Contaminants in the cow's milk we consume? Pasteurization and other technologies in the elimination of contaminants

Cow's milk is currently the most consumed product worldwide. However, due to various direct and indirect contamination sources, different chemical and microbiological contaminants have been found in cow's milk. This review details the main contaminants found in cow's milk, referring to the sources of contamination and their impact on human health. A comparative approach highlights the poor efficacy and effects of the pasteurization process with other methods used in the treatment of cow's milk. Despite pasteurization and related techniques being the most widely applied to date, they have not demonstrated efficacy in eliminating contaminants. New technologies have appeared as alternative treatments to pasteurization. However, in addition to causing physicochemical changes in the raw material, their efficacy is not total in eliminating chemical contaminants, suggesting the need for new research to find a solution that contributes to improving food safety.


Introduction
Milk is a fluid secreted by the female of the mammalian species and fulfills the nutritional requirements of the neonate, for instance: (i) the energetic part (provided by lipids, lactose, and in excess by proteins), essential amino acids, and (ii) amino groups necessary for the biosynthesis of non-essential amino acids (provided by proteins), essential fatty acids, vitamins, inorganic elements, and water. 1 Global milk production has increased by about 20% in the last decade, from 694 million tons in 2008 2 to 843 million tons in 2018. 3 As a result, bovine milk is the most consumed food product representing about 48% of the total milk consumed globally, the European Union (EU), Australia, and New Zealand being the most important producers, followed by the United States and India. 4 Collection and processing expose milk to different contaminants, mainly pesticide residues, metals, mycotoxins, hormones, and others reaching the cow through feeding or drug administration by producers. 5 Thus, milk can contain hazardous materials, of either biological or chemical origin.
Although pasteurization has been an efficient antimicrobial method and has contributed to reducing many diseases, several infectious episodes associated with pasteurized milk have continued to occur, mainly when raw milk has an exaggerated population of microorganisms that increase the margin of survival and by post pasteurization contamination. 6 The biggest problem of pathogens in pasteurized milk is that they persist without causing any organoleptic alteration, increasing sanitary risk since the consumer cannot suspect their presence, showing that pasteurization has some drawbacks in treating pathogens. 7 As population and industrial growth increased, new contaminants appeared, and with this, contamination of cow's milk also increased not only by compounds of biological origin but also by compounds of chemical origin, as mentioned above. 8 However, pasteurization has remained the only established treatment, even though it is only effective for eliminating most biological and non-chemical compounds. 9 In contrast, the literature mentions very few alternative treatments to treat chemical contaminants in cow's milk, leading to a critical analysis of their application to ensure sufficient quality in the milk consumed. Given this evidence, the bibliographic review here aims to identify the different types of contaminants in raw/pasteurized cow's milk and analyze the application of alternative processes for the elimination or degradation of contaminants.

Contaminants present in cow's milk
There are several hazards of contamination of cow's milk, ranging from biological to chemical compounds. The risk of biological contamination of cow's milk derives mainly from cattle milking due to the exposure of udders to the environment, equipment, storage, dirty pipes, and others. 10 Chemical contamination of cow's milk comes from several sources: application of agrochemicals, 11 use of legal or illegal veterinary products, 12 feed and forages contaminated with natural toxins, 13 or through the improper use of chemicals during milk production, processing and packaging stages. 14 Figure 1 shows the direct and indirect pathways for contaminants entry into bovine milk. Indirect contamination is associated with the ingestion of contaminants both from the environment and from substances of veterinary use. The most common environmental contaminants are mycotoxins, pesticides, and metals consumed by cattle through feed, forages, and water. In addition, antibiotics and hormones are administered to the cow orally, by injection, or as intramammary infusions to treat diseases, promote animal growth and increase milk production. 5 On the other hand, direct contamination occurs during milk processing from milking, handling, storage and even pasteurization. During the industrialization process, milk comes into contact with metals, residues of cleaning products, mycotoxins, among others.
For better analysis and understanding, the classification of contaminants according to the origin is microbial contaminants and chemical contaminants ( Figure 2). About 14.57% of the literature reports contamination of cow's milk by pathogenic microorganisms. Although the objective of the pasteurization process is the elimination of these microorganisms, there is evidence of their presence in pasteurized milk, which will be presented later. Although pathogenic microorganisms are considered the main hazard that threatens the safety of milk, they do not represent the highest percentage of reported cases. The contaminants that have been more reported in the literature are of chemical origin ( Figure 2). Among chemical contaminants, metals, pesticides, and antibiotics stand out. Among chemical contaminants, the most reported are heavy metals (22.18%), pesticides (22.05%), and antibiotics (22.18%); due to bad practices in agriculture and cattle. Although reports of mycotoxins in milk are relatively low (9.97%), they are of great importance due to the increase in reported cases of contamination with Aflatoxin M1 (AFM1). The International Agency for Research on Cancer has classified AFM1 as a carcinogenic substance. 15 This means that the food safety of milk is at risk, as any of these compounds compromise the health of the final consumer. Below is a detailed classification of the different types of contaminants present in both raw and pasteurized milk and the negative effects they have on consumer health.

