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Soybean oil quality.

Have you ever tasted soy oil? Probably not. Oh, it's in food items like salad dressing, margarine, mayonnaise, and even Big Mac sauce. And french flies and chicken pieces are cooked in soy oil at many fastfood restaurants. Potato chips and other snacks, too, are fried in soy oil.

So why haven't you tasted it, you ask? The answer is: because it's tasteless.

But it hasn't always been this way. "Fifty years ago, soybean oil tasted like painL" recalls Herbert J. Dutton, retired ARS chemist. "It was the major problem of the soybean industry to improve the taste of soy oil."

At the request of soybean processors, ARS scientists at the National Center for Agricultural Utilization Research (NCAUR) in Peoria, Illinois, began to look at what caused off-flavors and to devise workable solutions. They identified trace metals from the processing equipment and naturally present linolenic acid as sources of off-flavors.

"We had been told before we started that oxidation of the oil was not responsible. But we soon found that linolenic acid did oxidize when the oil was exposed to air," recalls Dutton.

In those days, scientists didn't think that the linolenic acid content could be genetically changed through plant breeding, so they tried hydrogenation as a way to remove it from the oil. To solve the flavor problem, ARS researchers recommended two processes: hydrogenation and the addition of citric acid.

Both steps inhibited the breakdown of fatty acids when oil was exposed to air, says chemist Timothy L. Mounts, who is in charge of Food Quality and Safety Research at the center. The early researchers also recommended replacing iron processing equipment with stainless steel.

"Vegetable oils have become popular today because consumers are more health-conscious in the 1990's. People want to lower the amount of cholesterol in their food and this is a good way to do it, since plants don't contain cholesterol," says ARS food technologist Kathleen Warner.

Warner coordinates the sensory evaluation panels at the NCAUR. Out of the 50 members on the panels, 15 are experts in sniffing the aroma of cooking oils, intensively trained in the art of recognizing characteristic odors. Some testers have as many as 20 years of experience in evaluating oils.

"Consumers don't know it, but ARS employees have done behind-the-scenes sensory evaluations since 1940 to evaluate vegetable oils and their end-use quality ," says Warner.

Testing the Taste of Vegetable Oils

In the 1940's, Dutton and others at the Peoria center came up with standardized taste tests for oils that were eventually accepted worldwide. Says Dutton, "Before then, taste-testing was a rather biased affair."

Today, the big problem is odors--odors given off during high-temperature frying with several types of vegetable oils. Odor problems stem from volatile fatty acids that break down under high temperatures and longer cooking times.

During heating, various types of oil may emit as many as 40 different characteristic odors. For example, soy and canola oils smell fishy. Corn oil has burnt or corny odors. In contrast, cottonseed oil develops a more fried-foodlike aroma, so it's often used in blends with other vegetable oils to mask objectionable odors.

In the 1960' s, the Peoria center began studying and evaluating soy oil. Special rooms were set aside to check aromas given off by frying oils.

At first, these rooms were just large, empty labs in which pans of heated oil were set. ALl exterior doors were taped shut to keep other odors out---except for one door for panel members to enter, sniff, and record their perceptions.

Later, small 5 (feet) by 8(feet) by 10(feet) rooms were constructed with airflow and temperature controls. Panelists enter these through a 2(feet) by 3(feet) by 10(feet) anteroom that serves as an airlock. Odors to be sensed are ducted in through a ceiling vent and exhausted through vents in the four bottom comers of the room. The location of the exhaust vents ensures the even mixing of the odors with the air in the room.

Several major food companies have used the Peoria aroma lab as a model for their own similar facilities.

Now, 40 years after scientists abandoned the idea of genetically changing the composition of oils, plant breeders have found they can genetically alter the seed to produce oils with modified fatty acids.

The panels' reactions to the performance of these modified oils during cooking and frying will tell plant breeders how well the modifications affect eating quality. Someday, these new-generation oils may be stable enough for frying without prior hydrogenation, says Warner.

The panel is currently evaluating oils from experimental soybean lines bred for 1ow-linolenic acid content developed by plant breeders at Purdue, North Carolina State, and Iowa State.

In another project, panelists are evaluating soybean and canola lines developed from special breeding programs by InterMountain Canola Co. in Cinnaminson, New Jersey. A cooperative agreement between the two organizations makes this work possible.

Yes, soy oil has come a tong way in the last 50 years...from a product that once tasted like paint to one with 75 percent of the U.S. market for edible oil.--By Linda Cooke, ARS.

Timothy L. Mounts and Kathleen A. Warner are in the Food Quality and Safety Research Unit at the National Center for Agricultural Utilization Research, 1815 N. University Street, Peoria, IL 61604. Phone (309) 6854011.
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Author:Cooke, Linda
Publication:Agricultural Research
Date:Jul 1, 1992
Words:888
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