Food components and analyses

Question 1

What are the major components of food dry matter?

Answer 1

Organic: CHOs, lipids, Protein, Nucleic acids, organic acids and Vitamins
Inorganic: Minerals

Question 2

What are the three major components of the organic matter of foods?

Answer 2

CHOs, lipids and protein

Question 3

What are the six fractions quantified by the proximate system of analysis of foods?

Answer 3

DM (moisture), CP, EE, CF, Ash and NFE

Question 4

What is the major component of ash?

Answer 4

Silica

Question 5

Why Crude Protein is not = true protein?

Answer 5

The Kjeldahl method determines nitrogen from sources other than protein, such as free amino acids, amines and nucleic acids, and the fraction is therefore designated ‘crude protein’.

Question 6

What does the the nitrogen-free extractive fraction includes?

Answer 6

includes starch, sugars, fructans, pectins, organic
acids and pigments + variable proportion of the cell wall material

Question 7

What does CF contains?

Answer 7

Crude fibre fraction contains cellulose, lignin (an indigestible component of plant fibre) and hemicelluloses

Question 8

What is the Luff-Schoorl method?

Answer 8

It is an official EC method to determine the amount of sugars and with this, the amount of starch can be calculated

Question 9

What does the neutral-detergent fibre (NDF) comprises? Method by Van Soest

Answer 9

Consists mainly of lignin, cellulose and hemicellulose

Question 10

What is the non-structural carbohydrate (NSC)?

Answer 10

the fraction obtained by subtracting the
sum of the amounts (g/kg) of CP, EE, ash and NDF from 1,000.

Non-structural carbohydrate (NSC) = 100 - (crude protein + fat + (NDF - NDF protein) + ash)

Question 11

What is the acid-detergent fibre (ADF)?

Answer 11

represents the crude lignin and cellulose fractions of plant material but also includes silica.

Question 12

What is dietary fibre?

Answer 12

Dietary fibre (DF) are carbohydrates (polysaccharides,
oligosaccharides and lignin) resistant to digestion in the small intestine but that may be fermented in the large intestine and promote beneficial physiological effects.

Question 13

The carbohydrates are classified according to their degradation rate by rumen microbes. What are the 4 fractions?

Answer 13

• fraction A – fast (comprising the sugars);
• fraction B1 – intermediate (starch, pectins, b-glucans);
• fraction B2 – slow (available cell wall material represented by lignin-free NDF);
• fraction C – indigestible (unavailable cell wall in the form of lignin).

Question 14

What are the functions of Water-soluble and insoluble non- starch Polysaccharides?

Answer 14

Water-soluble NSP is known to lower serum cholesterol, and insoluble NSP increases faecal bulk and speeds up the rate of colonic transit.

Question 15

Butyric acid is a source of?

Answer 15

is an important source of energy for the growth of cells in the epithelium of the colon, promoting the development of the cells and enhancing the absorption.

Question 16

What is the importance of b-glucans to the small intestine and digestibility?

Answer 16

b-glucans influence the viscosity of digesta and thereby reduce the absorption of other nutrients from the small intestine and depress digestibility and adversely affect faecal consistency in pigs and poultry.

The water-holding properties lead to beneficial effects on the behaviour of pregnant sows by increasing time spent eating and resting, owing to increased gut fill, and by reducing inappropriate behaviour, such as bar chewing.

Question 17

What is the Dumas method used for?

Answer 17

The Dumas method is an alternative to the standard Kjeldahl method for the determination of nitrogen
(crude protein)

Question 18

What is the Dumas method used for?

