ALS14SA(FOOD) - Section 14.2/ Chemistry and food / SKH...

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Unformatted text preview: Section 14.2/ Chemistry and food / SKH Bishop Baker Secondary School AL Chemistry Section 14 Chemistry and Society (14.2 Chemistry and food) AS95A Q.7 ( II ) Chemistry and food (i) The browning process initially involves an oxidation of the phenol in apple (to give a diquinone) which [ ½ ] polymerizes to form a brown compound . [ ½ ] Sulphur dioxide is a reducing agent /an antioxidant which [ ½ ] prevents atmospheric oxidation of phenols . [ ½ ] ∴ browning is prevented. (ii) preservative. [1] (ii) attack the respiratory system (Do not accept SO 2 is harmful). [1] (b) Sodium citrate NaX together with citric acid HX form a buffer system. HX === H + + X- Presence of a small amount of H + or OH- in the system will be taken up by the X- and HX respectively. [1] (b) As a sweetener/increases the nutritional value. [1] AS96A Q.4 ( II ) Chemistry and food (a) (i) Marking one of the three peptide linkages. [1] (ii) (Accept the Zwitterion, cationic and anionic forms of the amino acid.) [1] AS96A Q.7 ( II ) Chemistry and food (a) carbonated water [1] (b) water containing carbon dioxide under pressure [1] to confer to the drink a sharp taste /CO 2 can remove heat [1] from the body and hence can produce a cool feeling . (b) Aspartame/saccharin [1] (c) Brown to dark colour [1] because of presence of caramel [1] (d) To control acidity /to confer a sour taste [1] (e) Stimulant [1] 1 (1) Section 14.2/ Chemistry and food / AL90IA Q.1 (b) (i) (ii) Hemiacetal group [ ½ ] account for reducing properties. This is because they exist in equilibrium [ ½ ] with the open chain form (i.e. aldehyde form ). [ ½ ] R’- O O- H === R’- OH + RCHO R H Non-reducing form is NOT a hemiacetal. [ ½ ] AL91IA Q.1 (c) Dipeptide : R O R’ R O - H 2 N- CHCNHCHCO 2 H or H 3 NCHCNHCH(R’)CO 2 [2] Note : The dipeptide must be formed from α-amino acids (R, R’ can be H- , CH 3- , Et- /C 2 H 5- , (CH 3 ) 2 CH- , Ph- /C 6 H 5- , etc....
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This note was uploaded on 08/17/2011 for the course CHEM 100 taught by Professor Fleet during the Fall '08 term at Oxford University.

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ALS14SA(FOOD) - Section 14.2/ Chemistry and food / SKH...

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