Environmental chemistry towards food processing

Environmental chemistry

towards food processing

Introduction

What is environmental chemistry?

Environmental chemistry is the discipline that describes the origin, transport, reactions, effects, and fate of

chemical species in the hydrosphere, atmosphere, geosphere, biosphere, and anthrosphere.

Formation of sulphuric acid can on one hand affect the living being, on the other hand lead to the acidification

of water. different spheres

In general we need to understand how the in the environment work and are related one to

each other.

Hydrosphere:

The is the sphere that contains all the water present on the planet (underground water, seas,

• lakes etc.);

The hydrological cycle starts with the evaporation of water that comes from seas etc. (processes guided by

the energy coming from the sun), then we have the condensation in the clouds, then the water can come

back to the surface in from of rain or ice.

Atmosphere:

The is air; it's an envelope of gases (80% nitrogen, 20% oxygen, CO , argon and other gases)

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in contact with the surface of the Earth;

CO might be a problem because, together with other classes is responsible for the greenhouse effect; The

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layer of CO can prevent the heat generated by the sun to leave, so it remains trapped to the surface

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causing the global warming.

Oxygen is used by aerobic living organism for respiration, they will release CO which will be used by other

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organism such as plants for the production of sugars and oxygen. Biosphere and atmosphere are

connected because the oxygen is used for respiration but also the atmosphere could be an important

source go nitrogen which is fixed by some bacterials (N fixing bacteria); they catalyse aa reaction in which

nitrogen is converted into ammonia.

Anthrosphere is that part of the environment that is made or modified by humans for use in human activities

• and human habitats. The atmosphere and anthrosphere are related to each other because the atmosphere

can be source of oxygen for combustion, nitrogen for the production of liquid nitrogen but also for the

synthesis of other compounds. We release CO and other gases into the atmosphere as waste.

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One of the most important ways of relating the environmental chemistry of the five spheres is the

biogeochemical cycles of elements.

They often involve the atmospheric compartment, but an exception is represented by P; it doesn't present a

cycle in the atmosphere compartment.

The cycles of elements

- Oxygen cycle: animals, by the respiration process, take O from the atmosphere and produce CO

2 2

meanwhile plants, by the photosynthesis process, take CO from the atmosphere to produce O .

2 2

- Carbon cycle: the CO coming from the anthrosphere (industries, respiration of living organism) can go

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through different stages: the fixation of the photosynthesis (connection to the biosphere), diffusion in the

atmosphere and eventually the solubilisation in the water bodies that leads to the generation of several

compounds but the main one is carbonic acid, which in the presence go high concentration of calcium,

may precipitate in the soil as calcium carbonate int the soil. Emission of metabolites of bacterias present i

the sea.

- Nitrogen cycle: N is important for amino-acids and so on that are fundamental for living beings. There’s N

in the atmosphere but is not available for us because the molecule of N is very stable so in order to fix it to

produce ammonia, it requires a very expensive industrial process. Anyway in nature the atmospheric N

fixation is catalysed by the energy released by lightenings and by nitrogen-fixing bacteria. The N fixed can

reach the soil; here, in the form of ammonia, urea or nitrate, can be used by the plants. Or the nitrogen

might be catalysed by bacteria, with the formation of nitrous oxide that induce the denitrification and the

volatilisation of nitrogen from the soil.

- Sulphur cycle: starts with the presence of gases containing S in the atmosphere but it can also come from

the anthrosphere (industries). There is a big amount of sulphur dioxide present in the atmosphere which is

brought back to the surface in form of acidic rain. The sulphur in the soil can be up-taken by plants and

animals and then the cycle can start again. Another important source of sulphur int the atmosphere is the

metabolism of anaerobic bacteria which can be release in form of dimethyl sulphide as product of their

metabolism.

- Phosphate cycle (exception): does not take place in the atmosphere and basically the majority of P is

immobilised in the soil. That's a problem because it's not available for the plants. It can be realised in the

water leading to a slight acidification of water and that might increase the insolubility of P. When we have

too much P we have a phenomena called eutrophication. It induces excessive growth of algae. This

process may result in reduction of the concentration of oxygen in the water body.

Environmental chemistry

is a science that describes the cycle of elements or chemicals trough these spheres that compose

It

the environment. It wants to find solutions to pollution related problems.

People became aware of pollution after the industrial revolution.

3 mains tasks:

Environmental chemistry has

1. Finding and quantifying the pollutants, so identify the pollutants;

2. Control what we are releasing in the environment;

3. Remediation of polluted areas.

At the moment all the solution have already been taken or are very expensive so we’re trying to find new

ones. green chemistry

A possible approach could be is the practice of chemistry in a sustainable way from the

point of view of emission of waste (no waste during the process or not toxic but degradable); the main goal is

to minimise the waste, the toxic material and the harmful waste.

