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148 Cards in this Set
- Front
- Back
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What are the goals of wet milling? |
To anatomically separate the germ and pericarp To isolate the starch and protein |
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How must maize be physically modified for wet milling? |
* Kernel hydration * Plasticization of hull and germ * Swell germ *Chemically modify endosperm protein to release starch |
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Name two aspects unique to maize wet milling |
* Effluent recovery - water leaves the system only as stem *Counter-flow water movement |
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Describe "steeping" |
In the process of wet milling maize, kernels are steeped in tanks at high temperature and SO2 with XS water running counter current |
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Function of SO2 in steeping |
*Control fermentation *Modify proteins by cleaving disulfide bonds |
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Describe the fermentation that occurs during steeping |
Lactobacillus produces lactic acid early in production, reducing pH and inhibiting other bacteria |
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What happens to the germ in maize wet milling? |
It is released in the first and second grind mills (function is to release germ and not to reduce the endosperm) The germ is recovered using density-based hydrocyclones |
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After the germ has been removed in maize wet milling, what is the next step? |
The fiber, protein and starch is separated in the third grind using double disk attrition mills which grind finely |
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What happens to the fiber in maize wet milling? |
About 8-15% of the initial dry weight of the kernel is fiber Insoluble fiber is caught as an "over" and then goes to the dewatering press then to the feed dryer |
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How is the starch and protein recovered in maize wet milling? |
Soluble starch and proteins are separated based on density differential using continuous, sequential centrifuges or hydroclones Higher density starch sinks out (underflow) Starch is purified through washing/hydrocloning then dried |
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What happens to the protein recovered in maize wet milling? |
Separated from starch using hydroclones (less dense than starch) Protein in concentrated and dried, may be combined with steep solids Referred to as corn "gluten" |
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Name four differences between wheat and maize wet milling |
1. Wheat milling primarily produces vital wheat gluten 2. Starch is the primary product of maize milling, but secondary product for wheat milling 3. Wheat milling starts with flour, maize with whole kernel 4. Wheat process differences: no counter flow, no concentration of steep, no SO2 |
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What materials are used to start the wet wheat milling process? |
Low grade flours such as clear or high extraction Higher quality flour can be used, but is more expensive Whole wheat flour is more difficult to process Flour is first made into a thick batter / weak dough |
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What is the first process step of wet wheat milling? |
Washing/kneading Goal is to form gluten (protein self-associates and starch will separate) Creates water-soluble slurry |
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What happens in wet wheat milling after the washing step? |
Product is screened Through: starch, solubles, water Retained: crude "gluten" |
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How is the soluble starch isolated in wet wheat milling? |
Isolated using centrifuges, hydroclones, starch tables, or sieves Goal: remove remaining gluten Then dry (explosion hazard) |
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What are the grades of wheat starch? |
Prime - valuable, mostly large lenticular granules B - mostly small and/or damaged granules, also includes cell walls and WU arabinoxylans |
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How is wheat gluten isolated? |
After screening it is critical to retain functional properties ("vital") Drying must be well calculated as heat damage will reduce functionality |
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What are the basic steps in wet milling rice? |
* Protein and starch is very tightly associated, must be dissociated by steeping at alkaline pH * Recover starch using centrifuge, drying is similar to wheat starch *Protein must be neutralized |
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What are the major characteristics of wheat germ oil? |
Very minor presence in marketplace Oil is highly unsaturated, so very perishable High in vitamin E |
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What are the two major cereal oils? |
Rice bran oil - byproduct of solvent extracted bran Maize germ oil - used in cooking and frying |
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How is maize oil produced? |
Germ is flaked and steamed Processed through expeller at high temperature and pressure Several passes are made to achieve about 95% recovery Residue = foots (used for feed, solvent extracted) |
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What are the two ways oil can be extracted from maize germ? |
Expeller - problem with overheating the oil Extraction - use large volumes of hexane in a sealed system, high recovery and good quality |