Microbial contaminants
The presence of several pathogenic microorganisms has been reported in raw and pasteurized cow's milk (Table 1). Microbial contamination of raw milk can be due to diseases such as mastitis, improper handling on production farms, milking equipment, water sources, and feeding of cattle, utensils, and equipment used for milk storage on the farm or during transport. 16 Likewise, poor hygienic practices within the dairy industry can lead to the formation of biofilms on the sprinklers of cooling systems, pipes, cooling tanks, storage, and transport tanks. The contact of pasteurized milk with these surfaces increases the risk of contamination with pathogenic microorganisms, posing a danger to the consumer and the quality of the product. 17 According to Table 1, Most cases of contamination are recorded in raw milk due to inadequate milking, processing, storage, and transport conditions. On the other hand, although few studies report the presence of microorganisms in

Chemical contaminants
For a more detailed analysis, the chemical contaminants found in cow's milk have been classified into five groups: pesticides, metals, antibiotics, mycotoxins, and hormones (Table 2).

Pesticides
A variety of pesticide residues in detectable amounts in raw milk, pasteurized, and UHT (ultra-high temperature) milk has been reported by several authors. This is due, among other factors, to the lipophilic properties and resistance to biodegradation of these types of contaminants. 8 There are three possible forms in which pesticides can enter the animal's body 172 : (i) through contaminated water, (ii) through the pores of the skin when the animal is sprayed or soaked to treat ectoparasites, and (iii) through contaminated feed and forage, the latter being the main source of entry.  [177][178][179][180] This verifies that water contaminated by pesticides and supplied to cattle is one of the main routes of contamination of raw cow's milk.       Testosterone Raw -- 161,167 Pasteurized -- 161 4-Androstenediol Raw -- 161 (ii) According to the analysis of Table 2, Claborn et al. 181 report the presence of malathion residues in cow's milk after cattle were sprayed with this pesticide for the treatment of ectoparasites. Malathion was found to be completely secreted from the udder 24 hours after application. In contrast to malathion, lindane was reported not to be completely excreted in milk until seven days after application to the cow's skin. 182 Residues of chlorpyrifos and ethion have been found in cow milk up to 24 and 72 hours after application, respectively. 183 This confirms that skin contaminated with these pesticides is another route of contamination of raw cow's milk.
(iii) In forage, concentrations of 0.02 mg kg -1 of DDT residue were reported. 184 The presence of cypermethrin, chlorpyrifos, cyhalothrin, and deltamethrin in forage was reported in a range of mean concentrations between 1.03-6.01 ng g -1 . In addition to the presence of pesticides in forages, residues of lindane, DDT, fenvalerate, ethion, malathion, profenofos were also reported in feed. The mean concentrations of these varied in the range of 0.63-4.05 ng g -1 . 175 The presence of deltamethrin in feed was also reported in a concentration range of 41.99-381.30 μg kg -1 . 185 Another investigation revealed the presence of malathion, dimethoate, methyl-parathion, diazinon in the feed fed to cattle. The range of detected concentrations was between 0.01-80.45 μg L -1 . 62 All the contaminants reported in forage and feed were also detected in cow's milk. 11,54,55,57,60-62,177,179,186 Thus, like water, pesticide-contaminated forage and feed are a route of contamination as they are directly ingested by cattle and excreted through cow's milk.
Pesticides are one of the most commonly found contaminants, not only in raw cow's milk but also after the pasteurization and UHT process. Their presence in milk, even below the maximum permitted levels, represents a health risk to the consumer. It is related to Hodgkin's disease (HD), non-Hodgkin's lymphoma (NHL), Parkinson's disease, endocrine disruption, respiratory and reproductive disorders, among others. 187 It is important to note that organochlorine pesticides such as hexachlorocyclohexane, dichloro diphenyl trichloroethane, and endosulfane are still present despite having been banned since the 1970s because of their high persistence in the environment and their harmful effects on human health, 188 are still detected in cow's milk. This indicates that they are still used in agriculture and animal husbandry. With a few exceptions (cyhalothrin, cypermethrin, fenvalerate, deltamethrin, permethrin, and diazinonella), the vast majority of pesticides found in cow's milk are not regulated by Codex and the EU. This demonstrates the low efficiency of the regulatory controls of these contaminants in the unprocessed and postprocessed product, leading to an inefficient safety of this food product.

