WHITE-SMOCKED scientists are exploding eggs in impact chambers, bombarding fish with acoustical waves, crunching potato chips in mechanical jaws and redesigning the tomato. In laboratories across the country, they talk of universal testing machines, genetic engineering and extrusion-cooking of snack foods and cereals.

Working mostly out of universities and in corporate research, these scientists, or food engineers, are transforming the nature and variety of the American menu.

Only a few decades ago, for example, most tomatoes were handpicked. Nowadays, unless they're destined to be eaten fresh, tomatoes are picked by mechanical harvesters, costing upward of $200,000, that separate the fruit from vines and clumps of earth by pneumatic devices and sort them according to color by electric "eyes." Eggs and apples, among other foods, are also sorted this way.

A tour de force of genetic engineering, tomatoes now ripen en masse, permitting entire fields to be harvested at once. They also contain more solids, helping them hold up better under 20-ton loads and making for thicker catsups. (Contrary to the popular catsup ad, it's more than "anticipation" that keeps us waiting.)

All of this has brought a tomato revolution of sorts. Roughly seven million tons of the crop are harvested in the United States annually, double the figure of 20 years ago, as indicated by today's growing sea of supermarket sauces, spaghetti and pizza mixes, and increasingly popular Mexican and Spanish foods.

Keeping tomatoes, melons and bananas from ripening too quickly is a classic accomplishment of food engineers. Bananas, for instance, are picked green in Honduras or Ecuador and then shipped and stored in special refrigerated containers that are kept low in oxygen and high in carbon dioxide. Ethylene gas is injected into the compartments at the appropriate time to trigger ripening.

Control-ripening also helps keep apples in our fruit bowls all year. "An apple still breathes after it's picked," says Gene Haugh, professor of agricultural engineering at Virginia Polytechnic Institute and State University. "Like corn, or eggs even, it continues to take on oxygen and give off carbon dioxide. Vegetables do this even more after they're picked -- until they die and turn rotten."

Thus, controlled-atmosphere storage amounts to a kind of biological slowdown, or suspended animation. (Haugh recommends wrapping apples in newspaper before refrigerating to trap carbon dioxide and retard aging.) An apple in a warehouse can stay fresh for half a year or longer, say experts. Some even claim the minor gasses that build up in the fruit make it more a connoisseur's delight than when freshly picked.

If food engineering often involves drawing parallels between biological systems and mechanical ones, what do eggs have in common with airplane fuselages and submarine hulls?

All three, it turns out, can be viewed as cylinders with tapered and closed ends. Such structures are strong, says Haugh, yet in the case of eggs not strong enough to prevent roughly 5 percent breakage during laying or handling, another 5 percent during processing or marketing.

So, drawing on traditional engineering techniques, Haugh set out to quantify eggshell strengths in order to assist poultry breeders in identifying stronger strains for crossbreeding.

First, Haugh and coworkers crushed eggs in universal testing machines (bulwark of food industry research) to study shell-strength features in eggs from different families of chickens.

Next, they battered eggs in oscillators at 60 cycles per minute to simulate forces during collecting and handling. Then they drilled holes through the shells of test eggs, inserted hypodermic needles and pumped in air until the sacrificial things exploded. They found that a pressure greater than that in automobile tires was required to fracture the shells.

Using these and other tests, Haugh confirmed, as many had claimed, that the bluish-green eggs of some South American chickens are indeed more durable than white or brown eggs.

Finally, Haugh decided to trace the egg breakage problem to the laying process itself and discovered that some chickens have a tendency to lift their tails a bit too high, causing the eggs to break when they drop.

"That type of bird usually ends up in the soup," Haugh quips.

Ignoring "Brave New World" overtones, a few researchers have even attempted surgical implantation of a force transducer into chicken ovaries, trying to get the device incorporated inside a developing egg.

This would, in theory, allow the monitoring of forces on the egg (to be signaled out by a transmitter) as it forms. So far, however, mother nature has resisted this sort of probing.

Another classic food engineering quest took on a special urgency during World War II when pilots began reporting serious bouts of gastrointestinal distress in flight, according to Joseph Rackis, research chemist with the U.S. Department of Agriculture.

