Blog Directory - Blogged foodliterate: November 2007

Wednesday, November 28, 2007

C is for Carbohydrate

Now that everyone has recovered from their Thanskgiving carbohydrate-induced lethargy (or at least I hope you have), it's time to talk about those carbs. Carbohydrate, not surprisingly, means 'hydrates of carbon' (see told you) and has the chemical structure of Cx(H2O)y. Carbohydrates are really a large category of items that include sugars, dextrins, starches, pectin, cellulose, gums, and fiber. Carbs are saccharides, a word which comes from latin for 'sweet sand'.

The role of carbohydrates in human nutrition is to supply a readily accessible and quickly utilizable form of energy. They allow your body to spare its muscles (protein) from being broken down to supply the needed fuel. We may be complex creatures, but we run on the simplest of sugars, glucose. In fact, it is the only fuel our nervous systems and brain can use.
So let's start our foray into this topic with the simplest of the carbs - sugars. Sugars come in multiple forms: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. As you can tell from the prefixes, they are made of sugar molecules ranging from one (mono) to many thousands (poly). Sugars also have the suffix '-ose', which designates them as being part of the sugar family. {For those of you who are chemistry junkies, this is the site for you.}

Monosaccharides are single sugar molecules, as I've mentioned, and the most important of these is glucose (also called dextrose). It has the chemical structure [C6(H2O)6] and exists in a ring (cyclic) formation. But there are other monosaccharides besides glucose such as fructose, xylose, galactose, and ribose.

Disaccharides are, as their name suggests, sugars comprised of two monosaccharides. They occur when the two monosaccharides join together and kick out a water (H2O) molecule in a dehydration reaction forming a glycosidic bond. Different combinations of monosaccharides come together to form different disaccharides. Glucose + Fructose = Sucrose (what we call table sugar), Glucose + Galactose = Lactose (milk sugar), and Glucose + Glucose = Maltose (malt sugar).

Oligosaccharides are sugars comprised of 4 to 8 monosaccharides (oligo means few) and are known as simple sugars. The most common are fructo-oligosaccharides which occur in vegetables (like asparagus & onions) and are short chains of fructose molecules. They are of particular interest these days because of research that proves they enhance the growth of beneficial gut bacteria - this is called a prebiotic effect. Because of this, food scientists are finding new applications where they can add oligosaccharides.

And lastly, polysaccharides are long chains (100+) of monosaccharides. Typically they are insoluble in water and are not sweet. You know some of them as starches and cellulose. There is also one which you may not be as familiar with (yet) called inulin. And like a fructo-oligosaccharide, has a prebiotic effect that aids in digestive health. Inulin belongs to a category of carbs called fructans. {For more information on inulin: click here}

So to recap - carbohydrates are the fuel our bodies run on. Sugars are the simplest forms and as you add on molecules, they become strings and those strings become chains, which makes them less soluble and less sweet. In the next post I will continue to discuss this category of carbohydrates and some of their individual details. Until next time - Stay sweet!

Friday, November 16, 2007

Talking Turkey

In the spirit of Thanksgiving, and since we've covered proteins for the past 3 weeks, I thought this was perfect timing for our seasonally favorite protein - turkey.

Both the domestic and wild turkey are the same bird, (not that you'd guess that by looking at them), Meleagris gallopavo. For this year (2007) 272,000,000 of them were raised for US consumption { }. Back in May those turkeys were just eggs in incubators. About 28 days later those eggs hatched into poults (baby turkeys) and the poults were moved to barns. For the next 4-6 months, yes - that is all the time most Thanksgiving turkeys spend on earth, they are fed corn and soybean meal supplemented with vitamins & minerals. Contrary to popular belief, turkeys are not fed hormones to get those big meaty breasts - that is done with breeding; federal regulations prohibit the use of hormones for poultry. Ranchers are allowed to give the birds antibiotics, but there must be no trace (residue) in the birds at the time of slaughter. The presence of antibiotics is part of the inspection process and if any is found, the turkey is considered adulterated and is rejected for consumption.

The most common designations of turkey available for purchasing are the following (per AMS 70-US Classes, Standards, & Grades for Poultry):
1. Fryer-Roaster - a young, immature turkey (usually younger than 16 weeks) of either sex (label won't say hen or tom) that is tender-meated with soft cartilage and smooth skin.
2. Young Turkey - a young turkey (usually younger than 8 months) of either sex that is tender-meated with less flexible cartilage and smooth skin.
Don't get one of these for Thanksgiving unless you are serving Turkey soup:
1. Yearling Turkey - a fully mature turkey (usually between 8 and 15 months) that is primarily used as breed stock.
2. Mature Turkey - an old hen or tom (usually older than 15 months).
For more information on this topic look here.

