Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: 6/6/2013
Publication Date: 7/9/2013
Citation: Ren, D., Van Hekken, D.L., Tunick, M.H., Tomasula, P.M. 2013. Comparison of the in vitro digestion of raw pasture milk and commercial HTST and UHT pasteurized milk. Joint Meeting of the ADSA, AMSA, ASAS and PSA. 96: E-Suppl. 1,78, T220.
Technical Abstract: Consumption of raw milk from pasture-fed cows, typically purchased at local farms, is steadily increasing in the US because many consumers believe that high-temperature short-time (HTST) or ultrahigh temperature (UHT) pasteurization affects the digestibility of milk proteins and thus the bioavailability of their nutrients. The objective of this study was to compare the evolution of curd or clot size distribution with time during in vitro digestion of protein under simulated fasting gastro-intestinal conditions for commercial whole and skim milk treated by HTST or UHT pasteurization and raw whole and skim milk from pasture-fed cows. Milk digestion procedures followed the 2012 US Pharmacopeia with simulated gastric fluid (SGF) using pepsin and simulated intestinal fluid (SIF) using pancreatin. The in vitro protein digestibility of the whole milk samples was greater than that of the skim milk samples (P < 0.05), with milk fat acting as a barrier to the protein aggregation observed in the skim milk samples. In a second series of experiments, the degradation kinetics of clots that formed upon initiation of SGF digestion were followed for 3 h using a light-scattering particle-size analyzer. The average clot sizes of the proteins upon initiation of digestion decreased in the order raw pasture>HTST>UHT milk with the clot sizes for skim milk (130.5, 128.3 and 52.9 um, respectively) being larger than those for whole milk (98.5, 86.3 and 32.7 um) (P<0.05). After 3 h of digestion, a single particle-size peak was observed for all samples. With the exception of the UHT milk samples, the clot sizes in skim milk samples averaged 38.5 micrometer and were larger than those in whole milk which averaged 29.3 um (P < 0.05). Protein clot sizes of the skim and whole milk UHT samples averaged 8.0 um (P < 0.05), indicating that UHT milk was the most digestible since the smaller clot sizes offered increased surface area for enzyme contact. The results showed an inverse relationship between clot size and extent of in vitro digestibility. Moreover, the results indicate that raw pasture milk is as digestible as commercial HTST milk and not as digestible as commercial UHT milk.