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What process steps are used to further treat crude maize oil? |
Particulate removal Alkali treatment Bleaching Winterization Deodorizing |
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How are particulates removed from crude maize oil? |
Filter press |
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Describe the alkali treatment used on crude maize oil |
Short time necessary to prevent saponification Converts free FA and polar lipids to water soluble salts |
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Describe bleaching of crude maize oil |
Pigments/flavors adsorbed by acid activated clay |
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Describe winterization of crude maize oil |
Rapidly cool oil, hold, and filter Removes those molecules that are insoluble at low temperatures to prevent clouding |
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Describe deodorization of crude maize oil |
Vacuum distill at high temp to remove volatile compounds (flavors, aromas, color) |
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How is maize oil packaged? |
UV-intercepting material inhibits rancidity |
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Starch in plants |
Temporarily in leaf, long term in endosperm Granules formed in amyloplasts |
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How is starch chemistry different from typical polymer chemistry |
Branched polymer is crystalline Linear is amorphous |
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How are starches used outside of the food industry? |
textiles pharma paper wallboard, drilling mud |
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What are the sources of starch? |
cereal grains roots and tubers fruits lentils/beans/peas |
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Mineral component of starch |
phosphorus from phospholipids in cereals not covalently linked to starch polymer (it is in potato) Nitrogen at low levels from lipid and protein |
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What is the major component of starch |
alpha-D-glucose referred to as dextrose in industry |
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Describe the two forms of glucose |
Open chain = aldehyde, reduces Cu++, a reducing sugar, basis for assays Ring form = hemiacetal, cannot reduce Cu++ |
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Linkages of starch vs cellulose |
Starch - alpha-1,4 linkage Cellulose - beta-1,4 linkage |
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What is amylose |
Minor polymer of starch Usually 20-30% Linear with alpha-1,4 linkages 80K-1000K MW; 500-6,000 AGU |
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What are the properties of amylose? |
Strongly interacts with self and other CHO polymers Results in strong gels and films Stable helix: left handed, 6 AGU repeat that maximizes h-bonding opportunities intra chain and inter chain Helix can trap molecules in the core (iodine, FA, alcohols) |
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What is a clathrate? |
Complex of amylose helix and molecule trapped within |
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How are clathrates used? |
FA clathrate - reduce granular swelling, viscosity Iodine - used to quantitate amylose |
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What is amylopectin |
major glucose polymer (70-80%) Branches with individual alpha-1,4 linkages with branch points at alpha-1,6 linkage Very large 100,000K MW, 600,000 AGU Highly branched (about 5% of bonds) |
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Describe the branching structure of amylopectin |
A chains = outer chains with no branches and no free reducing groups B chains = at least 1 branch point and no free reducing group C chains = at least one branch point and contains the ONLY reducing group for the entire molecule |
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How does amylopectin interact? |
with self and other molecules primarily with A chains (h-bonding, entanglement) Basis of granular structure and integrity |
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What is the typical amylose:amylopectin |
Ratio generally consistent within plant species Normal cereals 18-33% amylose Rice has large variation, more amylose=less sticky |
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What is considered "waxy"? |
Essentially 100% amylopectin |
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What is considered "high amylose"? |
Up to 70% amylose |
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How are starch granules organized? |
About 30% is crystalline, rest is amorphous Many small crystalline regions = crystallites Regularly arranged in granule as shown by birefringence |
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What is birefringence? |
light and dark regions when viewed under polarized light pattern indicates crystal arrangement in starch = Maltese cross with arms crossing at hilum There is NO direct correspondence of light and dark to crystalline and amorphous |
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Why are starch granules so insoluble? |
Interactions of h-bonding Crystallites are very organized, no room for H2O Amylopectin ties together |
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How are starch granules disrupted? |
crystallites must be melted replace intermolecular h-bonding with water h-bonding energy is required |
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Relationship of amylopectin and crystallites |
Amylopectin and not amylose is important for crytallites Amylose is not necessary for birefringence |
