drc
Figure 30 Schematic depiction of rate of partial coalescence Q in protein-stabilized emulsions as influenced by a shear rate G sec -1 b volume fractionp c proportion of fat soliy d mean droplet diameter 44n e protein surface load mg .m -2 and f concentration of added small-molecule surfactant c , on partial coalescence rate Q. Various sources. a protruding crystal can pierce the film between them. b The encounter rate between particles is proportional to shear rate Section 3.4.3 . c The shear...
Oxidation with Singlet Oxygen
As just discussed, the major pathway for oxidation of unsaturated fatty acids involves a self-catalytic free-radical mechanism autoxidation that accounts for the chain reaction of hydroperoxide ROOH formation and decomposition. However, the origin of the initial free radicals necessary to begin the process has been difficult to explain. It is unlikely that initiation occurs by direct attack of oxygen in its most stable form triplet state on double bonds of fatty acids RH . This is because the C...
Chemical Agents
Proteins are more stable against denaturation at their isoelectric point than at any other pH. At neutral pH, most proteins are negatively charged, and a few are positively charged. Since the net electrostatic repulsive energy is small compared to other favorable interactions, most proteins are stable at around neutral pH. However, at extreme pH values, strong intramolecular electrostatic repulsion caused by high net charge results in swelling and unfolding of the protein molecule. The degree...
Dependent Between Tm and Tg Note Tm Here Is Taken to Mean Either or Whichever
Within this temperature range, which for foods may be as large as 100 C or as small as about 10 C, the vast array of products having amorphous regions will exhibit a temperature depend ency for Mm and viscoelastic properties that is unusually large. The Mm is quite intense at Tm and is very subdued for most molecules at or below Tg. This temperature range encompasses product consistencies termed rubbery and glassy although the rubbery term applies only when large polymers are present ....
Betalaines Structure
Plants containing betalaines have colors similar to plants containing anthocyanins. Betalaines are a group of pigments containing betacyanins red and betaxanthins yellow and their color is not affected by pH, contrary to the behavior of anthocyanins. They are water soluble and exist as internal salts zwitterions in the vacuoles of plant cells. Plants containing these pigments are restricted to 10 families of the order Centrospermae. The presence of betalaines in plants is mutually exclusive of...
Stability and Modes of Degradation Wgw
Riboflavin exhibits its greatest stability in acidic medium, is somewhat less stable at neutral pH, and rapidly degrades in alkaline environments. Retention of riboflavin in most foods is moderate FIGURE 25 Oxidation-reduction behavior of flavins. FIGURE 25 Oxidation-reduction behavior of flavins. TABLE 19 Distribution of Riboflavin Compounds in Fresh Human and Cow's Milk TABLE 19 Distribution of Riboflavin Compounds in Fresh Human and Cow's Milk Following pasteurization, FAD in bulk raw milk...
Immobilized Enzymes in Food Processing Advantages and Disadvantages
A acetolactale digarbqi ylaifi, B dehydrogenase A acetolactale digarbqi ylaifi, B dehydrogenase Why immobilized enzymes The objectives of immobilizing enzymes are to permit their repeated use to make products, and at the end, to have a product free of enzyme. In Section 7.8.2, Acetolactate decarboxylase Source .Ref. 110, p. 690. Convert nonmalt starch to maltose and dextrins fermented by yeast to alcohol and CO2 Hydrolyze proteins to amino acids used by yeast to grow Chillproofing beer...
Stability and Modes of Degradation Vhr
In solution, pantothenic acid is most stable at pH 5-7. Pantothenic acid exhibits relatively good stability during food storage, especially at reduced water activity. Losses occur in cooking and thermal processing in proportion to the severity of the treatment and extent of leaching and range from 30 to 80 . Leaching of pantothenic acid or its loss in tissue fluids can be very significant. Although the mechanism of thermal loss of pantothenic acid has not been fully determined, an...
Info Amj
Restriction endonuclease-catalyzed hydrolysis of the 3'-O-P bond between two nucleotides. From Ref. 111, p. 462. Restriction endonuclease-catalyzed hydrolysis of the 3'-O-P bond between two nucleotides. From Ref. 111, p. 462. 7.13.2 Applications Raw Food Materials Many possibilities exist for improving our raw food materials by genetic engineering. Proteins from legumes are deficient in the essential amino acid methionine, while the cereal proteins are deficient in lysine. As an example, the...