Metals
Although metals are found in the environment either naturally or due to industrial and/or agricultural activities, there are several routes by which they reach the milk. Namely, ingestion of contaminated food, fodder, and/or contaminated drinking water. In the soil, they are absorbed by many crop plant species, which, when ingested by animals, are transferred to the lactating glands and finally excreted in milk. 172 Equipment used in the dairy industry is another source of contamination directly to milk with metals such as chromium and nickel. 189 Heavy metals such as cadmium, lead, mercury, and arsenic reach milk by indirect contact through feed consumed by cattle. 189 Although the literature does not report the presence of metals in water or fodder destined for cattle, as well as in pesticides, these can be another of the main routes of contamination.
Several heavy metals have been reported in the literature to be found in raw cow's milk. The metals least found in studies of raw cow milk are tin and molybdenum. These elements are not abundant in nature, and their presence in fodder or water for animal consumption will depend on soil characteristics, while the most reported are lead, cadmium, copper, and zinc, due to environmental pollution produced by man mainly in industrial activities. 79,190 Minerals such as Fe, Cu, and Zn are necessary for various biological functions. However, high concentrations of these minerals have negative effects on human health. 96 Lead is one of the non-essential metals classified as carcinogenic to humans by the International Agency for Research on Cancer. 191 Cadmium is associated with the formation of human lung, kidney, breast, prostate, urinary tract cancer because it affects cell proliferation, differentiation, and other cellular activities. 192 None of the heavy metals reported in the literature consulted have established maximum residue limits (MRLs) by Codex 193 and the EU. 194 However, these contaminants are known to represent a high risk to human health. Stricter control measures should be adopted in the dairy industry, considering that cow's milk is one of the most consumed products by humans worldwide.

Antibiotics
Antibiotics are used in livestock activities in three basic ways: therapeutic, prophylactic, and growth promoters. About 80% of dairy cattle are subjected to antibiotic treatments on at least one occasion throughout their lives, mostly used as growth promoters and for the treatment of various diseases such as mastitis, arthritis, respiratory diseases, gastrointestinal diseases, and bacterial infections. 195 Cows eliminate antibiotics and their metabolites through milk, depending on the dose and route of application, level of milk production, type and degree of mammary disease, and time between treatment and milking. On the other hand, oral, intramuscular, or intravenous administration is less important from the point of view of milk hygiene than intramammary application. However, intramammary antibiotics are easy to apply and generally cheaper, so they are preferred in dairy farms.
The most common disease in dairy cows is mastitis, whose treatment includes the wide use of tetracyclines, β-lactams, oxytetracycline, difloxacin, among others, being the β-lactams of greater application. 8 Within the latter group, the most employed are penicillin, ampicillin, and amoxicillin. 196 According to the literature, the presence of antibiotics in milk has been evidenced, highlighting tetracycline, oxytetracycline, penicillin, and amoxicillin. 103, 124,197,198 While other antibiotics less reported in milk were rifamixin, gatifloxacin, spiramycin, and lomeflaxacin, with no indication in the studies of the purpose of their application in cattle. 101,112,126,127 The consumption of contaminated milk with antibiotic residues is an emerging public health problem worldwide. Therefore, it is important to control the presence of antibiotic residues in food to avoid the appearance of resistance to these antibiotics in humans. The presence of antibiotics at concentrations even below the MRL in milk can cause undesirable effects on human health such as ototoxicity and nephrotoxicity, 199 endocrine disruption, 200 hypersensitivity, and especially bacterial resistance. 130 According to the literature consulted, 43 antibiotics present in cow's milk have been identified, of which 18 are not regulated by Codex 193 and EU standards. 194 Considering that the use of antibiotics in cattle generates residues in milk, their excessive use should be avoided, and the elimination times before milking should be respected in order to avoid the presence of these contaminants.

