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Out of the three main categories of food components (carbohydrates, fats, proteins), why is protein likely to be a limiting factor in food supply?

Protein contains the element N (nitrogen), in addition to C, H & O. N comes from soil - only a limited supply, whereas the other elements are contained in the products of photosynthesis, which relies on CO2 and water - reasonably easily available to plants.

Animal sources

Intensive production (or extensive production) of protein from animal sources (meat) depends on protein from plants: grass for grazing or or for production of animal feeds requires large areas of land, which may require nitrogenous fertilisers which can cause a variety of problems if not used at the correct amounts ; stored and prepared animal feeds also present a variety of economic and environmental problems.

What is the difference between intensive production and extensive production of livestock? Give an example of each.

Intensive - maximum number of animals per unit area, with all requirements provided for quickest growth and maximal conversion efficiency - very labour intensive, e.g. dairy farming, battery hens,veal calves in crates etc.

Extensive - fewer animals, much more space and less economic inputs, e.g. hill farming of sheep, cattle on prairies, wild game, etc.

What is meant by a nitrogenous fertiliser?

Inorganic salts, e.g. nitrates / ammonium salts Ca(NO3)2, KNO3, NH4NO3

or Organic compounds/ products of living origin e.g urea, animal droppings/ composted matter

What could happen if less than the optimum amount of nitrogenous fertiliser was used?

lower production

What could happen if more than the optimum amount of nitrogenous fertiliser was used?

waste of money - runoff - pollution of watercourses - eutrophication

Give an example of a stored animal food and a prepared animal food. Briefly describe how these are made, including ingredients.

Hay/ silage from cut/dried grass, stored (green, wet) grass

Cattle "cake" - mixture of cheap components - grains/other plant products, e.g. brewer's grains, yeast extract, other cheap protein, e.g. fish meal, (permitted?) rendered meat products

Similar problems exist for fish protein, whether caught from the wild or from farmed stocks.

Plant Sources

Protein from plant sources can be produced more efficiently, because it is effectively harvesting a different trophic level in the ecosystem. However, in less developed countries it is especially difficult to make improvements in arable productivity to compare with Europe and Northern America.

Explain why production of protein from plant sources is more efficient than from animal sources.

fewer stages in food chain - conversion loses about 90% so only 10% is passed on

What is a trophic level?

position in food chain - plants are producers, animals consumers

List some factors which may prevent less developed countries from most efficient production of plant protein.

not enough rainfall/too much/ not dependable rainfall

other climatic effects, e.g wind/flooding

poor soil - best land given to cash crops for balance of payments

not enough nitrogenous fertiliser - expensive chemicals/fewer animals?

most productive / newest crop varieties may not be suited to climate

mechanisation problems - staff training, investment, terrain

damage/ loss due to wild animals

overstocking with domesticated animals causing soil erosion

Micro-organisms as alternatives in food production

Edexcel On the other hand, protein from microbial sources should theoretically offer a variety of advantages.

When grown in ideal conditions, similar to the brewing and antibiotic production processes, the special characteristics of microbial growth should result in:

- rapid population growth

- ease of manipulation

- predictable and reliable product independent of climate

It is also potentially possible to use waste products from other industrial processes.

What is meant by "microbial sources"? Give some examples.

micro-organisms: bacteria/fungi/algae e.g. ???SCP / yeast/moulds / Chlorella/Spirulina

How would you define population growth in a microbial population in such a way as to be able to make comparisons with conventional systems?

biomass production rate/ doubling time

biomass per unit area per year

compare with yield from same amount of nutrients in other systems

Explain what you understand by "ease of manipulation".

no need to feed/otherwise manage/ eventually slaughter animals

no need to plant/hoe/manage/water/harvest crop

just inoculate medium with starter, wait then "harvest"

Why is the product likely to be independent of climate?

fermentation carried out inside vat-like container inside building

Can you think of some problems with using waste products from industrial processes?

supply could dry up/ price could alter

(undefined) pollutants could contaminate product

Production of yoghurt

This process relies on the growth of bacteria - usually mixed cultures including Lactobacillus species - on milk, and the conversion is due to anaerobic respiration by the bacteria. The milk is usually skimmed milk - "low fat"- often concentrated with extra "milk solids".

yoghurt production flowchart

Give 2 reasons for the first heat treatment:

to kill unwanted bacteria in milk - could cause e.g. food poisoning to remove oxygen so that bacteria from starter culture respire anaerobically

Why is the incubation phase so short compared to brewing?

higher temperature - faster metabolism AND not such a major (percentage) conversion as alcohol production

Give 2 advantages for the second heat treatment:

pasteurised product keeps longer AND does not need to be kept in fridge

As the bacteria respire anaerobically, they produce lactic acid:

lactose ­­­> lactic acid + energy

(milk sugar)

In fact, it is said that Lactobacillus bulgaricus breaks down milk protein to chains of amino acids, which are then used by Streptococcus thermophilus to make methanoic acid (formic acid) which Lactobacillus bulgaricus uses to convert lactose into lactic acid.
The acidic conditions (pH 3.7-4.3) cause milk proteins to be coagulated, which provides the thickened texture of yoghurt. Other chemical products from the bacterial growth, e.g. ethanal (acetaldehyde) contribute to the flavour.

