Milk-and-Dairy-Products-in-Human-Nutrition-FAO

Chapter 3 – Milk and dairy product composition 71
at the time of processing. When the UHT treatment is combined with aseptic packaging,
it results in a commercially sterile product”.
The process criteria are reported to be the following: “UHT treatment is
normally in the range of 135 to 150 °C in combination with appropriate holding
times necessary to achieve commercial sterility. Other equivalent conditions can be
established through consultation with an official or officially recognized authority.
Validation of milk flow and holding time is critical prior to operation”.
Typical UHT heating times are 2–10 seconds at 135–150 °C (Montilla, Moreno
and Olano, 2005). Although UHT milk used to be mainly cow milk, recently other
UHT milks have become available in several countries, such as UHT goat milk in
the UK and Italy and UHT buffalo milk in India, UK and Egypt.
Commercial sterilization: “The application of heat at high temperatures for a time
sufficient to render milk or milk products commercially sterile, thus resulting in
products that are safe and microbiological stable at room temperature”.
The typical condition for sterilizing milk is heating at 110–140 °C for 20–30 minutes
(Montilla, Moreno and Olano, 2005).
Impact of heat treatment and storage on the nutrient profile of milk
The literature mainly covers the effects of pasteurization or UHT treatment on milk
composition. Few studies are available on sterilization, and these generally concern
infant formula. The main effects of heat treatment that are of nutritional significance
are: (i) degradation of vitamins; (ii) denaturation of whey proteins (which can be beneficial,
improving protein digestibility and decreasing their allergenic properties); (iii)
Maillard reactions between reducing sugars and the epsilon amino groups of lysine
residues in proteins; and (iv) reactions of lactose. These effects are discussed below.
Degradation of vitamins
The effects of heat processing and storage on water-soluble vitamins in milk have
been well-documented, although most studies are fairly old. Vitamin C is particularly
prone to degradation during processing because of its high susceptibility to
oxidation in the presence of oxygen and metal ions, and to degradation during heat
treatment (Gliguem and Birlouez-Aragon, 2005). Other factors that influence the
nature of the degradation mechanism of vitamin C are salt and sugar concentrations,
pH, enzymes, the initial concentration of ascorbic acid and the ratio of ascorbic acid
to dehydroascorbic acid (Andersson and Öste, 1994). Riboflavin is very sensitive
to light and UV radiation but relatively stable to heat and atmospheric oxygen.
Thiamine is sensitive to heat and alkaline conditions.
Losses in vitamin C, folate and vitamin B 12 increase with increased severity of
treatment, and sterilization caused significant losses of all vitamins shown above
except riboflavin (Figure 3.4). Vitamin C degradation is particularly influenced by
the presence of dissolved oxygen in milk: when milk was UHT treated without
degassing, 82 percent of the ascorbic content was lost (Andersson and Öste, 1994).
Several studies looked at the effect of packaging materials and storage conditions on
vitamin stability. Vitamin C content of raw and heat treated milks decreased significantly
even during storage for two weeks in a freezer. It is important to note that
degradation during storage occurs even in vitamin C-fortified milk (semi-skimmed