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Pasteurisation, UHT, microfiltration...All the processes don't affect the nutritional quality of milk in the same way

Heat treatments applied to milk provide the consumer with somewhat long-term stability, but their effect on protein quality is often compromised. Despite this, their impact has never been measured in vivo in humans, though, in France, UHT milk accounts for 90% of milk consumption...

Trois types de  LAIT  UHT normalisé (entier, demi écrémé, écrémé ). Cruche et verre de  LAIT  UHT demi écrémé.. © INRA, BOSSENNEC Jean-Marie
Updated on 06/04/2013
Published on 07/26/2010

Pasteurised or UHT Milks : the heat treatments may affect the nutritional quality of proteins

Milk is mainly consumed in its pasteurised form in industrial countries, but in some European countries such as France, UHT milk accounts for 90% of milk consumption.

Microfiltration was recently developed as a microbiological stabilisation treatment that does not denature the organoleptic qualities of milk. The protein fraction constitutes a major nutritional benefit of milk, along with calcium. However, heat treatments can lead to structural modifications that are well recognised at this time and that may affect the nutritional quality of proteins. These modifications can, for example, induce a loss of certain amino acids or the formation of neoformed protein aggregates (Léonil et al., 1997; Guyomarc et al., 2003).

Nevertheless, no data exists today that enable us to quantify these structural alterations during treatment in humans.

The digestive tract of milk proteins monitored on healthy volunteers

Healthy volunteers (n = 24) drank the equivalent of a half litre of microfiltred, pasteurised or UHT milk. The milk proteins were intrinsically marked beforehand with 15N nitrogen. This stable isotope, thus representative of milk proteins, was monitored in different nitrogen pools (urea, amino acids and plasma proteins, urinary urea) for 8 h after the meal. 15N nitrogen found in urea is considered to be irreversibly lost and therefore not retained by the organism.

We show that the kinetics and the 15N nitrogen transfer balance in nitrogen pools are identical between pasteurisation and microfiltration, indicative of a similar metabolic utilisation of the milk proteins. In contrast, an increase in the transfer of 15N nitrogen in all of the nitrogen pools studied was observed for the UHT milk, resulting in an increase of 7% in food nitrogen losses in the urea. However, we also observed that the incorporation of food nitrogen into plasma proteins is increased in UHT milk, evidence of the good capacity of food amino acids to sustain protein syntheses. As a result, the most plausible hypothesis to explain the increase of irreversible losses of food nitrogen in the case of UHT milk is an acceleration of the gastric emptying kinetics and not a biochemical modification of the proteins. The acceleration of digestive kinetics is a major factor in the stimulation of food amino acid catabolism.

The hypothesis of an acceleration of the kinetics of UHT milk proteins is most certainly linked to the fact that the UHT treatment leads to a greater particle scattering of casein micelles due to the formation of soluble aggregates induced by heat and less apt to precipitate in the stomach.

How to preserve the nutritional quality of proteins?

The nutritional quality of proteins in UHT milk could therefore be preserved by modulating their gastric emptying speed, thus emphasizing the need to study food digestion mechanisms, a project to be carried out in partnership with nutritionists from INRA’s Nutrition, Chemical Food Safety and Consumer Behaviour division.

A partnership between Biochemists, Physico-chemists, Nutritionists and the dairy sector

This work is part of an integrated project between the division for Science and Process Engineering of Agricultural Product and the division for Nutrition, Chemical Food Safety and Consumer Behaviour. It has been funded by the Ministry of Research and the dairy sector, Arilait Recherches

Scientific contact(s):

  • Joëlle Léonil Science et Technologie du Lait et de l'Oeuf, INRA-AGROCAMPUS Ouest, 65 rue de Saint-Brieuc, 35042 RENNES, France
  • Claire Gaudichon Physiologie de la Nutrition et du Comportement Alimentaire, INRA-AgroParisTech, 16 rue Claude Bernard, 75231 PARIS, France

Find out more

  • Lacroix M, Bon C, Bos C, Léonil J, Benamouzig R, Luengo C, Fauquant J, Tomé D, Gaudichon C. Ultra high temperature treatment, but not pasteurization, affects the postprandial kinetics of milk proteins in humans. J Nutr. 2008 ;138(12):2342-7