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The Mystery of the Brown Spots

In July of 2005, several volunteers noticed brown splotches on their shirts and safety vests. This splattering of brown varied from light to dark and would not come out in the wash. By August the brown spots became a subject of discussion and sparked our curiosity. We were curious about the source, especially since no such spots appeared while we were working in "the patch".

The first theory advanced was that the stains came from bits of matter cast about in the process of using the string trimmer. This line of thinking fell apart when someone observed that another volunteer's attire had the mysterious spots, but she did not use the string trimmer.

A small light bulb clicked on when a moist drop was felt on my face while cutting vertical kudzu vines. This suggested that there might well be a kind of sap in the vines that could be flung around when vines are attacked aggressively.

Barbara Daniels and I took time off to explore whether we could get liquid from kudzu vines. By clipping the vines at its flexible ends, we noticed that a drop would slowly appear at the tip of the cut. No drops came forth when a normal vine was cut — only the tender ends and no more than a few inches from the end.

We collected this "sap", one tiny drop from each cut, and placed it into a cleansed pill bottle. The process was slow — often taking 30 seconds to a minute for the drop to form. The drops would not break free and fall into the bottle. We had to brush the tip of the vine against the side of the bottle. Some of the liquid was milky in color, and some was clear. We then brushed several tiny droplets off onto a white handkerchief and outlined a small square with droplet moisture in the middle of the handkerchief.

Microwave treatment at home produced no visible spots. Hot water was tried next and again no brown appeared. Then the handkerchief went into the washing machine. Voila, when it was washed and dried, light brown spots and the outline of the square were clearly visible.

Several days later some of the “sap” in the pill bottle had turned reddish brown. The bottle and a spotted shirt were taken to the laboratory of a leading textile organization for analysis.

Newt Hardie
September 25 2005

Is it a Mystery?

By custom I eat an apple after dinner. If drops of apple juice fall on my tee-shirt, it turns brown when it dries. It does not wash out, even with bleach, and the result is very similar to kudzu stains.

Many fruits and vegetables have the property of turning brown (apples, bananas) or black (potatoes) when freshly cut and exposed to air. I've always heard that this is an oxidation process acting on sugars. Cooking has a similar effect because it accelerates oxidation. Heating sugar to produce caramel causes the sugar to turn brown. Cooks counter this effect on fruits and vegetables by keeping the material immersed in water (vegetables), or by coating it with an acidic liquid such as lemon juice or orange juice (fruits). That is one reason why lemon juice is added to fruit pies: Maintain color. Acids, such as vitamin C (ascorbic acid), are "natural" preservatives of food. (Vitamin C is also a free-radical scavenger, but that is a different topic.) Hence the value of vinegar (acetic acid). Sugars are also preservatives (a primary ingredient in fruit "preserves", and sugar-cured ham and bacon), but only when sealed from oxygen ("canning") in the case of fruits and vegetables.

Lou Adams
September 26 2005

What is Known about the Biochemistry

This oxidation reaction is speeded up with the enzyme Tryrosinase. The compound acted upon is a catacol-like compound. Anything that denatures proteins will work or anything that blocks the oxygen gas from getting to the cell juices. But to stop the reaction the cell must be cut, or the cell membrane constructed of proteins and lipids must be destroyed.

Catacol and tyrosinase are compound found in cells. When exposed to oxygen and in the presence of the enzyme tyrosinase the catacol oxidizes and turns brown. This is the reaction in potatoes and apples. When you bite into an apple the cell membranes are ruptured and oxygen comes in contact with the catacol and tyrosinase.

Gillian Newberry
September 28 2005