The Principles and Applications of Phosphates


The Principles and Applications of Phosphates

Phosphates play two main roles in food processing:

  1. As quality improvers to enhance the texture and mouthfeel of food.
  2. As mineral nutrient fortifiers.

The functionalities of phosphates in food processing are primarily based on their characteristics:

  1. Buffering Capacity:

    • The pH value of phosphates ranges from moderately acidic (pH4) to strongly alkaline (pH12).
    • By combining different phosphates in various proportions, buffering agents can be obtained that stabilize the pH within different ranges, from pH 4.5 to 11.7.
    • Within the pH range of most foods (pH 3.5-7.5), phosphates can serve as efficient pH adjusters and stabilizers, enhancing food flavor. The strongest buffering capacity is exhibited by orthophosphates. For polyphosphates, as the chain length increases, the buffering capacity decreases.
  2. Water Holding Capacity:

    • Polyphosphates are hydrophilic and act as effective moisture retainers, stabilizing the water content in food.
    • The water-holding capability depends on the type of polyphosphate, the amount added, food pH, ion strength, etc.
    • For meat and seafood products, pyrophosphates exhibit the best water retention, followed by tripolyphosphates. As chain length increases, the water-holding capacity of polyphosphates diminishes.
  3. Polyanion Effect:

    • Polyphosphates act as polymeric electrolytes and have the characteristics of inorganic surfactants, dispersing insoluble substances in water or forming stable suspensions to prevent sedimentation and coagulation.
    • They enable the formation of a gelatinous protein sol on fat globules, dispersing fat more effectively in water. Hence, they are widely used in starch phosphorylation, pigment dispersion, emulsification in dairy products, ice cream, salad dressings, and as stabilizers in sausages, minced meat products, and fish mince.
    • For straight-chain polyphosphates, their emulsification and dispersion capabilities increase with chain length.
  4. Chelating Ability:

    • Polyphosphates readily form soluble complexes with metal cations in solution, reducing water hardness.
    • They inhibit oxidation, catalysis, discoloration, and degradation of Vitamin C caused by metal cations like Cu2+ and Fe3+.
    • This helps in preventing and delaying fat oxidation, inhibiting spoilage in meats, poultry, and fish, and maintaining color, thereby extending the shelf life of food products.

The chelating effect of polyphosphates depends on the length of the chain and pH value. Generally speaking, long-chain polyphosphates have a strong chelating ability for light metal ions, which increases with the pH value. Short-chain polyphosphates have a strong chelating ability for heavy metal ions, but this ability weakens as the pH value increases.

  1. Protein Function: Phosphates enhance the effects of proteins and myosin, thereby improving the hydration and water-holding capacity of meat products, enhancing water penetration, softening food, improving food quality, and maintaining food flavor. Meanwhile, phosphates in dairy products can prevent milk from clotting during heating and prevent the separation of casein and fat.

  2. Leavening Effect: Acidic phosphates (such as sodium acid pyrophosphate, calcium dihydrogen phosphate) are commonly used as leavening acids in baked goods. They react with bicarbonates to provide the necessary carbon dioxide gas during baking.

  3. Anti-caking Effect: Tricalcium phosphate is usually used as an anti-caking agent to improve the free-flowing properties of powdered or hygroscopic foods. Due to its large surface area, it can bind more moisture. Its unique spherical crystal structure can produce a "rolling effect", thereby giving the powder good free-flowing properties.

  4. Extending Food Shelf Life: Polyphosphates can enhance the storage stability of food and extend the shelf life of products. This effect is mainly based on: (1) pH regulation; (2) Antibacterial effect: Microbial cell growth depends on divalent metal cations, especially Ca2+ and Mg2+. Phosphates can chelate with these metal cations and reduce the stability of the cell wall during cell division. It can also reduce the thermal stability of many cells, effectively inhibiting bacterial growth.

The antibacterial effect of polyphosphates is related to its type (chain length), content, pH value, salt content, nitrite content, etc. Generally, as the chain length increases, the antibacterial effect strengthens.

  1. Mineral Nutrition Enhancement: Calcium phosphate, magnesium phosphate, iron phosphate, and zinc phosphate are commonly used as mineral nutrient enhancers in food processing. Adding iron and zinc phosphates to gastric juice can enhance its bioavailability due to their good solubility, and they will not promote natural oxidation.

02 Application of Phosphates in Food

  1. Application in Meat and Poultry Processing:

1.1 To improve the quality of meat products, phosphates are usually added during meat processing for the following purposes:

a. Improve the binding of meat products and enhance slicing performance;

b. Increase the water-holding capacity of meat, allowing it to retain its natural moisture during processing and cooking, reducing nutrient loss, preserving the tenderness of meat, and increasing yield;

c. Control the pH value of meat products within the range most suitable for protein swelling and produce optimal color;

d. Improve emulsifying properties and emulsion stability, effectively preventing fat and water separation;

e. Seal metal cations, delay oxidation reactions during meat processing, effectively reduce product spoilage, discoloration, and extend the shelf life of meat products;

f. Improve processing performance and increase production efficiency.

1.2 Meat water-holding capacity generally refers to the ability of meat and added water to retain moisture during processing. The water-holding capacity directly affects the texture and yield of meat products. Adding phosphates can effectively increase the water-holding capacity of meat products.

