
Saponification value or saponification number (SV or SN) represents the number of milligrams of
potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...
(KOH) or
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly corrosive base (chemistry), ...
(NaOH) required to
saponify one gram of
fat
In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food.
The term often refers specif ...
under the conditions specified.
It is a measure of the average
molecular weight
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
(or chain length) of all the
fatty acid
In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...
s present in the sample in form of
triglyceride
A triglyceride (from '' tri-'' and '' glyceride''; also TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids.
Triglycerides are the main constituents of body fat in humans and other vertebrates ...
s. The higher the saponification value, the lower the fatty acids average length, the lighter the mean molecular weight of triglycerides and vice versa. Practically, fats or oils with high saponification value (such as coconut and palm oil) are more suitable for
soap
Soap is a salt (chemistry), salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. In a domestic setting, soaps, specifically "toilet soaps", are surfactants usually u ...
making.
Determination
To determine saponification value, the sample is treated with an excess of
alkali
In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...
(usually an
ethanol
Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
ic solution of potassium hydroxide) for half an hour under
reflux. The KOH is consumed by reaction with triglycerides, which consume three equivalents of base.
Diglycerides consume two equivalents of KOH.
Monoglyceride
Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differe ...
s and free fatty acids, as well as other esters such as
lactones, consume one equivalent of base.
At the end of the reaction the quantity of KOH is determined by
titration
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of Quantitative research, quantitative Analytical chemistry, chemical analysis to determine the concentration of an identified analyte (a substance to be ...
using standard solution of
hydrochloric acid
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
(HCl). Key to the method is the use of
phenolphthalein
Phenolphthalein ( ) is a chemical compound with the chemical formula, formula carbon, C20hydrogen, H14oxygen, O4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in ...
indicator, which indicates the consumption of strong base (KOH) by the acid, not the weak base (potassium carboxylates). The SV (mg KOH/ g of sample) is calculated as following:
:where:
:
is the volume of HCl solution used for the blank run, in mL;
:
is the volume of HCl solution used for the tested sample, in mL;
:
is the
molarity
Molar concentration (also called molarity, amount concentration or substance concentration) is the number of moles of solute per liter of solution. Specifically, It is a measure of the concentration of a chemical species, in particular, of a solu ...
of HCl solution, in mol / L;
: is the molecular weight of KOH, in g / mol;
:
is the weight of sample, in g.
For example, standard methods for determination of SV of vegetable and animal fats are as follows:
The SV can also be calculated from the fatty acid composition as determined by
gas chromatography
Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for Separation process, separating and analyzing compounds that can be vaporized without Chemical decomposition, decomposition. Typical uses of GC include t ...
(
AOCS Cd 3a-94).
Handmade
soap makers who aim for
bar soap use
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly corrosive base (chemistry), ...
(NaOH), commonly known as
lye
Lye is the common name of various alkaline solutions, including soda lye (a solution of sodium hydroxide) and potash lye (a solution of potassium hydroxide). Lyes are used as cleaning products, as ingredients in soapmaking, and in various other c ...
, rather than KOH (caustic potash) which produces soft paste, gel or liquid soaps. In order to calculate the lye amount needed to make bar soap, KOH values of SV can be converted to NaOH values by dividing KOH values by the ratio of the molecular weights of KOH and NaOH (1.403).
Calculation of average molecular weight of fats and oils
The theoretical SV of a pure triglyceride molecule can be calculated by the following equation (where MW is its molecular weight):
:where:
:3 is the number of fatty acids residues per triglyceride
:1000 is the conversion factor for milligrams to grams
:56.1 is the molar mass of KOH.
:38.049 is the molecular mass of glycerol backbone
For instance,
triolein
Triolein (glyceryl trioleate) is a symmetrical triglyceride derived from glycerol and three units of the unsaturated fatty acid oleic acid. Most triglycerides are unsymmetrical, being derived from mixtures of fatty acids. Triolein represents 4� ...
, a triglyceride occurring in many fats and oils, has three
oleic acid
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish due to the presence of impurities. In chemical terms, oleic acid is cl ...
residues esterified to a molecule of
glycerol
Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...
with a total MW of 885.4 (g / mol). Therefore, its SV equals 190 mg KOH / g sample.
In comparison, trilaurin with three shorter fatty acid residues (
lauric acid) has a MW of 639 and an SV of 263.