Upon investigation, the Air Force found that fliers not normally given to flatulence would often experience difficulties at high altitudes, where reduced pressure "allows gas to expand and makes a little of it feel like a lot more," Rackis explains.

Tracking the problem to its source, the Air Force discovered that the men's diets were rich in beans and other legumes and promptly declared these foods "off limits."

But not until 20 years later did scientists (still searching for a gas-free bean) determine why legumes are such offenders when Rackis and others demonstrated that the chains of sugar molecules in these foods are the culprits.

These sugar chains, it turns out, won't break down in the stomach but do so readily in the bacterial environment of the intestines, where fermentation occurs. And fermentation means gasses -- plenty of offending carbon dioxide, hydrogen and methane.

One new engineering approach to deflating the volatile legume, reported recently out of the Bhabha Atomic Research Center in Bombay, is to shower it with gamma rays from Cobalt-60, which weakens some of the sugar chain links and makes the food more digestible (without causing it to become radioactive).

Nor are the seas' fishes beyond the fathomings of food scientists. At Cornell University, food process engineer Sy Rizvi and colleagues are developing a new way of ferreting out worms in codfish.

Traditionally, fish filets are slapped onto a glass table illuminated from underneath, highlighting worm silhouettes. Infested fish hit the garbage pail. Rizvi's new method would bypass human sighters by sending sound waves through the fish and then, in effect, taking laser pictures of the patterns of propagation. The "ripple effect" is different if the waves encounter worms, explains Rizvi.

Eventually, he says, the laser-and-acoustics images will be programmed to trigger a robot arm that finds the right place, bores a hole in the fish and then draws out the wormy core with a vacuum.

In general, researchers don't do enough investigation into the physical properties of foods, argues Nuri Mohsenin, director of Food Physics Information Systems Inc. in State College, Pa.

"A chunk of food is just like a piece of glass or any other object," he asserts.

Along these lines, Mohsenin has studied the feasibility of compressing wheat or other grains (they're about 50 percent air) for more economical storage. He thinks it can be done, at great savings, but cautions that more studies are needed to determine how this would affect grain quality.

Foods might even be compressed into knobs or other objects that would be functional in a spacecraft, but could be eaten in an emergency. Mohsenin investigated this several years ago and thinks the idea may be usable by a space agency.

A more far-reaching application of this physical analysis of foods is "component analysis," a powerful new technique for "fingerprinting" foods.

The basic theory is that everything in nature absorbs or reflects certain colors of light, in a pattern unique for every substance.

By bombarding a food with a whole rainbow of colors, and seeing which are absorbed and which reflected, scientists can draw conclusions about moisture, fat and protein content. This, in turn, can tell them much about taste, texture and shelf life.

The approach holds so much promise that it's surprising that component analysis units aren't standard fixtures in today's supermarkets. Actually, units for checking fat content in hamburger have already been featured in a few stores, according to Karl Norris, chief of the Instrumentation Laboratory of the USDA. In a matter of moments, shoppers could tell how much fat they'd be feeding their families.

The trouble was, Norris explains, these figures sometimes didn't jibe with the grade of meat marked on the package -- a legal as well as a public relations problem for the stores. The instruments were discreetly withdrawn.

As for shoppers being able to bring their own portable watchdog units with them to the store, Norris says, "It'll take some improvement in the technology before these instruments become individually affordable. But when it happens, we'll see a new day in supermarket shopping."

But perhaps the real revolution in food engineering is in the area of factory-created foods, wholly new foods never before tasted by man. Today, our overstuffed supermarkets attest to a veritable New Foods Explosion -- endless varieties of cereals, hot dogs, snack foods, salad dressings, chewing gums, soft drinks, artificial meats.

These so-called engineered or manufactured foods (straight out of a laboratory) are strictly the name of the game as far as industry profits are concerned.

Actually, engineered foods are not always the newest thing under the sun. Bread, perhaps the world's first manufactured food, goes back to the Stone Age. Margarine, which simulates butter by blending oils from soybeans and other sources, has been mimicking nature for more than a century.

