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Sat 28 Oct, 2006 06:29 pm
So is unflavored gelatin (the kind you put in Jello) a mixture, element, compound, solution?
Gelatin is a protein made from animal skins and bones.
Excerpts from How Stuff Works:
Quote:What exactly is gelatin? Gelatin is just a processed version of a structural protein called collagen that is found in many animals, including humans. Collagen actually makes up almost a third of all the protein in the human body. It is a big, fibrous molecule that makes skin, bones, and tendons both strong and somewhat elastic. As you get older, your body makes less collagen, and individual collagen fibers become crosslinked with each other. You might experience this as stiff joints (from less flexible tendons) or wrinkles (from loss of skin elasticity).
The gelatin you eat in Jell-O comes from the collagen in cow or pig bones, hooves, and connective tissues. To make gelatin, manufacturers grind up these various parts and pre-treat them with either a strong acid or a strong base to break down cellular structures and release proteins like collagen. After pre-treatment, the resulting mixture is boiled. During this process, the large collagen protein ends up being partially broken down, and the resulting product is called gelatin. The gelatin is easily extracted because it forms a layer on the surface of the boiling mixture.
Gelatin is a common ingredient in foods because it is so versatile. It can be used as a gelling agent (as in Jell-O), as a thickener, an emulsifier, and a stabilizer.
At room temperature, the gelatin protein is in the form of a triple helix. This is a fairly ordered structure not unlike that of DNA. With DNA, two chains of nucleotides are twisted together in a spiral pattern. In the gelatin protein, there are three separate chains of amino acids (polypeptide chains) have lined up and twisted around each other, and the helix is held together by weak bonds that form between the amino acids that end up on the inside of the coiled structure.
What happens to gelatin when you add boiling water? The energy of the heated water is enough to break up the weak bonds holding the gelatin strands together. The helical structure falls apart, and you are left with free polypeptide chains floating about in solution.
The next step is to add cold water and stick the dissolved gelatin in the refrigerator to chill for several hours. When you cool down the mixture, the polypeptide chains begin to reassociate and reform the tight triple helix structure. However, the chilling process is slow, and the individual strands have been widely dispersed by mixing, so the helices aren't perfectly formed. In some places, there are gaps in the helix, and in others, there is just a tangled web of polypeptide chains. When the gelatin solution is chilled, water is trapped inside these gaps and pockets between chains. The protein net that is left after chilling gives the gelatin mold its shape, and the trapped water provides the characteristic Jell-O jiggle that makes it a popular food for kids to eat.
http://home.howstuffworks.com/question557.htm
I'm no expert in mixture, element, compound, solution but this sure sounds like a mixture, element, compound, solution to me! Any mixture, element, compound, solution experts care to rebuke?
I vote compound.
mabey I ought to phone a friend though.
A lady I once knew was the chief engineer for Eastman Gelatin and she knew everything about industrial gelatin, which is about the same as edible gelatin. Seeing as how the stuff needs an engineer, I vote compound.
I think it starts as a compound, at least in the Jello packages, and then is dissolved in water and becomes ... a solution. Then it forms an aspic...
kidding.
I'm confident I understood gelatin, chemically, some time ago, but I don't remember what I understood. Wigglyness is a key factor in my present grasp of it.
Gelatin is a colloidal gel. That means it's halfway between being a solution and a mixture because it exhibits properties of both.
Agents commonly used to induce gelation in the lab are agar and gelatin. Both as solids are first dissolved in water, which is then brought to boil and then allowed to cool down. As these agents cool down, they form a structure known as a gel.
When gelatin is at a temperature below 32˚C (or within a few degrees thereof), it is a semisolid material. At temperatures above 32˚C, it is a viscous liquid.
Gelatinase is an enzyme that allows micro-organisms that produce it to hydrolyse gelatin into smaller polypeptides, peptides, and amino acids that can cross the cell membrane and be utilized by the microbe.
When gelatin is broken down, it can no longer solidify. If an organism can break down gelatin, the areas where the organism has grown will remain liquid even if the gelatin is refrigerated.
The test for gelatinase activity can be used to differentiate between Staphylococcus aureus and Staphylococcus epidermidis. It can also be used to differentiate Serratia marcescens, Proteus vulgaris, and Proteus mirabilis from other enterics. In this test, the microbes are allowed to grow on a medium containing gelatin plus nutrients. When the extra-cellular enyzme, gelatinase is secreted by the bactria and then allowed to hydrolyse the gelatin there will be a clear, watery zone around the bacterial colonies where the gelating has been enzymatically digested.,
One of the most common agents normally found in a bacteriology/microbiology lab is agar.
According to the US Pharmacopeia, agar can be defined as a hydrophilic colloid extracted from certain seaweeds of the Rhodophyceae class. It is insoluble in cold water but soluble in boiling water. A 1.5% solution is clear and when it is cooled to 34-43°C it forms a firm gel which does not melt again below 85°C. It is a mixture of polysaccharides whose basic monomer is galactose. These polysaccharides can be sulphated in very variable degrees but to a lesser degree than in carrageenan. For this reason the ash content is below those of carrageenan, furcelleran (Danish agar) and others. A 5% maximum ash content is acceptable for agar although it is normally maintained between 2.5-4%.
