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Micronutrients and Calories

Minerals and Trace Elements

Within the category of micronutrients we can classify things further into:

  • Minerals - are elemental nutritional components that we require in quantities of \(>100\:mg/day\)
    • These are either structural elements or large components of biochemical processing
    • e.g. Na, K, Ca, Mg, Cl, P, S
  • Trace elements - elemental nutritional components that we require in quantities \(<100\:mg/day\)
    • These are typically required for hormonal and metabolic function and are quite often, involved in enzymatic processes
    • e.g. Fe, I, F, Zn, Se, Cu, Mn, Cr, Mo, Co, Ni

Their deficiency leads to very specific symptoms:

Trace Element Deficiency Symptom
Fe Unusual tiredness, paleness, brittle nails
I Swollen neck, unexpected weight gain, weakness, hair loss, heavy or irregular periods
F Tooth decay
Zn Wounds that won’t heal, open sores on the skin, lack of alertness
Se Muscle weakness, mental fog, weakened immune system
Cu Weakness, difficulties walking, vision loss
Mn Skeletal defects, slow or impaired growth, abnormal metabolism of carbohydrate and fat
Cr Inhibition of protein synthesis, impaired insulin function, elevated cholesterol levels, anxiety and fatigue
Mo Developmental delays, visual alterations and neurological changes
Co Numbness, fatigue and tingling sensations in hand and feet
Ni Changes in skin colour, hair becomes coarser

Detection and Quantification - Minerals and Trace Elements

There are two primary methods used for the determination/quantification of elemental micronutrients, these typically involve ICP-EOS, which is a type of Atomic Excitation Spectroscopy (AES) and through the process of ashing.

Dry Ashing

This is the process of heating the sample to high temperatures (\(500-600^\circ C\)) to drive off moisture and oxidise the elements for quantification. A benefit is that there is no need for the use of blanks, however more volatile elements such as Hg and Ni may be lost. There may also be chemical interaction between the oxides formed and the crucible that’s used for the ashing.

Wet Ashing

Rather than heat being using to oxidise the samples, they are chemically oxidised using acids, peroxides, etc. Since there is no volatilisation, there is no loss through this method, however it requires more attention and is harder to automate.

It is possible to accelerate both methods with the addition of microwave reactors.


Fat Soluble

Name Structure Food Source Function RDI (daily)
Liver, butter, egg yolk, carrots, spinach, sweet potatoes Vision, healing eye and skin injuries \(800-1500\:\mu g\)
Salmon, sardines, cod liver oil, cheese, milk, eggs Promotes calcium and phosphate absorption and mobilisation \(5-10\:\mu g\) (and sunlight)
Vegetable oils, nuts, potato chips, spinach Antioxidant \(8-10\:mg\)
Spinach, potatoes, cauliflower, beef liver Blood clotting \(65-80\:\mu g\)

Water Soluble

Name Structure Food Source Function RDI (daily)
Beans, soybeans, cereals, ham, liver Coenzyme (oxidative decarboxylation) \(1.1\:mg\)
Kidney, liver, yeast, almonds, mushrooms, beans Coenzyme of oxidative processes \(1.4\:mg\)
Chickpeas, lentils, prunes, peaches, avocados, figs, fish, meat, mushrooms, peanuts, bread, rice, beans, berries Coenzyme of oxidative processes \(15-18\:mg\)
Pantothenic acid
Peanuts, buckwheat, soybeans, broccoli, lima beans, liver, kidney, brain, heart Part of CoA; fat and carbohydrate metabolism \(4-7\:mg\)
Meat, fish, nuts, oats, wheat germ, potato chips Coenzyme in transamination; heme synthesis \(1.6-2.2\:mg\)
Folic Acid
Liver, kidney, eggs, spinach, beets, orange juice, avocados, rockmellon Coenzyme in methylation and DNA synthesis \(400\:\mu g\)
Oysters, salmon, liver, kidney Part of methyl removing enzyme in folate metabolism \(1-3\:\mu g\)
Yeast, liver, kidney, nuts, egg yolk Synthesis of fatty acids \(30-100\:\mu g\)
Ascorbic acid
Citrus fruit, berries, broccoli, cabbage, capsicum, tomato Hydroxylation of collagen; wound healing; bond formation; antioxidant \(60\:mg\)

Detection and Quantification - Vitamins

Due to the variety and size of vitamins, the simplest and most effective way to identify them is to use HPLC.

Reverse Phase HPLC can be used for fat soluble vitamins and regular phase of water soluble ones. A strong solvent gradient can be used to separate out a combination of both, such as from a multivitamin

Calorific Value

Can be measured using a calorimeter, though the amount of energy released form burning will not be indicative of how much is available through digestion, so tables tend to be used instead, though these are rough values and the specific calorific content will be dependent on the food product.

Macronutrient \(kcal/g\) \(kj/g\)
Protein 4 16.7
Carbohydrate 4 16.7
Fat 9 37.7
Dietary Fibre 4 16.7
Alcohol 7 29.3

Metabolisable Energy (ME)

Is the amount of “food energy available for heat production and body gains”. These are based on the Atwater Factors, though they may not be truly indicative of all foods. This metric aims to consider only the nutritional value that can be actively utilise by the body to produce ATP.

The Atwater General Factor System

Is based on the heats of combustion of the macronutrients and corrects for losses i digestion, absorption and urinary excretion of urea.

The Extensive General Factor System

Is based on the Atwater system, however it makes a few modifications and refinements, such as accounting for dietary fibre separately from bulk carbohydrates

The Atwater Specific Factor System

Takes the system one step further by considering the food that these bulk nutrients come from

Food Product Protein Factor (\(kcal/g\)) Fat Factor (\(kcal/g\)) Carbohydrate Factor (\(kcal/g\))
Meat, fish, poultry 4.27 9.02
Eggs 4.36 9.02
Dairy products 4.27 8.79 3.87
Animal fats 8.93
Cereals 3.91 8.37 4.12
Legumes and nuts 3.47 8.37 4.07
Vegetables 2.62 8.37 3.90
Fruits 3.36 8.37 3.60
Sugars 3.87
Vegetable Fats 8.84