is very unstable in the air and under light conditions, it is prone to degradation, which causes the product to fade. Therefore, Shahidi F [10] used spray drying to microencapsulate nitrosylated hemoglobin. However, the microencapsulated pigment is water-insoluble, and the light and thermal stability is still not ideal. Matsudomi N [11] prepared glycosylated nitrosated hemoglobin by the Maillard reaction of proteins and polysaccharides under controlled conditions. The solubility, light and thermal stability of this pigment were significantly improved. Yang Xihong et al. [12] used polysaccharides to treat nitrosylhemoglobin, and the light and heat stability of the resulting glycosylated nitrosylhemoglobin pigment was significantly improved.

The researchers achieved good results by using nitrosylated hemoglobin instead of nitrite as a color developer in meat products, which not only ensured that the meat products had a bright rose red color, but also reduced the residual amount of NO2- in the meat products.

Ma Meihu et al. [13] used hemoglobin from pig blood and NO- in sodium nitrite to synthesize nitrosylated hemoglobin, which was added to sausage as a meat product color developer. After testing and analysis, it was found that the product had a good coloring effect, was stable and long-lasting, had a unique flavor, and had a certain preservative effect. The NO2- residue in the sausage was only 1.75×10-6, which can achieve low nitrification of meat products.

Zheng Lihong [14] added an appropriate amount of nitrosylhemoglobin pigment as a coloring agent to pork and chicken ham sausage. The results showed that the sensory state of the product in the two kinds of ham sausage was completely close to the color development effect of sodium nitrite, and was better than the coloring effect of red yeast pigment.

Huang Qun et al. [15] used extracted hemoglobin as a raw material, reacted it with NO under acidic conditions, added ascorbic acid and nicotinamide, stirred, and then freeze-dried under vacuum to obtain nitrosyl hemoglobin, which was added to the sausage as a coloring agent instead of sodium nitrite. The dosage was combined with color enhancers, sensory evaluation, the effect of reducing nitrite and increasing iron was studied. The results showed that the sensory evaluation of the nitrite-hemoglobin-added sausage was not significantly different from that of the traditional product. The nitrite residue in the product was only 1/9 of that in the traditional product, but the Fe2+ content increased by 41%. It can also prevent and treat iron deficiency anemia [16].

Yang Xihong et al. [17] added prepared glycosylated nitrosated hemoglobin pigment to the enema product. The results showed that after the raw meat was pickled, the new pigment was added to the enema product during the chopping process, which could give the meat product an ideal and stable color and a good texture.

2 Red yeast rice coloring

Monascus pigment is derived from microorganisms and is a natural pigment produced by the fermentation of Monascus [18-19]. Monascus pigment is composed of six basic pigments: erythrosine, monascorubrin, monascin, monascanin, erythro-amaranth and monascin-amaranth. Monascus pigment is a red or dark red liquid, powder or paste with a slightly peculiar smell. It has a melting point of about 60 °C, is soluble in ethanol, ether and glacial acetic acid, but not in water or glycerin. It is considered to be pH-stable, heat-resistant (above 100 °C) and has good dyeing properties for proteins [20-21].

The main production methods for red yeast rice pigment are solid-state fermentation and liquid fermentation. Solid-state fermentation is the traditional production method, in which rice, bread crumbs, etc. are used as raw materials and directly inoculated with red yeast rice to ferment. The main products are red yeast rice and red yeast rice pigment. Among them, red yeast rice pigment is an alcohol-soluble red yeast pigment obtained by extracting the fermented raw material, or by adding a nitrogenous substance such as a soy flour enzymatic solution to react with it to produce a water-soluble red yeast rice pigment. The liquid fermentation method is an improved production method based on the solid-state fermentation method. The main component of the red yeast rice pigment produced by this method is a water-soluble complex pigment. This production method has the advantages of short cycle, high yield, few impurities and stable product quality [22].

Monascus pigment has good coloring properties, which can give meat products a unique reddish color and flavor. At the same time, Monascus pigment has a strong antibacterial effect. The results of antibacterial tests conducted by Endo Akira in Japan show that red yeast rice can produce active substances with bactericidal or bacteriostatic effects during growth and metabolism. Some of these antibacterial active substances have been proven to be pigment components [23-27]. As a natural pigment, red yeast rice pigment can be used in meat products to not only reduce the amount of nitrite used by 60%, but also increase the amino acid content of the product and give it a special flavor.