Mycotoxins
The quality of food products is commonly affected by toxin contamination, of which 60 to 80 % are caused by mycotoxins. 201 This means a risk for human health and great economic losses in the industrial sector.
Mycotoxins are natural contaminants produced by Aspergillus, Penicillium, and Fusarium fungi, 154 the most prominent being AFM1, which results from the metabolism of aflatoxin B1 in the liver of contaminated animals. 15, 143 In the 1960s, the first reported case of aflatoxin contamination was reported for the first time, beginning the concern for this type of contaminant. Even during this decade, high consumption of feed contaminated by this mycotoxin was reported, which led to indirect contamination of cow's milk for consumption, compromising the safety of this product. 202 Therefore, it is considered that the main routes of entry of mycotoxins into milk are contaminated crops and feed ingested by cows. 136 It is known that approximately 0.3-6.2% of AFB1 (Aflatoxin B1) present in animal feed is converted to AFM1. 15 This mycotoxin is neither degraded nor removed by industrial food processes such as pasteurization and sterilization, nor by the cooking of feed. 203 This represents a difficult problem to deal with at the industrial level due to the stability of mycotoxins in general to thermal, physical, and chemical treatments. 204 AFM1 mycotoxin is the only regulated by Codex 193 and EU 194 and the most reported in cow's milk according to the literature. However, other abundant mycotoxins have been identified in this food product, such as ochratoxin A and zearalenone. The fungi of the genus Aspergillus and Penicillium produce Ochratoxin A, while fungi of the genus Fusarium produces zearalenone, commonly found in cattle feed. 138 On the other hand, aflatoxin G2, aflatoxin G1, aflatoxin B2, and zearalanol show a lower incidence in cow's milk. The literature on the effects on human health associated with the ingestion of mycotoxin-contaminated milk is scarce or almost non-existent, unlike AFM1. Therefore, studies on this type of contaminants should be expanded.

Hormones
The use of hormones in the livestock industry increases production yields and medical treatments. Their fat-soluble characteristics favor their high persistence and presence in cow's milk due to the high-fat contents. 156 Therefore, the supply of hormones to cattle represents a form of direct contamination that, like other contaminants, is excreted through milk. However, the European Union banned the use of hormones through the Directive 96/22/EC, and enforcement is regulated by Directive 96/23/EC. 165 Prednisolone in combination with amoxicillin and clavulanic acid is used to treat mastitis in cows' udders, 205 being an access route of this contaminant to milk. The 17β-estradiol and progesterone, with the highest presence in cow milk, are sex hormones widely used to induce lactation, improve fertility and synchronize the estrous cycle. 8,168 The hormones least found in studies in milk were testosterone, somatostatin, and cortisone. The presence of estrogens in cow's milk has been linked to diseases such as breast cancer 206 and conditions in the gastrointestinal tract. 156 Other diseases associated with the presence of hormones in cow's milk have included acne, prostate cancer, uterine cancer, and male reproductive disorders. 167 Table 2 shows that several hormones are frequently present in cow's milk, with prednisolone being the only one regulated by the EU. 194 This indicates that regulations should be established for different hormones considering that they are the chemical compounds mostly used to increase milk production yield to preserve quality and consumer safety.

