Functionality of Protein

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2 Protein Polymers of aa:20 different aa Primary structure aa sequence Secondary structure- chains take up conformations which may crosslink to form helices ie α helix and β pleated sheet Tertiary structure- helices fold in various ways to form bulky irregular shapes. Diff non-covalent bonds are responsible for tertiary structure Quaternary structure- three dimensional structure that determines its properties

3 Functionality of Protein aa content controls functionality of proteins Proteins are denatured by heating, resulting in viscosity increases functional structure is lost, increased digestibility Primary structure is not disrupted Change in ph, salts may also cause denaturation During processing such as breadmaking proteins are exposed to these effects Denaturation is non reversible event, but can be reversed in some cases- when denaturation agent has been removed

4 Protein as enzymes Act as enzymes in enzymes ie proteinases, lipases Hydrolytic enzymes make a critical contribution in the malting of barley Provides nitrogenous nutrients for germinating and in growing plants Provides nutrients for fermentation processes Provides rheological properties especially wheat and rye to form extensible, elastic, gas retaining doughs in breadmaking Need right type of glutens to make extensible doughs

5 Protein dough forming prperties Among all cereals wheat has the ability to form a strong cohesive dough due to presence of gluten In milling wheat to white to white flour the total protein content decreases Protein of other grains do not have dough forming properties. Protein content important in the determination of price in animal feeding

6 Protein composition Composition provides valuable indication of genotype, for distinguishing between varieties within a species, Serves in analyses of taxonomic relationships. Critical at several levels, namely, as amino acids (composition being relevant to feedvalue),as the amino acid sequence(relating to characterization),as polypeptides (valuable to indicate genotype), and as native proteins (as enzymes or with other functional properties). All these aspects of protein composition relate to grain quality for wheat.

7 Protein composition Other proteins of wheat endosperm are identified as markers of important quality attributes: Granule-bound starch synthase (for starch properties), The purindolines (in relation to grain hardness), and various hydrolytic enzymes(produced in relation to grain defects) Protein content is a critical aspect of grain quality for all grain whether protein relates to feed quality or to specific functional properties, such as for barley and wheat.

8 Protein content Varies from between 6-27% due to genetic and environmental effects Other effects of protein content : availability of nitrogen ie drought Protein content is important for nutritional as well as functional reasons As plant produces more protein less is required for physiological functions and more is available for storage

9 Protein content Protein Content Corn, sorghum and pearl millet are used to make dough type products eg tortilla,roti or chapati of India In maize, protein occurs in the endosperm as discrete protein bodies and as matrix and has high levels of glutamic acid and leucine Endosperm contains 5% albumins and globulins, 44% zein, 28%glutelins. The other fraction 17% found in wheat by Osborne Mendel classification

10 Protein content A higher protein content generally attracts better market value, A lower protein content (not too low) is desirable for malting barley as a high potential for starch modification is needed during malting and brewing

11 Protein Classification Osborne Classification Wheat protein divided into 4 classes based on solubility 1. Albumins- soluble in water :metabolically active 2. Globulins- soluble in dilute salt solutions (10% NaCl) but insoluble in water: metabolically active Metabolically active proteins contain lower glutamic acid and proline with higher lysine and arginine ( higher biological value)

12 Protein Classification- Osbourne classifcation 3. Gliadins- soluble in 70-90% alcohol (storage protein) 4. Glutenins- insoluble in neutral aqueous solutions, saline solutions, alcohol but soluble in acids and bases (storage proteins) *** Gliadin and Glutenin reserved for wheat proteins Prolamins and Glutelin equivalent for protein fractions of other cereals Storage proteins have large proportions of glutamic acid and proline and small amounts of lysine, arginine, threonine and tryptophan

13 Protein Classification Advantages: Fractionation of protein gives reproducible results Gives some information about proteins Disadvantages: Fractions are mixtures of different proteins Each protein group has subgroups and none of the subgroups consists of a pure protein Some proteins do not fall into any of the four groups There is residue protein even after extraction procedure of Osborne (some proteins are just insoluble)

14 Importance of protein classification 1.Aquire nutritive as well as biological value knowledge 2.Location of such protein in grain to allow manipulation of milling process so as to get required protein content for processed foods 3.Grading of a particular flour/grit depending on protein content and aa availability 4.Protein or aa supplementation to compliment different grains thus maintaining product consistency

15 Possible Protein classification On basis of morphology On basis of biological function According to solubility (Osborne) On basis of chemical composition Endosperm proteins Proteins of the aleurone layer Proteins of the embryo Metabolically active cytoplasmic proteins Enzymes Membarane ptns Ribosome ptns Regulatory ptns Other proteins Storage proteins Low mwt ptns High mwt ptns Albumins Globulins Prolamins Glutelins Residue proteins Simple proteins Complex proteins Lipoproteins Glycoproteins Nucleoproteins Metalloproteins Chromoproteims Phosphoproteins

16 Protein Starch Complex Starch surrounded by protein in a matrix-endosperm Explains kernel hardness In soft grains protein starch bond ruptures easily and kernel crashes with minimal force In harder grains protein starch bond is stronger Matrix affects hardness as well as appearance ie vitreous /hornlike/transluscent and opaque/mealy/floury

17 Protein Starch Complex Opacity- air spaces in kernel diffract and diffuse light and make the kernel appear opaque and floury Air spaces are formed during grain drying. As grain loses water protein shrinks, ruptures and leaves air spaces Translucent -tightly packed kernels with no air spaces light is diffracted at air grain interface but travels through grain without being diffracted again and again

18 Protein Starch Complex Vitreous - endosperm shrinks but remain intact giving a denser kernel In general high protein hard wheat tend to be vitreous and low protein soft wheat tend to be opaque Hardness also caused by genetically controlled strength of the bond between protein and starch in the endosperm

19 Lipids The relatively small amount of lipid of cereal grains is mainly associated with the germ (embryo) and scutellum tissues. lipids in cereals contain a high concentration of unsaturated fatty acids, UFA are protected in the intact grain from oxidation by the presence of tocopherols. The oil from wheat germ was the starting material for the isolation of α-tocopherol (vitamin E).

20 Lipids Cereal grains stored as whole kernel Milling destroys integrity of the grain, bringing lipases in contact with their substrates. Oat grain has a relatively high lipid content, and milled oats are steamed to inactivate lipase activity immediately after removal of the husks by abrasive milling.

21 Lipids Hydrolytic and oxidative rancidity are estimated by determining the free fatty acid content: The amount (in mg) of potassium hydroxide required to neutralize the free fatty acids from 100 g of moisture-free grain= fat acidity value Milling removes the germ to reduce lipid concentration and the risk of oxidative rancidity to extend shelf life.

22 Average gross composition % Dry weight basis Cereal Grains Protein Fat Starch Fiber Ash Wheat Rye Barley Oats Maize Millet Sorghum Rice