Lecture 5: carbohydrates Flashcards
what are the functions of carbohydrates in foods?
- sweet taste (flavour)
- digestible and non
- water fixation
- tenderizing agent, viscocity and texture control
- emulsifying agent
- stabilizing agent
- thickening agenet
several steps need to occur to prepare the sample before test what are they?
- depending on nature of food the target compound must be extracted like if in a matrix but if its like juice where sugar is already in it then just remove what interferes
- extract mono/oligosacchrides with alchols
- remove and clarify interfence: remove colored substance, subtances that cause trubidity or optically active material
- clarifiaction is done by neutral or basic lead salts. aluminum hydroxide and other agents and it just depends on the type and quantity of interfering agents
- extract mono/oligosachrides: with ethanol and calcium carbonate
what are the three methods for determing carbs?
- chemical methods : semi empirical since measure properties not just special to carbs and different carbs respond differently to the same reagents
- reduction method: based on reducing properties in alkaline and hot medium
- condensation reactions: methods based on formation of color in acidic and hot enviorments via dehydration
- enzymatic reactions
- physical properties
briefly describe reduction methods, the principles and techinques
- non specific
- need to get rid of anything that is reducing since it will interfere
- alhyde/ketone groups react with metal ions in akaline solution to form reduced specicies in metal form
- standarizing and mainting controlled enviorment essential
What are the three reduction methods?
- Munson-Walker Method:Gravimetric method,
- Nelson-Somgyi Method: colormirty method,
- Lane-Eynon Method: volumetric method:
Describe the method of condensation method
- need the action of hydrchloric, phosphoric, sulfuric acid on carbohydates since the acid breaks the bond and transforms into monosachrides then into furfural/derivatives throigh dehydration
- deravtives are condendensed with pehnols to form colored compounds that absorb at a specific wavelength
Give an example of a condensation method
- easy, senstive, cheap, accurate
- can react all classes of carbs
- colometric
- determines total [] of CHO in foods
- add phenol and sulphuric acid and then dehydrate forms a yellow brown color and absorbance is measured
Describe the principle of enzymatic methods and give examples
- very specific
- need to use carrez solutions to no disrupt enzymatic properties but still achieving clarification
- examples: GOPOD method, determine glucose via reaction to glucose oxidase
- Hexokinase method
Describe the two physical methods polarimetry and refractive index
- Polarimetry: using the rotating power of sugars since carbs have optical properties, uses biots law which states that the rotational power of the carbohydrate in solution is poroptional to [] and lenght of path so higher [] of solution rge more plane of polarization of light is deflected
- Refractive Index: the increase in carb [] increases the degree of refraction of light using the brix scale
Describe the munslon-walker method
uses a conversion table to link the perciptate formed by fehling rxn to an amount of reducing sugar since free groups can reduce the copper hydroxide
describe the Nelson-Somgyi Method:
colormirty method, forms a blue complex of arsenomolybdate
describe the Lane-Eynon Method:
uses a conversion table to calculate amount of reducing sugars in a volume of solution need to reduce fehling reafent , through titration using methylene blue (TITRATION)