Keeping qualities
As the yoghurt is cooled, the bacterial growth rate is reduced and the product can keep for about 10 days at 5 C. The normal numbers of bacteria are about 108 (100,000,000) per gram. After some time, acid slowly released by the bacteria gradually kills them and causes the proteins to separate into curds and whey.
Yeasts and moulds can cause problems if they contaminate yoghurt - causing pots to become "blown", due to the production of carbon dioxide.

The production of myco-protein

Edexcel Myco-protein is a product produced from a selected strain of fungus within the genus Fusarium. This was at first identified as Fusarium graminearum - but it has been recently shown by molecular biology techniques to be a different species - Fusarium venenatum, and commercially it is nowadays known as Fusarium ATCC 20334. This organism is a mould naturally found in soil, and was in fact originally taken from soil in Marlow, Buckinghamshire. Being derived from a filamentous fungus, it has a naturally fibrous texture, which enables it to be used as the major ingredient in a range of meat alternative products marketed by Marlow Foods under the Quorn brand name.

What dietary similarities has Quorn with meat?

high in protein

What dietary advantages has Quorn over meat?

contains fibre - low fat - no cholesterol


Fungi have been eaten for thousands of years in the form of mushrooms (picked from the wild or, more recently, cultivated). Yeast is effectively eaten cooked in bread, and blue cheeses contain living mould mycelium. There are other examples of fungal foods such as tempeh, made in the East by growing fungus on soy beans.

Several companies started looking at so-called single cell protein (SCP) from the 1960s onwards. Some large companies were interested in growing micro-organisms on oil, but despite much money being spent on research and development, these enterprises were stopped by the rise in oil prices in the 1970s. RHM was interested in growing fungi on a sugar-based medium obtained from starch from cereal sources, and started a 10-year long testing programme to find an appropriate organism. 3000 fungal isolates "from all over the world" were tested for efficiency of growth, and safety as food.

The main problem for such ventures was getting the product accepted - firstly by regulatory authorities, then by consumers. Other companies concentrated more on low-technology approaches using waste products which are in greater abundance in less developed countries.

The myco-protein production process

The Fusarium is inoculated into a sterilised airlift, "pressure cycle" or "loop" fermenter, operated as a continuous system which runs for several weeks at a time (see previous notes).

A sterilised liquid medium is continuously pumped into the fermenter, and so some of the Fusarium flows out continuously with the effluent. The medium contains food grade sugars, mostly glucose, obtained from the breakdown of starch, together with mineral salts, and a growth factor which causes hyphae to grow longer. Sterilised air and ammonia are also pumped in. The temperature is maintained at 30-32C, and the biomass doubles every 5 hours.

The resulting fungal mycelium is heat treated at a temperature between 65-70C, in order to reduce the content of RNA, which would otherwise be a dietary problem for consumers (exceed RDI level). It is then filtered out of the liquid by centrifugation, dried, pressed, cut, coloured and flavoured before further treatment.

Production efficiency

Production of myco-protein represents a more efficient conversion of carbohydrate than production of animal protein, although it is less efficient than direct consumption of the plant foods.

Protein source
myco-protein chicken pork beef wholemeal flour
Protein yield (g)
from 1000g of plant





(in addition to carbohydrate!)

Myco-protein can be processed to resemble several meat products. In its raw form it is said to have a fairly bland mushroomy flavour, but adding various flavours and processing its texture makes it a versatile food product. It may be argued that its promotion appears to have been targeted on (middle class?) health conscious markets - vegetarians, sport fanatics, etc., who are prepared to accept the price incurred in the processing.

As yet, the promise of cheap single cell protein for underdeveloped countries has still to be fulfilled. It has been said that when SCP can be made more palatable, it will be a way to increase the protein content of the diets of the ever-increasing hungry world population.

What is meant by the term "single cell protein"?

(whole) cells of bacteria, fungi or algae - grown together

Is it acceptable to describe filamentous fungi in this way?