Many newly engineered foods are updated versions of older products (improved ways of leavening bread, for instance). Or they're slightly modified issues of classic mainstays -- such as the new O'Grady's Extra Thick & Crunchy Potato Chips.

Have you eaten one yet? Whether you're aware of it or not, those chips represent the labors of some 200 scientists working full time for two years -- creating the first "phase shifted" potato chip, its maker, Frito-Lay Inc., boasts.

Starting with a conventional ruffled chip, Frito-Lay set out to shift the ridges, or waves, so that the ripples on top would be out of synch with those on the bottom -- producing regions of thickness and thinness instead of a uniform chip.

Using computer models, scientists experimented with different ripple patterns and heights, and varying peak-to-peak distances. Finally, a chip was designed with "just the right ratio of rigidity to fragility" (not difficult to chew, but still crunchier).

To prove its claim, Frito-Lay employed a universal testing machine fitted out with waffled metal jaws to simulate chewing. At precisely 374 grams per square centimeter (more than twice the force required to break an ordinary ridged chip), Frito-Lay reported, the test chip fractured.

The scientists also set out to fine tune the new chip's flavor to give it more of a baked (rather than fried) potato taste. Sample chips were pulverized and the gaseous flavor compounds drawn off and analyzed into basic components. Then these "essences" of potato chip were bombarded with electrons to reveal their identities.

Once the desired relation between "texture profile" and "flavor profile" was attained, Frito-Lay sent its new chip off to market.

The unseen hand of the food engineer is also behind new (and said to be improved) chicken breading. Darrel R. Suderman, a scientist with Durkee Foods in Cleveland, explains that the traditional way to increase breading adhesion is to add more egg albumen, a protein in egg whites. But this works only up to a point.

So Suderman looked for another approach to improving breading coatability. On the most fundamental level, a breading material sticks due to particles becoming lodged in the tiny pits or valleys of the chicken epidermis. Therefore breading manufacturers try to include a variety of particle sizes in the mix (tiny sugar granules, larger salt particles, etc.).

Extending this line of reasoning, Suderman wondered if it might not be possible to increase the roughness, or bumpiness, of chicken surfaces being breaded.

Using a scanning electron microscope, he made an important discovery. Beneath the smooth layer of cells on the chicken skin surface is a more rugged underlayer that looks, under magnification, like a kind of moonscape terrain -- ideal for better adhesion.

But how to expose this rough underlayer for breading purposes? Suderman found that higher scalding temperatures used in the commercial defeathering process cause the silken cuticle (smooth layer) to slide off, uncovering these subterranean niches.

Right at the core of the New Foods Explosion is a little-known process called extrusion-cooking that has revolutionized the cereal and snack food industries.

Picture, if you will, a mass of superheated free-flowing dough moving through a long tubular barrel under very high pressure. As it passes from section to specialized section the dough is cooked, pasteurized, colored, refined and shaped -- until, at the end of the barrel, the dough exits suddenly into a low-pressure zone and the moisture inside "flash boils," dramatically puffing the piece.

It is this dramatic expansion or puffing that accounts for much of the crunchiness, airiness or fluffiness you hear, taste or feel when eating such products as corn puffs, cheese balls, corn curls, Cheerios, Alpha Bits or granola bars (they're lighter and easier to chew than they used to be, thanks to this new method).

From the manufacturing standpoint, it's really quite amazing.

For example, in the old days, says Judson Harper, vice president of research and professor of agricultural and chemical engineering at Colorado State University, most cereals were manufactured by steaming grains in large cookers, then flaking and pressing them. Finally, the pieces were dried and toasted.

But the new extrusion-cooker does all the cooking and forming in one continuous piece of equipment -- a sort of small factory rolled into one. What used to take hours can now be done in seconds, he says.

Sections, or blocks, can be added or eliminated easily, permitting an almost endless nuancing of products.

Says Joe Hegadorn, manager of engineering development for General Foods: "It's largely because of this process that every time you go to the store these days there's some new snack food or cereal on the shelf -- with a shape, color, texture and flavor not quite what you've ever seen before."