Crystal Structure [
Most of our present knowledge regarding the crystalline structure and behavior of fats has resulted from x-ray diffraction studies. However, significant insights also have been gained from the application of other techniques, such as nuclear magnetic resonance, infrared spectroscopy, calorimetry, dilatometry, microscopy, and differential thermal analysis. Indeed recent advances in magnetic resonance imaging MRI will allow greater insight into the actual dynamics of the crystallization process...
Reduction of Carbonyl Groups [
Hydrogenation is the addition of hydrogen to a double bond. When applied to carbohydrates, it most often entails addition of hydrogen to the double bond between the oxygen atom and the carbon atom of the carbonyl group of an aldose or ketose. Hydrogenation of d-glucose is easily accomplished with hydrogen gas under pressure in the presence of Raney nickel. The product is d-glucitol, commonly known as sorbitol, where the -itol suffix denotes a sugar alcohol an alditol Fig. 15 . Alditols are also...
Oxidation to Aldonic Acids and Aldonolactones
Aldoses are readily oxidized to aldonic acids. The reaction is commonly used for quantitative determination of sugars. One of the earliest methods for quantitative measurement of sugars employed Fehling solution. Fehling solution is an alkaline solution of copper II that oxidizes an aldose to an aldonate and in the process is reduced to copper I , which precipitates as brick-red Cu2O. Variations, the Nelson-Somogyi and Benedict reagents, are still used for determining amounts of reducing sugars...
Carrageenans [
The carrageenans are mixtures of several related galactans having sulfate half-ester groups attached to the sugar units Table 2 . They are extracted from red seaweeds with a dilute alkaline solution the sodium salt of a carrageenan is normally produced. Also prepared and used is an alkali-modified seaweed flour called processed Euchema seaweed PES or Phillippine natural grade PNG carrageenan. To prepare PES PNG carrageenan, red seaweed is treated with a potassium hydroxide solution. Because the...
Factors Influencing Flavor Binding
Since volatile flavors interact with hydrated proteins mainly via hydrophobic interactions, any factor that affects hydrophobic interactions or surface hydrophobicity of proteins will influence flavor binding. Temperature has very little effect on flavor binding, unless significant thermal unfolding of the protein occurs. This is because the association process is primarily entropy driven, not enthalpy driven. Thermally denatured proteins exhibit increased ability to bind flavors however, the...
Factors Influencing Emulsification
The properties of protein-stabilized emulsions are affected by several factors. These include intrinsic factors, such as pH, ionic strength, temperature, presence of low-molecular-weight surfactants, sugars, oil-phase volume, type of protein, and the melting point of the oil used and extrinisic factors, such as type of equipment, rate of energy input, and rate of shear. Standardized methods for systematically evaluating the emulsifying properties of proteins have not been agreed upon....
Structure and General Properties Jyj
L-Ascorbic acid AA Fig. 14 is a carbohydrate-like compound whose acidic and reducing properties are contributed by the 2,3-enediol moiety. This compound is highly polar thus, it is readily soluble in aqueous solution and insoluble in less nonpolar solvents. AA is acidic in character as a result of ionization of the C-3 hydroxyl group pKa1 4.04 at 25 C . A second ionization, dissociation of the C-2 hydroxyl, is much less favorable pKa2 11.4 . Two-electron oxidation and hydrogen dissociation...
Protein Denaturation
The native structure of a protein is the net result of various attractive and repulsive interactions emanating from various intramolecular forces as well as interaction of various protein groups with surrounding solvent water. However, native structure is largely the product of the protein's environment. The native state of a single protein molecule is thermodynamically the most stable with lowest feasible free energy at physiological conditions. Any change in its environment, such as pH, ionic...
Info Hht
Several natural food proteins, such as caseins, are phosphoproteins. Phosphorylated proteins are highly sensitive to calcium-ion-induced coagulation, which may be desirable in simulated cheese-type products. Proteins can be phosphorylated by reacting them with phosphorus oxychloride POCk Phosphorylation occurs mainly at the hydroxyl group of seryl and threonine residues and at the amino group of lysyl residues. Phosphorylation greatly increases protein electronegativity. Phosphorylation of...
General Characteristics of the Autoxidation Reaction
Our present knowledge regarding the fundamental mechanisms of lipid oxidation resulted largely from the pioneering work of Farmer and his coworkers 36 , Bolland and Gee 12 , and Bateman et al. 10 . Autoxidation of fats proceeds via typical free radical mechanisms as characterized by a marked inhibition in rate by chemicals known to interfere with other well-established free radical reactions, b catalytic effects of light and free radical-producing substances, c high yields of the hydroperoxide,...
