Food Biochemistry Past Paper PDF 2021/2022

## UNIVERSITY OF CAPE COAST ### COLLEGE OF AGRICULTURE AND NATURAL SCIENCES ### SCHOOL OF BIOLOGICAL SCIENCES ### DEPARTMENT OF BIOCHEMISTRY **END OF FIRST SEMESTER EXAMINATIONS: 2021/2022** **BCH 431: FOOD BIOCHEMISTRY** **TIME: 2 HOURS** **SECTION A (50 marks)** **ANSWER ALL QUESTIONS IN THIS S...

## UNIVERSITY OF CAPE COAST ### COLLEGE OF AGRICULTURE AND NATURAL SCIENCES ### SCHOOL OF BIOLOGICAL SCIENCES ### DEPARTMENT OF BIOCHEMISTRY **END OF FIRST SEMESTER EXAMINATIONS: 2021/2022** **BCH 431: FOOD BIOCHEMISTRY** **TIME: 2 HOURS** **SECTION A (50 marks)** **ANSWER ALL QUESTIONS IN THIS SECTION** 1. Explain, with examples, the formation of clathrate hydrate. [5 marks] Clathrate structures result from water interactions with non-polar substances. They are ice-like structures where water (the host) physically entraps the low molecular weight compounds (guest - hydrocarbons, rare gases, carbon dioxide, sulfur dioxide). The interaction may be through van der Waals or electrostatic interaction. 2. Explain the difference in dough formation of maize flours with and without calcium hydroxide. [6 marks] The flour with calcium hydroxide will need more water to form dough than the one without calcium hydroxide. This is because, calcium is a net structure forming when in water, and so the flour will not easily hydrate in the presence of water and will require more than it is needed for one with no calcium. 3. Which commercial starch enzyme(s) could be used for the production of the following products and why? [6 marks] a. Bel Malt * Exo-amylases - removes glucose or maltose from the non-reducing ends of starch by cleaving a-1,4-glucosidic bonds e.g. glucoamylase (GA) and β-amylase. * Debranching enzymes - cleave starch molecules at a-1,6-glucosidic linkages, e.g. amylo-1,6-glucosidase (pullulanase). b. Ruut beer * Endoamylase (α-amylase), Exoamylase (glucoamylase (GA) and β-amylase) and debranching enzymes amylo-1,6-glucosidase (pullulanase). * The amylases will make glucose and maltose available which will be acted upon by yeast to provide the alcohol that is associated with beer. Debranching enzymes will lyse a-1,6-glucosidic linkages. 4. Using chemical structures, show the importance of protein in enzymatic browning. [6 marks] *Image of chemical structures depicting enzymatic browning with monophenal, ortho-diphenol, and quinone* 5. Explain the incidence of colour loss in an enzymatically clarified orange juice. [5 marks] An example of clarification enzymes is pectinase. Some commercial pectinase products contain anthocyanase (α-glucosidase). Fruit juices contain anthocyanins. Treating fruit juice with anthocyanase will help to convert the anthocyanins to anthocyanidins and glucose, changing the aglucones to colourless derivatives. 6. Indicate, with explanation, the type(s) of non-enzymatic browning in each of the following products: [8 marks] a. Nkatle coke - caramelization, sucrose is cooked to brown which serves to bind the ground roasted peanut. b. Roasted ripe plantain - since it is ripe, it is possible for the sugar(s) to undergo browning by caramelization. However, there may be some amino-carbonyl reactions resulting in Maillard reaction browning. c. Aheil/Nmeda/Asaana - caramelization, this is basically in the sugar which is heated to brown before it is added to the malt extract. d. Bread - all breads have some amount of sugar as ingredient. In most cases, it is to provide nutrient for yeast to aid in rising of the dough. Depending on the type, which means it may have more sugar than required for yeast activation, there will be caramelization. Moreover, since wheat flour is rich in amino acids, it is possible for some Maillard reaction to take place if somehow, there is availability of reducing sugar. 