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What is the French-Kainuma model |
Granule grows radially, shown in growth rings length of crystallites limited by max length of amylopectin chains |
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How does starch behave in XS water at RT? |
About 30% absorption Slight granular swelling Water uptake and swelling is reversible Birefringence and crystallinity not lost Solubility not changed |
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How does starch behave in XS water at elevated temps? |
Simultaneous irreversible changes * granular swelling * water uptake * Birefringence lost *crytallinity lost *system viscosity increases Occurs at specific and characteristic temp |
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Define solubilization |
Starch granule dissolves, starch molecules are lost to the water |
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What molecular changes occur during gelatinization? |
h-bonds disrupted molecules plasticize amylose solubilizes |
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What two things are required for gelatinization? |
1. heat - increases molecular motion 2. water - plasticizes the polymer |
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What occurs after gelatinization? |
Pasting *granule continues to swell *granule is totally disrupted |
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What is retrogradation? |
After gelatinized/pasted starch cools, molecules reassociate into ordered structure |
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How is a paste defined? |
starch granules that have been heated sufficiently to: 1. lose birefringence 2. solublize part of the granule *primarily or exclusively viscous |
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How is a gel defined? |
Liquid-polymer system with some properties of solids (elasticity) Small amount of solid will control a large amount of liquid |
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What are characteristics of starch gels? |
Distance between the chains is large water in the gel behaves like pure water occurs at low conc of starch more time and cooling leads to firmer gel |
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List three ways the gelatinization process can be measured |
1. polarized light microscopy 2. DSC differential scanning calorimetry 3. recording viscometer |
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What does a viscoamylograph show? |
starch in XS water with controlled heating, holding, and cooling *Pasting *Peak viscosity *Shear thinning *Set back |
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What regions can be identified in viscograph curve? |
1. Pasting - granular swelling, dissolution, temp dependent 2. Cooking - no further solubilization w/o more temperature, decrease in viscosity attributed to shear thinning 3. Set Back - cooling, viscosity increases, more h-bonding as motion slows, gel may form if not stirred 4. Retrogradation - more h-bonding, syneresis |
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How do damaged starch granules behave? |
Similar to gelatinized starch More digestible Less order/structure More viscosity More water absorption More susceptible to amylase |
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Effect of alpha-amylase |
Endo-hydrolase: randomly breaks a-1,4 links Breaks both sides of a branch point w/in 2-3 AGU of a-1,6 link "Liquifying" produces dextrins - large molecular chunks Givn time, will produce glucose Amt naturally present in cereal flours varies |
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Effect of maltogenic amylase |
Exo-hydrolase: breaks a-1,4 links at non-reducing end Produces varying sizes of oligosaccharides |
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Effect of isoamylase |
Endo-hydrolase: breaks a-1,6 link debranching Requires >3AGU |
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Effect of pullanase |
Endo-hydrolase: breaks a-1,6 link debranching Requires >2 AGU |
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Effect of beta-amylase |
Exo-hydrolase: breaks every other a-1,4 link @ non-reducing end Cannot pass 1,6 branches produces maltose leaves b-limit dextrins |
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Effect of glucoamylase |
Exo-hydrolase: breaks both a-1,4 and 1,6 links Produces glucose From non-reducing ends |
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List endo-hydrolases |
alpha-amylase isoamylase Pullanase |
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List exo-hydrolases |
Maltogenic amylase beta-amylase glucoamylase |
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What are the three primary methods of starch modification? |
Chemical Physical Enzyme |
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What are the three ways starches are chemically modified? |
acid-thinned cross-linked substituted |
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What are the two ways starches are physically modified? |
pre-gelatinized granular instant |
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How is starch acid modified? |
Start with conc starch slurry Add HCl at 1-3%, heat 50C X12-14 hours Neutralize *The amorphous regions are penetrated and hydrolyzed NOT the crystalline regions |
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Results of acid modification of starch |
Reduced molecular weight Intact crystalline structure Intact granule During gelatinization: less swelling, more fragmentation, increased temp range During pasting: more solubilization, lower viscosity RAPID GELATION RIGID GELS |
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Types of cross-linking |
