New Spins on Flavor

August 2000

New Spins on Flavor
By Lynn A. Kuntz
Editor

  Flavors have a profound influence on the success of a product. Traditional flavor compounding involves mixing botanical isolates with aroma chemicals to produce a finished commercial flavor. Volatility, solubility and reactivity of the flavor components affect flavor performance. Flavor is actually 70% to 80% aroma that is perceived through the oral cavity.

"Our job today at flavor companies is to emulate nature at its best by creating fresh and accurate flavors," says Clive Redfern, chief flavor chemist, T. Hasegawa Co., Cerritos, CA. "It has become more difficult to reproduce nature in our flavors with the array of legal, religious, and marketing constraints under which we work, such as natural, kosher, free of genetically-modified ingredients, non-allergenic, vegetarian, and so on."

Extracting flavor volatiles is essential to the creation of authentic flavor profiles. At times, these delicate flavors need protection from harsh processing conditions and benefit from encapsulation, which not only lends to their stability, but effectively times their release. For years, the flavor industry has relied on certain techniques to volatalize and encapsulate flavors, but it is now looking to other industries for new technologies, such as spinning cone column (SCC) technology and liposome technology.

"It is purported that the spinnng cone column was used for early 20th century nuclear energy programs," says Redfern. Liposome technology, which has been around since the 1960s, is now used in the pharmaceutical and cosmetics industries for controlled release of active ingredients, although the food and flavor industries are just uncovering its potential.

Spinning out freshness

Producing fresh-tasting or "true-to-nature" flavors has its challenges. Commonly used batch distillations can be inefficient and time-consuming. In a typical distillation, the starting material is a liquid mixture that is separated into various components through the volatilization of the lighter components, followed by condensation of the vapor back into a liquid. This method can capture volatile flavor compounds, however, it might also lose volatiles or alter their composition.

State-of-the-art distillation technology, such as a spinning cone column, make it possible to capture fresh flavor substances today.

This highly efficient liquid-gas contacting column, also known as a distillation or stripping column, uses gentle mechanical forces to enhance the distillation process. By this means, volatile flavor compounds are rapidly separated from a thin-film liquid system. Viscous slurries with high levels of suspended solids as well as clear liquids can be processed without damage to the flavor or extracted product.

"SCC technology originated in Australia, achieving early success as a method of capturing and removing the grassy notes from milk in this region, and has been commercially viable for about 12 years now," says Tony Dann, president, Flavourtech Americas, Inc., Graton, CA. "Since then, the industry has begun to use it for flavor management to transfer positive flavors from one product to another such as transferring full cream flavor to nonfat products." The first unit was brought to the United States about eight years ago.

Fruits, vegetables, tea, coffee, peppermint, beer, wine and citrus are key flavor categories that benefit by SCC technology.

Operation and advantages

SCC offers an efficient, cost-effective method of removing flavor volatiles, with high throughput capabilities, continuous processes, elimination of heat-induced off-notes, and the ability to extract volatiles from slurries.

Inside a vertical stainless steel cylinder, an inert stripping gas removes a vapor stream of volatile compounds, typically under vacuum. The SCC contains two series of inverted cones that are parallel to each other. A series of fixed cones is attached to the inside wall, while another series of cones is attached to the rotating shaft. These cones alternate vertically one stationary and one spinning.

The product is fed to the top of the column, then pulled down by gravity. Material flows down the upper surface of the first fixed cone, then drops onto the first rotating cone where centrifugal force spins the liquid into a thin turbulent film that is forced upward, out and off the rim of the spinning cone, dropping onto the next stationary cone below. The material works its way from cone to cone to the bottom of the column. This stripping technique is repeated 29 times with the 30 cone sets in the column.

Volatile compounds are distilled under vacuum at low temperatures. The stripping gas is fed into the bottom of the column and flows upward, passing across the surface of the thin film of liquid, collecting volatile compounds as it rises. Fins underneath the rotating cones induce a high degree of turbulence in the rising vapor stream. Volatiles are transferred from the liquid to the vapor stream with this turbulent thin film of liquid through the long vapor and liquid path.

The vapor flows out of the top of the column and passes through a condensing system, which captures the volatiles in a concentrated liquid form. The remaining liquid or slurry is pumped out the bottom of the column.

"With a continuous process, undesirable cooked notes are eliminated from the biomass because the flavor volatiles are rapidly removed from the spent stream before these notes begin to form," says Dann.

