lips/triglycerides- week 3/4
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what is the melting point of a triglyceride based on
its dependent on its fatty acids & its crystal structure (polymorphism)
1) TG with high melting points are ………. at room temp. 2) TG with low melting points are ……. at room temp.
1) solid 2) liquid
when do fatty acids melt
occurs when intermolecular (van de waals) are broken by heat energy (not intramolecular bonds)
what decreases the melting point of a fatty acid
increasing unsaturation The more C=C bonds the lower the melting point
what increases the melting point of fatty acids
increases with chain length (number of carbons) The longer the chain, the higher the melting point Longer chains = more intermolecular bonds = more heat energy needed
how does the unsaturation of the fatty acid influence the melting point (2 points)
-trans C=C bonds introduce a slight kink and lower intermolecular bonds and thus less heat energy needed to melt -cis C=C bonds introduce a larger kink (~42o ) and lower intermolecular bonds even more and thus even less heat energy needed to melt
Triglycerides are polymorphic, what is it meant by polymorphic
means that TG can exist in more than one crystalline form
what are the three main polymorphic forms
α : alpha β’ : Beta prime β : Beta
what is the melting range of MP of fats dependent on
on the arrangement of TG molecules i.e. their crystal structure
What are the properties of α-types (3 points)
• Limited applications in foods and food processing (don’t form solids) • Randomly formed • Melts very easily
what are the properties of β’ -types (2 points)
• Form small needle like crystals • Form soft plastic fats for use in margarine
what are the properties of β -types (3 points)
• Form large crystals giving grainy texture (cocoa butter, lard)- too hard • Well ordered; hard texture • Not good for margarine
what is the definition of Tempering explain in terms of chocolate
controlled crystallization that is necessary to induce the desired form of cocoa butter in the finished product (Used to Prepare Food with Desired Polymorphic State of a Lipid)
what are the 3 states that lipids can exist depending on temperature
-solid (All TGs liquid) -plastic (TGs with short chain FA liquid TGs with long chains solid) -liquid (All TGs liquid)
Outline the difference between a simple and mixed triglyceride
In a simple triglyceride such as palmitin or stearin, all three fatty-acid groups are identical. In a mixed triglyceride, two or even three different fatty-acid groups are present; most fats and oils contain mixed triglycerides.
how is the process of tempering used to form chocolate
-Liquid cooled to initiate crystallisation -Reheated to 32 degrees (just below the mpt of β-3 type) and held – this melts out unwanted crystals -Stir at 32 degrees, allow formation of very small β-3 crystals and then finally solidify
what are the natural commodities lipids are obtained from (3 points and give examples of each)
-plants- Oil Seeds (Rape, Sunflower, Palm Kernel, Soybean, Cottonseed, Corn germ, Peanut, Coconut) Fruit Pulp (Olive, Palm Fruit) -animals & Fish- * Lard (rendered from pig kidney fat, fatback, caul fat) * Tallow (The rendered form of fat from sheep and cattle) * Marine oils (Fish, Whales) -Milk fats- produced from churning whole milk or cream
Describe how lipids are purified from natural commodities from FRUIT (4 points)
-Grinding to a paste -Pressing -Separation (decantation or vertical centrifuge) -Heating/Solvent Extraction
Describe how lipids are purified from natural commodities from seeds (5 points) - Milling
-Cleaning -Breaking -Cooking 70-100oC (to denature the enzymes like lipase & killing microbes) -Expelling -Solvent Extraction (hexane/heptane)
what are the 2 ways of Oil/Fat Extraction from Lipid-Rich Animals
wet rendering and dry rendering
what are the steps for wet rendering (5 steps)
• Tissue heated with steam (high temp of about 100-110oC) • Lipid melts • Lipid separated by decanting or centrifugation • White lipid with neutral flavour, e.g., Lard • Process milder than dry rendering
what are the steps for dry rendering (4 steps)
• Uses high heat alone • A harsher process than wet rendering • Browner lipid with stronger flavour • Non food uses e.g. soap
what are the 2 ways of refining oils
• Caustic or chemical refining • Physical refining
what are the steps for caustic or chemical refining (6 steps + define each step)
-Crude Lipid (TGs, water, protein, phospholipids) -DEGUMMING (Removal of phospholipids + some protein) -NEUTRALISATION (Removal of free fatty acids) -BLEACHING (Removal of colour and pro-oxidants) -DEODORISATION (Removal of volatile compounds and flavours) -Crude Lipid (TGs, water, protein, phospholipids) Refined Oil (one of the purest foods known) Refining Steps in Detail DEGUMMING 2-3% water added + agitation at ~50 degrees Water phase removed after phase separation