Principles of Food Analysis

• In quality control: for safety and quality
• In the government: for regulation, consumer protection, health and food safety, to protect against fraud
• For research: to measure (quantities), analyze characteristics

Need to find/use the more reliable methods

Lead to regulations, have legal implications - need high degree of reliability

• Rapid results needed sometimes - rapid methods (especially for process control).
• Although may have some legal implications, all depend on the contract with the customer/supplier

A combination of the specificity, accuracy, precision (or variability), and sensitivity of a set of results

the ability of a method to measure a component of interest in the presence of other components without interference

the ability of a method to measure the true value of a component (where true = near standard)

The ability os a method to give a value from a singe measurement that comes close to the average from a large number of measures

The number of decimals when measuring trace components

• A way of measuring the major components of foods.
• It is based on assumptions.
• This method is used most of the time for nutritional labels.

• water
• non-water

• Total solids (TS) vs Dry matter (DM)
• we can determine liquids by using TS - DM

• Organic nitrogenous: (nitrogen-containing components are assumed to be proteins, so we count this as "protein content")
• Organic non-nitrogenous: (either lipids for lipid content calculations, or carbs and fiber)
• Inorganic: (ash)

%water + % ash + % Crude proteins + % crude fat + % dietary fiber = 100% - % carbs

Nitrogen amount (g)/16% = protein amount

non polar extractible material

• Can help prevent food spoilage
• Gives us an idea of food safety
• Economics- some foods are purchased by weight

• Drying methods
• Distillation
• Physical methods (electrical properties)
• Chemical methods (sensitive and specific)
• Others (spectroscopic)

• Oven-drying (convection oven, forced-air oven, vacuum oven)
• Freeze drying (very low pressure, very low temperature, water evaporates) 
• Spectroscopic (IR, NMR)
• Microwave
• Chromatographic

• Does not directly measure water, simply a loss of weight
• not-specific--> anything lost while heating will be included

• Uses weight differences (before and after drying)
• A gravimetric method
• Indirect method
• Inexpensive, easy, short time

• Air moves through the oven- no fan, air stays in chamber
• Reaches vapor pressure equilibrium

• Contains a fan
• Temperature can be higher and time shorter

• If you lower the pressure, you need to lower temperature to evaporate water
• The heated chamber is connected to a vacuum pump (with a pressure controller)
• The vacuum also pumps the water evaporating from the sample
• If all the air is pumped out, noting can heat, so some air has to be put in and it needs to be dry
• Drying agents are often used such as CaCl₂, SiO₂, P₂O₅, H₂SO₄

• Particle size- loss of water takes place at the surface of a particle, grinding the sample increases the surface- reduces the migration distance that water needs to travel before evaporating
• Time
• Temperature

• It is a physical method - uses the boiling point
• Direct method - water is physically removed and collected and the amount of water is then measured
• This is done by: (1) heating the sample, (2) water vaporizes, (3) water condenses

Volatile compounds will still be present in the H₂O distillate

Do the distillation in the presence of a heat transfer medium

• Unmiscible liquid in water
• Stable
• Free of water
• example: toluene, aromatic hydrocarbon, mineral oil

• Boiling point is 110.5^oC
• Volatile, but unmiscible
• Preferred because it take 2-3 hours instead of 8 hours for vacuum-oven drying
• If you pour the sample into toluene, both will evaporate, but will form 2 separate layers which can then be separated

• Fire safety (can be flammable)
• Toxic vapors
• Environmental concerns

Takes advantage of a chemical reactive substance (with a high specificity)

• The Karl Fischer method
• Most widely used because of its high degree of specificity and high sensitivity with water
• Used mostly with low moisture foods

• Use Bunsen reaction to develop the KF reaction (2H₂O + SO₂ + I₂ --> H₂SO₄ + 2HI)
• Use pyridine as the solvent (non-aqueous solvent, basic)
• Pyridine equilibrates the acidic H₂SO₄ which pushes the reaction more towards the products
• BI₂ + BSO₂ + B + H₂O --> 2BH⁺I^- + BSO₃, then BSO₃ + ROH --> BH + ROSO₃^-

• SO₂, I₂, pyridine, methanol (to dilute pyridine)
• Pyridine is hazardous

• Conductance (1/resistance)
• Capacitance (high dielectric constant)

Assume all of the electrical properties of a sample are due to the water

Oven drying is the reference method for calibrating

The inorganic residue afer complete combustion of the organic material

• Food material is oxidized at 500-600 degrees for 2 hours
• CO₂, H₂O, nitroxides (NO, N₂O, NO₂) escape, residues remain (such as Cl-, SO₄-, PO₃-, silicate)
• Residues contain mixtures of metal oxides and salts (like chloride sulfate, phosphate, silicate)

• For nutrition: essential minerals need to be measured individually (such as Ca, Na, Fe)
• Undesirable minerals: (Pb, Hg, Cd, etc)
• Food safety/food quality: useful in wheat flour where higher ash content in bran and endosperm may not be good, also in raw sugar where there are specifications. Ash in sugar comes from the soil which has silicate, higher ash content in raw sugar means poorer quality

• Sample --> preashing --> furnace --> residues
• After incineration the sample should be grayish-whiteish (if all organic matter is combusted). Sometimes even at more than 530 degrees for 2 hours, the sampe does not get completely combusted (black spots). You don't want to go up to 550 degrees where some minerals may become volatile (such as lead or mercury)

• To remove some gases, smoke the sample initially
• Does not come from furnace
• Care required by analyst to prevent loss of sample

• Metals/oxies/salts
• Chlorides and phosphates fuse with salts (like Na and K) at high temperatures and trap organic material, rendering them unavailable for combustion. The organic material can be released by dissolving the sample/salt in a small amount of water
• Black spots are quite common with high CHO/high sugar samples

Sample + diluted H₂SO₄ (just a few drops) --> preash/ash --> grey/white residue (with no black spots)

• Most of salt in residue is in metal sulfates - does not form fused salts
• In these cases, "sulfated" ash determination is done

• Ashing process is dry, meaning no solvent or liquid is used during the ashing process
• Result gives total ash content

• Remove all organic material via oxidation
• Objective: obtain a solution with all the minerals, and then analyze them one by one
• This provides a clear solution which has all minerals dissolved in it
• Extremely strong oxidizing agents are used (i.e. concentration HNO₃, H₂O₂ + heat are used if the oxidizing power needs to be increased)
• Na, K, Ca, Fe, Cl, P, S contents can be measured by flame photometry, atomic absorption, or other techniques