Enzymic analyses of sweet potato AusAID CARD Project 008/07VIE Workshop 4, FCRI February 2009 Les Copeland University of Sydney Outline  Theory  Starch  Maltose, sucrose and D-glucose  α-Amylase Sweetpotato (Ipomoea batatas L.)  Belongs to Convolvulacae family – different family to potato  Grown in over 100 countries, mostly by small holder farmers – ranked seventh in world crop statistics  Diverse uses of sweetpotato roots – food for humans  good source of edible energy (starch)  proteins and vitamins (A and C)  dietary fibre – animal feed – flour and starch for domestic and industry use  noodles, natural colorants, snack foods, alcoholic beverages Postharvest  Sweetpotatoes best stored at 13–15°C and 80–90% relative humidity  Quality deteriorates rapidly during postharvest storage; changes evident as early as the second week of storage – loss of water and dry matter content – reduction in starch content, increase in total sugars – changes in texture and taste, starch properties – high temperatures increase rate of deterioration  Weight loss caused by metabolism in the root – greater just after harvest – greater in roots with low DM content; have a shorter storage life – greater in damaged roots  Microbial spoilage; greater in damaged roots Composition of fresh sweetpotato roots 1-1.5%Ash 0.001-0.014%Carotenes 2-6%Lipid 1-2.5%Protein 0.5-5%Sugars 0.5-7.5%Non-starch polysaccharides 8-30%Starch 50-80%Moisture Composition varies according to cultivar, environment, cultivation practices, postharvest storage Composition of sweet potato root dry matter 0.6-5%Ash 1-2%Lipid 1-10%Protein 5-30%Sugars 0.5-7.5%Non-starch polysaccharides 50-80%Starch  About 90% of dry matter as carbohydrates  Sweetness is due to sugars  mainly maltose (formed by starch hydrolysis), but also sucrose, glucose, fructose  Composition determines nutritional properties and quality  taste, texture, firmness, mouthfeel  Starch is a major determinant of sweetpotato quality Starch is an important industrial material Worldwide, 60 million t/yr manufactured from wheat, corn, potato, rice, cassava, sweetpotato – 60% used in foods bakery products, sauces, soups, confectionery, sugar syrups, ice cream, snack foods, meat products, baby foods, fat replacers, coffee whitener, beer, soft drinks, … – 40% for non-food uses pharmaceuticals, tablets, feeds, fertiliser, seed coatings, paper, cardboard, packing material, adhesives, textiles, fabrics, diapers, building materials, cement, oil drilling, … – Demand for starch for industry in VN is about one million tonnes annually Starch is a natural polymer Polymers may be  Homopolymers  Heteropolymers  Unbranched  Branched Solubility of polymers  Solubility in H 2 O is related to size and how well polymer molecules fit together  Large linear polymers with regular structures tend to be more stable in solid (insoluble) state; form semi-crystalline structures – solubility is increased by branching and substituents Crystalline Semi-crystalline Random coils Crystalline Semi-crystalline Random coils Polysaccharides gels are common in foods  Gels have a network in which there localised regions of ordered interactions between polymer molecules (junction zones)  Junction zones are held together by weak intermolecular forces – hydrogen bonds, ionic interactions, hydrophobic interactions  Gel networks entrap liquid, including dissolved solutes Gel networks [...]... and AP content of common food starches Starch source AM AP Wheat 25 75 Corn 25 75 Waxy corn 99 55-70 45-30 Potato 20 80 Rice 19 81 Tapioca 17 83 Sweetpotato 20 80 High AM corn Properties of amylose and amylopectin Amylose Amylopectin DP 1000 and 20,000 DP 300,000 – 3,000,000 MW 130,000 - 3.5 x 106 Low solubility in water MW > 108 Soluble in water Firm gels, good film properties Very soft gels High... starches) Granule size of common food starches Source Diameter (µm) Wheat 1-50 Corn 5-30 Rice 1-5 Potato 5-100 Sweetpotato 5-40 Isolated wheat starch granules Rice starch granules in situ Starch structure AM (10-35% of most starches) Essentially unbranched α[1 → 4] links (0.2 - 0.5% α[1→6] links) AM AP (65-90% of most starches) Highly branched α(1 → 4) and 4 - 5% α[1→6] links Complex molecular architecture... constituent of many foods – 50-70% of dietary energy intake of humans Homopolymer of glucose made up of two fractions – amylose (AM) and amylopectin (AP) Deposited in insoluble semi-crystalline granules – vary greatly in size (1-100 µM) between and within species – moisture content is 10-12% – contain small amounts of lipid (0.1% in root and tuber starches, 1-2% in cereal starches) Granule size of common... rheological properties Decrease gel rigidity, retard retrogradation Reduce susceptibility to enzymic hydrolysis Involve only amylose Starches vary considerably between and within species Size, shape, degree of crystallinity of granules Content and properties of AM and AP, branching architecture of AP Organization of AM and AP into crystalline and amorphous phases in starch granules Influenced by genetics... Measurement of starch Total starch Starch damage – milled grains, water absorption Degree of gelatinisation and retrogradation – properties of cooked starches AM/AP ratio – plant breeding, specific industrial/food applications Resistant starch – dietary fibre, nutrition Analytical methods Physical, chemical and biochemical analyses of form and structure – AM and AP content, structure and properties of AM... dimethyl sulfoxide – low solubility and tendency to retrogradation of high AM starches may be a problem Removal of interfering compounds – mono-, oligosaccharides removed by washing with ethanol – lipids removed by dissolving starch in DMSO and precipitating with ethanol Drying to known moisture content (usually 10%) Extraction of starch from sweetpotatoes Roots are cut and crushed in water Starch is left... (pure starches only) – enzymic hydrolysis with specific glucose determination (generally applicable) Extraction of starch Obtaining a representative sample is essential – starch should be extracted quantitatively, as unchanged as possible from its in situ form Appropriate sample preparation – milling/grinding/blending to fine particle size – grains softened by soaking in solution of NH4OH Starch is extracted... of AM and AP molecules Microscopy and imaging (form of granules, gels) X-ray and neutron scattering techniques (crystallinity of granules) Functional analyses – Rapid Visco Analyser (gelatinization, viscoelasticity) – Differential Scanning Calorimetry (transitions related to heating) – starch swelling power (water absorption) – susceptibility to enzymic attack by α-amylase (digestibility) Quantitative... amorphous phases in starch granules Influenced by genetics and environment Affects the functional and nutritional properties, digestibility, suitability of grains for end uses Variability of starch properties causes problems for industry – extensive use of modified starches – trend towards “more natural” ingredients Raw and processed starch are very different Most starch in foods has been processed –... (centrifuged) Starch is air-dried Addition of lime to increase pH enhances yield and improves colour Dissolved AM, AP and starch can be quantified by iodine binding Iodine (I5-) is included in α[1→4]glucan chains of DP > 12 to form a coloured complex CL > 100 λmax ~700 nm CL ~ 25 λmax ~550 nm Glycogen 500 nm AP AM 600 nm 700 nm Older methods for determination of starch Pre-extract sample with hot 80% . a major determinant of sweetpotato quality Starch is an important industrial material Worldwide, 60 million t/yr manufactured from wheat, corn, potato, rice, cassava, sweetpotato – 60% used in. Enzymic analyses of sweet potato AusAID CARD Project 008/07VIE Workshop 4, FCRI February 2009 Les Copeland University of Sydney Outline  Theory  Starch . 10-12% – contain small amounts of lipid (0.1% in root and tuber starches, 1-2% in cereal starches) Granule size of common food starches 5-40Sweetpotato 5-10 0Potato 1-5Rice 5-30Corn 1-50Wheat Diameter