Wang Boqin et al. [28] added red yeast rice pigment to fermented sausage [29] and found that fermented sausage made with 1.6 × 10-3 red yeast rice pigment as a coloring agent had a color close to that of fermented sausage made with 1.5 × 10-4 sodium nitrite as a color developer. The color of the sausage remained unchanged during storage at 4 °C for 30 days. The red yeast pigment had no significant effect on the growth of Lactobacillus plantarum and Pediococcus pentosaceus in fermented sausages and produced acid. In addition, the red yeast pigment had a certain inhibitory effect on Clostridium botulinum [30].

Wang Ye et al. [31] studied the application effect of red yeast rice pigment as a color-developing agent in bacon instead of sodium nitrite. The results showed that when red yeast rice pigment was added to bacon in an injection form at a concentration of 0.001% by weight, the color-developing effect was similar to that of the control group. However, red yeast rice pigment has poor diffusivity in bacon and tends to accumulate at the injection site and adhere to the proteins there.

Li Kaixiong et al. [32] studied the effect of adding red yeast rice pigment on the color of donkey ham. The study found that not only can the redness value of meat products be increased by using red yeast rice pigment, but the amount of NaNO2 can also be greatly reduced, making the meat products safer and with a more satisfactory color.

3 Sorghum red pigment

Sorghum red pigment is extracted from blackish-purple sorghum hulls. Its main coloring substance is apigenin. Sorghum red pigment is a dark red liquid, paste or powder; it is easily soluble in water and ethanol, but insoluble in oil or fat; aqueous solutions are red in acidic conditions and purple in alkaline conditions; it is very stable to light and heat, but is easily affected by metal ions, especially iron ions, which cause it to turn brown; the addition of trace amounts of sodium pyrophosphate can inhibit the effect of metal ions [33].

The traditional method of preparing sorghum red pigment uses blackish-purple or reddish-brown sorghum seed exocarp as the raw material. The pigment is extracted with hot water or acidic aqueous ethanol, or extracted with warm alkaline aqueous solution and then neutralized, and then concentrated and dried to obtain the finished product [34].

The general process for preparing sorghum red pigment is as follows:

raw material selection → impurity removal → water washing → extraction → filtration → concentration → dehydration → spray drying → testing → packaging → finished product.

According to national standard GB 2760[35], sorghum red pigment can be used in cooked meat products, jelly, beverages, pastries, etc., with a maximum use of 0. 4 g/kg. Sorghum red pigment has good coloring properties for proteins, and the hue is close to the natural color of meat, giving a realistic feel. In products such as ham and sausage, an ideal coloring effect can be achieved by adding 0. 3 to 0. 5 g/kg. Compared with other pigments used in sausage products, sorghum red pigment has better light resistance. After repeated experiments, the absorbance of the pigment solution did not change significantly after being placed under indoor scattered light for one month, so it has a very good shelf life and color retention [36].

Shenyang Kela Gusi Food Factory and Shenyang Jin Meat Food Factory use sorghum red pigment water-soluble products as a coloring agent for ham and sausages at a dosage of 0.34 g/kg. Baked at a temperature of 300 °C, the ham and sausages have a soft, natural color and a sense of authenticity, and are very popular with consumers [37].

Liang Chengyun et al. [38] added red yeast rice pigment and sorghum red pigment to sausage in combination with sodium nitrite in order to reduce the amount of sodium nitrite used in sausage. The test results showed that the optimal amount of the three pigments in sausage was 0.08 g/kg for sorghum red pigment, 0.03 g/kg for red yeast rice pigment, and 0.10 g/kg for sodium nitrite.

4 Conclusion

Nitrite has been used for many years as a curing agent in meat products. It has various functions in the curing process, but due to its toxicity and the carcinogenicity of the nitrosamines it produces, partial or complete replacement of sodium nitrite is inevitable. Natural pigments are non-toxic and have certain health benefits, so they are increasingly being valued. The three natural pigments nitrosylhemoglobin, red yeast rice pigment and sorghum red pigment have been studied extensively as substitutes for nitrite salts in meat products. The results show that these three natural pigments can partially or completely replace nitrite salts as colorants in meat products. However, these natural pigments all have certain shortcomings. For example, red yeast rice pigment contains patulin, a fungal toxin that is harmful to humans and animals. Sorghum red pigment gradually darkens in color as the temperature rises and begins to blacken. Therefore, how to improve their properties and how to apply them in meat products after compounding is the focus of future research.

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