GB/T 15550-1995 in English

《GB/T 15550-1995活化乳中乳过氧化物酶体系保存生鲜牛乳实施规范》由326（农业农村部）归口，主管部门为农业农村部。
本标准规定了生鲜牛奶挤下后，在贮存、搜集和运输到乳品加工厂期间利用乳过氧化物酶体系防止其细菌性腐坏的方法。本标准适用于利用乳过氧化物酶体系保存生鲜牛奶防止牛奶腐坏变质的技术要求。

ChinaStandards.net is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.



Contents

1 Subject content and applicable scope 1
2 Normative references 1
3 Terms 1
4 Method principle 2
5 Preparation of preservative 2
6 Operation method 4
7 Use requirements 4
8 Use control 5
Annex A Specification standard of sodium percarbonate (Supplementary) 6
Annex B Analysis of thiocyanate (SCN-) in milk (Supplementary) 8
Additional explanation: 9




Code of practice for the preservation of raw and fresh milk by activating the lactoperoxidase system

1 Subject content and applicable scope

This standard specifies the method for preventing bacterial spoilage of raw and fresh milk (including buffalo milk, the same below) by lactoperoxidase system during storage, collection and transportation to dairy processing plants after extrusion.

This standard is applicable to the technical requirements for the preservation of raw and fresh milk from putrefaction and deterioration by lactoperoxidase system.

2 Normative references

GB 268 Chemical reagent - Sodiumthiocyanate
GB 2760 Hygienic standards for uses of food additives
GB 6684 Chemical regents - 30% Hydrogenperoxide
GB 6914 Standards for the qualifications of raw and fresh milk received from farms

3 Terms

3.1 lactoperoxidase
iron-containing whey protein, code-named LP, found in milk's whey, which accounts for 1% of whey protein. The content of LP in milk is about 10~30 ug/mL, with the characteristics of relative stability to heat. Ordinary pasteurization (62℃ for 30 min or 72℃ for 15 s) cannot make it lose its vitality, but it can be destroyed at 80℃ for 2.5 s

3.2 lactoperoxidase system
antibacterial system composed of lactoperoxidase, thiocyanate and hydrogen peroxide, code-named LPS, naturally found in raw and fresh milk (including buffalo milk) and human saliva

3.3 hydrogen peroxide
strong oxidant, with the molecular formula of H2O2; the specific gravity of 100% hydrogen peroxide at 18℃ is 1.4465

3.4 sodium percarbonate
a dry, white, crystalline fine powder compound which is extremely soluble in water and can slowly release hydrogen peroxide in water, thus it is a strong oxidant. At present, it has been used as the main ingredient of milk preservative abroad, with the molecular formula 2Na2CO3·3H2O2

3.5 thiocyanate
anion with the molecular formula of SCN- or CNS- which presented in all tissues and secretions of animals. The SCN- content in milk is 2~7 (1~15) ppm. With weak toxicity and accumulation toxicity, when used as milk preservative, SCN- must be strictly used in accordance with the Code, and be not abused

4 Method principle

The concentration of lactoperoxidase in raw and fresh milk is quite high, which is enough to meet the need of LPS formation and antibiosis (0.5μg/mL). In the presence of H2O2, SCN- is promoted to be oxidized into thiocyanate (HOSCN). When the milk has a pH of 6.4~6.8, thiocyanate will be separated, and OSCN- is the main existence form. This ion is specially combined with the free hydrogen sulfide (SH) on the surface of bacterial cells, which results in the inactivation of several enzymes related to life metabolism of bacteria and hinders the metabolism and proliferation of bacteria.

This antibacterial thiocyanate oxide is unstable at neutral pH and is easily decomposed into thiocyanate spontaneously. The speed of decomposition reaction depends on temperature, the higher temperature, the faster decomposition. Pasteurization of milk can ensure that the residue of this active oxidation product is completely removed.

The oxidation degree of thiocyanate is very low when the milk just leaves the breast, but by adding hydrogen peroxide with low concentration, the oxidation can be promoted. When raw milk is stored by H2O2 with high concentration (300~800 ppm), lactoperoxidase in the milk is destroyed, oxidation of thiocyanate is prevented, and the H2O2 is used for antibiosis.

SCN- combines with H4O2 in equimolar form. If the concentration of HO2 is low, some SCN- cannot be oxidized, OSCN- yield decreases, and the fresh-keeping effect correspondingly weakens. If the concentration of H2O2 is high, higher oxyacid with a shorter existence time than OSCN- is produced, such as cyanosulfurous acid (HO2SCN) and cyanosulfuric acid (HO3SCN), which are decomposed into O2SCN- and O3SCN- respectively in milk. Although its bactericidal power is stronger than OSCN-, it is extremely unstable and its existence time is too short, so its fresh-keeping effect is still weakened.

When H2O2 is equimolar, the antibacterial effect of LPS is positively correlated with SCN- concentration within a certain limit. When this method is used to keep fresh, SCN- needs to be added to ensure that the SCN- level in milk reaches the required antibacterial effect.

5 Preparation of preservative

5.1 The preservative is composed of sodium thiocyanate and hydrogen peroxide or sodium percarbonate which shall be not lower than the analytical purity grade in GB 2168 and GB 6684 respectively. Because no national standard is available to apply, sodium percarbonate is temporarily not lower than the Specification standard of sodium percarbonate (Annex A) formulated by the 35th session of the United Nations JECFA1).

Note: 1) JECFA is the Joint FAO/WHO Expert Committee on Food Additives.

5.2 Preservatives are divided into solid and liquid depending on their forms, with the same preservation effect.

5.2.1 The solid preservatives consist of sodium thiocyanate and sodium percarbonate.

5.2.1.1 Addition of sodium thiocyanate: 15 mg per kg of raw and fresh milk.

5.2.1.2 Addition of sodium percarbonate: 30.8 mg per kg of fresh milk when the purity is 85%.

5.2.1.3 Package: The above two drugs must be separated, packaged separately with food-grade translucent plastic film, and sealed in vacuum; or lactose and other appropriate amount of filler are added into tablets, and sealed with blister plastic film to prevent moisture. The name and weight of the drug are indicated on the package.

5.2.2 The liquid preservatives consist of sodium thiocyanate solution and hydrogen peroxide solution.

5.2.2.1 Preparation of sodium thiocyanate solution: weigh 15.0 g of sodium thiocyanate into a 100mL volumetric flask, add 50 mL of distilled water, shake well, add distilled water to the mark of the volumetric flask after dissolution, then subpackage the solution into nontoxic plastic bottles or glass bottles, and seal. The name and concentration of the drug (15g/100mL) are indicated on the solution bottle.

5.2.2.2 Preparation of hydrogen peroxide solution: Pipette 19.6 mL of 30% hydrogen peroxide solution into a 100mL volumetric flask and add distilled water to the mark, then dispense the solution into non-toxic plastic bottles or brown glass bottles, and seal. The name and concentration of the drug (8.5g/100mL) are indicated on the solution bottle.

5.2.2.3 Instructions must be attached when packing the above two kinds of solutions. The commodity name, the factory name, the sealing date, the effective period, and the precautions during storage and transportation (such as moisture proof, pressure proof, etc.) must be printed on the box.

1 Subject content and applicable scope
2 Normative references
3 Terms
4 Method principle
5 Preparation of preservative
6 Operation method
7 Use requirements
8 Use control
Annex A Specification standard of sodium percarbonate (Supplementary)
Annex B Analysis of thiocyanate (SCN-) in milk (Supplementary)
Additional explanation: