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FDSC 305 Remember stuff on this for food chem midterm.doc

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Food Science
FDSC 305
Benjamin Simpson

Epimerases and Racemases Both are isomerase enzymes that catalyze the reverse stereochemistry of biological molecules.   Racemases act on compounds with one asymmetric center whereas epimerases act on compounds with  more than one asymmetric center (epimers). Chlorophyllase: index of blanching and heat labile True or false? ­ False.  Chlorophyllase eliminates the phytyl group from chlorophyll, turning it into the bright green water  soluble pigment chlorophyllide.   4 ways to stop discoloration/destruction of chlorophyll ­ ­avoid heat; ­ avoid acid; ­ lower the water activity (lipoxydase); ­avoid contact to light and oxygen;  ­avoid irradiation (peroxidase degrades chlorophyll) and fermentation Explain all enzymatic equations. 1/v …0how did you get to this using the K  equmtion.  Lab questions (Ex. 4 ways to minimize enzyme activity)  Reduce contact with oxygen (to prevent oxidation­ add liquid such as water or other without oxygen, add  additives such as EDTA), reduce pH to decrease rate of enzymatic browning, avoiding high temperatures  (freezing) Guaicol use? What does it do? Guiacol turns from colorless to brown after reacting with oxygen.  Peroxidases converts hydrogen  peroxide to water and oxygen.  The concentration of this pigment is therefore related to peroxidase  activity and can be measured by using a spectrophotometer. Measures we can take to stop green discoloration of chlorophyll ­avoid contact to air and light, avoid heating of chlorophyll, avoid  The table on the relationship between V maxand K m Calculate the ratio of km/vmax What enzymes are part of the hydrolases? Proteases, carbohydrases (amylases, lactases, etc.), nucleases, lipases What is hydrophobic interaction chromatography? Attach a hydrophobic ligand to resin that will bind to proteinthat is to be purified/extracted.   Separation using HIC is based on the reversible interaction between a protein and the hydrophobic ligand bound to the chromatography matrix. Hydrophobic amino acids of proteins and peptides are usually located away from molecular surfaces. However, many biomolecules have some hydrophobic groups that are sufficiently exposed to allow interaction with hydrophobic ligands on media. Compared to reversed phase chromatography, the density of the ligand on the matrix is much lower and allows mild elution conditions, helping to preserve biological activity. HIC is particularly suitable for samples precipitated with ammonium sulfate or eluted in high salt concentrations since high ionic strength buffers enhance the hydrophobic interaction. The interaction is enhanced by buffers with high ionic strength, which makes HIC an excellent purification step after ammonium sulfate precipitation or after elution in high salt during ion exchange chromatography (IEX). HIC is well- suited for the capture or intermediate steps in a purification scheme. During HIC, sample components bind to the column in high ionic strength buffer, typically 1 to 2 M ammonium sulfate or 3 M NaCl. High concentrations of salt, especially ammonium sulfate, may precipitate proteins. Therefore, check the solubility of the target protein under the binding conditions to be used. Elution is usually performed by decreasing the salt concentration, stepwise or using a gradient. High T may decrease enzyme activity? True or false.   True.  Enzymes operate at an ideal temperature range.  Temperatures above this range can either denature  or diminish enzyme activity. 3 enzymes used in enzymatic browning PPO, peroxidases and catechol oxidase a)Boiling H20 causes loss of color in green vegetables true or false true.  Though chlorophyll, which is responsible for the green pigments in green vegetables, is water  insoluble, boiling water causes the photooxidation of chlorophyll, replacing its central Mg with an H,  becoming pheophytin (brown color). b) list 3 ways to avoid this loss (bonus) ­avoid heat; ­ avoid acid; ­ lower the water activity (lipoxydase); ­avoid contact to light and oxygen;  ­avoid irradiation (peroxidase degrades chlorophyll) and fermentation Explain the use of protein­carotenoid complex in food industry? Carotenoids are not absorbed by fish and shellfish, accumulating under their skin to give their  characteristic orangy color.  Therefore, this compound is given to fish and to create customer appeal.  It is  extracted from shellfish by 1)demineralization (remove shell ie Ca2+ ion using citric acid or EDTA) and  are left with chitin­protein­carotenoid complex 2) Remove protein and pigment together as complex  (carotenoprotein)  by using proteolytic enzymes such as typsin or papain. Then 3) enriched in protein and  pigment and depleted in chitin and Ca2+­>protein provides protection to pigment against oxidation.  It  therefore creates longer shelf­life (synthetic pigment requires antioxidant addition), but this product is  seasonal.  This process is done by the company Neptune and the synthetic pigment is produced by 
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