Pasteurization process in cow's milk
The principles and name of pasteurization come from the studies of the French scientist Louis Pasteur. His interest in milk and other food products was due to their putrefaction, which he later attributed to the growth of undesirable microorganisms. 207 Several pathogenic microorganisms are found in raw milk: Pseudomonas, Enterobacter, Bacillus, Clostridium, Microbacterium, and Micrococcus. Pathogenic microorganisms in cow's milk have been linked to infectious diseases such as campylobacteriosis, salmonellosis, yersiniosis, listeriosis, tuberculosis, brucellosis, staphylococcal enterotoxin intoxication, streptococcal infections, and Escherichia coli O157: H7 infection. 208 It was not until the end of the 1880s that heat treatment began to be used to commercialize milk. This arose with the main objective of inactivating Mycobacterium tuberculosis, the cause of tuberculosis in humans associated with the consumption of raw milk. Thus, pasteurization became a process universally employed by developed countries after World War II. However, there is evidence that not all pathogenic microorganisms can be eliminated during pasteurization, such as Staphylococcus aureus, micrococci, Streptococcus spp, and Bacillus. 209 Which calls into question the efficiency of this process.
The US Food and Drug Administration (FDA) establishes a maximum limit for bacteria in raw cow's milk of 100,000 cfu ml -1 and 20,000 cfu ml -1 for pasteurized milk. 209 Pasteurization is a technology classified on the basis of operating temperatures and exposure times as follows: LTLT, HTST, and UHT. Low-temperature long-time pasteurization (LTLT) uses a minimum temperature of 62.8°C and a minimum time of 30 min. High-temperature short-time pasteurization (HTST) uses a minimum temperature of 71.1°C, a minimum time of 15 seconds, and ultra-high temperature pasteurization (UHT) works at a minimum of 135°C and during a minimum time of 1 second. 210 Pasteurized milk under UHT conditions can be stored for several months without refrigeration. 211 Whereas the shelf life of pasteurized milk ranges from 10 to 20 days when kept under refrigerated conditions below 6.1°C. 212 It has been shown that the application of pasteurization denatures proteins with bacteriostatic capacity, as is the case of lactoferrin. This is a glycoprotein that binds iron, and its complete denaturation has been evidenced losing its inhibitory capacity on Escherichia coli under UHT conditions. 213 For this reason, it is suggested that heat treatment should be applied below 75°C to avoid denaturation of proteins with bacteriostatic capacity and at the same time cause inactivation of pathogenic microorganisms. 213 On the other hand, the HTST process degrades up to 20% of the vitamins (B1, B6, B12, and C) present in milk. 214 This evidence shows that, although pasteurization and UHT have been widely used to eliminate pathogenic microorganisms, it is not entirely efficient for this purpose. There are even losses of milk mineralization, varying its nutritional composition.
The presence of microbial contaminants in different samples of pasteurized milk shows that, although pasteurization aims to eliminate microorganisms present in milk, it is not totally effective. Moreover, with the appearance of other contaminants, the quality of milk no longer depends only on the presence of microorganisms. It is, therefore, necessary to study other methods of decontamination to ensure the safety and health of consumers.

Alternative methods for the treatment of cow's milk
International regulations require maximum limits for microbial and chemical contaminants to ensure the quality of drinking milk. Pasteurization is a technology widely used in the dairy industry. However, it is exclusive for the elimination of microbial contaminants. The literature mentions alternatives for eliminating specific microbial and chemical contaminants (Table 3).
Supercritical carbon dioxide has been used as an inactivating agent for E. coli, where the greatest reduction in the content of microorganisms was observed during a residence time of 20 minutes, achieving almost complete inactivation after 70 minutes. 215 Complete inactivation of coliforms, molds, and yeasts was achieved, while a maximum reduction of aerobic bacteria of 4.96 log was obtained using high-pressure carbon dioxide. 221 Using a thin-film UV-C (Ultraviolet-C) reactor with flow-guiding elements allowed a 4.58 log and 3.19 log reduction for E. coli and L. innocua, respectively. 216 Makarapong et al. 218 employed a UV-C reactor for the inactivation of aerobic bacteria achieving a 4.60 log and 4.70 log reduction at 48W and 39W, respectively. UV-C lamp wattage did not significantly influence the fat concentration in the milk, which means that it is necessary to improve the method to guarantee an effective reduction of these microorganisms if milk transport time exceeds two hours without cooling. It was verified that L. monocytogenes was completely inactivated in milk with ozone for 15 minutes. However, nutritional values were affected. 219 Exposure of milk to Nd: YAG laser did not alter the physicochemical properties of milk, but the percentage of reduction was low for E.coli (30%), Salmonella sp (25%), yeasts (47%), and Lactobacillus sp (30%). 223 The combination of ultrasound with hydrogen peroxide and an active lactoperoxidase system was able to guarantee the microbial quality of milk as it was able to completely inactivate Staphylococcus aureus, Listeria monocytogenes, Lactobacillus plantarum, Lactobacillus pentosus, Salmonella Typhimurium, Escherichia coli, and Pseudomonas fluorescens at 10 minutes at an amplitude of 125 μm. 220 The application of ultrasound in combination with variations in temperature, time, and constant pressure (manothermosonication) achieved minimal reductions of up to 1.6 log CFU/ml for E. coli and P.fluorescens and 1.05 log CFU/ml for S. aureus. Further studies are needed to ensure effective inactivation using manothermosonication. 225 The application of high pressures (400-600MPa) effectively inactivated (5 log CFU/ml) E. coli, Salmonella and L. monocytogenes, Enterobacteriaceae, lactic acid bacteria, and Pseudomonas spp. 222 One of the most widely used methods for the inactivation of microorganisms in cow's milk is pulsed electric fields (PEF). This method was applied for the inactivation of E.coli and L. innocua, achieving a reduction of 2 log CFU/ml. 217 It was found that combining this method with preheating at 50°C achieved a 5-6 log CFU/ml reduction of Pseudomonas aeruginosa and a total reduction of E. coli, S. aureus, and L. innocua. 224 Biosorption methods employing the use of microorganisms prove to be efficient in the removal of pesticides, metals, and mycotoxins. Biosorption with lactic acid bacteria managed to eliminate organophosphate pesticides from cow's milk, Table 3. Alternative methods to pasteurization for removal of contaminants in bovine milk.

