INTRODUCTION:

Milk is a whitish liquid, it is rich in its nutritive value, and it contains carbohydrates, vitamins, minerals, and fats. It is obtained from the mammary glands of female mature animals. Milk obtained from female animals is used for human consumption. The nutritional quality of milk is used for preparing desired food items for humans and young animals too. Milk contains many proteins which may improve the growth of adults and infants.

Adulteration of milk is an act, adulteration in milk is done intentionally for improving the quantity, offering for sale either by admixture, substituting of other substances [or] by withdrawing some ingredients in the milk mostly adulteration in milk is done intentionally to earn more capital by adding of some of the adulterants like water, starch, detergents, gelatin, urea, cane sugar, colostrum, etc. Adulteration can also occur unintentionally by naturally like dust particles and rodent dropping, pesticides, antibiotics, etc. However, the history of milk adulteration is old. Milk adulteration came into global concern after the breakthrough of melamine contamination in Chinese infants’ milk products in 2008 (1). Swill milk scandal is a major adulterant it has been reported in 1850s which killed 8000 infants in New York alone (2). Milk is an ideal food for humans and animals because of its high nutritive value, but unfortunately, milk is being adulterated very easily throughout the world. The reason behind for adulteration of milk may include the “demand and supply gap”, the perishable nature of milk, low purchasing capability of customers, and lack of suitable detection tests. The motivation for food fraud is economic, but the impact is a real public health concern (3,4). The situation is significantly worst in undeveloped and developing countries due to the absence of adequate monitoring and lack of proper law enforcement.

Types of milk:

a) Whole milk

b) Toned milk

c) Double toned milk

d) Standardized milk

e) Flavored milk

f) Boiled milk

g) Condensed milk

h) Skimmed milk

Whole milk:

Whole milk means milk having all the constituents which are obtained from milk giving animals. It has high nutritional value and it is good for human health. The whole milk has a fat content of about (3.2%) and S-N-F is about (9.0%) (5).

Toned milk:

Toned milk is a type of milk that is by admixture of cow milk [or] buffalo milk with the fresh skimmed milk [or] both the milk with fresh skimmed milk [or] by admixture of buffalo [or] cow milk [or] both the milk standardized to fat [or] S-N-F percentage about (3.0%)

Double toned milk:

Double toned milk is prepared by mixing whole milk with skimmed milk or skimmed milk powder. This double toned milk has a very low fat content; this milk is ideal for people who are trying to lose body weight. This having fat percentage is about (1.5%) and S-N-F percentage is about (9.0%)

Standardized milk:

Standardized milk is a type of milk which is prepared by adjusting fat [or] solid not fat content of milk to predetermined level. This standardized milk having fat percentage is about (4.5%) and solid not fat percentage is about (8.5%)

Flavored milk:

It is prepared by adding some flavors to the milk. It is a dairy drink it is made with milk sugar flavorings and sometimes food colorings. This flavored milk can also sold as pasteurized, refrigerated product, UHT [Ultra High Temperature] treated product means the product does not require refrigeration.

Boiled milk:

Approximately 99% of milk sold in UK is heat treated by heat treating. It may kill harmful bacteria and also increases the shelf life of milk.

Condensed milk:

It is cow milk where water has been removed about 60%. Sugar added in condensed milk is called sweetened condensed milk. It is used in preparing numerous desert dishes in many countries

Skimmed milk:

It is a type of milk where the fat content of milk has been completely removed mechanically. It having fat percentage is about not more than (0.5%) and S-N-F is about (8.7%)

Table 1. Composition of fat and solid not fat percentage of different milks

S. No	Type of milk	Minimum fat %	Minimum S-N-F %
1.	Whole milk	3.2	9.0
2.	Toned milk	3.0	8.0
3.	Double toned milk	1.5	9.0
4.	Standardized milk	4.5	8.5
5.	Skimmed milk	NMT 0.5%	8.7

Adulteration:

Adulteration is an act of making something impure or altering its original form by adding materials that aren’t usually part of it (6).

Types of Adulteration:

· Intentional Adulteration: Adulterants are added as a deliberate act with intention to increase profit. Ex sand, chalk powder, talc.

· Incidental Adulteration: Adulterants are found in food due to negligence or ignorance or lack of proper facilities. Ex pesticide residues, or larvae in food.

Adulteration in Milk:

Milk adulteration causes a reduction in its quality and an increase in its quantity. Adulterants are added to rise the milk shelf life when milk is diluted with water, on consumption not only reduces its nutritious value but also poses a health risks. Either for financial procurement is lack of proper hygienic conditions adulteration in food is done and it is quite common in developing countries

Types of Adulterants in Milk:

· Starch

· Colostrum

· Cane sugar

· Gelatin

· Urea

· Detergents

1. Detection of Starch:

Take milk 2ml of milk sample in test tube boil in water bath for few min, after 2-3 min remove it and add few drops of iodine solution presence of blue color indicate starch in sample.

2. Detection of Colostrum:

Colostrum has a special property of coagulating; when fresh milk sample coagulates on heating it indicates presence of colostrum in sample.