1. Covalent bonding (inter polyer more important than intra) 2. diester cross-link (phosphate rxs with phosphoric acid) 3. ether cross-link (propyl rxn with epichlorohydrin) |
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Define DS |
Degrees of substitution Average number of crosslinks per AGU Max for linear starch=DS3 Max for branched<DS3 For food applications: DS 0.01-0.1 *No change in gelatinization temp *Significant change in paste/gel properties |
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Properties of cross-linked food starch |
Less swelling at gelatinization Less solubilization Lower pasting viscosity LESS SHEAR THINNING INCREASED VISCOSITY IN ACID shorter paste texture slower retrogradation INCREASED FREEZE-THAW STABILITY |
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How are starches substituted? |
mono ester formation of phosphate groups bulky charged |
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Properties of substituted starch |
starch polymers repel each other More swelling and solubility at gelatinization higher viscosity greater shear-thinning once soluble, phosphate groups inhibit inter-chain interaction and charges repel LESS RETROGRADATION INCREASED FREEZE-THAW STABILITY at DS 0.7: gelatinization at RT (instant pudding) |
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Characteristics of pregelatinized starch |
Pre-cooked viscosity may change during storage, so reduced shelf life May have slight visual grittiness granule integrity has been lost |
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What is granular instant? |
AKA cold water swelling not pregelatinized granule integrity maintained smooth consistency (surface gloss) freeze-thaw stable |
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Differences between pregelatinized and granular instant |
Both hydrate quickly Both cold water soluble PG swells in cold water where GI is pre-swollen PG may have grainy appearance where GI is smooth and glossy |
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Types of resistant starches |
RS1 - starch is physically inaccessible RS2 - granules are resistant RS3 - retrograded starch RS4 - chemically modified |
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Dextrose Equivalent |
DE measures the % of glucosidic bonds that have been broken Measures the number of reducing ends formed (C1) DE= reducing power/wt of CHO X100 glucose = 100 maltose = 50 measures the number of breaks, not the size of polymers indicates fermentability and sweetness |
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How are starches hydrolyzed? |
Gelatinized first Acid + heat = random hydrolysis, can generate off color/flavor (often used for thin pastes to further processing) a-amylase b-amylase |
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Maltodextrins |
DE <20 Made with acid or acid+a-amylase Useful as viscosity builder, fat extender |
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Intermediate DE syrup (42-70) |
Acid thinned starch + a-amylase + b-amylase properties depend on DE (70DE is complete, glu + stubs) For high maltose: +pullanase +b-amylase |
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High DE syrup (92-95) |
Sweeteners start for HFCS +glucoamylase |
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HFCS |
glucose isomerase: glucose ->fructose single pass = 42% fructose, iso-sweet with sucrose Higher osmotic pressure than sucrose (higher aW) More susceptible to brownign than sucrose |
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Essential AA and plant proteins |
Lysine and tryptophan poorly represented |
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General structure of AA |
NH2 - CH- R - COOH |
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Classification of proteins |
Albumins - soluble in water Globulins - soluble in salt water Prolamins - soluble in 70% ethyl alcohol Glutelins - soluble in dilute acid/base |
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Characteristics of albumins and globulins |
enzymes (metabolic protein) good AA balance minor quantities in cereals concentrated in aleurone, germ, pericarp |
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Characteristics of glutelins and prolamins |
storage protein major quantities in cereals concentrated in endosperm composition varies greatly b/w cereals |
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Wheat protein |
8-16% varies depending on genetics and env protein made through dev, starch at end |
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How is a higher % protein wheat different from lower in composition? |
Higher protein = lower proportion of albumins and globulins (total amount greater) |
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Proteins of gluten |
When gluten is acid treated then extracted with EtOH and spun: Soluble - gliadins Precipitate - glutenins gliadins (prolamins) and glutenins (glutelins) in equal amts |
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AA composition of gluten |
35% glutamine (%P = Nx5.7) > hydrophobic side chains 14% proline Low % basic AAs |
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Gliadins |
single chain - three subunit types moderate MW NO inter-chain linking STICKY EXTENSIBLE |
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Glutenins |
ELASTIC RESILIANT synthesized as monomers - two subunits (HMW and LMW) polymerization between flowering and maturity S-S bonds link subunits >> HUGE polymers RESPONSIBLE FOR DOUGH STRENGTH/ELASTIC |
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Triticale protein |
Forms weak dough |
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Rye protein |