Contaminant Process Reference
Pathogens Escherichia coli Inactivation with supercritical carbon dioxide technology 215 Escherichia coli and Listeria innocua Inactivation using a UV-C thin film reactor 216 Inactivation by pulsed electric fields 217 Aerobic bacteria Reduction by UV-C irradiation 218 Listeria Chlortetracycline and cefazolin Electrochemical method 237 Tetracycline Electrochemical method 238 Adsorption with molecularly imprinted polymer 239 being more effective for chlorpyrifos, fenitrothion, and malathion, whose degradation constants were greater than 0.018 h -1 . On the other hand, diazinon and methyl parathion were more resistant when applying of the different strains of lactic acid bacteria separately and in combination. The degradation rate constants were correlated with the measurement of phosphatase activity, and it was found that the lower the phosphatase activity, the lower the degradation constant. 226 The same method was applied for this group of contaminants finding that dimethoate and methyl parathion were the most stable with the lowest degradation rate constants (0.0165-0.0184 and 0.0213 h -1 , being more efficient for the removal of malathion with higher degradation rate constants (0.0218-0.0420 h -1 ). 228 Although the application of lactic acid bacteria was shown to be an effective method for removing diazinon, dimethoate, and methyl parathion in cow's milk it was not very selective since it cannot eliminate all the organophosphates studied.
Biosorption with Saccharomyces Cerevisiae allowed the removal of 70% of lead, mercury, and cadmium metals. 230,[233][234][235] The removal percentage was higher when Lactobacillus Acidophilus was used, eliminating 80, 75, and 72%, respectively. 231,232 The use of Saccharomyces cerevisiae and Lactobacillus helveticus removed AFM1 from milk by an as yet unknown binding mechanism. 243 A combination of probiotic bacteria with yeast species managed to remove 90.88% of AFM1 within 72 hours. 245 This percentage of removal was higher than that obtained in another study (19-61%). 246 By applying a biofilm of Lactobacillus rhamnosus, an AFM1 removal of 60.74% was achieved. Despite that, the method is not a viable alternative for application because a reduction in the percentage of fat and total dry matter was observed. 247 Biosorption methods employing microorganisms (Lactobacillus acidophilus and Saccharomyces cerevisiae) are efficient for removing heavy metals in cow's milk (lead, mercury, copper, and cadmium). However, they require a minimum fermentation period of 4 days. When using lactic acid bacteria to degrade organophosphorus pesticides, a minimum fermentation period of 24 hours is required. These times would represent economic losses for the industry, and given the existing world demand for milk, it would be almost impossible to apply them on a large scale.
Adsorption methods prove to be efficient for removing metals, antibiotics, and mycotoxins. By adsorption with diacrylate Pluronic P123 (P123-DA) hydrogels removed about 85.3% and 81.9% of Pb 2+ , and Hg 2+ ions, respectively. 229 Resins have been another adsorbent used in the adsorption of heavy metals in cow's milk. IMAC HP resin was described for the removal of copper ions (76.89%). 92 Tetracycline, oxytetracycline, chlortetracycline, and doxycycline have been removed by adsorption on a molecularly imprinted polymer, achieving 81.83, 95.47, 96.44, and 93.25% removal, respectively. 239 A photocatalytic-fluorescent polymer, produced from graphene oxide and bismuth phosphate with molecular magnetic imprinting, allowed ciprofloxacin's complete degradation. 240 Bodbodak et al., 242 developed a molecularly imprinted polymer coated on the surface of a stainless-steel plate as an adsorbent material for the decontamination of AFM1 in cow's milk. This method was able to remove 87.3 to 96.2% of AFM1 without causing a change in the physicochemical Table 3. Continued