Most of the flavor volatiles are countercurrently stripped out with steam in less than a minute, while batch distillations can take an hour or more.

The thin film is key in the efficiency of the SCC. The thin film provides a maximum contact surface with the steam going across the film in the opposite direction.

Typical batch-distillation processes cannot handle distillation of slurries. With a continuous process, the system is automatically fed from the top to the bottom, and then the waste is pumped out of the bottom of the equipment.

Using SCC

"One of the keys to capturing the fresh volatile notes from fruits and vegetables is placing our equipment at the source point of the raw materials," says Dan Wampler, Ph.D., president, Sensus LLC, Cincinnati. Plant materials begin enzymatic degradation shortly after harvesting, especially the flavor. By the time plant materials are harvested and brought to a central plant for processing, valuable fresh flavor notes are lost. In order to minimize the time between harvesting and processing, Sensus was able to bring SCC to the source in the processing plant.

One example of bringing this technology to the field is in tomato processing. Enzymatic degradation of fresh tomato volatiles occurs seconds after a tomato is macerated. By moving SCC technology to a tomato processing facility, fresh tomato volatiles that would ordinarily be lost can be captured. Applications for these fresh tomato essences include tomato-based sauces, retort products and dressings.

"Creating a fresh tomato flavor was almost impossible until we were able to employ SCC technology," says Wampler. "Minute concentrations of important aroma chemicals are ordinarily lost by other processing methods." For example, much of the beta-ionone present in fresh tomato is generally lost. This chemical gives the impression of raspberry flavor at higher concentrations, but at about 4 ppb in a typical tomato, it adds to the overall freshness profile.

In another instance, Sensus, in partnership with SupHerb Farms, Turlock, CA, offers Sensus™ Herb Essences, concentrated herb essences in basil, cilantro, oregano, garlic, and onion. These natural clear, colorless, concentrated flavor-essences contain no added preservatives or sulfites. They can be used in a variety of foods including salad dressings, sauces, baked goods, dips and spreads, and beverages.

The keys to capturing the freshness of herbs involve expertise in growing and harvesting the materials as well as employing unique flavor-recovery technology. The herbs are harvested at their optimum maturity and the herb flavor volatiles are extracted with the SCC at SupHerb Farms facility. "When we process basil, we begin by harvesting basil around daybreak, followed by washing, comminuting, distilling, and finally, refrigerating basil concentrate at 33°F this entire process takes only a few hours," says Wampler.

"We are taking a classic flavor-management approach that begins with seed selection through harvesting and processing," says Wampler. "When you are extracting essential oils in herbs, you almost let them go to flower to maximize the oil content. However, this decreases the fresh character that is in the leaf of the plant."

The waste streams from the SCC are analyzed organoleptically for residual flavor to ensure removal of flavor.

"We are trying to capture that super-fresh character," says Wampler. "There arent aroma chemicals in the industry that will do the complete job that this technology offers to provide fresh-from-the-field character." Natural aroma chemicals are critical to compounding true-to-nature flavors.

SCC-extracted materials perform well during shelf-life studies. "Weve done retort studies on finished products as well as stability tests in packaged and refrigerated low acid and high acid foods the materials have held up very well in these instances," says Wampler.

The coffee and tea industries have been embracing SCC technology in the past several years. "This technology has enabled coffee companies to create a new generation of instant coffees with fresh, true flavor," says Dann.

The SCC is used in about a dozen countries (not including the United States) to produce instant coffee. Conventional coffee processing to produce high-solids extracts involves exposing the grounds to very high temperatures for long periods of time, which damages the delicate flavor compounds. The most efficient way to produce intense fresh-roasted character is by brewing coffee in the SCC itself, in the closed, oxygen-free system.

The recovery of tea volatiles illustrates the importance of capturing aroma when a high proportion of suspended insoluble solids is present. The ability to handle solids is important because the yields of volatile flavor components from streams containing solids are much greater than yields obtained from feed streams from which the insoluble solids have been removed. SCC allows the recovery of volatile components as well as the simultaneous extraction of soluble solids. This process preserves tea polyphenols for the functional food market.

For example, studies from Flavourtech have shown that up to six times more trans-2-hexenal and linalool (two volatile tea compounds) were extracted into the distillate from a tea slurry than from tea liquor with SCC. The yields of certain aldehydes were increased up to 15 times.

