When we use the word “milk”, in Italy at least, we mean cow’s milk, but the term is also used for its other variants (sheep’s milk, buffalo’s milk etc)
- In all cases, water is the main component;
- Fats, mostly saturated, are the main energy source found in milk, generally in the form of triglycerides. In commercial whole milk taken from cows, there are 3.5 – 3.7 g of fat per 100 ml. This is reduced to 1.5 – 1.8% in semi-skimmed milk, and to less than 0.5% in skimmed milk.
- The sugars in milk, which are its second highest energy source, are almost entirely made up of the disaccharide known as lactose. Cow’s milk contains around 4.9 g of lactose per 100 ml
- Two thirds of the proteins found in milk are made up of casein. The remainder consists of serum proteins or whey proteins, which can be separated from the casein when the milk coagulates. Among these are lactoglobulin, lactalbumin and lactoferrin. Milk proteins have a high biological value since they supply all the amino acids that the body cannot synthesise itself (“essential” amino acids). These make up 3.1-3.4% of the composition of cow’s milk;
- Mineral substances, especially calcium, but also phosphorus, potassium, magnesium, zinc, selenium;
- B vitamins, vitamin C, and the fat-soluble vitamins A, D and E. However, the content of fat-soluble vitamins is very low in skimmed milk.
Milk nearly always undergoes a heat treatment to make it “safe”, which allows it to be stored for different lengths of time. The heat treatments used today to reduce the bacteria in milk only marginally lower the content of some water-soluble vitamins.
So, commercially, there are many different types of milk:
- “Fresh pasteurised” which should be kept at 4-6°C (in the fridge) for 6 days;
- “Microfiltered and pasteurised” which can be kept for 15-18 days in the fridge;
- “High-temperature pasteurised” which can be kept for 15-18 days in the fridge;
- “UHT (Ultra High Temperature)”, which can be kept for around 3 months at room temperature
Technological improvements and general hygiene have made it possible for Italian and European legislation to allow the sale of raw milk, which is not heat-treated. The sale of raw milk is permitted exclusively between the producer and the consumer, as long as the breeding farm of origin has the appropriate health and hygiene conditions. Raw milk must be boiled before consumption, and is still riskier than heat-treated milk.
Milk and dairy products belong to the second group of foods, which, like those in the first group, contain proteins with high biological value. Unlike the foods in the first group, those in the second do not contain significant amounts of iron, but are good sources of calcium.
Milk should form part of a healthy diet for those of all ages. The 2003 guidelines of the Italian National Research Institute for Food and Nutrition (now called CRA-Nut) recommend the consumption of 3 portions (one portion = 125 ml) a day of milk or yoghurt, to which can be added, according to the energy needs of the individual, 2 or 3 weekly portions of cheese (each portion totaling 50 g for hard cheeses and 100 g for soft cheeses).
Department of Agricultural and Food Sciences
University of Bologna