Contaminant Process Reference
Ciprofloxacin Adsorption with BiPO 4 @ fluorescent photocatalytic graphene oxide-based magnetic molecular imprinted polymer 240 Amoxicillin, ciprofloxacin, doxycycline Decomposition by gamma irradiation 241 Mycotoxins Aflatoxin M1 Adsorption with molecularly imprinted polymer coated on the surface of the stainless-steel plate 242 Removal using Saccharomyces cerevisiae and Lactobacillus helveticus 243 Adsorption with clay minerals (kaolin and bentonite) 244 Elimination by a combination of yeast and probiotic bacteria species 245,246 Biofilm elimination of Lactobacillus rhamnosus gg properties of the milk. Adsorption with kaolin and natural calcium bentonite clay for adsorption was able to remove AFM1 by 86.1-93.3% and 93.7-97.7%, respectively. It was observed that no change in the nutritional properties of milk would occur. 244 Despite this, few studies have been reported in cow's milk. Therefore, there are not enough to consider its application at the industrial level.
Other methods less reported in the literature were also applied for the removal of pesticides and antibiotics. The ultrasonic treatment proved to be effective for the degradation of 97.10% of methyl parathion. However, this method is limited by the generation of degradation products with toxic effects. 227 For the elimination of antibiotics in cow's milk, methods such as ozonation have been applied, with about 95% degradation for amoxicillin, doxycycline, ciprofloxacin, and sulfadiazine. 236 Electrochemical oxidation applied for the removal of small concentrations of chlortetracycline, cefazolin, 237 and oxytetracycline 238 was also described. Gamma radiation was also found to be effective for the removal of amoxicillin, ciprofloxacin, and doxycycline by 90% in cow's milk samples. 241 However, of all the antibiotics detected in cow's milk, they have only been tested for the elimination of amoxicillin, doxycycline, ciprofloxacin, sulfadiazine, chlortetracycline, cefazolin, y tetracycline. More studies are needed to validate the application of these methods for the decontamination of cow's milk.
It has not been demonstrated that a single method is capable of eliminating different groups of contaminants, as is the case of pasteurization for microbial contaminants. Despite the wide use of hormones in the cattle industry and their consequent generation of traces in cow's milk, no removal methods have been reported for them. The alternative methods studied to date have been applied on an industrial scale, and many of them alter the nutritional properties of milk. The fact that most of these chemical contaminants are not regulated by standards does not oblige the dairy industry to use alternative methods to pasteurization. Nor is it economically viable to use a different method for the elimination of each contaminant present in milk. However, to guarantee the safety of milk, it is essential to study processes that complement pasteurization and can eliminate pathogenic microorganisms and chemical contaminants.

Conclusions and future prospects
The presence of contaminants in raw cow's milk (many of them banned) is an indication that they are currently used illegally in both agriculture and animal husbandry. Although the presence of contaminant residues in milk represents a health risk to the consumer, there are no MRLs established for all of them. In addition, pasteurization processes are not efficient for the degradation or elimination of the different contaminants addressed.
Although, the literature exposes alternative methods for removing various contaminants in milk, they are still not sufficient nor applied on an industrial scale. Instead, they have been applied individually or in very small families of contaminants. There are no evidence or results concerning the interactions between them or with intermediate products formed on cow's milk, nor changes in the organoleptic properties. A particular case is hormones, which although they are a direct source of contamination, with evidence of their presence in raw, pasteurized, and UHT milk, the literature does not report specific elimination methods for these types of contaminants.
However, alternative methods have proven to be efficient in degrading several contaminants present in milk. Based on this hypothesis, it is suggested to deepen the application of these methods, including the study of interactions between different families of contaminants, application of new materials, or modification of existing ones. Studies on toxicity or changes in organoleptic properties. In this sense, the field of nano-biotechnology, nano-fibers, nano-membranes, biochar, MOF's (metal-organic framework), among others, could play a relevant role, guaranteeing the safety of the milk consumed, and consequently, a better quality of life for consumers.

Data availability
No data are associated with this article.   The review topic: "Contaminants in cow's milk, pasteurization and alternative technologies in the removal of these contaminants" is discussed extensively in the context of the paper. Table 1 shows the pathogens in cow's milk reported in the literature and Table 2 summarizes the chemical contaminants in cow's milk reported in the literature. All statements are adequately supported by citations.
Pasteurization is a technology used in the industry, however it is exclusive for the elimination of microbial contaminants. Table 3 describes alternative methods to pasteurization: supercritical carbon dioxide, inactivation by pulsed electric fields, inactivation by ozonation. Alternative methods have proven to be efficient in degrading several contaminants; however, they are still not sufficient nor applied on an industrial scale.
The conclusions are appropriate. It is suggested to continue research on alternative methods.

