Water is an unusual compound with unique physical properties due to its affinity towards a variety of polar organic compounds such as alcohols like di propylene glycol, propylene glycol, triacetin, ethanol and aldehydes, acids, amines, ketones, etc. which added in flavor and fragrance products. It contains 33427959970647100 molecules per 1.0 microgram of water
Acid: substance containing hydrogen which gives free hydrogen (H +) when dissolved in water
Polarity & hydrogen bonding:
The oxygen atom also has two lone pairs of electrons. The charge differences cause water molecules to be attracted to each other and to other polar molecules like alcohols, aldehydes, amines etc.
A single water molecule can participate in a maximum of four hydrogen bonds; any polar organic compound with hetero atoms like O and N will form the hydrogen bond with the water molecule. These hydrogen bonds are constantly breaking, with new bonds being formed with different molecules.
What is a limit test or residuals test, impurity test, toxins test?
Limit ingredients are nothing but the components which affect the quality, stability, and safety of the products. These elements need to control in the products.
Here, a presence of residual water in flavor fragrance ingredients may affect the quality of goods. Simply, a limit test is nothing but any testing which has only the upper specification like < 0.1 %, < 5.0 ppm etc.
Water, acids, etc. may not be added as the ingredient in flavor and fragrances but it may be the carryover from raw materials, so these should be minimized to increase the consistency of flavor fragrances product’s quality
Water Activity in Flavor Fragrances:
Water in the presence of acid/base will induce some internal reactions in flavor and fragrance like esterification, ester hydrolysis, acetal, ketal, Schiff’s base formation; water and acids will be available as residuals in the F&F Ingredients for these reactions.
these reaction products will influence the smell and color of the products; sometimes these will be called as maturation but in the high level of reaction products will totally change the flavor fragrances profile.
Acetal, ketal, and Schiff’s base formations are equilibrium reactions, and no catalyst will influence this reaction, can be minimized only by minimizing the reactants especially the residual water and acids in flavor fragrance ingredients.
Le Chatelier’s principle:
If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new one is established.
When more reactants, A and/ B is added, the equilibrium shifts to reduce A and B by producing more C and D
When more products, C and/ D is added, the equilibrium shifts to reduce C and D by producing more A and D.
Acetal or Ketal Reaction
Aldehyde reacts with Alcohol to form Acetal and water; Ketone reacts with Alcohol to form Ketal and water.
Esterification and Ester hydrolysis:
Esterification and Ester’s hydrolysis is occurring in the presence of acid or hydronium ion to give ester or alcohol and acid as below.
esterification is not equilibrium reaction rather it is reversible reaction, a reversible reaction is a reaction where the reactants form products, which react together to give the reactants back
Schiff’s Base Reaction:
Some of the Schiff bases with precipitates in the internal reaction as it is un-dissolved solid in the fragrance, H2O is the by-product in esterification, acetal, ketal and Schiff’s base formation
Many other reactions and products are possible in flavor and fragrance products like aldol condensation, dimer/polymerization, oxidation, anhydride formation etc. we discuss only the reactions induced by hydronium ions and control the water activity in the flavor and fragrance products.
Determination of water in flavor and fragrance’s raw materials and stable its quality:
It is highly recommended to determine and control the water content in polar perfumery ingredients, mainly the ingredients which is used in large quantity
There are two techniques in Karl Fischer Titration namely volumetric and coulometric Karl Fischer Titrations as below:)
Volumetric titration is good enough for flavor and fragrance ingredients for water content determination and the comparison is shown below
Selection Karl Fischer Method:
Sample contains aldehyde, ketone will not be suitable to analyze the regular KF Solvent and reagent as it will produce water by reacting with methanol which is present in KF reagent as well as used as medium in the regular KF Titration.
Volumetric Karl Fischer Titration with non-methanol solvent:
Karl Fischer volumetric method can be employed for flavor fragrance ingredients and products to determine the water activity; there are commercially available KF reagent and medium especially for aldehyde and ketone containing samples from Sigma and Merck.
Water content is a critical factor in the reaction of acetal, ester, Schiff base formation etc. therefore it should be controlled by Karl Fischer Titration by determination of water content in flavor fragrances ingredients y in polar ingredients which is used in large quantities in the Flavor and fragrance.