RandomRandom
The fatty acid composition at the 2 position is known to be different from that of the 1 or 3 positions. This theory assumes that two different pools of fatty acids are separately and randomly esterified to the 2 and 1,3 positions. Thus, composition at positions 1 and 3 will, presumably, be identical. On the basis of this hypothesis, the amount of a given triacylglycerol can be computed as sn-XYZ mol X at 1,3 x mol Y at 2 x mol Z at 1,3 x 10-4 Composition of the sn-2 and or the combined 1,3...
Directed Interesterification
A random distribution, such as that produced by intersterification, is not always the most desirable. Interesterification can be directed away from randomness if the fat is maintained at a temperature below its melting point. This results in selective crystallization of the trisaturated glycerides, which has the effect of removing them from the reaction mixture and changing the fatty acid equilibrium in the liquid phase. Interesterification proceeds with the formation of more trisaturated...
Allosteric Inhibition
Allosteric inhibition usually results from the binding of inhibitor to multi-subunit enzymes, in the same way as described for allosteric behavior on substrate binding Eq. 28 . Whenever Ki2 and subsequent K values are smaller tighter binding than Ku, positive allosteric inhibition results. Negative allosteric inhibition results when Kil, is smaller than Ka and subsequent K values. Allosteric inhibition can be quantified by the methods of Monod et al. 80 and Koshland et al. 66 or by the modified...
Flavors from Lactic AcidEthanol Fermentations
Involvement of microorganisms in flavor production is extensive, but often their specific or definitive role in the flavor chemistry of fermentations is not well known or the flavor compounds do not have great character impact. Much attention has been given to cheese flavor, but apart from the distinctive flavor properties given by certain sulfur compounds to surface-ripened cheeses, microbially derived flavor compounds cannot be classified in the character-impact category. Similarly, yeast...
Allosteric Behavior
Allosteric behavior is defined by a plot of Vo versus S o giving a sigmoidal shaped curve Fig. 11 solid line , in contrast to a right hyperbola Fig. 11 dashed line found for Michaelis-Menten Comparison of effect of substrate concentration on the intial velocities of two enzyme-catalyzed reactions, one that obeys Michaelis-Menten kinetics dashed line and one that shows allosteric behavior solid line . The designations and indicate the substrate concentrations at which the initial velocity is 0.1...
Enzymes in Waste Management
It is estimated that the annual production of major carbohydrate feedstock for use as potential fuels or for manufacturing chemicals in the United States is about 1160 million tons, versus 50 million tons of organic chemical feedstocks 42 . This number includes 160 million tons of municipal solid waste, 400 million tons of agricultural residue, 400 million tons of forest residue, and 200 million tons of corn and grains. These residues pose major environmental problems, since a large amount of...
Gelation
A gel is an intermediate phase between a solid and a liquid. Technically, it is defined as a substantially diluted system which exhibits no steady state flow 33 . It is made up of polymers cross-linked via either covalent or noncovalent bonds to form a network that is capable of entrapping water and other low-molecular-weight substances see Chap. 3 . Protein gelation refers to transformation of a protein from the sol state to a gel-like state. This transformation is facilitated by heat,...
Antioxidants [
Antioxidants are substances that can delay onset, or slow the rate, of oxidation of autoxidizable materials. Literally hundreds of compounds, both natural and synthesized, have been reported to possess antioxidant properties. Their use in foods, however, is limited by certain obvious requirements not the least of which is adequate proof of safety. The main lipid-soluble antioxidants currently used in food are monohydric or polyhydric phenols with vari ous ring substitutions Fig. 30 . For...
Stability and Modes of Degradation Folate Stability
Folic acid exhibits excellent retention during the processing and storage of fortified foods and premixes 49 . As shown in Tables 2 and 3, little degradation of this form of the vitamin occurs during extended low-moisture storage. Similar good retention of added folic acid has been observed during the retorting of fortified infant formulas and medical formulas. Many studies have shown the potential for extensive losses of folate during processing and home preparation of foods. In addition to...
Physical Agents
Heat is the most commonly used agent in food processing and preservation. Proteins undergo varying degrees of denaturation during processing. This can affect their functional properties in foods, and it is therefore important to understand the factors affecting protein denaturation. When a protein solution is gradually heated above a critical temperature, it undergoes a sharp transition from the native state to the denatured state. The temperature at the transition midpoint, where the...
Dimer Esters [
This technique involves complete conversion of the oil to the corresponding methyl esters followed by separation and detection on a short column in a gas chromatograph. The increase in dimer esters is used as a measure of thermal decomposition. Changes in the dielectric constant of the oil can be measured quickly in an instrument known as the Foodoil Sensor 44 . The dielectric constant increases with an increase in polarity, and increased polarity is used as an indicator of deterioration. This...
