代写QUIZ 5 Example Questions 2017代做Java程序

日期：2024-04-12 04:15

QUIZ 5 Example Questions 2017

. ???What?molecular?features?give?rise?to?the?colour?in?chlorophyll?

. ???Why?might?cooking?green?leaves?result?in?a?change?in?their?colour?

. ???Both?real?egg?yolks?and?the?yolks?of?chocolate?filled?cream?eggs??(which?contain tartrazine?!) appear yellow.

. ???What?classes?of?compounds?give?rise?to?these?yellow?colours?

. ???How?could?you?quantify?the?exact?difference?between?these?two?yellows?

. ???Why is it that if?you shine?a white?light?on?an?egg yolk?it?still?appears yellow?

. ???Egg?yolks?may?get?colour?from?carotenoids. ?Explain?why?feeding?chickens carotenoids results in deeper yellow egg yolks but does not turn egg whites?yellow?

. ???How can you explain that fresh meat often?has?a?different?colour?on?the?surface compared to its interior??

. ???Draw?the?general?structure?of?an?anthocyanin. ?Where?are?anthocyanins?found?and what?features?of?anthocyanins?are?of?importance?in?food?science?

. ???Explain?what?is?meant?by?the?aglycone?structure?of?anthocyanins. ?Is?this?the?most water soluble?form?

. ???Explain?why?the?colour?of?anthocyanins?is?pH?dependent.

. ???Why?do?raw?sweet?potatoes?readily?turn?brown?after?peeling?and?cutting?

. ???Name?3 ways?that?you?can?reduce?this?type?of?browning

. ???If?these?cut-up?peeled?sweet?potatoes?are?roasted??they?will?turn?brown?at?their surface. What?is?the?cause?of?this?type?of?browning?reaction?

. ???Anthocyanins?are?known?to?be?part?of?the?general?class?of C6-C3-C6 Flavanoids. Explain what is meant by this description and draw the basic anthocyanin?(flavan)?structure. ?Why might they be coloured compounds?

. ???Describe the molecular features?that?are?thought?to?give?rise?to?sweetness. Give an example of both a natural?and?synthetic?sweetener?and?outline?how?each of?them contains the molecular feature?you?have?described

. ???Describe the molecular features?that?are?thought?to?give?rise?to?colour.?Give an?example?of both a natural food?colour and a?synthetic?food?dye?and?outline?how each of?them contains?the?molecular?feature you?have?described

. ???Explain what gives rise to?the?colour?in?chlorophyll. In?your?answer?discuss?the various molecular features that most commonly?give?rise?to?colour?in foods.

. ???How do?chemical leavening?agents?(which?may?include?salts?like?sodium?bicarbonate) work and what is their function?in?foods?

. ???Chemical leavening systems?are?sometimes?mixtures?of several ingredients. Why is this necessary and what are the?functions?of?these?ingredients?

. ???What is meant by the?odour?(or?aroma) threshold??How?can?this value?be?determined?

. ???What are the characteristics of aroma?active?compounds? Give?3?examples?of?classes of molecules that are well-known odourants found?in?foods.

. ???Briefly describe?2 processes?that?can?result?in?the?formation?of ?volatile?aldehydes during food processing?or?storage?

. ???In what foods would you?expect to?find the?following?aroma?compounds:

a) ??Trimethylamine

b)??Hexanal

c) ??3-methyl butyl?acetate?(isoamyl?acetate)

d)??Furfurylthiol

(a)?At pH 5 a the predominant anthocyanin structure may look?like?the?structure

below. Explain why this is colourless whereas the flavylium ion and?many?other?flavonoids are coloured

(b)?Common anthocyanidins found in foods vary only by the number of?hydroxyl?and?methoxyl groups attached to the basic flavylium ion. Does this affect?the?colour of?these?compounds?and?why?

(a)?Why do raw sweet potatoes readily turn brown after peeling and/or cutting? In?your?answer?explain?the?types?of?compounds?involved.

