Effect of high hydrostatic pressure processing on in vitro digestion of milk proteins and fats

Abstract Text: The use of high hydrostatic pressure processing (HPP) is increasing in popularity in the food industry. Its ability to modify milk proteins and fats suggests that it may be useful in creating foods that suppress appetite; however, its effect on the digestibility of proteins and fats is unclear.  The objective of this study was to compare the change in clot size with time during in vitro simulated fasting gastro-intestinal digestion of protein and fat for HPP-treated raw whole milk (WP), homogenized raw whole milk (WHP), and skim milk (SP) to that of untreated raw whole (WR) and raw skim milk (SR), and WR and SR milk treated by HTST pasteurization (72ºC, 15 s) with or without homogenization.  HPP was conducted at 600 MPa (3 min, 21ºC). Milk digestion procedures followed the 2012 US Pharmacopeia using simulated gastric fluid (SGF) for 1 h followed by simulated intestinal fluid for 2 h. The average particle size of WR 8.5 ± 0.3 µm remained unchanged with all processing treatments while the average particle size of SR increased from 1.3 ± 0.3 µm to 4.6 ± 0.6 µm with HPP treatment only. The clots that formed upon addition of SGF for WR and SR and with the various processing treatments were then followed for 3 h using a light-scattering particle-size analyzer. The clot sizes of processed WR samples were > those for the raw samples but were not different after 3 h.  The clot size for SR was < that for SP after 3 h but the amounts of SR and SP protein digested were not different (P < 0.05). In vitro % protein digestibilities of WR and SR were similar regardless of treatment, ranging from 85-90%, except for HPP-treated WR and SR which ranged from 62-70%. Free fatty acid release (FFAR) decreased in the order WHP>WR>WP, indicating that WHP was the most digestible due to the increased surface area for enzyme contact and fat breakdown.  Stearic and oleic acids, located on the outside of the triglyceride molecule, degraded approximately twice as fast as the other fatty acids. FFAR for WP was 40% < that of WR. Results indicate that HPP processing may possibly be used to moderate in vitro protein and fat digestion of milk.

Keywords: high pressure processing; digestibility; free fatty acids