ALS14SA(FOOD) - Section 14.2 Chemistry and food 1 SKH...

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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)
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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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