Agar is the phycocolloid of most ancient origin. In Japan, agar is considered to have been discovered by Minoya Tarozaemon in 1658 and a monument is Shimizu-mura commemorates the first time it was manufactured. Originally, and even in the present times, it was made and sold as an extract in solution (hot) or in gel form (cold), to be used promptly in areas near the factories; the product was then known as tokoroten. Its industrialization as a dry and stable product started at the beginning of the 18th century and it has since been called kanten. The word "agar-agar", however, has a Malayan origin and agar is the most commonly accepted term, although in French- and Portuguese-speaking countries it is also called gelosa.
A Japanese legend is told about the first preparation of agar:
"A Japanese Emperor and his Royal Party were lost in the mountains during a snow storm and arriving at a small inn, they were ceremoniously treated by the innkeeper who offered them a seaweed jelly dish with their dinner. Maybe the innkeeper prepared too much jelly or the taste was not so palatable but some jelly was thrown away, freezing during the night and crumbling afterwards by thawing and draining, leaving a cracked substance of low density. The innkeeper took the residue and, to his surprise, found that by boiling it up with more water the jelly could be remade".
Agar production by modern techniques of industrial freezing was initiated in California by Matsuoka who registered his patents in 1921 and 1922 in the United States. The present manufacturing method by freezing is the classic one and derives from the American one that was developed in California during the years prior to World War II by H.H. Selby and C.K. Tseng (Selby, 1954; Selby and Wynne, 1973; Tseng, 1946). This work was supported by the American Government which wanted the country to be self sufficient in its strategic needs, especially in regard to bacteriological culture media.
Apart from the above American production, practically the only producer of this phycocolloid until World War II was the Japanese industry which has a very traditional industrial structure based on numerous small factories (about 400 factories operated simultaneously). These factories were family operated, producing a non-standardized quality, and had a high employment rate as production was not mechanized. For this reason, and in spite of the later installation of some factories of a medium to small size, only in recent times has Japan operated modern industrial plants.
During the second world war the shortage of available agar acted as an incentive for those countries with coastal resources of Gelidium sesquipedale, which is very similar to the Gelidium pacificum used by the Japanese industry. So in Portugal, Loureiro started the agar industry in Oporto while at the same time J. Mejias and F. Cabrero, in Spain, commenced the studies which led to the establishment of the important Iberian agar industry. Other European countries which did not have agarophyte seaweeds tried to prepare agar substitutes from other seaweed extracts .
SOURCES OF AGAR
Different seaweeds used as the raw material in agar production have given rise to products with differences in their behaviour, although they can all be included in the general definition of agar. For this reason, when agar is mentioned, it is customary to indicate its original raw material as this can affect its applications . Hence we talk about Gelidium agar, Gracilaria agar, Pterocladia agar, etc. To describe the product more accurately, it is usual to mention the origin of the seaweeds, since Gracilaria agar from Chile has different properties from Gracilaria agar from Argentina and Gelidium agar from Spain differs from Gelidium agar from Mexico.
Originally Gelidium agar constituted what we consider genuine agar, assigning the term agaroids to the products extracted from other seaweeds. Although these agaroids do not have the same properties as Gelidium agar, they can be used as substitutes under certain conditions. After World War II, the Japanese industry was forced to use increasing quantities of raw materials other than the traditional Gelidium pacificum or Gelidium amansii due to the growing demand of the international food industry.
An increase in the agar gel strength was obtained through improvements in the industrial process during the fifties, and the differences between the genuine Gelidium agar and the agaroids then available became clearer. The gel strength increased from 400 g/cm2 (the maximum for natural agar produced by the cottage industry) to 750 g/cm2 or more for the agar produced by industrial methods. The gel strength data refer to the Nikan-Sui method which replaced the primitive Kobe method used in the past. The Nikan method is more precise and easier to reproduce. A short description of the method is included in the section on "Properties".
The Japanese discovery of the strong alkaline methods for agar extraction (see section on "Manufacturing Processes") meant an increase of the Gracilaria agar gel strength with the subsequent utilization of seaweeds imported from South Africa to increase the raw material available.
Nowadays the world agar industry basically uses the following seaweeds:
(1) Different species of Gelidium harvested mainly in Spain, Portugal, Morocco, Japan, Korea, Mexico, France, USA, People's Republic of China, Chile and South Africa.
(2) Gracilaria of different species harvested in Chile, Argentina, South Africa, Japan, Brazil, Peru, Indonesia, Philippines, People's Republic of China including Taiwan Province, India and Sri Lanka.
(3) Pterocladia capillace from Azores (Portugal) and Pterocladia lucida from New Zealand.
(4) Gelidiella from Egypt, Madagascar, India, etc.
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