Is the review written in accessible language? Yes
Are the conclusions drawn appropriate in the context of the current research literature?
Yes contaminants according to the origin is microbial contaminants and chemical contaminants ( Figure 2)" must be incorporated into a paragraph, it is not correct to leave it alone.
COMMENT 7: In the paragraph before point 2.1, two contiguous phrases initiate in this same way: "Among chemical contaminants.....". Please correct that.
COMMENT 8: This phrase "The main types of microorganisms present in milk are bacteria, yeasts, and molds, which represent the different types of microorganisms present in cow's milk." It is redundant. Please improve it.
COMMENT 9: When a bibliographic reference is made within the text, indicate the year after appointing the authors. Apply in all cases.
COMMENT 10: In reference to Figure 1: specify contaminants that come from milk containers (each type).
COMMENT 11: Last paragraph of section "2.", third line: indicate the reasons why there may be remanence of microbes even after pasteurization, considering that the process (pasteurization) has been carried out correctly.
COMMENT 12: SECTION 2.1: Here the "non-pathogenic" organisms should be included and those that cause alteration of milk, whose result is harmful to consumer. Improve the format of the tables.
COMMENT 13: SECTION 2.2.1, Literal "ii". What mean "According to the analysis of Table 2, Claborn et al. 181 report……". What type of analysis was made with " Table 2"?, Who made it?
COMMENT 14: SECTION 2.2.1, Literal "II". In reference to "This confirms that skin contaminated with these pesticides is another route of contamination of raw cow's milk." The evidence presented is causal, the most appropriate term, in this case, would be "evidence suggests...". " COMMENT 15: SECTION 2.2.1, Literal "II". "In forage..." is indicated. Specify the conditions of the sample and the possible source of contamination, allowing each case to understand more dynamically. Apply in all cases.
COMMENT 16: Throughout the text, there are many redundant ideas in the same phrase or paragraph, please correct that. This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Esmeralda García Díaz
Centro de Química, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico The manuscript entitled: "Contaminants in the cow's milk we consume? Pasteurization and other technologies in the elimination of contaminants" is valuable and presents an exhaustive review of the different types of contaminants in raw/pasteurized cow's milk and analyze the application of alternative processes for the elimination or degradation of contaminants. It provides relevant information about the sources of contamination and the health implications of ingesting these contaminants through milk, adequately supported by citations. It presents a wide variety of contaminants with their details regarding the contamination of milk. Information about alternative treatments to remove contaminants is also relevant and abundant. However, the tables need to be improved to present relevant information, which the authors can surely provide. Please see the following comments regarding the tables:

COMMENTS
in Figure 1, the "processing and packaging stages" label is missing. Plasticizers that are used in containers, such as BPA need to be included. Page 4, sentence "For better analysis and understanding, the classification of contaminants according to the origin is microbial contaminants and chemical contaminants (Figure 2)", needs to be rewritten, since the word "contaminants" is repeated several times. I suggest: Figure 2 presents the classification of cow´s milk contaminants and their microbial or chemical origin. Table 1 is long but contains relatively little information for its size. The column "Type of milk" is repetitive -separate horizontally by type of milk and add a column with the main identification method used in each case. Table 2 is also long and contain repetitive information, with columns labelled as MRL being practically empty. it would be more useful to put the concentration interval reported in the referred works. MRL data can be mentioned in text.
Throughout the document, round percentage values to make analysis easy.
Page 14, In the sentence "Therefore, it is important to control the presence of antibiotic residues in food to avoid the appearance of resistance to these antibiotics in humans". Who becomes resistant, humans or microorganisms? Its unclear in the sentence with the expression "appearance of resistance". In sentence "Considering that the use of antibiotics in cattle generates residues in milk, their excessive use should be avoided, and the elimination times before milking should be respected in order to avoid the presence of these contaminants". Please, reference the "elimination times before milking" to support the establishment of this time in some reported work.

Page 16
The sentence "The literature mentions alternatives for eliminating specific microbial and chemical contaminants", change 'mentions' to 'reports' instead. This sentence is confusing: "UV-C lamp wattage did not significantly influence the fat concentration in the milk, which means that it is necessary to improve the method to guarantee an effective reduction of these microorganisms if milk transport time exceeds two hours without cooling". It's not clear the relationship between lamp wattage, fat concentration, microorganisms and time of cooling.
My conclusion: accept after minor revision.
water. Chromatography of compounds of ambiental and biological interest I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.
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