WPI is easier to digest because filtering removes the lactose content... However it would appear that this time frame is negligble...
There are 2 different types of filtering used to manufacture WPI. Ion Exchange or running it through filters,
Ion Exchange WPI reduces Biofractions (Not BCAA's it appears that alot of people including myself make this mistake)
Bio Fractions include
Beta-lactoglobulin
Alpha-lactalbumin
Glycomacropeptide
Immunoglobulin G (IgG) heavy Chain
Immunoglobulin G (IgG) Light Chain
Bovine serum albumin
Lactoferrin
http://whirlpool.net.au/wiki/exercise_faqs_whey
What's the difference between WPC and WPI?
Basics
WPC has a slightly lower concentration of protein, and absorbs a little slower than WPI. The benefit of this is that the rise in amino acids (building blocks of protein) in the bloodstream lasts longer than with WPI. This means that the benefits of whey intake – increased muscle building capacity – last longer with WPC than WPI, with little if any tradeoff.
Some argue that WPI is beneficial straight after a workout, while WPC is better at most other times. Despite this, WPC is still considered a fast absorbing source of protein when compared to other quality sources like casein and is therefore useful at any time around a workout or between meals1.
Casein, being a much slower absorber than the other two, may be useful at night before bed due to the long time before another meal.
In detail
A telling finding has been made by comparing the slow-digesting casein with the relatively fast-digesting WPC. As described in the Wilson and Wilson paper, athletes retain more protein and thus gain more benefit when the protein source is absorbed more slowly1. However, taking WPC in frequent, small doses (30 grams over four hours) mimics the benefits of slow-digesting casein and in fact leads to the greatest overall retention of protein – and thus potential for muscle growth.
This would suggest, without actually confirming it, that the slightly slower absorbing WPC might give a greater overall benefit than the faster absorbing WPI – unless you're willing to take WPI every 20 minutes.
Regardless, both WPC and WPI are considered very high "quality" protein sources, with WPC being high in leucine, a vital amino acid for regulating muscle building.
For even greater depth of answers, two highly-recommended sources of information are Wilson and Wilson (2006) as cited below and Campbell (2007), freely available at
http://www.jissn.com/content/4/1/8.
WPI is easier to digest because filtering removes the lactose content...
Also Ion Exchange removes Biofractions
Bio Fractions include
Beta-lactoglobulin
Alpha-lactalbumin
Glycomacropeptide
Immunoglobulin G (IgG) heavy Chain
Immunoglobulin G (IgG) Light Chain
Bovine serum albumin
Lactoferrin
Bodybuilding.com - The Rundown On Protein: Your Questions Answered!
WPI is made similarly to WPC except WPI undergoes an additional step of purification. In general there are two different ways to make WPI. One way is to use an ion-exchange column. A second way is to pass it through a series of filters.
Ion-exchange tends to increase the percentage of protein in the end product, but it also removes many of the bioactive fractions of whey that have positive benefits, and increases the content of Beta-lactalbumin, the most allergic sub-fraction in whey.
On the other hand, using a filtering process such as cross flow microfiltration, ultra filtration, micro filtration, reverse osmosis, dynamic membrane filtration, ion exchange chromatography, electro-ultrafiltration, radial flow chromatography, or nano filtration tends to purify the sample while still preserving many of the bioactive fractions in whey. These purification processes remove virtually all of the lactose and fat and what remains is generally as much as 90-96% protein.
Pros:
- A greater percentage of the actual protein powder is pure protein with less fat, lactose, and carbohydrates than with WPC. WPI also tends to be more easily digested than WPC because it has less lactose. It also causes a rapid spike in amino acid levels like WPC.
Cons:
- If ion-exchange is used to purify the powder, some of the bio-active sub fractions of whey are lost. Additionally, WPI is significantly more costly than WPC. WPI also tends to become foamy when mixed. It also has the downfall of a relatively fast clearance time, like WPC.