Course:FNH200/Projects/2020/The Food Science Behind Milk

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Diary Milk

This article aims to provide a wide range of information about milk, including its background history, methods involved in modern production, composition and their impact in detail, and the significance of its contained nutrients to human health.

History

Diary Milk

Animal milk is one of the ancient food that existed in human society for over 7000 years.[1] The earliest known regions that produced animal milk can be traced back to ancient Egypt and Southwest Asia in Neolithic age along with development of animal domestication.[2] As a natural replacement of human milk, animal milk has been used to feed human babies for millennia. It was also used as a nutritious beverage in some cultures. Cheese making methods developed later further concentrated the nutrients from animal milk. And eventually spread around the globe in the last several centuries.

Milk in history is a wide term which includes the milk from sheep, goats, buffalos, cows, and other mammals. “Milk” that is commonly seen today is mostly cow milk produced with industrial methods. We will be using cow milk as our subject of discussion for the rest of the article.

Processing

After the untreated milk arrives at the factory, the milk goes through three main steps. Pasteurization, homogenization and packaging. Pasteurization refers to heating at a temperature of at least 72 degrees Celsius for at least 15 seconds to kill pathogens in the product. In the factory, milk enters some metal pipes with good thermal conductivity. Next to him, there are cooling pipes and heating pipes that exchange heat to help the milk perform multiple cycles of heating and cooling for sterilization. During part of the cycle, the milk will be injected into the centrifuge for homogenization, so that the dispersion in the milk is micronized and homogenized, which can make the milk taste more delicate. In the end, the pasteurized and homogenized milk is packed in different packages and shipped out of the factory.[3]

Composition

From the book Milk and Dairy Products in Human Nutrition edited by Young W. Park and George F.W. Haenlein[4], it has been stated that dairy milk from cows is composed of approximately 87% water component and 13% solid substances. Specifically, the solid substances are highly discussed in recent. The solid substances are the combination of 3.4-5.4% fats, 3.5-4.0% protein, 4.6-5% carbohydrates, and 0.6-0.9% minerals, vitamins and the other minor constitutes.

Lipid

Milk fats may act as a carrier for fat-soluble vitamin A, D, and E, as well as β-carotene (p.65).[4] The main lipids that are presented in cow milk are triacylglycerols, which compromise more than 98%, but small concentrations of the other minor lipids are also present (p.65).[4] Interestingly, it was stated that long chain fatty acids in milk are considered to contribute to the elevation of LDL and total cholesterol concentration, which is an unhealthy cholesterol that may lead to many potential diseases (p.75).[4] However, the shorter fatty acids do not contribute to an atherogenic lipid profile (p.75).[4]

Protein

Milk proteins are extremely important for life processes since they perform a variety of functions in living organisms ranging from providing structure to reproduction (p.80).[4]  The nitrogen-containing portions of milk can be divided into three broad fractions: casein, whey protein and non- protein nitrogen (NPN)— 78.50% is casein, 16.5% is whey protein and 5.0% is NPN (p.80).[4] The two major categories of milk proteins are the insoluble proteins, which is the casein family and soluble proteins, which is whey proteins, found in lactoserum (p.97).[4] Noted, “most milk proteins are potential allergens, especially αs1-casein, αs2-casein. and β-lactoglobulin, which are lacking in human milk (p.97)”.[4]

Carbohydrate

Lactose is the dominant carbohydrate in milk, comprising more than 80% of milk carbohydrate (p.129).[4]  Many microorganisms grow in milk by making the use of lactose as their main source of energy (p.129).[4] In humans, lactose can be broken down by lactase, resulting in glucose and galactose sugar which are the main components in various energy mechanisms (p.138-139).[4] Carbohydrates other than lactose found in milk include oligosaccharides, glycopeptides, glycoproteins, and nucleotide sugars in small amounts (p.130).[4] Noted, in humans, lactose intolerance is caused by loss of lactase (p.130).[4]

Minerals and Vitamin

10 essential minerals that are mainly found in cow milk are calcium, phosphorus, magnesium, sodium, potassium, chloride, iron, copper, selenium, and zinc (p.172).[4] The most commonly known mineral that is found in milk is calcium. Calcium plays an important role in maintaining the structure of bone and health (p.172).[4] Calcium is associated with phosphate to form a crystallized salt named hydroxyapatite, providing rigidity, strength, and hardness for bone and teeth (p.172).[4]

“Milk and dairy products are good sources and among the first contributors to vitamin A, D, B2, B5, B9 and B12 intakes in human nutrition” (p.200).[4] However, those vitamins are found in very small amounts. It is important to add more vitamin supplements to satisfy the RDA requirement (p.215).[4] The book, Milk and Dairy Products in Human Nutrition, provides more detail about the other minerals and vitamins.

Milk also contains minor constituents, enzymes, hormones, growth factors, and organic acids, but in a very tiny amount, therefore, its roles will not be exclusively discussed here.

