Contaminants in Milk and Impact of Heating: An Assessment... : Indian Journal of Public Health (original) (raw)
Introduction
Milk, a rich source of readily available and assimilable nutrients including protein, fat, minerals, etc., is most susceptible to spoilage. If not handled properly, loses its quality during milching and processing. The major contaminants usually encountered in milk and milk products include pesticide residues, heavy metals, and aflatoxin M1. These become part of milk from a variety of sources. Primarily, milk get contaminated before milching, from the feed and fodder fed to the cattle, from sources/materials used during the processing of milk as well as improper handling of the milk during the pre- and postprocessing period.
Among the various contaminants, aflatoxins are a group of highly toxic secondary metabolic products of moulds such as Aspergillus flavus and Aspergillus parasiticus. These two moulds infect the cereals and oil seeds, the major constituents of cattle feed, during their pre- and postharvest management. Moulds occur in these agri products, during the growth of plants, maturity, harvesting, and processing of grains. Their presence is influenced by various factors like temperature, relative humidity, oxygen availability, and damaged or broken grain kernels.12
Aflatoxins are the most common mycotoxins occurring in feedstuffs around the world. Aflatoxin B1 (AFB1) produced by the two moulds in the contaminated cattle feed get transformed to 4-hydroxylated metabolite known as "milk toxin", i.e., aflatoxin M1 (AFM1) in mammals.3 Aflatoxins have been reported to withstand pasteurization and sterilization conditions and are thus heat resistant.4567 AFB1 is one of the most potent hepato-carcinogens known and even the chronic exposure to extremely low levels of aflatoxins in the diet is important for human health.8
Pesticides are widely used in agriculture to protect the crop from insects/pests, but, through water, forages and environment they become a part of the milk causing contamination of milk and milk products and thus confer a health risk.9
Milk and milk products, the most diversified food stuff in terms of its composition may also contain variable amounts of different heavy metals. The amount of heavy metals in uncontaminated milk is admittedly minute, but, their contents may be significantly altered through processing and packaging practices followed during processing of milk. The cattle feed and environment might be the source of heavy metals like lead, cadmium, chromium, nickel, cobalt, etc. in milk and capable of causing serious health problems among the people consuming milk with such contaminants.101112
The contaminations and their consequent impact on food quality and safety has been used as a base for the present study, which was intended to find the level of contaminants in different types of milk and to investigate the impact of household practices of heating milk on the level of these contaminants.
Materials and Methods
The study was conducted during of the period September 2010 to November 2010 at Punjab Biotechnology Incubator, Mohali (Punjab). Branded pasteurized milk with different fat compositions namely, standardized (SM) (4.5%), double toned (DTM) (1.5%), full cream (FCM) (6.0%), was procured from the local market and unpasteurized vendor's milk (VM) (variable fat composition, i.e., 4.1-6.7%) was procured from the local vendor. One sample of unpasteurized milk, six of pasteurized standardized milk, four of pasteurized double toned, and two of pasteurized full cream milk samples were analyzed for AFM1, pesticide residues, and heavy metals.
The milk samples were boiled as per simulated household conditions, i.e. at medium heat and under uncovered conditions to assess the impact of boiling on contaminants namely, AFM1, pesticide residues, and heavy metals in milk. Packets of pasteurized milk were opened and homogenized in the stainless steel container and divided into two parts: one part of milk was analyzed as such without any treatment (control) and other part was subjected to boiling.
The reference material used for aflatoxin M1 and pesticide residues were procured from M/s Supelco Sigma, USA. The standards for heavy metals were procured from M/s Merck, Germany. Aflatoxin M1 was analyzed by using the Elisa Test Kit method of r-Biopharma: Ridascreen.13 The residues of organochlorine (OCs) such as aldrin, dieldrin, chlordane (_cis_- and _trans_-chlordane), o,_p_-DDT, p,_p_-DDT, o,_p_-DDD, p,_p_-DDD, p, _p_-DDE, heptachlor, heptachlor epoxide, α-hexachlorocyclohexane, β-hexachlorocyclohexane, ?-hexachlorocyclohexane, ?-hexachlorocyclohexane, ethion, fenthion, fenthion sulphoxides, fenthion sulphones and organophosphorus (OPs) such as phorate, phorate sulphoxides, ?-endosulphan, ?-endosulphan, endosulphan sulphate, methoxychlor, permethrin, and dltamethrin were analyzed using GC-MS following the MPRA S-9 method.γ-hexachlorocyclohexane, δ-hexachlorocyclohexane, ethion, fenthion, fenthion sulphoxides, fenthion sulphones and organophosphorus (OPs) such as phorate, phorate sulphoxides, α-endosulphan, β-endosulphan, endosulphan sulphate, methoxychlor, permethrin, and dltamethrin were analyzed using GC-MS following the MPRA S-9 method.14 Heavy metals (lead, arsenic, tin, cadmium, mercury, chromium, aluminium) were analyzed using AAS-Perkin Model: AAnalyst 800 using the AOAC Method.15
Results
In this study, contaminant AFM1 was detected at a concentration ranging from 0.056 to 0.082 ppb in unpasteurized and pasteurized milk samples analyzed, reflecting that levels of AFM1 present in the milk is not impacted by the pasteurization process [Figure 1]. Similarly, boiling of milk in the household conditions did not change the AFM1 levels in the milk [Figure 2]. The level of AFM1 detected in this study was higher than the limit fixed by the Codex Alimentarius (0.05 ppb), but, lower than the specification limit of Indian Regulation, i.e., Food Safety Standards Regulation Act, 2011 (0.5 ppb). Table 1 gives the comparative maximum acceptable limit of AFM1 in milk in different countries of the world. Australia and Czech Republic specify more stringent maximum acceptable limits of aflatoxin M1 (20 ng/l and 100 ng/l, respectively) in milk used for feeding children.16
Aflatoxin M1 levels in different types of Milk. VM = vendor's milk, SM = standardized milk, DTM = double toned milk, FCM = full cream milk
The effect of boiling on the aflatoxin M1 level in different types of milk
Comparative maximum acceptable level of AFM1 in milk
In the present study, pesticide residues were not present in any of the raw and boiled milk samples up to 0.05 ppm. Similarly, heavy metals including cadmium and mercury up to 0.005 ppm, lead, arsenic, chromium and aluminium up to 0.05 ppm, and tin up to 0.25 ppm were not present in samples of unpasteurized and pasteurized milk analyzed during the course of this study.
