VOL.3. No. 10 CA&MISTRY OP I ~ C~mus E INDUSTRY m Cx,mom
1117
CHEMISTRY OF THE CITRUS INDUSTRY IN CALIFORNIA ~ I P O R N I A&urn GROWBRS' EXCHANGE, CORONA, CALIPORNIA ELOISB JIIMBSON, It is ordinarily supposed that chemistry touches agriculture only in the control of soil conditions, water, fertilizers, and insecticides. But chemistry and physics play very important parts not only in these particular phases but in almost every part of the citrus industry. The chemistry of the soil and water is very important as citrus trees are quite susceptible to alkalinity of either. Fertilizers are applied for their plant food value as, for instance, in the case of nitrogen and humus as well as for the physical effect on the soil which is accomplished by the use of such fertilizers as lime or gypsum. In general, California soils are considered to be rich enough in inorganic salts such as potash and phosphorus. Spraying and fumigating for various molds and scales give another opportunity for this science. Problems concerning these are being studied continually and new materials and methods applied. A great deal of work along this line has been done a t the Citrus Experiment Station connected with the University of California. Investigations have also been carried out by the California Fruit Growers' Exchange. The manufacture of cyanides and other economic poisons is quite an industry in itself. Chemistry also has its place in determining the maturity of fruit. Tests have been worked out on navel and Valencia oranges, and also the grapefruit, to determine chemically when the fruit is ripe. The ratio of the per cent of soluble solids in the juice as determined by a hydrometer to the per cent of acid titrated with a standard alkali and calculated as anhydrous citric acid has been found to give a reliable indication of maturity. The legal standard for the juice of a ripe orange is a ratio of 8 to 1 or above, of a ripe grapefruit 5 to 1or above. The packing house has begun to realize the value of chemistry. Great care has to be exercised in picking and handling the fruit to prevent cuts, bruises, or breaking of the cells of the skin, as it is through these apertures that decay enters. It has been found recently that the use of borax or a mixture of borax and boric acid in the water in which the fruit is washed renders the skin less susceptible to decay (refer to patent). Another interesting chemical treatment of citrus fruit was recently described by Chace. Citrus fruit is oftentimes ripe but not fully colored; in fact, the Valencia orange in some cases never becomes entirely colored on the trees. In order to bring out the attractive orange or lemon color the fruit used to be treated in a tight room at the proper temperature and humidity by the gases from coal oil stoves where the combustion was incomplete. Dr. F. E. Denny found that ethylene gas hastened the production of color with less fire hazard as well as greater convenience of handling. Its use has now replaced the older method. As to the fruit itself-the lemon juice contains chiefly about 6 per cent
.
citric acid and about 2 per cent invert sugar and its rind is rich in pectin and lemon oil. The per cent of citric acid varies in different localities and seasons and seems to be a t least somewhat dependent upon soil or weather conditions. I n the orange the pectin and oil are also present but the citric acid is comparatively low, ranging from 0.9 to 1.4 per cent and the sugar much higher, ranging from about 6 to 10.5 per cent. The variation of the per cent of the acid and sugar with the soil and climatic conditions is verv , nreat. In California, for instance, the percentage of these substances occurring in the California navel orange is much greater than in the same variety in its original home in Bahia, Brazil.' The per cent of acid is more than twice as great in the fully ripe California navel than in the Brazilian. The increase is more than 50 per cent in the sugars. The same difference occurs in the sugar and acid contained in the juice of the grapefruit. On the desert the grapefruit is less rich in sugar and acid than the samevariety produced in the other citrns districts. An average of analyses of a number of samples of desert grapefruit gave 6.64 per cent sugar and 1.45 per cent citric acid in the juice while a corresponding study of central and Pectin Plant, Enchangc Lemon Products southern California fruit gave 7.04 Co., Corona, Calif., April, 1926. Precipiper cent sugar and 1.79 per cent tating tanks with Alr(SO,).. Dosing tank citric acid. A study of the factors above. contributinz to these differences would be both interesting and enlightening as possibly some of them may be within our control. The presence of vitamins in citrus fruits and their juices has been established beyond any doubt. The value of these to supply deficiencies of diet is so well-known that i t needs no further mention here. We have just touched on the foregoing applications of chemistry in the citrns industry. Now we wish to consider in a little more detail the chemical problems concerned with the disposal of fruit that will not justify pack' P. H. Dorsett, A. D. Shamel, and Wilson Popenoe, U. S. Dept. of Agriculture
-
-
Ball. 445.