Most of what you find in the grocery store is the broad-breasted white (or bronze), which has a double breast so you get a lot more white meat. There are some producers raising heritage breeds - these are single breasted birds which are typically older (don't mature as quickly) and have a stronger flavor. Which to choose is a matter of personal preference, but whatever bird you do choose get a big one. There is roughly twice as much meat on a 15 pound bird as there is on a 10 pound one (assume 5 pounds of each is inedible bones, cartilage, etc.).

So now you have your bird, what's next? Brining. It is very popular, but why should you do it? Well, a brine is a salt solution, but many contain sugar & other flavorful seasonings. {Here is Alton Brown's recipe, but there are others. Typical brine solutions contain 1/2 cup kosher salt (or other non-iodized salt) per 1 gallon of water. If you choose to add sugar, add equal parts to the salt. Now if you remember the last post, or want to jump down now & review it, you'll know that there are salt soluble proteins in that turkey. And if you denature those proteins with the salt in the brine, they will increase their water holding capacity resulting in a juicier bird. Also in the last post you discovered the wonder of the Maillard reaction: sugar + protein = brown, yummy goodness. The sugar also helps balance the salty taste of the brine.

Now for the cooking. 165°F or 180°F? What if it is pink? If you use an old cookbook or follow Grandma's recipe you are probably familiar with the 180°F finished temperature. However, you are probably also familiar with overcooked, dry turkey. Pathogenic bacteria are dead meat (pardon the pun) after 140°F, and the meat of the turkey is perfectly fine for consumption at 165°F. Finished temperatures higher than this are a matter of preference (color & texture), not of safety. What about that pink tint? Well, you can't judge doneness by color, only by temperature. There are a few reasons why a fully cooked turkey may still be a little pink. Myoglobin is the oxygen-carrying pigment of muscle cells (what gives meat its pink/red hue). It can react with heated gases in the oven's atmosphere and maintain the muscle's pink hue even when cooked. Another possibility is nitrates (sometimes found naturally in water) can be converted to nitrites by the bacteria on the raw turkey which will cause the meat to retain a pink hue. If you have a good thermometer and it says 165°F in both the thigh and breast, you'll be fine. If you stuff your bird with dressing (and I don't recommend that you do), remember to check the temperature of that as well - it cooks the slowest and has absorbed all of the raw juices from the bird. It is cross-contamination of raw juices with cooked meat or shared utensils and undercooked dressing(stuffing) that cause the vast majority of food-borne illness at Thanksgiving.

And I can't forget about turkey causing sleepiness. Everyone has heard about tryptophan causing the post-meal nap crisis (heck, there was even an episode of Seinfeld based on this one). Tryptophan is one of the essential amino acids and it is a precursor to seretonin. However, you'd need an empty stomach and straight tryptophan to see any real results, and the levels in your turkey are too low to have any real effect. As a matter of fact, there is the same amount of tryptophan in an equal portion of chicken and more tryptophan in an equal portion of cheddar cheese, but no one complains of needing a nap after eating these. So why do you curl up on the couch after your Thanksgiving meal? You can blame it on all the carbohydrates and alcohol (i.e. sugars). They rev up your insulin and pull blood from your head to your gut to work on digesting all of that food. {more here}

I hope that you've all found this turkey talk informative and that you have a great Thanksgiving! Enjoy the meal, your family & friends and check back for my next post after I've slept off my dinner!

Monday, November 12, 2007

What's My Function?

Welcome back! So, we've covered what proteins are & how to score them. Now it's time to talk functionality. Why are they added to the foods you purchase and how do food scientists decide which ones to use where?

What do proteins do in food systems? They serve to provide structure & stability to food. Just a few of the functions they serve include: water binding, viscosity, emulsification, foaming, gelation, dough formation and texturizing. Proteins have primary, secondary & tertiary structures. This link is for chemistry junkies or those who want to understand the specifics. These structures and the protein's size, shape, charge, amino acid profile, hydrophobicity/hydrophilicity (water fearing/loving) and flexibility or rigidity determine how the protein will behave and interact with other food components.

Denaturation, the breaking of the protein chains and rearrangement of their structure, is how to accomplish changes in function. The behavior of proteins can be altered with denaturation by chemical (acid, salt), physical (heat, agitation), and/or biological (enzyme) means. How about some examples?

