fstc201 1-30-08

fstc201 1-30-08 - the charges are neutralized so that there...

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Food Sciences Week 3 Wednesday, January 30, 2008 Figure 2.12 (page 47) The importance of isolectric pH in cheesemaking Milk proteins (caseins, but not whey) coagulate to form a solid curd under acidic conditions. Key subject. Acidic = low pH Basic = high pH The reason had to do with the effect of pH on the protein molecules. Fresh milk is at a pH of about 6.6, nearly neutral. At this pH, the proteins carry overall repulsive electrical charges. Neutral pH = 7 (Does this mean they like to be near each other or not?) They repel each other, if they have the same surface charge. We must get the proteins to like each other to make cheese, so that they bond. 1. Overcome charge repulsion 2. Change milk into semi-solid mass Charge repulsion keeps the casein proteins dispersed (separated) in fluid milk. But, by acidifying milk to a pH of below 4.6, which is the isoelectric pH for casein
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Unformatted text preview: , the charges are neutralized, so that there is no net charge on the proteins.-Therefore, instead of repelling, proteins drift toward each other.-This means that their solubility and stability in milk have decreased .-As they touch, the proteins form chemical bonds with each other, and this creates a curd . So – what is the isoelectric point about? In cheesemaking (converting liquid milk into solid cheese), is it important for milk proteins to be attracted to each other or to repel? Half of the exam will reflect questions from the book. What can we say about ice cream? It is a complicated food system Figure 2.15 The ice cream system can be thought of as a foam that contains air bubbles trapped within a frozen liquid phase of lactose, sugar, polysaccharides, and milk solids. A gas dispersed in a system. Two phase system....
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fstc201 1-30-08 - the charges are neutralized so that there...

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