ing and shipping to the eastern markets and the establishment of factories producing useful and valuable products from this fruit. More particularly we will consider the work of the Research Laboratory of the California Fruit Growers' Exchange and the plants established by the members of that organization. The subject of citrus by-products is very old. It is mentioned in the most ancient existing manuscript on the orange which is a copy of one written about 1178 during the Tong dynasty in C h i ~ a . In ~ this most interesting paper references are made to various uses to which the orange can be put. A description is given of the preparation of an orange incense from orange perfume distilled from the blossoms. Methods of preserving the orange in honey or sugar are given. The peel is used as a medicine. "When all the white inner part of the peel has been removed what remains is called ching pi or red orange peel-generally speaking the chu orange peel is warm in nature and normal in its effect upon the system. I t lowers the ch'i, stops fever, relievesphlegm, and fever and ague. If it is taken a long time it will make the body light in weight." Perhaps even at this early date people were interested in reducing. Early records also remain of the distillation of lemon oil in Europe.' As to the history of early attempts to make citrus by-products in California, Will has given quite a complete account.' The first by-products plant was established in 1898 a t National City where the Bush factory is still in existence today. Other factories were started and discontinued for various reasons at Pasadena, Redlands, Santa Ana, Riverside, and other places. At present there are a number of factories making citrus byproducts, most of them concerned chiefly with the production of fruit juices or marmalade. Those now producing one or more of such chemical products as citrate, citric acid, lemon oil, orange oil, or pectin are the United Chemical Company at Corona, making citric acid, and the Exchange Lemon Products Company at Corona, making citric acid, lemon oil, and pectin, and the Exchange Orange Products Company at San Dimas, making orange oil. The work of developing citrus by-products has been fostered by the United States Department of Agriculture. In 1907 Mr. E. M. Chace was sent to Italy to study the industries there, where a large proportion of each year's crop is converted into by-products. In 1911 the U. S. government established the Citrus By-Products Laboratory a t Los Angeles. I t still exists as the Laboratory of Fruit and Vegetable Chemistry. Early work was done on the method of citric acid and oil production, as also on fruit maturity and pectin. At present an interesting investigation is Han Yen-Chih's Chu Lu, Etumct du T'oung Puo, 2nd Series, 22 (1923). W.A. Bush, Calif. CCitrograph, June, 1920, p. 250. ' Wii, I.Ind. Eng. Chen.. 8, 78-86 (1916). a
a
being begun on the changes taking place during freezing and the conditions controlling this. A systematic study has been made on the constitution of California orange and lemon oils. Although not complete it indicates the possible production of satisfactory pressed and distilled oils which, however, in the case of lemon contain less than 4 per cent citral. The flavor is excellent. The pressed orange oils meet fully the U. S. P. requirements. The California Fruit Growers' Exchange has been a pioneer in the field of cooperative marketing of perishable food products. It has also been a pioneer in the interest displayed in the fostering of the production of byproducts in order to eliminate the lower grades of fruit and that which
Pectin Plant, EnchangcLemon Products Co., Corona, Calif., April, 1926. Left side precipitation, tanks. Right side, extraction tanks.
does not have good keeping quality from the fresh fruit market. In order to do this and to be able to maintain the uniform excellence of the packed citrus fruit the necessity for a profitable outlet for the off grades was seen. In consequence the California Fruit Growers' Exchange established in 1920 a research laboratory to aid the work being done in the two by-products companies which had been formed by members of the Exchange, and also to work on the development of new by-products. This laboratory has been of very great help in the development of the citrus products work. At present there are fourteen chemists employed in the two by-products companies and the research laboratory. The three principal problems undertaken and which are still being considered in the research laboratory are the satisfactory preservation of fruit juices, either in the original state as expressed or in concentrated or dried form, the production of pectin, and improvements in the quantity
and the quality of citrus oils. Other problems referred by the salvage companies have been worked out, as well as some work done on fruit maturity standards and the effectsof some insecticides. The problem of juice preservation is a very knotty one and has led to an extensive study of the changes which take place in the various constituents of the juice during different treatments and while being stored. A great many interesting facts have come to light and progress is continually made in improving the methods of handling the juice. A study of the
Tanks in which the lemon juice is neutralized with Ca(0H)r and C ~ C O to I form calcium citrate.
volatile constituents has been published.' Due to the unsaturation of some of the flavoring compounds, their preservation in the presence of the acid juices is unusually difficult. During concentration most of these volatile substances are removed and can be restored to some extent by the reincorporation of citrus oils. It has also been found that some of the factors contributing largely to the change in flavor are the alterations in progress in the proteins. A study of these changes under diierent conditions is now being carried J. A. Hall and C. P. Wilson. I.A. C. S..47,2575 (1925).
