Lecture 13 - Minerals Flashcards
what are examples of minor food components?
minerals, vitamins, organic acids, enzymes, alcohols, neutraceuticals
what are examples of nutraceuticals
phenolic compounds, pigments, FAs, peptides
what is the classification of minor components based on?
distribution and amount of components
what is the definition of minerals
minerals are inorganic species or substances that are of neither animal nor plant origin
what constitutes the major part of dry ash after ignition of organic matter?
inorganic elements
which dietary macrominerals are needed at more than 100mg/day by adults?
Ca Mg Na K P Cl S
what is teh relevance of minerals in food
nutrition
food safety (contamination or adulteration)
food fraud (veg vs animal protein)
government regulations (nutrition labels)
food processing (fortification)
example of food safety issue with minerals?
contamination or adulteration
eg. siliceous matter in grans
seafood contamination w/ metal
what are examples of fortification? why is it important?
fortification of foods has allowed adding minerals above natural levels found in food
cereals w/ Ca, Fe, Zn
salt w/ iodine
what are 4 classifications of minerals in food
- macrominerals: need m
re than 100mg per day (adult) - trace minerals: required in milli or micrograms each day
- ultra trace minerals: being investigated for possible biological function, but don’t have a clearly defined biochemical role
- heavy metals: toxic to body
what are the macrominerals
Ca, P, Na, K, Mg, Cl, S
what are the trace minerals in food?
Fe, I, Zn, Cu, Chromium, Manganese, molybdenum, fluoride, selenium, silica
what are the ultra trace minerals in food?
vanadium tin nickel arsenic boron
what are the heavy metals in food?
lead
mercury
cadmium
arsenic
5 methods of food mineral analysis?
- potentiometry using ion-selective electrodes (ISEs)
- anodic stripping voltammetry (ASV)
- titrimetry (EDTA complexometric titration and precipitation titration)
- colorimetric methods or spectrophotometry methods
- instrumental methods (atomic absorption spectroscopy and atomic emission spectroscophy)
what are the forms of atomic absorption spectroscopy (an instrumental methods)?
forms of AAS:
- flame atomic absorption spectroscophy (FAAS)
- graphite furnace atomic absorption spectroscopy (GFAAS)
- cold vapour atomic absorption spectroscopy (CVAAS)
what are the forms of atomic emission spectroscopy (an instrumental methods)?
forms of AES:
- flame atomic emission spectroscophy (FAAS)
- inductively coupled plasma atomic emission spectroscopy (ICP-AES)
- inductively coupled plasma optical emission spectroscophy (ICP-OES)
what are 2 forms of titrations used for mineral analysis?
- EDTA complexometric titration
2. precipitation titration
what is the principle behind EDTA complexometric titration? what is it used for?
- used for testing hardness of water
principle:
- EDTA forms stable 1:1 complexes with mineral ions.
- This gives complexometric titration using EDTA broad application in mineral analysis
- endpoints are detected using mineral chelators that have coordination constants lower than EDTA (less affinity for mineral ions) and produces different colors in each of their complexed and free states
what are the indicators used in EDTA complexometric titration? what colors do they change to?
calmagite and erinochrome black T (EBT)
changes from blue to pink when they complex with Ca or Mg
in EDTA complexometric titration, when a sample with Ca or Mg is mixed with calmagite, what color forms? what pH is needed?
forms pink complex
at pH 10
in EDTA complexometric titration, how does the blue complex form
pink complex (product of first reaction) mixes with EDTA to form a blue complex
procedure of the analysis of calcium in milk?
calmigite indicator
- weigh EDTA. dissolve in 1000mL. Results in 0.036M EDTA solution
- prepare ammonia buffer. Mix of ammonium hydroxide and ammonium chloride (pH 10-11)
- add milk + ammonia buffer and a few drops of calmagite indicator
- titrate with EDTA
what is the principle behind precipitation titration
when at least one product of a titration reaction is an insoluble precipitate
what are the 2 methods for precipitation titration
- mohr method
2. volhard method
what is the mohr method?
what reaction occurs?