We add salt to meat proteins to draw out the soluble proteins, which are very sticky, to allow us to make formed products like boneless hams and luncheon meats. We add rennet (an enzyme) or acid to milk to separate the casein proteins from the whey proteins and then innoculate with specific cultures, press, salt, and age to turn the casein proteins into cheese. Whey proteins, which are highly soluble, are added to beverages to give them a protein claim (like Accelerade®). Gliadin & glutenin (wheat proteins) are worked to produce gluten which gives bread its structure and elasticity. And egg proteins (albumen) can be whipped to make a foam for cakes and souffles. Most of the time, multiple proteins are used - like milk, cereal and egg - to obtain the desired finished product and for nutritional and economic reasons.

Proteins also play an important role in flavor-producing interactions. The wonderful smell of baking bread comes from the interaction of the amino acids in the cereal protein reacting with reducing sugars (aka the Maillard reaction.). Water binding is another important protein function since it is needed for viscosity & gelling which impacts the texture of foods (think juiciness or tenderness). For those who want more information on where we use certain proteins and why, this is a great article.
Ahh, time for a summary of our protein discussion. You've learned that proteins are chains of amino acids and that they differ from carbohydrates & fats because proteins contain nitrogen in addition to carbon, hydrogen & oxygen. You know proteins are required by our bodies to make glycogen, blood plasma, muscle & connective tissues, hormones & enzymes, and quite a few other processes. You've learned that there are 20 amino acids, 9 of which are essential because our bodies cannot produce them and must be obtained through the foods we eat. And that the proteins with the most complete sets of essential amino acids have the highest protein quality scores. And now you've learned why proteins are so important to the manufacturing of food products and why certain proteins are chosen for certain applications.

My next post will be about a very specific protein in honor of Thanksgiving - yes the Turkey. So, if you have specific questions about protein, its structure, function or uses, send me an email or comment on my post and I will be happy to provide you with the information you seek!

Tuesday, November 6, 2007

A Perfect Score

As I discussed in my last post, proteins are assembled from amino acids, and there are 9 essential amino acids our bodies require. Essential amino acids are those that our bodies cannot produce itself and so must be obtained through the foods we eat. Complete proteins contain all of the essential amino acids our bodies need and are considered high quality proteins. For those of you who are seriously interested - this is a great online book on proteins.

You see, the catch is that all of the amino acids needed for protein synthesis in your body must be in the cell at the same time, your body can't store seperately and put them together later. If you don't eat all the essential amino acids in the same meal, or a complimentary set (think beans & rice), your body will break down your muscles to obtain the missing amino acids. Not good. This is why essential amino acids are so important, their content determines the quality of a protein.

There are a number of ways to measure a proteins quality, but none of them are perfect measure of a proteins efficiency/digestibility. Here are the most common:

Bioavailability - the degree to which a substance can be digested and utilized by the body in the amount and form in which it is present.

% Biological Value (% BV) - the proportion of absorbed protein (Nitrogen balance) that is retained in the body for maintenance and/or growth.

Casein (milk protein) = 85% Whey Protein Isolate = 98% Soy Protein Isolate = 80%

Rice Protein = 64% Whey Protein Concentrate = 95% Whole Egg = 100%

Net Protein Utilization (NPU) - the proportion of protein intake that is retained; a completely digested protein would have an equal %BV and NPU value.

Casein = 76 Whey Protein Isolate = 92 Soy Protein Isolate = 61

Rice Protein = NA Whey Protein Concentrate = 93 Whole Egg = 94

Protein Efficiency Ratio (PER) - based on the weight gain of a growing test animal (rat) divided by its protein intake over a study period (usually 10 days).

Casein = 2.9 Whey Protein Isolate = 3.5 Soy Protein Isolate = 2.1

Rice Protein = 1.3 Whey Protein Concentrate = 3.0 Whole Egg = 3.8

Protein Digestibility Corrected Amino Acid Score (PDCAAS) - a method of comparing protein quality based on the amino acid requirements of humans (a score of 1.0 = a complete protein, i.e. 100% of the essential amino acids after digestion).

Casein = 1.23 Whey Protein Isolate = 1.14 Soy Protein Isolate = 0.92

Rice Protein = 0.55 Whey Protein Concentrate = 1.0 Whole Egg = 1.19

So, does anyone really pay attention to these values? A few do, (body builders, olympic atheletes) but most of us don't. Does this have any practical applications? Can you use this info? Well sure. If you happen to like protein bars, you can use this information when looking at the nutrition panel to determine the quality of the proteins it contains. If you are a vegetarian/vegan, you can use this information to make sure you are getting a complete compliment of proteins in each meal so your body doesn't feed on itself. And you can impress people at the gym with your newly acquired expertise on this topic! Ok, maybe that's just me.

So, what's next you ask? Well, you know what a protein is and you know how to judge their quality, so how about what it is they do in the food products you purchase? In my line of work we are far more concerned with the properties different proteins exhibit and I will tell you all about it in my next post.