J. Peter Clark

Single-strength orange juice that has not been concentrated (not-from-concentrate, NFC) is the most rapidly growing consumer product made from citrus fruit. Historically, frozen concentrated orange juice (FCOJ) was important, and concentrate for industrial uses is still a major product. Single-strength juice made from concentrate is the most popular consumer use. Much of this is made in local dairies for efficient distribution under refrigeration.

Florida and Brazil are the two most important sources of oranges. Citrus crops are also grown in Texas and California, as well as Israel, Spain, Australia, and South Africa. About 95% of the orange crop in Florida is processed, with the balance sold fresh.

Processing Steps
Oranges are picked from their trees by hand (although increasing amounts are harvested mechanically) and delivered to the plant in bulk trucks. There are standards for fruit grades, and prices are determined in part by yield and solids content. A sample is taken from each load, and the juice is extracted to determine yield and juice properties. Soluble solids, mostly sugar, and sugar-to-acid ratio are important parameters, which can vary with the time of year and variety. Color is also important and also varies. Juices from early and late in the season are often blended to standardize color and flavor. Yield of juice is generally about 50%, so profitable utilization of the remaining portion is critical.

Oranges are stored in bulk bins until needed. The outside surface is washed with a detergent and warm water, then the oranges are sorted by size. The machines used to extract the juice are size specific.

There are three approaches to extracting the juice:
One approach, utilizing the Brown Reamer, made by Brown International, Covina, Calif., uses the same principle as a kitchen juicer, namely, cutting the fruit in half and pressing each half against a rotating burr or reamer. On the commercial scale, each machine has pockets of a specific size arranged in a circle. Each fruit is cut in half, then pressed against a reamer. The peels are collected for further processing as the juice flows into tanks.

Another approach is offered by FMC Corp., Lakeland, Fla., in which the fruit is penetrated by a porous tube and then crushed by interlocking fingers. The juice flows through the tube, and the shredded peel is collected.

Both machines are in wide use. The major difference between them is the form in which the peel is recovered. Issues that can affect extraction include yield and the amount of peel oil that is in the juice. There are limits on the peel oil content of juice because the oil is bitter. Some oil is necessary for good flavor, but too much is a defect. Also, the oil is a valuable byproduct in its own right.

The third approach is usually applied to other fruits where peel oil is a primary product, such as lemons in Italy. In this approach, the peel is removed from whole fruit by abrasion, then the fruit is crushed for its juice. The resulting juice is inferior to that produced by the Brown or FMC machines and may be less sanitary.

Juice is normally passed through a finisher to remove seeds and membrane, or rag. This operation can also control the amount of pulp in the juice. Commercial juices are offered with various levels of pulp or juice sacs. The pulp removed from low-pulp products can be added to those with higher levels.

Juice is pasteurized to reduce pathogenic and spoilage microorganisms and to eliminate enzymes that can inactivate pectin and thus cause separation of pulp from serum. Pectin is a naturally occurring hydrocolloid that contributes to the desirable mouthfeel of juice and helps keep pulp in suspension.

Single-strength pasteurized NFC juice is stored aseptically in bulk under refrigeration for later packaging. Juice may be shipped under aseptic conditions in trucks, rail cars, and ships carrying millions of gallons. Consumer packages include single-serve aseptic boxes, gable-top coated paperboard cartons, glass bottles, and plastic jugs. Most are sold refrigerated, but aseptic packages are shelf stable.

The thermal treatment for NFC juice is less severe than that for juice that will be concentrated because there is additional heating in the evaporation process. The usual evaporator for making concentrate is the “thermally accelerated short time evaporator” (TASTE), which has seven effects and eight stages. The heat is exchanged in long vertical tubes. Temperatures start at about 100ºC and are reduced while water is removed until the soluble solids are about 65%. (Soluble solids are normally expressed in degrees Brix, and measured by refractive index; 1º Brix is 1% solids.)

Some competing evaporators use plate heat exchangers, and are also multi-effect, meaning that the steam evolved in one stage is used as the heat source in another. This is achieved by lowering the pressure in each successive stage. The result is that one pound of steam, applied in the highest-temperature stage, can remove several pounds of water from the juice, reducing energy costs.

The high-solids concentrate may be sold as is, around 65 % solids, or it may be diluted to about 42% with water and a commercial flavor mixture (derived from essence and peel oil) for consumer packaging as the standard 3:1 FCOJ.

Essence is concentrated flavor removed in the first stages of evaporation, then concentrated separately. The chemicals contributing to orange flavor are a complex mixture of higher alcohols and esters which normally would boil at temperatures higher than the boiling point of water. However, their solution with water is highly non-ideal thermodynamically, so they can be stripped from water by distillation. Most essence is sold to the flavor industry, where it is manufactured into flavors for use in commercial retail juices and beverages.

As is true of many other foods, byproducts are critical to the economics of citrus processing. Besides essence, some of the significant by-products are dried citrus pulp pellets (used for cattle feed), molasses (used in animal feed and beverage alcohol fermentation), pectin, peel oil (used in flavors), and d-limonene.

The major by-product of citrus processing is cattle feed and molasses made from the peel. The peel is first pressed, and the press cake is dried and pelletized. The press liquid is concentrated to make molasses, which may be added back to the dried peel or sold separately as a feedstock to make beverage alcohol by fermentation. Cold-pressed peel oil is recovered by extracting the oil from the peel by contacting with water, resulting in an emulsion. The oil is separated by centrifuging and is sold, mostly to flavor companies, who fractionate it into various components, most of which find their way back to the juice companies. During the evaporation process to concentrate the molasses from the press liquor, oil that remained in the peel is recovered. This oil is composed of terpenes, largely d-limonene, which is recovered by distillation and sold as a solvent or as a feedstock for chemical synthesis of terpene resins.

Pulp from the finishers may be washed with water to recover extra solids. Usually there are at least three stages of countercurrent washing, in which fresh water first contacts the exhausted pulp, then proceeds stage by stage until it exits after contacting the fresh pulp. The pulp and wash are separated by finishers. The wash water is concentrated to make water-extracted soluble orange solids (WESOS). This material cannot be added to pure juice but is used in other products, such as soft drinks.

Robert Braddock, Professor of Food Science and Human Nutrition at the University of Florida’s Citrus Research and Education Center, Lake Alfred, Fla. (phone 863-956-1151) and author of the textbook, Handbook of Citrus By-Products and Processing Technology, published by John Wiley & Sons, has studied many possible by-products. For example, there has been interest in the flavonoids of citrus, mostly minor organic compounds which have various activities. Each citrus fruit has characteristic flavonoids which contribute to its distinct flavor in some cases. For example, tasteless hesperidin is found in sweet oranges, bitter naringin is in grapefruit, and neohesperidin is in bitter oranges. Some of the dihydrochalcone derivatives of these compounds, made by hydrogenating them, are intensely sweet. The sweetness, however, also lingers, so their applications in foods have been limited. However, at least one, neohesperidin dihydrochalcone, is approved for food use.

There is recent research to find biological activities for the minor constituents of citrus fruit, but commercial application may be limited because of the expense of extraction and purification of minor components from large amounts of peel residue, requiring treatment or disposal of large waste streams. The pharmaceutical approach of organic chemical synthesis would probably be more efficient for any component with true biological activity, according to Braddock.

Contributing Editor
Consultant to the Process Industries
Oak Park, Ill.
[email protected]