Acid value

For example, for analysis of crude oil:{{Cite patent |number=CN103776825A |title=Determining method of acid value of deep-color grease |gdate=2014-05-07 |inventor1-first=Ji |inventor1-last=Junmin |inventor2-first=Wang |inventor2-last=Dongmin |inventor3-first=Liu |inventor3-last=Huamin |url=https://patents.google.com/patent/CN103776825A/en}}

:$AV=(V\_\{eq\}-b\_\{eq\})N\backslash frac\{\backslash text\{56.1\; g/mol\}\}\{W\_\backslash text\{oil\}\}$

:Where KOH is the titrant, wherease crude oil is the titrand.

:{{mvar|V{{sub|eq}}}} is the volume of titrant (ml) consumed by the crude oil sample and 1 ml of spiking solution at the equivalent point,

:{{mvar|b{{sub|eq}}}} is the volume of titrant (ml) consumed by 1 ml of spiking solution at the equivalent point,

:56.1 g/mol is the molecular weight of KOH,

:{{math|W{{sub|oil}}}} is the mass of the sample in grams.

The normality (N) of titrant is calculated as:

:$N\; =\; \backslash frac\{1000\; \backslash times\; W\_\backslash text\{KHP\}\}\{\backslash text\{204.23\; g/mol\; \}\; \backslash times\; V\_\{eq\}\}$

:Where {{math|W{{sub|KHP}}}} is the mass (g) of potassium hydrogen phthalate (KHP) in 50 ml of KHP standard solution,

:{{mvar|V{{sub|eq}}}} is the volume of titrant (ml) consumed by 50 ml KHP standard solution at the equivalent point,

:204.23 g/mol is the molecular weight of KHP.

An increment in the amount of FFAs in a fat or oil sample indicates hydrolysis of triglycerides. Such reaction occurs by the action of lipase enzyme and it is an indicator of inadequate processing and storage conditions. The source of the enzyme can be the tissue from which the oil or fat was extracted or it can be a contaminant from other cells including microorganisms.

For determining the acid value of mineral oils and biodiesel, there are standard methods such as ASTM D 974 and DIN 51558, and especially for biodiesel the European Standard EN 14104 and ASTM D664 are both widely used worldwide. Acid value of biodiesel should be lower than 0.50 mg KOH/g in both EN 14214 and ASTM D6751 standard fuels. This is because the FFAs produced can corrode automotive parts, hence these limits protect vehicle engines and fuel tanks.

Low acid value indicates good cleansing by soap.{{cite book |doi=10.1016/B978-1-63067-065-8.50012-8 |quote=Lower acid value means more cleansing (detergency). |chapter=Glossary |title=Soap Manufacturing Technology |date=2016 |last1=Spitz |first1=Luis |pages=267–280 |isbn=978-1-63067-065-8 }}

When oils and fats become rancid, triglycerides are converted into fatty acids and glycerol, causing an increase in acid value.{{cite journal |last1=Fernando |first1=S |last2=Karra |first2=P |last3=Hernandez |first3=R |last4=Jha |first4=S |title=Effect of incompletely converted soybean oil on biodiesel quality |journal=Energy |date=May 2007 |volume=32 |issue=5 |pages=844–851 |doi=10.1016/j.energy.2006.06.019 |bibcode=2007Ene....32..844F }} A similar situation is observed during aging of biodiesel through analogous oxidation and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester hydrolysis).{{Cite web |title=Acid Value Number or Neutralization Number of Oil |url=https://www.engineersedge.com/lubrication/acid_number_neutralization_number.htm |access-date=2022-10-28 |df=mdy-all |website=www.engineersedge.com}}