- type of precipitation titration (direct or forward)
- used for chloride determination
reaction:
- AgNO3 + Cl- –> AgCl + NaNO3 (until all Cl- is complexed)
- 2Ag + K2CrO4 –> Ag2CrO4 (orange only after Cl- is all complexed)
Ag2CrO4 = silver chromate (orange colored). This is formed after silver from silver nitrate has complexed with all available chloride)
the mohr method is for ___ determination
it is a ____ or ___ titration method
chloride
direct or forward
what color is silver chromate formed in the mohr method
orange
Ag2CrO4 = silver chromate (orange colored). This is formed after silver from silver nitrate has complexed with all available chloride)
procedure of the mohr method to determine Cl in butter?
- weight butter and add boiling H2O
- let stand for 5-10 min
- add 2mL of 5% solution of K2CrO4 with H2O
- titrate with 0.1N AgNO3 until orange-brown color forms
what is the procedure of the volhard method?
- treat sample with excess AgNO3
- wet ash with HNO3
- add FeHN4 (SO4)2.12H2O (indicator)
- excess AgNO3 is back titrated with potassium thiocyanate (KSCN)
- formation of ferric thiocyanate FeSCN2+ complex
why is it important to add AgNO3 before HNO3 in the volhard method?
- to ensure complete precipitation of the chlorides
- if HNO3 is added first, there will be loss of Cl- by volatilization as HCl (b/c HCl has a higher vapor pressure than HNO3
in the volhard method, why does AgNO3 need to be added in excess to the solution?
so that there is enough AgNO3 to react with ALL the chlorides in the sample
in the volhard method, what is added as an indicator?
what does it react with? what does this form?
FeNH4(SO4)2
reacts with excess thiocyanate
forms ferric thiocyantate (FESCH2+), which is salmon colored. This indicates the endpoint of the reaction
what indicates the endpoint in the volhard method?
the formation of ferric thiocyanate (FeSCN2+)
salmon coloured complex
what are chromogens
chemicals that form a colored product upon reaction with the compound of interest
they selectively react with a wider variety of minerals
eg. alizarin 3 sulphonate for calcium determination
ferrozine and ferene-5 for iron determination
what is alizarin-3-sulphonate?
it is a chromagen used for calcium determination
what is ferrozine and ferene-5?
they are chromagens used for Fe determination
describe the determination of Fe in meat
what reaction occurs?
react ferrous (Fe2+) with o-phenanthroline to form an orange-red complex ion (phenanthroline2+)
reaction:
ortho-phenanthroline + Fe2+ –> ferrous tris-o-phenanthroline 2+
what are 2 types of instrumental spectroscopy methods?
- atomic absorption spectroscopy (AAS)
2. atomic emission spectroscopy (AES)
what are 3 types of atomic absorption spectrscopy (AAS)?
- flam AAS (FAAS)
- graphite furnace AAS (GFAAS)
- cold vapour AAS (CVAAS)
what are 3 types of atomic emission spectroscophy (AES)?
- flame AES (FAES)
- inductively coupled plasma AES (ICP-AES)
- inductively coupled plasma optical emission spectroscopy (ICP-OES)
when are absorption spectra produced?
when ground state atoms (or ions) absorb energy from a radiation source
when are atomic emission spectra produced?
when excited neutral atoms emit energy on returning to the ground state or a lower energy state
what does atomization involve?
separating particles into individual molecules (vaporization) and breaking molecules into atoms
usually accomplished by exposing the analyte (substance being measured) to high temperatures in a flame or plamsa
what are sources of energy for atomization?
flame elctrothermal
inductively coupled argon plasma
stages of atomization?
- solution to solid (desolvation)
- solid to gas (vaporization)
- gas to atom (atomization)
- atom to ion (ionization)
atoms and ions can both be excited