"Very few technologies can handle solids no distillation process in the world can handle solids in the way SCC does. It is a very important factor in aroma recovery," says Dann.

"In the creation of true coffee and tea flavors, it is important to capture the nonvolatile ingredients that are important to the overall flavor profile as well as the volatile aroma," says Wampler. Unlike basil extraction where the spent slurry is not added back to the flavor, the slurry of soluble components is added back as part of the overall coffee and tea flavor. "This allows us to create true coffee or tea flavor associated with tea steeping or coffee brewing," he says.

One might ask what SCC cannot process? "If you can pump it, you can process it through the spinning cone column," says Wampler. "The only problems are when you cant get the equipment located to the raw material." Wampler cites the case of muskmelons in Indiana where there are no processing facilities they are picked and sold for fresh market.

Even thick, gooey materials such as peanut butter and honey can be extracted by the process. "SCC can handle viscous materials as long as they can slide down a 45° slope (inside the equipment)," says Dann.

Sealing in flavor

In the flavor industry, encapsulation of a liquid material into a solid matrix is common practice for various reasons: it facilitates mixing of incompatible ingredients, overcomes binding with the food matrix, prevents unwanted changes during processing, improves hydrolytic and oxidative stability, and masks unpleasant odor or taste. Much as an eggshell protects the inner contents of the egg from the outside environment, a "microcapsule" protects its inner contents. The use of microcapsules is a way to achieve controlled release of the inner material in the core. Technically speaking, microcapsules are capsules that range in size from 1 to 1,000 microns. Capsules below 1 micron in size are frequently referred to as nanocapsules.

Flavor encapsulation traps a flavor into a matrix to give controlled or targeted release in a food or beverage. Encapsulants also help protect flavors from degradation during processing. While there are many ways to encapsulate flavors for food systems, one method does not work in every system.

Various encapsulation methods include: spray-drying with fat, protein or carbohydrate matrices; extrusion; coacervation; molecular inclusion; and liposome entrapment.

Over the years, techniques developed for one industry have been adopted by different industries for different applications. Such is the case with liposome technology that has been widely used for many years in the pharmaceutical industry for controlled release and transfer of drugs, and more recently by the cosmetics industry. Versatile liposomes have been used in cancer therapy, gene manipulation and skin care. The food industry is just beginning to discover liposome technology as a means to encapsulate various ingredients such as flavors, functional ingredients and vitamins. In this industry, liposomes have the following functions: controlling crystallization, lowering the freezing point, water retention, enzyme functionality, protection of yeast cells against cold, and flavor retention.

"Liposome technology has been around for a long time. In 1964, British researcher, Alec Bangham, first identified and characterized liposomes," says Charles Brain, president and founder, Ingredient Innovation International, Wooster, OH. "While lack of stability and high cost have been barriers to the acceptance of liposome technology by the food and nutritional product industries, today, these issues have been largely overcome."

What are liposomes?

Liposomes, Greek for "fat bodies," are microscopic, spherical lipid vesicles formed by a bilayer of lecithin molecules surrounding an aqueous core. Liposomes can carry fat-soluble materials in the bilayer area and water-soluble materials in the aqueous core.

There are three types of liposomes small and large unilamellar vesicles, and multilamellar vesicles. Typical sizes range from 20 nm to 1,000 nm (1 micron). A unilamellar liposome is one bilayer or one hollow ball. When liposomes are produced, the result is a combination of unilamellar and multilamellar forms, the latter being concentric rings of bilayers which have a larger holding capacity for oil-soluble ingredients.

Phospholipids are mainly used to produce liposomes, although other ingredients may be used. Phospholipids are composed of a glycerol backbone with two long fatty-acid chains (R-groups), and a polar portion of the molecule. The polar portion, a phosphate ester group, can be attached to a phosphatidyl ethanolamine, a phosphatidyl choline, or a phosphatidyl inositol.

"Lecithin is a very good natural surfactant that has a very lipophilic, oil-loving portion of the molecule, and a hydrophilic, water-loving portion of the molecule that gives lecithin its functionality in many applications," says Joe Casey, manager, Lecithin Technical Support, Central Soya Co., Inc., Fort Wayne, IN.

Liposomes are bilayers of phospholipids, not a monolayer. "Think of a liposome as a hollow sphere with polar head groups on the phospholipid molecules and lipophilic tails," says Casey. "You can think of this as a nice package for encapsulating materials. You can encapsulate aqueous soluble materials in the core of the liposome, and to a lesser extent, you can encapsulate lipophilic materials in the liposome bilayer."