Coalescence
The mechanism differs with circumstances. Three cases are important. 1. Thick films. This refers to films thick enough so that colloidal interaction between the two surfaces is negligible. In this section the Gibbs stabilizing mechanism is essential Sec. 3.2.6, especially Fig. 9E . Film rupture, and thereby bubble coalescence, will occur only when surfactant concentration is very low, and only during foam formation. If a film is rapidly stretched, as will always occur during whipping, rupture...
Enzyme Activity at Low Temperatures
See also Chap. 2. Intuitively, we might suppose that enzyme activity ceases at temperatures below 0 C, especially after the solution appears to be frozen. If so, this would be an important way of preserving our food indefinitely. Also, perhaps enzymes are denatured by freezing. Figure 21 shows the effect of temperature on invertase-catalyzed hydrolysis of sucrose from 49.6 to 19.4 C, and b-galactosidase-catalyzed hydrolysis of o- and -nitrophenyl-P-galactosides from 25 to -60.2 C. Note that...
Functional Properties of Proteins
Food preferences by human beings are based primarily on sensory attributes such as texture, flavor, color, and appearance. The sensory attributes of a food are the net effect of complex interactions among various minor and major components of the food. Proteins generally have a great influence on the sensory attributes of foods. For example, the sensory properties of bakery products are related to the viscoelastic and dough-forming properties of wheat gluten the textural and succulence...
I
Speculative mechanism for malonaldehyde formation. From Ref. 120. Speculative mechanism for malonaldehyde formation. From Ref. 120. dinitrophenylhydrazine. However, under the experimental conditions used for these tests, car-bonyl compounds may be generated by decomposition of unstable intermediates, such as hydroperoxides, thus detracting from accuracy of the results. Attempts to minimize such interference have involved reduction of hydroperoxides to noncarbonyl compounds prior to...
Texture
Texture is a very important quality attribute in foods. In fruits and vegetables, texture is due primarily to the complex carbohydrates pectic substances, cellulose, hemicelluloses, starch, and lignin. There are one or more enzymes that act on each of the complex carbohydrates that are important in food texture. Proteases are important in the softening of animal tissues and high-protein plant foods. Three types of pectic enzymes that act on pectic substances are well described. Two pectin...
Factors Influencing Enzyme Reactions
In the previous sections, we developed the basic concepts and kinetic equations required to quantify the velocity V and v of enzyme-catalyzed equations. In developing Section 7.4, only the substrate concentration was considered as a variable. All other conditions were assumed to be held constant. In Section 7.5, we will expand further on the effect of substrate concentration on the velocity of enzyme-catalyzed reactions. In addition, the effect of enzyme concentrations, pH, temperature, water...
Info 1
Figure 19 Examples of sugar phosphate metabolic intermediates. Figure 19 Examples of sugar phosphate metabolic intermediates. methyl -O-CH2-CO2 Na , and hydroxypropyl -O-CH2-CHOH-CH3 ethers of cellulose and hydroxypropyl ethers of starch, all of which are approved for food use. A special type of ether, an internal ether formed between carbon atoms 3 and 6 of a d-galactosyl unit, is found in the red seaweed polysaccharides, specifically agar, furcellaran, kappa-carrageenan, and iota-carrageenan...
R S System Triacylglyserol
Use of the prefixes R and S was proposed by Cahn et al. 17 . A sequence of priority is assigned to the four atoms or groups of atoms attached to a chiral carbon, with the atoms of greatest atomic number assigned the highest priority. The molecule is oriented so that the group of lowest priority is directed straight away from the viewer, and the remaining groups are directed toward the viewer in a tripodal fashion. If the direction of decrease in order of priority is clockwise, the configuration...
Stability and Modes of Degradation 1
Because of the high solubility of AA aqueous solutions, the potential exists for significant losses by leaching from freshly cut or bruised surfaces of fruits and vegetables. Chemical degradation primarily involves oxidations to DHAA, followed by hydrolysis to 2,3-diketogulonic acid and further oxidation, dehydration, and polymerization to form a wide array of other nutritionally inactive products. The oxidation and dehydration processes closely parallel dehydration reactions of sugars that...
Activation Energy of the EnzymeCatalyzed Reaction
To determine activation energies, two plots are required, the first is a plot of experimentally determined product concentration versus time at various temperatures Fig. 17 , and the second a plot of log k, the zero-order reaction rate constant versus 1 T in K Fig. 18 . For the first plot, TABLE 8 Transition-State Denaturation Constants for Various Enzymes TABLE 8 Transition-State Denaturation Constants for Various Enzymes bNumber of noncovalent bonds broken on denaturatAfiJ 5000, where the...