How to use phosphates and other additives reasonably without affecting the flavor of meat products and maximize the water-holding and binding properties of meat products while reducing cooking loss has always been an important topic in meat product research and development.

1.3 Reasonable use of phosphates in meat processing:

In practical applications, suitable types and amounts of phosphates should be selected based on the type of meat product, texture requirements, production processes, raw materials, etc.

Meat products with added pyrophosphates can restore and enhance the natural water-holding capacity of muscle proteins. Polyphosphates can quickly convert into pyrophosphates under the action of muscle enzymes, achieving the same effect.

Although pyrophosphates have the best water-holding effect, their solubility is poor, so they cannot be used alone in most cases. They are often used in combination with long-chain polyphosphates or potassium phosphates with better solubility. Furthermore, to achieve the synergistic effect between various phosphates and between phosphates and other additives, various complex meat product improvers are often used.

a. For sausages and minced meat products, pyrophosphates and medium-chain polyphosphates are usually used, added in dry powder form during chopping. The pH value of the composite phosphate used is generally around 7, and sometimes composite phosphates with a pH value higher than 9 are also used.

b. The composite phosphates used for injecting brine must meet the following requirements: 1) Good solubility in brine; 2) High dissolution rate; 3) Good stability in brine.

The pH value of the composite phosphate used is generally between 8.5-9.5. To achieve the best muscle protein activation effect when making brine, it is best to dissolve the phosphate in ice water first, then add salt. This sequence should generally not be reversed.

c. The amount of mixed phosphates added is generally 0.1-0.4%, but the dosage should be strictly controlled. If the amount added is too high, it will damage the original flavor of the meat and affect the color due to the increase in pH value.

  1. Application in Seafood Processing:

2.1 Phosphates are widely used in the processing of seafood, especially frozen seafood, as excellent water-holding agents, pH regulators, and antifreeze agents. Their functions are:

a. Effectively increase the water-holding capacity of seafood, make the meat juicier, and effectively retain nutrients and moisture;

b. Inhibit fat oxidation, effectively extend the shelf life of seafood;

c. Reduce drip loss after thawing and minimize weight loss during cooking;

d. Maintain the natural color and flavor of seafood;

e. Synergize with sugars to effectively prevent cold denaturation of fish myosin proteins.

2.2 When processing frozen shrimp, fish, and shellfish, the products are usually soaked in a 3~10% composite phosphate solution (temperature below 10℃). The concentration and soaking time of the soaking solution are determined based on the type, size, and catch time of the seafood.

When selecting composite phosphates for soaking, the following factors should be considered:

a) Can effectively increase the water-holding capacity of seafood;

b) Good solubility in ice water;

c) Rapid dissolution in ice water;

d) Good stability in ice water.

The pH value of the composite phosphate used is generally higher than 9.

2.3 The composite phosphates commonly added to frozen fish paste mainly include sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, with an addition amount of 0.1-0.3% of the fish paste.

  1. Application in Bakery Products:

3.1 Application in baked goods: Acidic phosphates (such as sodium acid pyrophosphate, calcium dihydrogen phosphate) are usually used as leavening acids in baked goods. They react with bicarbonates to provide the necessary carbon dioxide gas during baking. Different phosphates have different dough reaction rates (ROR). Phosphates can also be used as flour improvers, dough conditioners, buffers, and yeast nutrients.

3.2 Phosphates as noodle quality improvers are widely used in the processing of instant noodles and regular noodles, with the main functions of:

a. Increasing starch gelatinization degree, increasing starch water absorption capacity, increasing dough water-holding capacity, making instant noodles rehydrate quickly and easy to soak;

b. Enhancing the water absorption and swelling properties of gluten proteins, improving their elasticity, making noodles smooth and chewy, and resistant to cooking and soaking;

c. The excellent buffering effect of phosphates can stabilize the pH value of the dough, prevent discoloration and deterioration, and improve the flavor and texture;

d. Phosphates in the dough can complex with metal cations, bridge glucose groups, cross-link starch molecules, making noodles resistant to high-temperature steaming and frying, and can maintain the viscoelastic characteristics of starch colloids after rehydration;

e. Improve the appearance of noodles;

  1. Application in Dairy Products:

Phosphates, as stabilizers and emulsifiers, are used in UHT sterilized milk, cream products, condensed milk, milk powder, coffee creamers, milk drinks, and cheese products, with the functions of:

a. Buffering and pH stabilization;

b. Interaction with proteins: Disperse food ingredients, stabilize emulsion systems, enhance casein's water-binding capacity, effectively prevent protein, fat, and water separation;

c. Chelate multivalent metal ions, greatly reducing the phenomenon of protein aggregation and precipitation during heating and storage. It can also effectively delay the occurrence of lactose crystallization.

  1. Phosphates are also widely used in the following food processing areas:

◎ Beverages: Used as acidity regulators, stabilizers, and mineral nutrient enhancers;

◎ Potato products: Used as stabilizers and color protectors;

◎ Rice products: Improve product elasticity and texture;

◎ Seasonings and instant soups: Stabilizers and acidity regulators;

◎ Hygroscopic powdered foods: Anti-caking agents to improve their free-flowing properties;

◎ Starch products and modified starch;

◎ Baby food, functional food: Mineral nutrient enhancers.

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