Biotechnology in food

Question 1

What is the protein percentage of bacteria and what are their nucleic acid percentage?
What is the protein percentage of filamentous fungi and what is their nucleic acid percentage?

Answer 1

Protein percentage is 50-85%; nucleic acid is 10-16%

Filamentous fungi is 30-55%; nucleic acid is 3-10%

Question 2

What makes a suitable SCP microbe?

Answer 2

Performance (growth rate),
Temperature and pH tolerance,
Oxygen requirements,
Growth morphology,
Genetic stability,
Ease of recovery of product,
Structure and composition of final product.

Question 3

What is an issue with safety of single cell protein products?

Answer 3

One issue is elevated nucleic acid levels in the protein. These nucleic acids would be digested to form purine compounds which form Uric acids. These crystallise at the joints and form symptoms similar to gout.

Question 4

What is the largest cost in SCP processes?

When choosing a substrate what must be considered?

Answer 4

The cost of SCP is heavily influenced by the cost of the carbon substrate. 
When choosing a substrate the following must be considered: 
The cost,
The availability,
The biomass yield,
The oxygen requirement,
The heat produced during fermentation,
Downstream processing costs.

Question 5

Describe the Bel process.

Answer 5

The dairy industry generates 80 million tonnes of whey per year. Whey is a pollutant due to its high COD value of 60 g oxygen/L. The Bel process utilises lactose utilising yeasts to produce a marketable protein product. The whey is pasteurised and the lactose concentration is reduced and mineral salts are added. This is added to a continuous fermenter maintained at 38 degrees.

Question 6

Describe the Symba process.

Answer 6

This was developed in Sweden to produce SCP for animal feeds from potato processing wastes. Potato waste contains high levels of starch which not many microbes can utilise directly. This process uses two microorganisms: Saccharomyces fibuligera and Candida utilis.

Question 7

Describe the Pekilo process.

Answer 7

This was the first operating process developed for a filamentous fungus. It utilises the spent sulphur liquor waste from wood processing. The waste is supplemented with molasses and whey before inoculation with Paecilomyces variotii. The resulting dried Pekilo protein is used in the preparation of animal feeds.

Question 8

Describe the Pruteen process.

Answer 8

The process uses methanol and the process produces a very pure protein that doesn’t need to be purified. The process is used by the bacterium methylophilus methylotrophus to produce feed for chickens, veal and pigs. Production stopped in 1987 due to the rising cost in methanol.

Question 9

What is Toprina?

Answer 9

Toprina was a product developed by British Petroleum and ANIC. It aimed to form a product by yeast grown on residues of oils spills. Its market was the animal feed industry as an alternative to soybean cake. It was a failure due to the oil market crashing in the 1970s. Also Toprina was found to have a high nucleic acid content.

Question 10

What is the Quorn production process?

Answer 10

Quorn is a health food which contains no fat or cholesterol and is thought to help reduce fats in the bloodstream. It is made in a fermenter that is operated continuously at 30 degrees with a pH of 6. Glucose syrup is used as a carbon source. Ammonia is used to control pH and this also acts as a nitrogen source.

Question 11

Why has oxygen concentration got to be strictly maintained?

Answer 11

Because a too high oxygen concentration can lead to a loss in productivity whereas a too low oxygen concentration can lead to anaerobic metabolism occurs whereby the by-products impair the Quorn flavour.

Question 12

When Quorn is grown in a prolonged culture what can occur?

Answer 12

When grown for approx 100-1200 hours highly branched forms of the fungus can form. The system has to be shut down when this is detected as it can remove the fibrous nature of the final product.

Question 13

How much RNA does the final Quorn product contain?

Answer 13

It contains 10% RNA which is too much for human consumption. RNA levels are reduced back to normal levels by thermal shocking at 64 degrees, for 30 min. This renders the fungus non viable and activates RNases which break down the RNA into nucleotides which diffuse out of cells.

Question 14

How is the Quorn product harvested?

Answer 14

It is harvested via vacuum filtration. The filter cake is a intertwined mass of fungal hyphae that can be frozen into sheets and formed into various food shapes.

Question 15

What is the organism that produces Quorn?

Answer 15

Fusarium venenatum.

Question 16

What are the four main stages in the brewing process?

Answer 16

Malting,
Mashing and wort preparation,
Yeast fermentation,
Post fermentation.

Question 17

What is the mashing process of brewing?

Answer 17

Malting is the controlled partial germination of barley grains. This softens the seeds which then contain starch which is more readily available and also generates hydrolytic enzymes such as proteases and amylases. Malting starts by soaking the grains in water for 2 days at 10-16 degrees. The barley is then germinated for 3-5 days at 16-19 degrees on a mashing floor. The malt is then kilned.

Question 18

What is the wort?