Consistency of Commercial Fats
Although natural fats and products derived from them contain exceedingly complex mixtures of large numbers of individual acylglycerols of different composition and structure, they show a remarkable tendency to behave as simple mixtures of only a few components. Each group of similar compounds appears to act as a single component, so only the distinctly different groups are apparent in melting behavior. This tendency for simplification in the melting behavior of complex mixtures is indeed...
The Water Molecule
Water's unusual properties suggest the existence of strong attractive forces among water molecules, and uncommon structures for water and ice. These features are best explained by considering the nature of first a single water molecule and then small groups of molecules. To form a molecule of water, two hydrogen atoms approach the two sp3 bonding orbitals of oxygen and form two covalent sigma o bonds 40 partial ionic character , each of which has a dissociation energy of 4.6 102 kJ mol 110 kcal...
Structure and General Properties Rfz
The generic term folate refers to the class of compounds having chemical structure and nutritional activity similar to that of folic acid pteroyl-L-glutamic acid . The various components of this class are designated as folates. The use of folacin and folic acid as generic terms is no longer recommended. Folic acid consists of L-glutamic acid that is coupled through its a-amino group to the carboxyl group of ara-aminobenzoic acid, which, in turn, is linked to a 2-amino-4-hydroxypteridine Fig. 35...
Behavior of the Food During Frying
The following events occur during frying of food Water is continuously released from the food into the hot oil. This produces a steamdistillation effect, sweeping volatile oxidative products from the oil. The released moisture also agitates the oil and hastens hydrolysis. The blanket of steam formed above the surface of the oil tends to reduce the amount of oxygen available for oxidation. Volatiles e.g., sulfur compounds and pyrazine derivatives in potato may develop in the food itself or from...
Algins [
Commercial algin is a salt, most often the sodium salt, of a linear poly uronic acid , alginic acid, obtained from brown seaweeds Table 2 . Alginic acid is composed of two monomelic units, b-d-mannopyranosyluronic acid and a-L-gulopyranosyluronic acid units. These two monomers occur in homogeneous regions composed exclusively of one unit or the other and in regions of mixed units. Segments containing only d-mannuronopyranosyl units are referred to as M blocks and those containing only...
Molecular Mobility Mm and Food Stability Introduction
Even though the RVP approach has served the food industry well, this should not preclude consideration of other approaches that can supplement or partially replace RVP as a tool for predicting and controlling food stability and processability. In recent years, evidence has become increasingly compelling that molecular mobility Mm translational or rotational motion may be an attribute of foods that deserves attention because it is related causally to many important diffusion-limited properties...
Amylopectin [
Amylopectin is a very large, very highly branched molecule, with branch-point linkages constituting 4-5 of the total linkages. Amylopectin consists of a chain containing the only reducing end-group, called a C-chain, which has numerous branches, termed B-chains, to which one to several third-layer A-chains are attached. The branches of amylopectin mole- A-chains are unbranched. B-chains are branched with A-chairs or other B-chains. A trisaccharide segment of an unbranched portion of an amylose...
Concentrated Starch Gels [
Starch see Chap. 4 occurs naturally in rigid granules, mostly between 5 and 100 mm in diameter, that are insoluble in water. Part of the amylopectin is present in microcrystalline regions, which gives the granules considerable rigidity. If starch granules are heated in excess water, they gelatinize. This involves swelling, as water up to several times their own weight is taken up melting of microcrystallites and leaching of some amylose. The swollen granules remain intact upon cooling, unless...
Quaternary Structure
Quaternary structure refers to the spatial arrangement of a protein when it contains more than one polypeptide chain. Several biologically important proteins exist as dimers, trimers, tetramers, etc. Any of these quaternary complexes also referred to as oligomers can be made up of protein subunits monomers that are the same homogeneous or different heterogeneous . For example, b-lactoglobulin exits as a dimer in the pH range 5-8, as an octomer in the pH range 3-5, and as a monomer above pH 8,...
Bioavailability of Vitamin B
The bioavailability of the total vitamin B6 content of a typical mixed diet has been estimated to be approximately 75 for adult humans 129 . Dietary PL, PN, PM, PLP, PMP, and PNP, if the latter is present, appear to be efficiently absorbed and effectively function in vitamin B6 metabolism. Schiff base forms a PL, PLP, PM, and PMP dissociate in the acidic environment of the stomach and exhibit high bioavailability. PN glucoside and other glycosylated forms of vitamin B6 are inefficiently...