(b)?Name?3 ways?that?you?can?reduce?this?type?of?browning

(c)?If?these cut-up peeled sweet potatoes are roasted they will turn brown at their surface. ?What?is?the?cause?of?this?type?of?browning?reaction?

(a)?Describe the molecular features that are thought to?give?rise?to?sweetness. Give an example of both a natural?and?synthetic?sweetener?and?outline?how each of?them contains the molecular feature?you?have?described

(b)?Chemical leavening systems are sometimes mixtures?of several?ingredients.

Why is this necessary and what are the?functions?of?these?ingredients?

(c)?What is meant by the odour?(or?aroma) threshold??How?can?this value?be determined?

1)??For each of?the following compounds?indicate?if?you would?consider?it?to?bean?aroma active compounds.?For those that are, indicate?atypical?food??source?of??such an?aroma.

(a)?Trimethylamine

(b) 3-methylbutyl acetate?(isoamyl?acetate)

(c)?Monosodium glutamate

(d) Limonene

(e)?Furfurylthiol

(f)??Stevioside

(g)?Hexanal

1. ??Why is spinach green coloured?whereas?refined?sugar?is?often?white???In?your answer describe the physical reason why?some?substances appear?as?coloured?and the molecular features that give?rise to?colour.

2. ??If?you were to record the visible?absorption?spectrum?of?the green?pigment?from?spinach what would be the main?features you would?see?

3. ??At pH 5 a the predominant anthocyanin structure may?look?like the?structure below?on?the left whereas at pH 7 the structure on?the?right predominates.

(a) Which of?them is coloured and which is colourless?and?why???(3)

(b) In each case, explain what might be the effect on?its?colour?if?some?of?the?hydroxyl groups (-OH) were replaced by methoxy groups (-OCH3)? ?(?1)

4. ??What is the reason that ground beef?is typically red and tends to go brown?on the surface whereas freshly cut beef?is purplish red?

5. ??Why does blanching fruits/vegetables inhibit enzymatic browning?

1. ??In what ways?do the?following?types?of sweetener?differ???(Think?of both their?chemical form(s) and their sensory or?physical?effects?in?foods)??(6)

1.???Sugar?(sucrose)?crystals

2.???Stevia

3.???Sorbitol

4. ??(a) What?are?the?characteristics?of?aroma?active?compounds and?what?is?meant?by?the?odour?(or?aroma)?threshold?

(b) Nonanal?has?an?odour?threshold?of?~1μg/kg?dissolved?in??water?but?>10,000?μg/kg?dissolved?in?oil. Explain?what?might account for this large difference?.

5. ??(a) What?classes?of?aroma?active?compounds?would?you expect?to?find?in?foods?as?a?result?of?:

i.?Oxidation?of ω-6 fatty?acids

ii.??????Fruit ripening

iii.????Fish?ageing

(b) Which?of?the?following?describes?1 part?per?billion? (1)

i. 1μg/mL

ii.??????10pg/g

iii.?????1ng/kg

iv.?????1μg/kg

v?. ??????1pg/g

6. ??In?eggs, the?yellow?yolks?are?usually?separated?from?the?whites by?a?membrane. If?this?membrane?is?broken?would?you?expect??the?yellow?colour?to?migrate?into?the?white? Explain?your answer?using?your?knowledge?of?food?chemistry. (hint: lutein?is one of?the yellow?colours)

7. ??Give?examples?of?3 distinct?types?of?emulsifier?and?for?each?a?brief?explanation?of how they function as?an?emulsifier.

8. ??Explain what is meant by HLB value and for each?of?the?3 types you have?described?above indicate with reasons whether you expect the HLB value to be >7 or <7

9. ??How could you form. a nanoemulsion from an?oil/water mixture?and?what?would be the advantage in doing over compared to gently?stirring the two?components?together?

10. Explain how emulsifiers help to stabilize emulsions.