REAGENT or RESOURCE	SOURCE	IDENTIFIER
Chemicals, peptides, and recombinant proteins
Acetic acid	Sigma-Aldrich	Cat# 338826
Hydrochloric acid	Thermo Fisher Scientific	Cat# 1559100
PBS (without calcium or magnesium, pH 7.2)	Sigma Aldrich	Cat# D8537
Iodixanol solution OptiPrep™ (60% (w/v))	Sigma Aldrich	Cat# D1556
Biological samples
Skim milk/ defatted milk (< 1% fat)	Local sources	n/a
Infant milk formula powder	Local sources	n/a
Other
Optima XPN-100 Ultracentrifuge	Beckman Coulter	Cat# A94469
Type 70.1 Ti Fixed-Angle Titanium Rotor	Beckman Coulter	Cat# 342184 (https://www.beckman.com/centrifuges/rotors/fixed-angle/342184)
SW Type 32 Ti swinging bucket rotor	Beckman Coulter	Cat# 369650 (https://www.beckman.com/centrifuges/rotors/swinging-bucket/369650)
17 mL polyallomer tube	Beckman Coulter	Cat# 344061
38 mL open-top polypropylene tubes	Beckman Coulter	Cat# 326823
pH meter	Mettler Toledo, FiveEasy Standard pH Meter Line	Cat# 30266627
Sorvall ST 8 R centrifuge	Thermo Fisher Scientific	Cat# 75007205
Pal-Ri Refractometer	ATAGO	Cat# 3850
WhatmanTM Grade 1 filter paper (diameter 150 mm)	GE Healthcare Life Sciences	Cat# 1201
0.45-μm membrane syringe filters	Thermo Fisher Scientific	Cat# 15216869
0.22-μm membrane syringe filters	Thermo Fisher Scientific	Cat# 15206869
Disposable needles, 18-gauge, 1.5in. long, w/polypropylene luer-fitting	BD Microlance	Cat# 304622
Disposable syringe, 10 mL, luer-lock, sterilized	VWR	Cat# 613-2008