They're still finding out what potentiality this chemistry has. In general it should be sustainable, safe, non-

polluting and cheap (consumes minimum amounts of

materials and energy, while producing little or no waste material).

Environmental chemistry towards food

Food processing makes a lot of products given by the activity of the anthrosphere (we're polluting our

environment). We use the same contaminated environment for the production of food and we use pesticides,

fertilisers in order to improve the quality and so on.

Food safety is a permanent challenge for scientists, advisory boards, regulators, risk managers, local and

regional authorities and consumers alike. The great importance of safe food is illustrated by the enormous

political, social and economic role of food production and manufacturing worldwide.

Food safety is a scientific discipline describing (production), handling, preparation, and storage of food in

ways that prevent food-borne illness.

Contaminants represent a major subgroup of unwanted food constituents.

Contaminants include:

- Environmental chemicals, coming from the environment;

- Production-related compounds (e.g. Acrylamide), that are created during the production;

- Residues (e.g. Phytosanitary products, veterinary drugs).

We can control residues and production related compounds whereas for the environmental contaminants we

have no way to control them.

Analytical methods for the detection of

contaminants

In environmental chemistry we can apply different methods in order quantify and qualify the contaminants.

One of the main of the methods that are applied in environmental chemistry for the identification of

contaminants is the chromatographic technique.

Chromatography liquid

Chromatography is a separation technique of molecules, the most applied in this field of study are: the

chromatography gas chromatography

(LC) and the (GC). Depending on the nature of the molecule we want to

determine they can be used alternatively or complimentary.

Chromatography is a physical method of separation in which the components to be separated are distributed

between two phases: phase)

1. one of which is stationary (stationary while the other

mobile phase)

2. (the moves through it in a definite direction.

The complex mixture of molecules we want to analyse/separate interacts differently with the two phases

(different affinity): stationary and mobile phases.

distribution constant [Kd=Cs/Cm]

The separation is obtained thanks to the that is the ratio between the

concentration of a given molecule in the stationary phase and the concentration of the same molecule in the

mobile phase.

( If we have a molecule that has a higher affinity to the mobile phase then the majority of the concentration of this

molecule will be in the mobile phase; it is carried along faster).

mobile phase:

Different classification according to the

- Liquid chromatography: mobile phase is a liquid (LLC, the mobile and stationary phases are both liquid

whereas in the LSC the mobile phase is liquid but the stationary one is solid).

- Gas chromatography: mobile phase is a gas. (GSC,GLC).

stationary phase:

Different classification according to the

- Thin layer chromatography (TLC): the stationary phase is a thin layer supported on glass, plastic or

aluminium plates.

- Paper chromatography (PC): the stationary phase is a thin film of liquid supported on an inert support.

- Column chromatography (CC): stationary phase is packed in a glass column (nowadays steal column are

more common). It’s the most used one.

Columnar chromatography (CC)

The stationary phase is packed into a column. The column in which you have the stationary phase is usually

solid, then you load your mixture and the mobile phase (it may be liquid or solid). The components will move

with different speeds according to the affinity with the different phases.

When a sample is loaded into the column, inside the column there’s already the stationary phase. Straight

after the mobile phase is added. The separation is achieved because the different molecules in the sample

have different affinity for either the stationary phase or the mobile phase. For eg. in the picture the molecule

that has the higher affinity for the mobile phase is A because it leaves the column quicker meanwhile the

molecule B has a higher affinity for the stationary phase because it will elute later on.

retention time (RT).

The time in which A leaves the column is called It is a measure of the time taken for a

solute to pass through a chromatography column. It is calculated as the time from injection to detection. The

retention time can be used to identify the nature of the molecule.

If we don't know anything about the molecule we may use standards (pure substances) that we can load in

the same column, using the same phases and at the end the retention time will be the same for both the

unknown molecule and the standard. We may have two different approaches when we want to identify a

molecule in complex mixture:

internal standard

I. An (IS) might be used. It is a known concentration of a chemical that is added in a

sample to quantify the components of the sample. The area ratio of IS peak and the analyte peak is

compared with the concentration ratio and as the concentration of IS added to the sample is known the

concentration of analyte in the sample can be calculated.

external standard

II. An is like the internal standard (known behaviour), but is not added to the unknown.

Rather it is run alone, as a sample, and usually at different concentrations, so you can generate a

standard curve. Again, the peak areas are related to the known amounts of external standard run. At the

end we’re able to construct a calibration plot in which we have the concentration of our analyte and the

area of the peak.

The chromatographic system is thought like a column composed by a series of

theoretical plates (N);

thin layers, known as in correspondence of each theoretical plate, the distribution

equilibrium of the analyte among the stationary phase and the mobile phase is achieved. The higher Is the

number of theoretical plates in the column, the higher will be the resolution.

The number of the theoretical plates (N) depends on the length of the column, and the chemical

characteristics of the phases. The number of the theoretical plates (N) and the Height Equivalent to

Theoretical Plate (HETP) are generally used to quantify the performances of a chromatographic system.

