This document contains the questions and answers of the practice exam for the course Food Digestion: Fermentation & Gut Health. The answers are given both for the closed and open questions.
1. The term Dietary Fibre (DF) includes many different carbohydrate structures having in
common that they are not digested in the human intestinal tract. Which statement is not
correct?
a. Only polysaccharides are part of DF.
b. DF could be both soluble and insoluble.
c. Resistant Starch is part of DF.
d. For adults, most DF in the diet is of plant origin.
2. Which statement on DF is correct?
a. Arabinoxylans are predominantly present in cereal DF.
b. Seed galactomannans solubility is independent on the level of substitution.
c. Pectin is a neutral DF.
d. Maltodextrins are soluble DF.
3. Which carbohydrate will not end up in the colon?
a. Gelatinized starch.
b. Galacto-oligosaccharides (GOS).
c. Cellulose.
d. Inulin.
4. Mother Milk Oligosaccharides are important for infants’ health. Which statement is not
correct?
a. HMOs consist only of lactose building blocks.
b. HMOs may contain both neutral and/or acidic sugar monomeric units as attachment.
c. HMOs may contain a glucose-amine building block linked to lactose.
d. Lactose dimer is not included in the definition of HMO.
5. Describe three in vitro fermentation models which can be used to study fibre fermentation
and mention for each model at least two advantages and disadvantages. Please limit your
answer to max 10-15 lines.
The 3-compartment continuous fermentation system (Reading model). This is a
fermentation model that is rather similar to the batch fermentation model. This
model mimics the different parts of the colon.
(+) There is the continuous feed and removal of (utilized) medium.
(+) There is a different pH per compartment, as this model mimics the ascending
colon (pH = 5.5), transverse colon (pH = 6.2) and descending colon (pH = 6.8).
(-) There is no dialysis (accumulation of metabolites) or peristaltic movement
incorporated in this model.
(-) A relatively long equilibration time is needed before having a stable microbiota
performance.
The Simulator of the Human Intestinal Microbial Ecosystem (SHIME). This a
commercially available fermentation model that can incorporate the entire GI tract.
(+) This model maintains microbiome stability for a relatively long time
(+) This model is very flexible and can be modified to the needs of the experiment.
(-) There is no dialysis (accumulation of metabolites) or peristaltic movement
incorporated in this model.
, (-) A relatively long equilibration time is needed before having a stable microbiota
performance.
The TNO’s in vitro fermentation model of the colon (TIM-2). Similarly to the SHIME
model, this fermentation model is commercially available.
(+) Both peristaltic movement and dialysis (no accumulation of metabolites) are
incorporated.
(+) This model offers possibilities to sample at many places.
(-) There is no feedback mechanism in the system
(-) There is a low throughput.
6. Please explain why butyric acid levels are increased when the diet of a human is enriched
with a prebiotic targeting Bifidobacterium, known to be a non-butyric acid producer.
Inulin is a prebiotic that targets Bifidobacterium. Inulin becomes degraded to all its
oligomers, making them available for all kinds of Bifidobacterium species. These bacteria
ferment these oligomers, producing lactate and acetate short chain fatty acids (SCFAs). These
SCFAs can than be used by other bacterial species to produce butyrate. This is an example of
cross-feeding. Cross-feeding is essential for Bifidobacterium, as they cannot produce butyric
acid themselves.
7. Explain why a glycosidic fermentation throughout the colon is highly relevant for host’s
health.
Glycosidic fermentation throughout the colon is highly relevant for host’s health, as this
protects the colon from performing protein fermentation. When glycosidic fermentation only
takes place at the beginning of the colon, proteins will be used as a substrate in the distal
part of the colon. Protein fermentation may lead to the formation of N-containing
compounds, which may be carcinogenic. The addition of resistant starch to one’s diet may
push other fibres to the distal part of the colon, achieving glycosidic fermentation
throughout the entire colon. Glycosidic fermentation may trigger different mechanism to
stimulate a healthy colon:
Faecal bulking.
Suppression of IBD inflammation.
Elimination of IBF antigens.
Prevention of allergy.
Reduced endogenous and exogenous intestinal infection.
Part 2:
1. Among the following items, which is the most important source of inoculum for the initial
colonization of the intestinal tract of new-borns?
a. The uterus of the mother.
b. The mother’s faeces.
c. The hands of the mid-wife.
d. Breastmilk of the mother.
2. Which of the following statements is wrong?
a. The large intestinal microbiota produces important nutrients for the surrounding
host tissues.
b. The composition of the intestinal microbiota is the same along the entire intestinal
tract, and only differs in concentration.
c. The majority of the intestinal microorganisms has not been cultivated yet.
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