Second best AA balance high level of albumins and globulins |
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Barley protein |
high level prolamin (hordein) |
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Maize protein |
high level prolamins (zein), some cross linked high leucine |
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Sorghum protein |
similar to maize more cross-linking |
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millet protein |
similar to maize but more variable relatively less leucine |
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oat protein |
highest % protein of cereals good AA balance mostly globulins |
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Rice protein |
lowest % protein of cereals relatively good AA balance difficult to solubilize |
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Proteases |
serine protease metalloprotease aspartic protease cysteine protease |
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What is required for viscoelasticity in dough? |
protein must be at a temperature above its glass transition temperature |
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Regions of glass transition curve |
glass Tg = glass transition leather rubbery plateau elastic flow liquid flow |
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Modulus |
stiffness of a material stress/strain |
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Glass transition temperature |
marks large modulus change mdpt of temp between glassy and rubbery varies with temp and moisture |
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Polymer behavior below Tg |
backbone configs immobilized no segmental motion or interaction glass-like |
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Polymer behavior above Tg |
Increased chain motion inter-chain interaction increases changes in properties: heat capacity modulus of elasticity |
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Importance of Tg in tempering |
Toughen bran: becomes leathery proteins are amorphous, cellulose semi-crystalline Mellow endosperm: become rubbery protein and NSPoly amorphous, cellulose semi-crystalline |
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Why do non-wheat prolamins not form viscoelastic doughs? |
Zeins (maize) and kafirins (sorghum) exist as protein bodies Zein doughs - viscoelastic at 40C or at RT if organic plasticizer added |
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Hemicellulose |
nonstarch, noncellulose polysaccharide vary widely in sugars, size includes: b-glucans arabinoxylans others |
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Lignin |
assoc w/cellulose, hemicellulose complex, diverse structure crosslinks with hemicellulose |
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Arabinoxylan |
hemicellulose in wheat WU = fiber WE = gum arabinose + xylose + ferulic acid |
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Properties of water extractable arabinoxylan |
increase absorption and viscosity cross-link and gel w/oxidation increased foam stability form network reinforcing gluten |
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Properties of water unextractable arabinoxylan |
not a true cellulose increase absorption and viscosity disrupts gluten film and foam stability |
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Arabinogalactan peptide |
hemicellulose of wheat involved in grain hardness/softness |
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Beta-d-glucan |
famous in oats hemicellulose of wheat soluble fiber |
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Hemicelluloses of wheat |
arabinoxylan WE, WU arabinogalactan peptides beta-d-glucan |
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hemicelluloses of rye |
arabinoxylans arabinogalactan peptides |
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hemicelluloses of barley |
arabinoxylans (minor) beta-d-glucan, WE and WU *linear polymers: b-1,4 and b-1,3 glu *highly viscous, gel forming *FDA health claim |
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hemicelluloses of oats |
beta-d-glucan *slightly higher than barley *FDA health claim |
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Nonstarch polysaccharide degrading enzymes |
endoxylanases (wheat inhibitors) lichenase cellulase |
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Smaller saccharides of cereals |
sucrose glucose, fructose and combos glucofructosan in wheat and barley occasional galactose |
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Phytic acid |
major phosphorus in cereals chelates divalent cations, so phytase added to feeds of monogastrics |
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Where are most minerals, B vitamins? |
aleurone |
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Fatty Acid definition |
carboxylic acid with long hydrocarbon chains even number of carbons in chain |
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monoglyceride naming |
1 - end 2 - middle |
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diglyceride naming |
1,2 - next to eachother 1,3 - ends |
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Primary type of lipid in cereals |
nonpolar unsaturated |
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Cereal high in tocopherol (vit E) |
wheat |
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Cereals high in wax |
maize sorghum |
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Cereal with lipid in endosperm |
oat |
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Cereal with lipid in bran |
Rice |
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Two cereals with high lipases |
oats barley |