on. It is possible to make a very good concentrated juice and to maintain i t in cold storage almost indefinitely in a satisfactory condition. The very important matter of the preservation of the vitamin content has been considered and it has been found possible to prepare products in which the rediluted juice has a vitamin content equal to tbat of fresh juice.' Investigations on the dried juice and the various problems tbat present themselves in this connection are in progress. The vitamin content can also be preserved during drying.% A process for the production of a pure dry pectin was worked out in the research laboratory. Previously pectin, which is the base of fruit jellies and which occurs in citrus peel, was prepared for the market either in the form of a concentrated extract or an alcohol precipitate. The problem that confronted the laboratory was a method by which a dry citrus pectin could be economically made, as the bitterness of the concentrates prevented their use. The other alternative was the removal of the bitter principle from the peel before extraction of the pectin as was done by Beylik.' It was found possible to remove the pectin by a double colloidal precipitation with aluminum hydroxide and then to remove the aluminum salts from the dried pectin by washing with acid alcob01.~ A very pure product r e ~ u l t e d . ~After the many mechanical problems were solved and the pectin was being made on a small commercial scale the process had to be improved so as to produce a pectin meeting the requirements of a commercial jelly maker, that is a pectin almost colorless and tasteless, of high jellying power and making a rapid setting jelly.1° This has already been successfully done." Lemon oil and orange oil have also been the object of considerable research. These oils are now prepared by mechanical pressing and also by distillation. The pressed oils being preferred to the distilled products, &orts are being made to increase the yield of pressed oil and to improve the quality of the distilled oils. Also experimental work is in progress on entirely new methods of recovering atrus oils. Studies are being carried out to increase the citral in lemon oils." Considerable progress is being made in all lines. The problems of the by-products companies are greatly increased by the fluctuating intake of oranges and lemons. In the past ten years, for instance, the Lemon Products Company has handled yearly anywhere from 1500 tons to 33,000 tons of lemons, this being from 3 to 25 per cent of the 9.I,. Preston, I. Roy. Nnu. Med. Sewvice, 12,. 1 (Jan.. 1926). . Beylik, U. S. patent 1,393,660, Oct. 11, 1921.
'E. Tameson, F.N. Taylor, C. P. Wilson, U. S. patent C.P Wilson, Ind. Eng. Chem., 17, 1065 (19%). Agriculture Bull. 1823. lo E. Jameson, Ind. Eng. Chem., 17,1291 (1925).
" W. E. Baier, private communication.
1,497,882. June 17,1924
H. E.
PO&
U. S. Dept. of
VOL.
3. No. 10 CHJ~MISTRY OF THE CITRUSINDUSTRY IN CALIFORNIA
1123
crop. It is necessary, then, to turn out products which can be stored to insure a steady supply to customers. In the Lemon Products plant the production of juice, citric acid, oil and pectin gives concentrated products and utilizes almost everything of value in the lemon. The juice production is just begun. Citric acid manufacture has increased in volume and eftkiency until a t present most of the lemons available for by-products purposes are utilized for this purpose. The yield of lemon oil is increasing constantly. Pectin production
Monel metal crystallizers and buggy used for transferring crystals to centrifugal hopper.
is in its infancy but not only have the by-products companies the possibilities of being a large factor in the pectin field but also they hope to fulfil these possibilities in the comparatively near future. The Exchange Products salvage plants occupy a unique position with reference to pectin production, having available a t two nearby points under unit control the peel from 20,000 to 60,000 tons of fruit per year. The pulp as delivered from the other operations is immediately available for making pectin without the cost of drying, transportation, or storage. Lemon pulp, too, has been found acceptable as stock food but the fluctuating supply limits its usefulness in the fresh state. A study of its value when dried is now in progress.
From the oranges a more varied list of products comes. About 15,000 tons of this fruit are handled yearly with a large increase assured in the next ten years. The unsalable fraction of the orange crop varies from 1 to 8 per cent. Orange oil pressed and distilled is the chief output. Pressed California orange oil shows complete agreement with the highest standards for this article. Distilled orange oil complies with all chemical and physical standards hut cannot be graded as a pressed oil on account of the method of manufacture. Both these oils are distributed throughout the world. The other products are fresh juice, concentrated juice, dairy and chirken feed, grated peel, and dried peel. Of these only orange oil, concentrated juice, raw juice, and d a i i and chicken feed are produced in quantity. The orange pulp after the removal of the oil and juice is used to feed cows and has proved of considerable value for its good effect on milk production, probably due to its vitamin content. Tests are in progress to determine its exact value. Indicating the demand of this material as chicken feed, lately a large milling concern ordered 1,000,000 pounds of dried peel to be used as an ingredient in chicken feed. Chemistry, it will thus be seen, becomes increasingly important in the citrus industry. Its knowledge aids in the control of soil, moisture conditions, insect pests, fruit maturity, packing-house care of the fruit, the testing of all fertilizers and supplies and the disposal of the low grades and consequent raising of the quality of merchantable fruit. It is difficult to look ahead far enough to see just where this chemical and physical control will lead, since it is only in its beginning. Already weather conditions are in a measure counteracted by orchard heating in cold weather. A study has been and is being made of the effect of soil moisture on the crop and as time goes on this very important factor in fruit productiou will come under better control. There is no doubt that more will be known both of the chemical and physical effect of fertilizers and it wiU be more possible to get the desired results. With insecticides and fumigations the field is unlimited. If the time should arrive when even a small profit can be made from the production of citrus fruits for manufacturing purposes we can hope to eliminate or bring to a minimum the hazards which attend the production of citrus fruits. Already a big step has been made in this direction.