Discussion
The presence of contaminants like heavy metals, pesticide residues, and aflatoxins above the permissible limits is a grave public health concern.
The presence of "mycotoxins" in milk is linked to inferior food hygiene. This study shows the presence of aflatoxin M1 (AFM1), a known "milk toxin" and a metabolite of aflatoxin B1 in all milk samples including the unpasteurized (raw) milk as well as heat-treated pasteurized milk. Earlier studies have reported that aflatoxins withstand the pasteurization and sterilization conditions and thus are heat-resistant.4567 Also, earlier finding reports that the milching animals fed on contaminated feed, yield milk with the presence of aflatoxin in milk within 12-24 h.171819 The presence of aflatoxin in milk samples tested under this study indicates that the milk was taken from the cattle fed on AFB1 contaminated rations. Many workers showed the factors which influences the concentration of aflatoxin M1 such as seasonal variations. The concentration of AFM1 in winters is more as compared to summers, the reason cited is that during the summers animals are fed on grass, but, in winters only compound feeds are fed to the milching animals which have relatively high content of AFB1 which in turn enhances the AFM1 level in milk.20
The health hazards of aflatoxins have been reported by International Agency for Research on Cancer (IARC 2002) with AFB1 and AFM1 classified and reaffirmed as human carcinogens under Group 1.21
Aflatoxins (AFB1 and AFM1) are one of the important etiological factors for primary liver cancer especially in people who are carriers of hepatitis B surface antigen. Increased aflatoxin metabolism by the virus has been identified as the cause for such correlation.2122
Measures should be taken to reduce the contamination of aflatoxin in raw milk and feed samples. Dietary supplementation of sodium bentonite: a mycotoxin binder has been reported to reduce the aflatoxin M1 levels in lactating crossbred cows.23
Pesticides and heavy metals were not present in the raw milk as well as heat-treated pasteurized and unpasteurized milk during course of the study. The results are different as compared to the findings of earlier studies which reported the presence of HCH residues. DDT and lindane levels exceeded the maximum residue limit (MRL) in liquid milk samples in Ludhiana district of Punjab. This discrepancy might be due the widespread ban on the use of pesticides in agriculture and public health programs (e.g. Malaria control program).24 Similarly, data from major metropolitan cities in India declining trends in the level of pesticides (DDT, HCH, etc.) found in breast milk. This clearly shows the focused approach and commitment of the Government towards public health along with the contribution from voluntary restriction for the use of pesticides in the country.25 As the major sources of such contaminations are from soil and polluted environment which is region specific, hence, further study in relation is proposed.2627
Conclusion
Mycotoxins, especially aflatoxins, are known carcinogens. The presence of aflatoxins in feedstuffs and their consequential appearances in milk and milk products is a serious health concern, as dairy products are consumed widely across age groups, including infants and children. The fungal toxins are resistant to high temperature treatments including pasteurization and sterilization. Eradication of this problem has recently become a major thrust area for research. The fungal growth on agri produces, which become the major component of cattle feed primarily depends on the temperature and moisture level of the crop and the environment. This thus becomes the critical point for controlling the presence of aflatoxin in milk and milk products. It is known that moisture level from 13% to 18% of animal feed and from 50% to 60% of environment favor the fungal growth. However, the concentration of AFM1 in milk is highly dependent upon dietary aflatoxin and the threats to humans make aflatoxin in dairy feeds a constant concern. It is difficult to eradicate its presence.
To check the proliferation of fungi and subsequent aflatoxin production in the cattle feed, it is advisable to keep the moisture level of feed below 11% as per the Indian Standards (IS2052 (R-1)).28 Constant evaluation of the cattle feed and the storage conditions should be undertaken in order to minimize the contamination. The State Co-operatives and Corporate sector which are actively involved in the organized manner for the production and processing of milk have to play a vital role of monitoring the production of animal feed fed to the milching animals to produce quality milk for consumption by consumers from all walks of life. The public sector can play a very important role through awareness programs, education to dairy farmers and milk processors about the ill effects of fungal toxins, such as aflatoxin, and take preventive steps to control the occurrence of such health hazards in the milk and milk products.
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Source of Support: The study was conducted with financial support from Nestlé India Ltd.
Conflict of Interest: Sanjeev Ganguly is an employee of Nestlé India Ltd. There are no other conflicts of interest.
Keywords:
Aflatoxin M1; Bovine milk; Dairy cattle feed; Heavy metal; Pesticide residues
© 2012 Indian Journal of Public Health | Published by Wolters Kluwer – Medknow