3. Detection gelatin:

To 10ml of milk sample, add acidic mercuric nitrate solution and 20ml water and mix them and filter. If filter is opaque, indicates presence of gelatin.

4. Cane sugar:

To 10ml of milk add resorcinol powder and mix it. Place it on boiling water bath and observe the color; appearance of red color indicates cane sugar in sample.

5. Detection of urea:

To 2ml of milk sample add dimethyl amino benzaldehyde solution, place it in hot water bath for few min appearance of yellow color indicates urea in milk.

Methods to Detect Adulterants in Milk:

Milk adulteration has rendered the food safety and regulatory authorities restless and bothering. A large number of methods and procedures have been developed which can be used for the detection of various milk adulterants

1. Physiochemical method:

Milk adulteration can be detected by physiochemical methods are depends upon the observable physiochemical changes. The reaction between the adulterant present in the milk and a particular chemical reagent is considered as a chemical changes. The physicochemical changes include pH of milk, density of milk, color of the milk, oxidation, reduction, and thermal properties of milk can be changed because of alteration due to milk adulteration. The above changes can be measured by using these physicochemical methods. It is used for both qualitatively and quantitatively analysis, the performance is easy, use, less concentration to detect the milk adulterants. The disadvantage is taking more time and requires testing equipment (7).

2. High Performance Liquid Chromatography [HPLC] and Other Chromatographic Techniques:

Reverse phase-high performance liquid chromatography [RP-HPLC] can be used to detect the adulterants present in the milk such as the presence of soy and extraneous whey proteins. Other type of chromatographic technique, such as Ultra- High Performance Liquid Chromatography (UHPLC) is used for skimmed milk powder to separate several foreign proteins present. The adulterant milk contains melamine can be detected by HPLC coupled with tandem mass spectrometry (HPLC-MS/MS). the other detection system, including UV-visible and fluorescence, can also be used for a combination of HPLC for the detection of adulterants present in the milk Another technique for identifying the adulterants present in the milk is Gas chromatography (GC) coupled with the time-of-flight mass spectrometry (GC-TOF-MS). The Advantage is highly sensitively, mainly used for quantitative detection, and the drawbacks of this chromatographic technique are cost effective and time consuming process (8).

3. Spectroscopic Techniques:

To detect milk and other food adulterants by using spectroscopic techniques. The spectroscopic techniques such as Raman spectroscopy (RS) and UV-Visible spectroscopy etc. the advantages are rapid analysis, minimum sample required for processing, and safer for detection of milk adulterants. To detect the melamine present in the adulterated milk by using near infrared (NIR) spectroscopy, single bounce attenuated total reflectance - Fourier transform infrared spectroscopy (SB-ATR-FTIR), and surface enhancement of Raman spectroscopy (SERS), sometimes UV Visible spectroscopy are also reported. The milk is adulterated by urea, water, whey protein, etc., detected by FTIR instrument.

4. Immunological Procedures:

The adulterants present in the milk and other foods are detected by several immunological procedures. The most commonly used immunological procedure is enzyme linked immune sorbent assay (ELISA) it is used for the detection of foreign proteins in milk and other foods, the technique also identifies the different types of analytes. It is used for both qualitative and quantitative detection of adulterants present in milk. ELISA can be used for the detection of proteins of vegetable origin in milk. ELISA can be classified into three types i.e., direct, indirect, and sandwich ELISA. In sandwich ELISA by using polyclonal antibodies to detect the whey present in the adulterant milk. By using immune-chromatographic technique and fluorescence polarization immune assay (FPIA) to detect the whey and melamine in milk. Both the methods exhibited specific detection with very less or no cross reactivity. Immunological assays are used to detect the various milk and food adulterants in various capacities (9,10).

5. Polymerase Chain Reaction:

Polymerase chain reaction (PCR) can be used for the specific and sensitive detection of milk and other food adulterants. PCR method is used for both qualitative and quantitative analysis of adulterants in milk. The different types of PCR such as multiplex PCR, Real-Time PCR, restriction fragment length polymorphism (RFLP), etc. these methods can be used to detect microbial and exogenous milk. PCR is used to detect the exogenous protein present in the milk. Nowadays the PCR is not used for some pitfalls.

CONCLUSION:

For increasing population all over the world, milk adulteration is done for financial gain. It is because of inadequate monitoring and law enforcement, it is becoming commonly done for many years the adulterants which are added to milk show serious health issues. It is very important to detect the adulterants to maintain good human health. Testing of these milk adulterants is simple but requires costly equipment and complicated operational procedures. HPLC (High Performance Liquid Chromatography), GC (Gas Chromatography), FTIR (Fourier Transformation Infra-Red Spectroscopy), ELISA (Enzyme Linked Immuno Sorbent Assay), PCR (Polymerase Chain Reaction), are some of the procedures used to detect milk adulterants.

ACKNOWLEDGEMENT:

The authors acknowledge to Vijaya Institute of Pharmaceutical Sciences for Women, Vijayawada for their valuable support to complete the review work in a successful manner.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 09.05.2022 Modified on 02.06.2022

Asian J. Res. Pharm. Sci. 2022; 12(4):272-276.

DOI: 10.52711/2231-5659.2022.00046