An oil-soluble material in the center of the phospholipid bilayer has much less holding capacity than a water-soluble material. Through other technologies, oil-soluble materials can be encapsulated into the center of the liposome, although these are not considered classic liposomes, says Casey. Although there are a range of numbers cited in the literature, generally, no more than 10% of oil-soluble material based on the weight of the phospholipid can be encapsulated, he adds.

Liposomal dispersions differ from emulsifications that have a single layer of surfactant such as phospholipids that line up at the interface between the oil and water phases. "Depending on whether its a water-in-oil or oil-in-water emulsion, the polar-head group always associates with the water, and the lipophilic tail associates with the oil in a classic emulsion," says Casey.

High phosphatidyl choline (PC) fractions of lecithin phospholipids can be used for creating liposomes. Two steps are involved in producing a high PC fraction: an alcohol fractionation step followed by a chromatographic isolation to purify the PC.

"You can take either crude lecithin or an oil-free lecithin, extract it with alcohol to solubilize the PC, then take this alcohol-soluble portion and run it through a chromatography column to further purify the PC," says Casey. "This will produce fractions that are 100% PC, but more typically 80% to 90% PC products are used in making liposomes."

Standard lecithin has a PC content of approximately 16%, whereas, by doing the alcohol extraction, products in the 35% to 40% range result. Elevated PC products in the 80% to 90% range result from further chromatography.

With an electron microscope, researchers can determine easily whether they have liposome molecules. In lieu of this expensive piece of equipment, "a good way to determine if you have achieved a liposomal dispersion is by doing particle size distribution with a light-scattering particle-size detector," says Casey. "If you have a unimobile distribution of particle sizes less than 100 nm in diameter, you can be fairly certain that you have achieved a liposomal dispersion."

Ideally, all the liposomes should be less than 100 nm in diameter with a very narrow particle size distribution to achieve optimal stability of the liposomal dispersion. "If you start putting too much material into the lipid bilayer, especially too much oil-soluble material, you will start to overload the liposomes and they will eventually break down and form a normal microemulsion," says Casey. The droplet sizes are larger in a microemulsion in a wider distribution.

One of the myths about liposomes is that they form spontaneously. "Liposomes only form with an input of energy into the system," says Brian Keller, Pharm D, founder of BioZone Laboratories, Inc., Pittsburgh, CA. BioZone Labs specializes in drug delivery primarily using liposomes as the delivery platform. "Only by putting shear into the system, can liposomes self-assemble into lamellar sheets. The more energy you put into the system, the smaller the liposome."

Once liposomes are created they can be spray-dried onto various carriers, such as maltodextrin or starch, to produce powdered products. When rehydrated, these powders will reform into liposomes.

Controlled Release

"Controlled release of flavors has been the Holy Grail in food science," says Casey. "You can take the flavor and mix it with an oil-soluble flavor in the bilayer or a water-soluble flavor in the core. Research has shown that this protects the flavor from degradation in some systems and gives longer flavor and better flavor, depending on the application."

While in the pharmaceutical industry, controlled release may refer to release in the bloodstream or the GI tract; controlled release of flavor only happens in the mouth when combined with air and saliva.

For water-soluble materials, liposomes release their contents by diffusion. "Generally, the water-soluble material in the core of a liposome reaches equilibrium with the medium surrounding the liposome," says Brain. "This means that in a product, only an equilibrium level of a water-soluble material will be contained in the liposome. When the surrounding medium is diluted, as by saliva in the mouth, the material in the liposome core diffuses out of the liposome at a rate that depends on liposome composition and physical properties of the material itself."

If the material encapsulated by the liposome is not volatile or water-soluble, the material can only be released when the liposome breaks down. This happens during enzymatic degradation or hydrolysis of the lecithin forming the liposomes.

A key element in the controlled-release action of the liposomes is controlling the release of the encapsulated material where it is needed. "Liposomes need to release flavor in the mouth over an extended period of time," says Brain. "Through targeting technology, liposomes can be anchored to the desired surface. This technology can maximize the opportunity for dramatic improvements in the flavor perception of foods, especially in low fat foods, for example," he adds. Ingredient Innovation International has a patent on the technology that causes liposomes to anchor to mucin-coated surfaces such as the oral cavity and the gastrointestinal tract.