Resolution is the ability to separate two peaks.

N is the width of the peak. The higher the number of plates

(N), the narrower the peak obtained.

a) Low resolution and low N

b) Better resolution but still low N

c) Optimal resolution and good N

The difference between a), b) and c) is the retention time.

interactions

The that take place among the analytes and the phases (stationary and mobile phase) are weak,

otherwise the solutes would not be either retained by stationary phase or eluted by the mobile phase. In

particular, in the context of a chromatographic separation, we may have:

H-bonds is an attraction between a slightly positive hydrogen on one molecule and a slightly negative atom

• on another molecule (eg. H-O, O is a more electronegative atom than H).

Van Der Waals bonds

• - Dipole-dipole bonds result when two dipolar molecules interact with each other through space.

When this occurs, the partially negative portion of one of the polar molecules is attracted to the

partially positive portion of the second polar molecule.

- Dipole-induced dipole bonds results when a molecule with permanent dipole polarises the other

molecule which has less or no dipole at all. The polar molecule with a permanent dipole instigates

dipole in an electrically neutral molecule by deforming the electronic cloud of that atom. This results

in the induction of a dipole in the other molecule.

Different types of chromatography

Separation mechanisms

On the bases of the interactions occurring between the analytes and the phases, the chromatographic

methods can be classified according with the different separation mechanisms.

force of separation:

Classification according to the

1. Adsorption chromatography.

2. Partition chromatography.

3. Ion exchange chromatography.

4. Gel filtration chromatography.

5. Affinity chromatography.

Adsorption chromatography:

1. The stationary phase is formed by a solid, in the form of a powder; on the

surface of the powder granules there are active sites, which are able to

establish weak, reversible bonds with the analytes. The adsorption

chromatography can be either a solid-liquid or a gas-liquid

adsorption chromatography, depending on the nature of the mobile

phase.

The adsorption chromatography is used to separate neutral, organic

and inorganic molecules, both polar and non-polar.

Partition chromatography:

2. The stationary phase is formed by a liquid soaking an inert solid in

granular form; the molecules of analyte to be separated by this methods

are soluble in the liquid forming the stationary phase. On the other

hand, the mobile phase needs to be immiscible with the

stationary phase. During the elution, the analyte molecules

dynamically distribute among the two phases, according with the

different solubility.

The partition chromatography can be either a gas-liquid or a liquid-liquid chromatography, depending on

the mobile phase.

The partition chromatography can be also defined as normal phase, when the stationary phase in more

polar than the mobile phase; on the other hand, if the mobile phase is more polar than the stationary

phase, then we have a reverse phase partition chromatography. This latter is the most used method for

the separation of organic substances. The stationary phase is an inert solid covered by a thin layer of

liquid. We need that the liquid in the mobile phase and the one on the stationary phase have to be

immiscible. The reverse phase: the mobile phase is more polar than the stationary one.

Ion exchange chromatography:

3. It separates molecules based on their respective charged groups.

Ion-exchange chromatography retains analyte molecules on the

column, based on ionic interactions. The stationary phase consists

of an immobile inert matrix that contains charged ionisable

functional groups. The stationary phase surface displays ionic

functional groups that interact with analyte ions of opposite

charge.

We can distinguish between cation-exchange (-) and anion-

exchange (+) chromatography depending on the charges present on the stationary phase.

Cation-exchange chromatography is used when the molecule of interest is positively charged so the

stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it.

Size exclusion chromatography:

4. The stationary phase is a porous solid or a gel. The analyte

molecules, dissolved in the mobile phase, can penetrate the pores if

their dimensions are compatible. The bigger molecules, on the other

hand, are excluded from pores, therefore they leave the column

very quickly. The size exclusion chromatography can be further

divided into:

Gel permeation if water insoluble substances are

• separated;

Gel filtration if water soluble substances are separated;

• This techniques are used for the separation of molecules with high molecular masses (eg. proteins).

Affinity chromatography:

5. The stationary phase is an inert solid modified on the surface with

molecules with high specificity for the analyte we want to

analyse.

On the surface of the granule there is a molecule, such as an

antibody, that can be very specific in binding a single kind of

molecule (antigen, just one). This approach is very expensive and

specific, so it’s not versatile (you isolate just one compound).

There are also versatile techniques for eg. the purification of recombinant proteins:

We produce a protein in a recombinant system (bacteria or yeast) and we attach a tail of histidine that can

be used to separate analytes. On the surface of the granules, instead of having an antibody, we will have

nickel ions that are able to interact with the histidine tail. That allow us to separate the recombinant

protein.

In this case the approach is specific because just the histidine-nickel will interact but it’s also versatile

because if we produce 100 different recombinant protein but we attach the histidine tail to all of them,

we’re able to separate all of them with the same chromatographic approach. The interacti