That depends on what system you are using and why you want to increase osmolality. Sometimes salts are fine, other times, people want a nonionic system. In many cases, people use sugars because they do not alter the ionic nature of the system. For that purpose, low molecular weight and absence of reactive groups is desirable. Non-reducing sugars and sugar alcohols seem to be best suited. Some examples include glycerol, sorbitol, mannitol, erythritol, maltitol, sucrose, and trehalose, 

Dear Carlos,

the KCl in high concentration is very toxic. Much better is to use the NaCl, which is not toxic a has lower molar mass (58,4 g/mol), usable is also the glucose with the molar mass 180,2 g/mol. The osmolality is directly proportional to the concentration, therefore the concentration should not be low with the existing compounds used for food purposes.

Best regards

Pavel

Dear Carlos Álvarez, 

 1) You want to make a food grade solution with a high value of osmolality.

 2) The osmotic pressure π of a solution is related to its water activity aW in the following way:

π = - (R • T • lnaW) / Vw

in which:

π = osmotic pressure  [Pa];

R = general gas constant; R = 8.31 J/(K mol);

T = temperature in K  (K = oC + 273);

ln = natural logarithm; so a logarithm with e = 2.718...  as base;

aW = water activity of the solution [-];

Vw = molar volume [in m3/mol] of water in the solution,

Vw = volume [in m3] of  1 mole of water (= 18 g of water) in the solution, 

Vw in [m3/mol water].

3) Thus a solution which has a low water activity aW, will have a high osmotic pressure.

If you find a food grade component at a concentration which will give the lowest water activity aW (without causing a saturated solution), this solution will also have the highest osmotic pressure π.

4) The Excel document “Water Activity aW Calculations (2.0) of Aqueous Solutions and of Solids Mixtures - Raoult - Norris - Ross”, at my Researchgate page, will calculate the water activity of a single component solution, and of multi-component solutions, caused by a considerable number of (food grade) components.

In the Excel document, please use p3) = tab 3 = Norrish-Ross,

a) Start with a total mass of water; 100 g makes an easy reference.

b) Add a number of grams of the solute = the component which should increase the osmotic pressure;

for example add 200 grams of sucrose; the Excel sheet calculates in column G that the contribution of the 200 g of this single component to the water activity is 0,8532; so 100 g of water and 200 g of sucrose have a water activity of aW = 0.8532.

c) Add 35 grams of NaCl; its single contribution to the aW = 0.7653.

d) Add 35 grams of KCl:  its single contribution is aW = 0.8637.

e) Add 100 g of glycerol (laxative; be aware): its single contribution is aW = 0.8110.

CONCLUSION of these 4 example solutions: The largest water activity decrease in these single component solutions is caused by 35 g of NaCl in 100 g of water; So of these example solutions, 35 g of NaCl will also cause the highest osmotic pressure.

5) The water activity reduction, and thus the osmotic pressure increasing effect of several of the components which were named by Greg Cote and Pavel Trávnik, can also be estimated by the Excel spreadsheet.

6) The spreadsheet will also calculate the water activity of a multi-component solution: see at last line “total aW of solution”. Thus you can convert the multi-component aW value to  the osmotic pressure of a multi-component solution by using the equation above at 2).

NOTE:  I did NOT include a warning if two or more solutes are not compatible, e.g. cause flocculation, etc.

6) NOTE: for very concentrated solutions of NaCl and of sucrose, the Excel file indicates “Crystals” if the mass of solute exceeds the maximum solubility. For all other components I have NOT included such a warning.

7) Be aware: not all components listed in the spreadsheet are food grade!

Best Regards,

Janwillem Rouweler

Thanks a lot dear Janwillem!!

All this information is very very useful for my  research. This is exactly what I was looking for.

Thanks a million

With respect

What foods can high-osmolar foods contain?

Tanks