It is not strictly single cells like bacteria, yeasts and some algae, but it grows in a similar way - needing the same sorts of nutrients and growing conditions

Do you think it is reasonable for the distributors to describe myco-protein as a "completely natural tiny plant"? Or as "of mushroom origin"?

All living organisms are natural - but the process needs plenty of human manipulation.

Being a micro-organism, it is certainly rather tiny, but fungi are nowadays classified as distinct from most (green) plants.

Mushrooms are the fruiting bodies, not mycelium which normally grows under the ground or in specially prepared compost, of higher fungi - a different taxonomic grouping

Why do you think microbial protein was only of interest to large companies?

Only they could afford such expensive, long term projects

Why do you think RHM and subsequently Marlow Foods stuck with the enterprise when others gave up?

Their interest was not confined to oil, and they had links with cereal industry and food production (bread, flour, etc.).

What do you think is meant by "cereal sources"?

Grain crops e.g. wheat, maize, etc. (and waste products?)

What is meant by "fungal isolates"?

Different (pure) varieties or strains (of different species ?) of fungi - obtained (isolated) from distinct sources - so specialised or adapted for different growing conditions

What stages do you think were involved in testing the product for safety as food?

Mandatory testing with animals, then (volunteer) humans before being released to the general public

What is meant by "regulatory authorities"?

Food safety committees, government ministries of different countries, etc.

What aseptic precautions are likely to be taken in the production process?

Sterilised fermenter, medium, air, ammonia - Heat (steam) - filtered?

Pure culture of a species of Fusarium (ATCC 20334) used as inoculum

How are soluble sugars obtained from insoluble starch?

broken down by enzymes, e.g. amylase or acid hydolysis

What chemical elements are in protein, and which nutrients provide them?

CHO - sugars

N - ammonia

What is the function of the air?

to provide oxygen for aerobic respiration and to mix contents.

If the fermenter contains 1 kg of fungal biomass per unit volume, how much will it contain after 10 hours?

4 kg (1x2x2)

biomass doubles every 5 hours, so 2 kg in 5 hours, 4 kg in 10 hours

Soy sauce bottle

The production of soy sauceEdexcel Soysa2

This process is also based on fermentation by several micro-organisms. Traditionally, it takes over 18 months, but through commercial application of scientific principles it may be speeded up considerably.

Dark soy sauce nowadays takes 6 months to produce commercially and light soy sauce takes 3 months. Production is a 2 stage process, incorporating fermentation principles similar to those involved in both yoghurt manufacture and also brewing.

Soy beans are a good source of protein by themselves. One hectare of soy beans can yield 162 kg of protein, as opposed to 9 kg for beef.

The soy beans are cooked and mixed with roasted wheat, although modifications such as steaming or autoclaving (pressure cooking) the soaked beans and adding wheat flour are commercial variations.

The first stage relies on the fungus Aspergillus oryzae or A. sojae, which is encouraged to grow on the mixture. To increase the efficiency of conversion, a culture of a known strain of the fungus is inoculated, and a suitable even, warm incubation temperature (30 C for 3 days) is provided. This is an aerobic phase, and several enzymes are produced which break down complex (food) substances in the beans to simpler soluble substances, some of which are later used by other micro-organisms.

What do you think are the main (food) components of the mixture?

starch, protein

What sort of enzymes will act on them?

amylase, protease

What do you think they will be converted into?

sugars e.g maltose, amino-acids and peptides

As this is an aerobic phase, how do you think the mixture of beans, etc is arranged?

spread out in a shallow heap to allow air (oxygen) to get in

The second stage is a further fermentation in deep tanks. This lasts for 3-6 months at 15C, rising to 25C.

The conditions here favour the growth the bacterium Lactobacillus, which produces lactic acid, lowering the pH. As in cheese and yoghurt production, this presumably acts on proteins and performs a conversion similar to curdling milk. Yeasts also grow, utilising free sugars from other conversions, producing as a result alcohol which has a preservative and flavour extracting function. The addition of salt presumably assists in the extraction of a liquid extract, as well as having a preservative function.

The product is then left to "age" for another 4-5 months.

Why do you think the tanks need to be deep?

no air needed for anaerobic fermentation - as in brewing, and yoghurt production

Why does this stage of the process take so long?

anaerobic growth is not so efficient

subtle changes to components are taking place

After these stages, the solids are filtered off and the liquid collected is heat treated (pasteurised) , then filtered again and finally bottled in sterile bottles.

Soy sauce is used as the basis of a variety of other sauces and marinades. It contains digestion products of proteins - amino acids - which are potent taste enhancers and stimulate the production of digestive juices.

In particular, it was found to contain the amino acid glutamic acid. The salt of this (monosodium glutamate) is now widely used as a flavour enhancer in modern foods, especially snacks.

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