Answer 18

The Dumas method is an alternative to the standard Kjeldahl method for the determination of nitrogen
(crude protein)

Question 19

What happens with the nutrients of a grass during maturation? (young grass vs mature grass - DM, CP, CF, moisture)

Answer 19

Young grasses have:
Higher moisture and lower DM
Lower CF
Higher CP

Mature grasses have:
Lower moisture and higher DM
Higher CF (increased cellulose and hemicellulose)
Lower CP

Question 20

Explain how the climate (sun vs cloudy/ rainy vs dry) can affect the nutritional composition of pasture

Answer 20

The concentration of sugars and fructans, for example, can be influenced markedly by the amount of sunshine the plant receives. Generally, on a dull cloudy day, the soluble carbohydrate content of grass will be lower than on a fine sunny day.

Rainfall can affect the mineral composition of pasture herbage. Calcium, for example, tends to accumulate in plants during periods of drought but is present in smaller concentrations when the soil moisture is high; on the other hand, phosphorus appears to be present in higher concentrations when the rainfall is high.

Question 21

Many legumes contain condensed tannins, which can be problematic for the digestion of protein. Why low amounts of these tannins can be beneficial to the ruminants?

Answer 21

By protecting proteins from hydrolysis
in the rumen, they increase amino acid absorption from the small intestine. They also modify gas production in the rumen, thereby reducing the danger of bloat (see later) and possibly reducing methane production.

Question 22

Which disorders can happen in cattle and sheep grazing on legumes?

Answer 22

Bloat

Redgut: caused by the rapid passage of highly digestible forage through the rumen that causes increased fermentation in the large intestine. e.g. sheep on pure Lucerne/alfalfa

Infertility due to the consumption of oestrogenic pasture plants by sheep

Question 23

Which methods can be used to evaluate the quality of a protein?

Answer 23

• Protein efficiency ratio (PER) is the gain in body mass or weight for a subject fed a particular food divided by the mass of the protein intake;
• Biological value (BV) is the mass of nitrogen incorporated into the subject’s body divided by the mass of nitrogen from protein in the food times 100. Thus 100% is the absolute maximum with lower values indicating lower quality.
• Net protein utilization (NPU) is the ratio of amino acids converted to protein to the amino acids provided by the food
• Protein digestibility corrected amino acid score (PDCAAS) is milligrams of limiting amino acid (for humans) in 1 gram of test protein per milligram of the same amino acid in 1 gram of reference protein times true digestibility percentage (fecal); values up to 1 can be achieved, and the closer to 1 the higher the protein quality.

Question 24

What are the classifications of protein? give examples

Answer 24

Globular: albumin, globulin, Glutelins, prolamines

Fibrous: collagens, elastins, keratins

Conjugated proteins: nucleoproteins, mucoproteins, glycoproteins, lipoproteins, chromoproteins

Question 25

Which amino acids are essential to poultry birds that are not for most other animals?

Answer 25

Glycine and tyrosine

Question 26

Which amino acids are essential to felines that are not for most other animals?

Answer 26

taurine and arginine

Question 27

Which amino acid is essential to fast growth in growing pigs that is not for most other animals?

Answer 27

Arginine

Question 28

Which are the 3 limiting amino acids in poultry diets?

Answer 28

Lysine, methionine and tryptophane

Question 29

Which are the amino acids that are ketogenic?

Answer 29

Leucine (only ketogenic). The lysine, isoleucine, threonine, phenylalanine, tryptophane and tyrosine are both glucogenic and ketogenic

Ketogenic amino acids produce acetyl-coA which is converted to acetoacetic acid (a ketone body).

Question 30

What can be caused after ingestion of xylitol by dogs?

Answer 30

Hypoglycemia. Profound hypoglycemia (D) can occur in dogs that ingest xylitol due to a dose-dependent release of endogenous insulin. Hepatic insufficiency or failure can also occur.

The presence of hyperphosphatemia is a poor prognostic indicator. Emesis is indicated after ingestion but activated charcoal is not because it does not bind to xylitol. Patients that have ingested more than 75 mg/kg of xylitol require hospitalization and blood glucose monitoring. The prognosis is good for uncomplicated hypoglycemia but guarded for patients with liver damage.