Preservation

Through the processing cycle much of the actions of preservation are done as explained above. The preservation of milk following the processing is mostly comprised of retaining a low temperature for the milk. Keeping the milk at below approximately 4 degrees celsius is essential in resisting bacterial growth.[5] After milk has been individually packed, it is refrigerated within grocery stores to ensure it is safely preserved.[6] Packaged and unopened pasteurized milk can stay preserved for only approximately four to five hours at room temperature, longer exposure to temperatures above 4 degrees celsius promotes bacterial growth making the milk unsafe to drink.[7] Expiration dates are also required on milk to ensure the product is consumed within a healthy time. Pasteurized milk typically lasts approximately 5 to 7 days when refrigerated at 4 degrees celsius.[7]

Health Benefits and Concerns

Milk contains many nutrients that are valuable and essential for health.[8] The combination of macronutrients and micronutrients that milk contains can be considered as a complete food source. Milk is rich in fats, proteins, lactose (milk sugar), vitamins, and minerals.[9] The protein in milk helps growth and development of muscles and other vital body functions. Milk protein contains all essential amino acids. The only addition to whole milk is a fat-soluble vitamin D.[10] Vitamin D is valuable for overall health and prevention of certain types of cancers.[8] In addition, vitamin D helps absorption of calcium which has protective effects against colon cancer.[9]

In Canada there are no additives, artificial hormones or antibiotics added to milk.[10] All the microbes are killed during the pasteurization process regulated by Food Regulations of the Food and Drugs Act of Canada.[11] All the research so far has shown no correlation between the negative concerns regarding milk consumption. There is no connection between milk and high risk of breast, colon, and prostate cancer.[9] Milk has no impact of increased risk of heart disease, stroke, or total mortality.[9] The only concern is for individuals that are lactose intolerant. They lack the enzyme lactase to digest milk which causes a few minor discomforts.

References

  1. ↑ Dunne, J., Evershed, R. P., Salque, M., Cramp, L., Bruni, S., Ryan, K., et.al (2012). “First dairying in green Saharan Africa in the fifth millennium BC”, Nature, 486(7403), 390-4. doi: http://dx.doi.org/10.1038/nature11186 .
  2. ↑ Beja-Pereira, A., Caramelli, D., Lalueza-Fox, C., Vernesi, C., Ferrand, N., Casoli, A., et.al. (2006). “The origin of European cattle: Evidence from modern and ancient DNA”, Proceedings of the National Academy of Sciences. 103 (21), 8113–18. doi:10.1073/pnas.0509210103 .
  3. ↑ Li, xiaochen. “How Is the Pasteurization Process Widely Used in Modern Milk Processing Realized?” Zhihu, 11 Apr. 2015, www.zhihu.com/question/29477974/answer/45756783.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 Park, Young W.; Haenlein, George F.W. (2013). Milk and dairy products in human nutrition: Production, composition, and health. Chichester, West Sussex, UK: John Wiley & Sons. pp. 1–215. ISBN 978-1-118-53422-9.
  5. ↑ Gateway to dairy products and production. FAO.org. (n.d.). Retrieved from http://www.fao.org/dairy-production-products/processing/milk-preservation/en/
  6. ↑ Looi, M. K. (2016, July 27). Scientists may have found a way to extend the shelf life of milk to two months. Retrieved from https://qz.com/740959/science-has-found-a-way-to-extend-the-shelf-life-of-cold-milk-300/
  7. ↑ 7.0 7.1 How Milk Gets from the Cow to the Store - Milk - ProCon.org. (2020, March 26). Retrieved from https://milk.procon.org/how-milk-gets-from-the-cow-to-the-store/
  8. ↑ 8.0 8.1 Dairy Nutrition (2020). Nutrients in milk products. Retrieved from https://www.dairynutrition.ca/nutrients-in-milk-products
  9. ↑ 9.0 9.1 9.2 9.3 Kurzgesagt-In a Nutshell (2020, January 26). Milk. White Poison or Healthy Drink? [Video]. YouTube. https://www.youtube.com/watch?v=oakWgLqCwUc
  10. ↑ 10.0 10.1 Dairy Farmers of Canada. (2019). Our Commitment to Food Safety. Retrieved from http://www.dairyfarmers.ca/our-commitments/to-food-safety
  11. ↑ Government of Canada. (2020, August 8). Food and Drug Regulations - Division 8 Dairy Products. Retrieved from http://laws-lois.justice.gc.ca/eng/regulations/C.R.C.,_c._870/page-87.html#h-74

Final Exam Question

Which one(s) is/are the characteristics of casein?

A.Casein, a kind of enzyme that acts an important role in making the grande cheese ？

B.casein acts as an emulsifier preventing the fat globules to separate (cream) from the skim milk portion.

C. Casein, milk protein, is a stabilizer that increases the viscosity of the continuous phase. (NOT A CHARACTERISTIC)

D.  casein forms a gel structure in the cheese curd.

Answer: according to lesson 2 in the protein section, it was stated that B.) casein acts as an emulsifier preventing the fat globules to separate (cream) from the skim milk portion and D.) forms a gel structure in the cheese curd.

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