Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2017
Publication Date: 7/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5729351
Citation: Van Hekken, D.L., Tunick, M.H., Ren, D.X., Tomasula, P.M. 2017. Comparing the impact of homogenization and heat processing on the properties and in vitro digestion of milk from organic and conventional dairy herds. Journal of Dairy Science. 100:6042-6052.

Interpretive Summary: Many American consumers believe that organic and grass-fed dairy foods are healthier than products from conventional farms. The reported differences between organic/grass-fed and conventional sourced fluid milk are often based on the raw product and do not account for the impact that processing may have on the properties of the packaged product. In this study, raw whole milk from organic (over 50% of feed energy is from pasture) and conventional (no access to pasture) farms were processed with various combinations of homogenization, pasteurization, and ultra-high temperature (UHT) pasteurization; and subjected to simulated gastrointestinal digestion. Findings showed that milk from the organic/grass-fed and conventional herds responded in similar ways to the typical homogenization, pasteurization and UHT pasteurization processing steps used by the U.S. dairy industry. Only minor differences were noted among the properties and digestion of samples from the organic and conventional herds although the organic herd had higher amounts of healthy lipids, omega-3 fatty acids and conjugated linoleic acid, than the milk from the conventional herd. Findings from this research enhance our knowledge of the impact of processing on the traits and digestibility of milk from organic/grass-fed and conventional herds and will help health conscious consumers make informed decisions on dairy selections.

Technical Abstract: The effects of homogenization and heat processing on the chemical and in vitro digestion traits of milk from organic and conventional herds were compared. Raw milk from organic (>50% of dry matter intake from pasture) and conventional (no access to pasture) farms were adjusted to commercial whole and nonfat milk fat standards, processed with or without homogenization and either high temperature, short time or UHT pasteurization; and then underwent in vitro gastrointestinal digestion. Comparison of milk from the organic and conventional herds showed that they responded to processing in similar ways. General composition was the same for the whole milk samples, as were the skim milk samples. Protein profiles were similar with intact caseins and whey proteins being predominant and only minor amounts of peptides. All of the raw and processed whole milk samples from the grazing cows contained higher levels of the omega-3 fatty acids and the conjugated linoleic acid (CLA) and tended to be lower in myristic, palmitic, stearic and oleic acids; processing resulted in minor (P > 0.05) shifts in FA distribution. Of the nine volatile compounds evaluated, milk from the organic herd contained lower levels of 2-butanone and milk from both farms showed spikes for heptanal in the UHT samples, and spikes for butanoic acid, octanoic acid, nonanoic acid, and N-decanoic acid in homogenized samples. At the start of in vitro digestion, raw and pasteurized non-fat milk samples from the organic herd formed larger acid curds (P < 0.05) and all of the organic samples tended to have higher zeta-potentials during gastric digestion than the samples from the conventional herd. Milk from the organic herd had lower levels of free fatty acids than the milk from conventional herds. In vitro proteolysis was similar in milk from both farms and resulted in 85-95% digestibility and a plethora of casein phosphopeptides within 120 min. Overall, milk from the organic/grass-fed and conventional herds responded in similar ways to the typical homogenization and heat processing steps used in the U.S. dairy industry and showed only minor differences in chemical traits and in vitro digestion. Findings from this research enhance our knowledge of the impact of processing on the chemical traits and digestibility of milk from organic/grass-fed and conventional herds and will help health conscious consumers make informed decisions on dairy selections.