Transesterification of waste cooking oil, having high acid value and high water content, can be performed using heteropolyacids such as dodecatungstophosphoric acid (PW12) as a catalyst.{{cite journal |last1=Cao |first1=Fenghua |last2=Chen |first2=Yang |last3=Zhai |first3=Fengying |last4=Li |first4=Jing |last5=Wang |first5=Jianghua |last6=Wang |first6=Xiaohong |last7=Wang |first7=Shengtian |last8=Zhu |first8=Weimin |title=Biodiesel production from high acid value waste frying oil catalyzed by superacid heteropolyacid |journal=Biotechnology and Bioengineering |date=September 2008 |volume=101 |issue=1 |pages=93–100 |doi=10.1002/bit.21879 |pmid=18646228 }}{{Cite patent|number=US 8962873 B2|title=Systems And Methods For Making Bioproducts|gdate=2015-02-24|invent1=A|invent2=Rebecca|invent3=Danny|invent4=Barrie|inventor1-first=Summers William|inventor2-first=Williams|inventor3-first=Gulledge|inventor4-first=Tripp Robert |url=https://lens.org/128-931-785-027-93X}}

In 2007, Sahoo et al. made biodiesel consisting of mono-esters of polanga oil extract of the plant Calophyllum inophyllum produced by triple stage transesterification and blended with high speed diesel, which was then tested for its use as a diesel substitute in a single cylinder diesel engine.{{cite journal |last1=Sahoo |first1=P.K. |last2=Das |first2=L.M. |last3=Babu |first3=M.K.G. |last4=Naik |first4=S.N. |title=Biodiesel development from high acid value polanga seed oil and performance evaluation in a CI engine |journal=Fuel |date=February 2007 |volume=86 |issue=3 |pages=448–454 |doi=10.1016/j.fuel.2006.07.025 |bibcode=2007Fuel...86..448S }}

Total acidity, fatty acid profiles, and free fatty acids (FFAs) can be determined for oils such as sunflower and soybean oils obtained by green processes involving supercritical carbon dioxide (scCO₂) and pressurized liquid extraction (PLE). The identification and separation of the primary fatty acids responsible for acidity can ensure higher quality of fat and oil products.{{Cite journal |last1=Medeiros Vicentini-Polette |first1=Carolina |last2=Rodolfo Ramos |first2=Paulo |last3=Bernardo Gonçalves |first3=Cintia |last4=Lopes De Oliveira |first4=Alessandra |date=2021-12-30 |title=Determination of free fatty acids in crude vegetable oil samples obtained by high-pressure processes |df=mdy-all |journal=Food Chemistry: X |volume=12 |pages=100166 |doi=10.1016/j.fochx.2021.100166 |pmid=34825173 |pmc=8604745 }}

In 2020, Dallas Group of America (DGA){{Cite web |title=Products & Applications |url=https://dallasgrp.com/products-applications/#:~:text=DALSORB |access-date=2022-10-28 |website=The Dallas Group of America |language=en-US}} and American Oil Chemists' Society (AOCS) devised a standard method (5a-40) for testing free fatty acid in cooking oils.{{cite journal |last1=Gordon I |first1=Virginia C |last2=Rainey |first2=Christopher C |last3=Studmire |first3=Willainia C |title=Validation of the Free Fatty Acid Test Kit for the Measurement of the Free Fatty Acid Content of Vegetable Oils, Fish Oils, Animal Fats (Tallows), Meat and Fish Meals, and Potato Chips and Grain-Based Snack Products: AOAC Performance Tested MethodSM 052004 |journal=Journal of AOAC International |date=21 May 2021 |volume=104 |issue=2 |pages=300–311 |doi=10.1093/jaoacint/qsaa086 |pmid=33367722 }} The DGA has produced a simplified test kit based on the 5a-40 test method. {{Cite web |date=2021-03-02 |title=How to Test for Free Fatty Acid in Cooking Oil |archive-url=https://web.archive.org/web/20221012031948/https://dalsorb.com/how-to-test-free-fatty-acid/ |archive-date=2022-10-12 |url=https://dalsorb.com/how-to-test-free-fatty-acid/ |df=mdy-all |access-date=2022-10-28 |website=DALSORB}}

{{div col|colwidth=120em}}

• {{anl|Amine value}}
• {{anl|Bromine number}}
• {{anl|Epoxy value}}
• {{anl|Hydroxyl value}}
• {{anl|Iodine value}}
• {{anl|Peroxide value}}
• {{anl|Saponification value}}
• {{anl|Redox}}
• {{anl|EN 14214}}
• {{anl|Rancidification}}

{{colend}}

{{reflist}}

Category:Analytical chemistry

Category:Lipids

Category:Food analysis

Category:Edible oil chemistry