7. Briefly explain the mechanisms leading to syneresis in carbohydrate and protein. [6 marks] * In carbohydrate, syneresis, which is exclusion of water occurs after retrogradation, an association of molecules to form crystalline sections. * In protein, syneresis occurs due to denaturation which causes protein-protein interaction. **SECTION B (50 marks)** **ANSWER ALL QUESTIONS IN THIS SECTION** 10. a. Explain why lipid oxidation is considered a free radical mediated process. [15 marks] It has been characterized by such events as: * Marked inhibition in rate by chemical species known to interfere with other well-established free radical reactions * Catalysis by light and by free radical producing substances * High yields of hydroperoxides, ROOH. And so, it is characterized by three major steps: initiation, propagation and termination. **Initiation** * Abstraction of hydrogen from a fatty acid chain. * Produces free radical (R, peroxy radicals ROO.). **Propagation** * Molecular oxygen (O₂) combines with free radicals to form peroxy radicals, ROO". * Peroxy radicals in turn abstract hydrogen atom from α-methylenic groups of RH to form hydroxyperoxides (ROOH) and free radicals (R). * New R' groups react with molecular oxygen and the sequence is repeated. **Termination** * This occurs when free radicals combine to form non-radical products. 10. b. Which specific test will be used to test for lipolysis in each of the following products and why? [10 marks] i. Fresh tuna - thiobarbituric acid test (TBA), this is used to test for lipid oxidation in systems that have at least three double bonds; Iodine value test could also be used since it is able to measure the level of unsaturated linkages in fat/oil, and marine oils such as in tuna has high number of unsaturated linkages. ii. Vegetable oil - Iodine value test could also be used since it is able to measure the level of unsaturated linkages in oil, and vegetable oils are rich in essential fatty acids such as oleic and linolenic and linoleic acids. iii. Cocoa butter - Saponification value (SV) and free fatty acid value could be used to test for lipolysis. SV will measure saponification of all acylglycerols and free fatty acids while FFA value will measure fatty acids that have been freed due to lipolysis. iv. Fresh milk - Iodine value test could also be used since it is able to measure the level of unsaturated linkages in oil, are rich in palmitic, oleic and stearic acids. SV and FFA test could also be used. Since it is rich in short chain fatty acids. 11. a. What conditions are necessary for each of Maillard reaction and caramelization to occur in foods. [5 marks] * Maillard reaction - proteins (aa), reducing sugars and heat (high temperature). * Caramelization - sugars and heat. 11. b. Describe the steps leading to browning development in soybean flour that has been kept for a considerable time on the shelf. [15 marks] 1) sugar-amine condensation, 2) rearrangements of condensation products, 3) dehydration of rearranged products, 4) degradation and fission reactions, 5) polymerization of brown products. 11. c. Briefly explain any five steps that can be used to decrease browning in the soybean flour in 'b'. [5 marks] i. Refrigeration - this decreases temperature which is an important factor in non-enzymatic browning. ii. Control of water activity in dehydrated foods. iii. Reduction of RS content in foods by storage or treatment with glucose oxidase. iv. Reduction of amino acids. v. Packaging with oxygen scavengers. *Use of sulfites including sulfhydryl-containing amino acids e.g. cysteine, methionine.* 8. What is the Osborn classification of proteins? [4 marks] a. Albumins - soluble in neutral distilled water e.g. egg albumin, ovalbumin. b. Globulins - soluble in neutral dilute salt solutions e.g. myosin, β-lactoglobulin. c. Glutelins - soluble in dilute acid/base, but not neutral solutions e.g. glutenin. d. Prolamines - soluble in 50-90% ethanol and insoluble in water e.g. zein (corn) and gliadins (wheat). 9. Distinguish between lipolysis and lipid oxidation. [4 marks] * Lipolysis - hydrolysis of the ester linkage in lipids to fatty acid and glycerol which could result from heating, chemical reaction (saponification) or enzymatic reaction (lipase). * Lipid oxidation is the oxidation (reaction with molecular oxygen) of the fatty acids resulting from lipolysis leading to production of off-flavours and off-odours in fat containing foods and decrease in nutritional quality.