Liposome at work

Searching the literature, one will find very little on liposomes in relation to the food industry. However, a patent pertaining to food does exist: "Extrusion baking of cookies having liposome encapsulated ingredients," U.S. 4,999,208 (B.V. Lengerich et al., Nabisco Brands, Inc., East Hanover, NJ, March 12, 1991). In this patent, the inventors attest that "the liposomes substantially retain their structural integrity during the processing, mixing, and post-extrusion baking and thus remain intact in the finished cookieThe liposomes may provide a sustained release of the encapsulant to the cookie during storage and prior to consumption. The encapsulant may be released when the cookie is baked or eaten by the consumerLiposomes may encapsulate flavorings, fragrances, preservatives, anti-staling agents or other labile food additives."

In a research study at Central Soya, Caseys group investigated the use of liposomes in microwaveable cakes. "The object of the study was to determine the effects of liposomal flavor dispersions prepared with PC-enriched fractions on the stability of flavor in microwaved cakes," he says. Microwaved cakes were chosen as the model system to demonstrate whether liposomes have protective effects with the flavors.

A control cake with vanilla (water-soluble) was compared to an experimental cake with vanilla added in the form of a liposomal dispersion, containing an equal amount of flavor. The dry ingredients were mixed together, the flavor emulsion added with the liquid ingredients, blended, and baked in a microwave oven.

In sensory studies, trained panelists ranked the flavor strongest in the cakes prepared with vanilla in the form of a liposomal dispersion. Ranking studies indicated that there was a significant difference between the control and cakes prepared with liposomal flavor dispersions, indicating that better flavor development occurred with the encapsulated flavors than with the control flavor. In similar studies of microwave baking applications by other researchers, panelists rated products containing liposomal flavor dispersions as higher in flavor, regardless of flavor type.

Liposomes can help incorporate flavor oils into soft drinks without the use of weighting agents such as brominated vegetable oils, says Brain. "This opportunity capitalizes on the colloidal nature of liposomes with their natural charge repulsion, minimizing opportunity for aggregation or coalescence of the flavor oil dispersion," he explains.

In some applications where clarity is desired in water-based systems such as beverages, liposomes may not be desirable. Depending on the concentration, the product can appear cloudy because liposomes are colloidal dispersions. "A typical liposomal dispersion looks like milk," says Brain. Less opacity can be achieved with liposomes that are below 100 nm in diameter with low- to medium-concentration of encapsulated material in the product, he says.

Another application where controlled release is important is in breath mints or flavored tablets. Brain has done research showing the cooling extension in tablets containing menthol in which a powdered version of liposomes was incorporated. In one sensory study, panelists rated coolness sensations every 10 minutes after the tablet was completely dissolved, for up to 70 minutes. The liposomal menthol provided more cooling at every time interval and extended the time for which cooling was perceived.

Although stability has been an issue with liposomes in the past, through a combination of formulation and processing techniques, stable liposomes can now be produced, says Brain.

Stability is determined by particle size of liposomes over time, with a stable particle size indicating that a stable liposome system has been obtained.

Several factors that can cause liposome instability include: high surfactant levels, high alcohol levels, certain co-solvents (such as propylene glycol), and pH extremes. Liposomes need to be tested under various conditions to determine their stability.

"In food systems, we find that if you can stay at pH 3 and above, this will give adequate stability in the system," says Brain. "Below pH 3, can create problems from lecithin hydrolysis." Since only a few food products fall below this pH, this technology can have wide-ranging applications.

Liposomes are typically produced with special fractions of lecithin or specialized types of lecithin, such as hydrogenated lecithins that are very expensive. The scale-up to produce commercial quantities of liposomes requires a large capital expense with very low output of finished liposomes.

"As part of our work with liposomes over the years, we have found the means to make stable liposomes with relatively low cost using standard types of lecithins," says Brain. "We have also developed efficient processing techniques to make liposome technology commercially viable."

Liposomes future

Some in the food and flavor industry who hear about liposomes and advise that the technology remain in non-food areas. However, many do not realize that advances have been made. "Now that the issues of cost and scale-up have been solved, we feel liposomes have applications in the food industry," says Brain. "There are no regulatory hurdles because food grade lecithin is used liposome does not appear on the label."

If the cosmetics and pharmaceutical industries use various techniques to isolate flavor volatiles or encapsulate flavors, can the food industry be far behind? This remains to be seen.

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