As it can be seen from equation (2), the SV of a given fat is inversely proportional to its molecular weight. Actually, as fats and oils contain a mix of different triglycerides species, the average MW can be calculated according to the following relation:
This means that
coconut oil
Coconut oil (or coconut fat) is an edible oil derived from the kernels, meat, and milk of the coconut palm fruit. Coconut oil is a white solid fat below around , and a clear thin liquid oil at higher temperatures. Unrefined varieties have a disti ...
with an abundance of medium chain fatty acids (mainly lauric acid) contain more fatty acids per unit of weight than, for example,
olive oil
Olive oil is a vegetable oil obtained by pressing whole olives (the fruit of ''Olea europaea'', a traditional Tree fruit, tree crop of the Mediterranean Basin) and extracting the oil.
It is commonly used in cooking for frying foods, as a cond ...
(mainly oleic acid). Consequently, more
ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
saponifiable functions were present per g of coconut oil, which means more KOH is required to saponify the same amount of matter, and thus a higher SV.
The calculated molecular weight (Eq. 3) is not applicable to fats and oils containing high amounts of unsaponifiable material, free fatty acids (> 0.1%), or
mono-
Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example:
* triangle, quadrilateral, pentagon, hexagon, oc ...
and
diacylglycerols (> 0.1%).
Unsaponifiables
Unsaponifiables are components of a fatty substance (
oil,
fat
In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food.
The term often refers specif ...
,
wax) that fail to form
soap
Soap is a salt (chemistry), salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. In a domestic setting, soaps, specifically "toilet soaps", are surfactants usually u ...
s when treated with alkali and remain insoluble in water but soluble in organic solvents. For instance, typical
soybean oil
Soybean oil (British English: soyabean oil) is a vegetable oil extracted from soybean (''Glycine max'') legumes. It is one of the most widely consumed cooking oils and the second most consumed vegetable oil. As a drying oil, processed soybean oil ...
contains, by weight, 1.5 – 2.5% of unsaponifiable matter. Unsaponifiables include nonvolatile components :
alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
s,
sterol
A sterol is any organic compound with a Skeletal formula, skeleton closely related to Cholestanol, cholestan-3-ol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on ...
s,
triterpene
Triterpenes are a class of terpenes composed of six isoprene units with the molecular formula C30H48; they may also be thought of as consisting of three terpene units. Animals, plants and fungi all produce triterpenes, including squalene, the pre ...
s,
fatty alcohol
Fatty alcohols (or long-chain alcohols) are usually high-molecular mass, straight-chain primary alcohols, but can also range from as few as 4–6 carbon atoms to as many as 22–26, derived from natural fats and oils. The precise chain length vari ...
s,
tocopherol
Tocopherols (; TCP) are a class of organic compounds comprising various methylated phenols, many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was named ''t ...
s and
carotenoid
Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...
s as well as those that mainly result from the saponification of
fatty esters (sterols esters, wax esters, tocopherols esters, ...). This fraction may also contain environmental contaminants and residues of
plasticizers,
pesticide
Pesticides are substances that are used to control pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for approximately 50% of all p ...
s,
mineral oil
Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils.
The name 'mineral oil' by itself is imprecise, ...
hydrocarbons and aromatics.
Unsaponifiable constituents are an important consideration when selecting oil mixtures for the manufacture of soaps. Unsaponifiables can be beneficial to a soap formula because they may have properties such as
moisturization,
conditioning,
antioxidant
Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
, texturing etc. On the other hand, when proportion of unsaponifiables is too high (> 3%), or the specific unsaponifiables present do not provide significant benefits, a defective or inferior soap product can result. For example,
shark oil is not suitable for soap making as it may contain more than 10% of unsaponifiable matter.
For edible oils, the tolerated limit of unsaponifiable matter is 1.5% (olive, refined soybean), while inferior quality crude or
pomace
Pomace ( ), or marc (; from French ''marc'' ), is the solid remains of grapes, olives, or other fruit after pressing (wine), pressing for juice or Vegetable oil, oil. It contains the skins, pulp, seeds, and stems of the fruit.
Grape pomace has ...
oil could reach 3%.
Determination of unsaponifiables involves a saponification step of the sample followed by extraction of the unsaponifiable using an organic solvent (i.e.
diethyl ether
Diethyl ether, or simply ether, is an organic compound with the chemical formula , sometimes abbreviated as . It is a colourless, highly Volatility (chemistry), volatile, sweet-smelling ("ethereal odour"), extremely flammable liquid. It belongs ...
). Official methods for animal and vegetable fats and oils are described by
ASTM
ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...
D1065 - 18,
ISO
The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries.
Me ...
3596: 2000 or 18609: 2000,
AOCS method Ca 6a-40.
Saponification values and unsaponifiables of various oils and fats
See also
*
*
*
*
*
*
*
*
*
*
Soapmaking — Small scale process of producing soap
References
{{reflist
Analytical chemistry