Answer 18

The wort is the liquid prepared from the malt and other ingredients known as adjuncts. Adjuncts can be unmalted barley, rice, non-cereal starches and sugar syrups. Milled ingredients are transported to the mash vessel and mixed with hot water which is called the liquor. Following the mashing the extract is separated from the remaining solids to form the wort which is then stabilised by boiling.

Question 19

Describe the boiling and clarifying wort stage of brewing.

Answer 19

The wort obtained from mashing is transferred to a ‘copper’ for boiling along with dried hops or hop extracts. Hops are flower cones of the female hop vine. Hops give the beer it’s characteristic bitter flavour. They also have an anti septic property. Boiling is conducted to: sterilise the beer, concentrate it, terminate any enzyme activity, precipitate any unwanted proteins, remove volatile chemicals and develop flavour.

Question 20

What is looked for in brewing yeasts?

What are the two types of brewing yeasts?

Answer 20

The yeast used must be able to utilise the nutrients from the wort and also give it it’s flavour. Additionally the yeasts must be easily removable after the process.
Top fermenting yeasts- Used to make ales and stouts, unable to metabolise melibiose.
Bottom fermenting yeasts- used to produce lager can metabolise melibiose.

Question 21

What is pitching?

Answer 21

This is when the yeast is grown and added to the mixture for brewing.

Question 22

What do yeasts need to grow?

Answer 22

They need an energy source such as a fermentable carbohydrate.
They need a nitrogen source, taken from peptides and amino acids.
They need minerals, such as calcium, magnesium, phosphorus and sulphur.
They need growth factors such as biotin.

Question 23

Not only are amino acids needed as a nitrogen source for the yeasts, they also are important for what?
What else is responsible for flavour in beers?

Answer 23

They are important for beer flavour as aromatic amino acids can be made from wort amino acids.
There are trace amounts of esters in alcohol but they are crucial for flavour.

Question 24

What is happens post fermentation?

What are two post fermentation processes?

Answer 24

Once fermentation is conducted and the yeast removed the alcohol has to mature before consumption. Maturation for lagers and ales depends on the rate of removal of diketones diacetyl.
One process used is for casked ales- priming sugar is added to allow the remaining yeast to do a secondary fermentation to carbonate the beer.
Another process is lagering used for lager. No priming sugars are added but the remaining yeasts continue to ferment the wort sugar. This generates CO2 which purges the beer of volatile chemicals.

Question 25

Before packaging what occurs?

Answer 25

Most beer is clarified by filtration before pasteurisation or sterile filtration. It is then packaged.

Question 26

Why is it difficult to generate new strains of yeast?

Answer 26

This is because they reproduce asexually and yeasts don’t have an obvious sexual stage, so it is difficult via traditional breeding techniques.

Question 27

What is the common yeast used for brewing?

Answer 27

Saccharomyces pastorianus.

Question 28

What are some areas for strain improvement?

Answer 28

Better utilisation of nutrients within the wort,
Better flocculation properties,
Better filterability,
Reduction of bad flavours,
Healthy beer.

Question 29

How can the utilisation of nutrients be improved?

Answer 29

Maltose is a major fermentable sugar, but the process is incomplete. The uptake of sugar is the rate limiting step, it is taken in by maltose permease. The genes that encode it can be cloned into yeast, producing a GM yeast.

Question 30

What is flocculation and why is it important?

Answer 30

This is when cells stick to each other to form flocs. Flocs are formed as an interaction between adhesins with mannan carbohydrates. Ideally the yeast needs to floc after the wort sugars have been fermented for easy removal, but different yeasts have different flocculation properties. Lg-Flo1 is present in S. pastorianus, the adhesion that this gene encodes ensures that flocculation will only happen after the wort sugars have been utilised.

Question 31

How can a low calorie beer be generated?

Answer 31

To get a low calorie beer the dextrin content must be reduced.

Question 32

In yeast what enzymatic reactions convert pyruvate to ethanol?

Answer 32

Pyruvate is first converted to acetaldehyde via the action of pyruvate decarboxylase, the acetaldehyde is then converted to ethanol via the action of alcohol dehydrogenase.

Question 33

What is the Crabtree effect?

What does this effect split yeast into?

Answer 33

This is fermentation in the presence of oxygen and with high glucose concentrations.
Crabtree positive,
Crabtree negative.

Question 34

Why may have fermentation evolved?

Answer 34

Fermentation could be seen as wasteful but it may have evolved because: when fruits ripen there is intense competition among the native microbial flora for sugar.
Yeasts tend to become the predominant group when mono and oligosaccharides are present. Winning traits which allow this are the fast sugar consumption, ethanol production and tolerance and ability to grow without O2.

Question 35

What is single cell protein?

What are the advantages of single cell protein over plant and animal protein?

Answer 35

Single cell protein is the production of protein from the biomass of different microbial sources.
Advantages over plant and animal protein are: rapid growth rate,
High protein content,
Ability to use a wide range of substrates,
Occupies little area,
Production independent of season.