PROCESSING SWEET POTATOES"

WOODROOF: SWEET POTATOES 223 Data in Table 2 show that the water-soluble pectin was always higher in the sections from unarsenated grapefruit than in those from arsenated fruit and there was a slight change in this fraction during storage. Information used in preparing data for Table 2, which are averages for the six examinations over the 36 week storage period, indicated that the oxalate-soluble pectin increased about 5 percent, due to the slow deterioration of the water-soluble pectin during storage at 80 F. In general, sodium hydroxide-soluble pectin or protopectin decreased during storage about 50 percent, except in sections from arsenated grapefruit picked and processed in March 1957, in which it remained approximately the same. This pectin fraction represented only about 16 percent of the total pectin present. Any slight increase or maintenance of water-soluble pectin in excess of its slow deterioration to oxalate-soluble pectin was due directly to acid hydrolysis of the protopectin, which proceeded slowly at ph 3.3 to 3.6 for the canned product. Data in Table 2 also show no marked difference in the averaged values for the oxa late-soluble pectin in the sections processed from either the arsenated or unarsenated fruit. Except for the sections processed in January 1957, the averaged values for the sodium hydroxide-soluble pectin were always higher for the arsenated fruit. Summary Silver Cluster grapefruit, from both ar senated and unarsenated trees and receiving the same fertilizer program, were used to prepare canned grapefruit sections. The can ned sections were examined six times over a storage period of 36 weeks at 80 F. The sections remained firm and the color un changed by the storage period except for slight softening in the products packed in March from the arsenated and unarsenated fruit. A trace of pectinesterase present initi ally disappeared during storage. Water-solu ble pectin was not converted to oxalate-solu ble pectin more rapidly than hydrolysis of the protopectin proceeded, thus keeping the balance between the water- and oxalate-solu ble fractions in the canned sections. Hydro lysis of the protopectin to water-soluble pec tin due to the acid content of the section and the slow degradation to oxalate-soluble pec tin resulted in an increase in both the watersoluble and oxalate-soluble fractions with a subsequent decrease in sodium hydroxidesoluble pectin. Apparently there was no sig nificant effect upon the keeping quality of sections due to arsenation of the fruit in these canned products. LITERATURE CITED 1. Huggart, R. L, F. W. Wenzel and E. L. Moore. 1955. Effect of storage temperature on quality of canned grape fruit sections. Food Technol. 9: 268-270 p«2* H(i95art' R; L" f- w- Wenzel and E. L Moore. 1957. Effect of date of packing on quality of canned grapefruit sections during storage at 90 F. Proc. Fla. State Hort. Soc. 3. Huggart, R. L, F. W. Wenzel and E. L. Moore. 1957. Relation of acidity to variation in browning of canned grapefruit sections during storage. Food Technol. 11: 638-4. Rouse, A. H. and C. D. Atkins. 1955. Pectinesterase and pectin in commercial citrus juices as determined by methods used at the Citrus Experiment Station. Fla. Agr. Exp. Sta. Bui. 570. 5. Rouse, A. H. and C. D. Atkins. 1955. Methods for estimation of insoluble solids in citrus juices and concen trates. Proc. Fla. State Hort. Soc. 68: 117-121. 6. Wenzel, F. W., R. L. Huggart, J. W. Sites, E. J. Deszyck, E. L. Moore, R. W. Barron and R. W. Olsen. Pre liminary study of relationship of fertilizer and spray prac tices on the quality of canned grapefruit sections. Citrus Station Mimeo Report 56-6. Sixth Annual Citrus Processors' Meeting, Lake Alfred, Fla. Oct. 4, 1955. 7. Wenzel, F. W., R. L. Huggart, E. L. Moore, J. W. Sites, E. J. Deszyck, R. W. Barron, R. W. Olsen, A. H. Rouse and C. D. Atkins. 1956. Quality of canned grapefruit sections from plots fertilized with varying amounts of potash. Proc. Fla. State Hort. Soc. 69: 170-175. PROCESSING SWEET POTATOES" J. G. WOODROOF Georgia Experiment Station Experiment, Georgia Sweet potato processing is necessarily as sociated with production of the crop. For more than 20 years there has been a decline Published as Ga. Expt. Sta. paper J. S. 352. 1958. **Crop Production Annual Survey, U.S.D.A. Agr. Marketing Service, Crop Reporting Board. Dec. 1957. in production, both in the acreage planted and tonnage produced, while the yield per acre has increased slightly.** From 1936 to 1957 the acreage of sweet potatoes in the United States declined from 737,700,000 to 357,400,000; the yield dropped from 64,200,- 000 to 38,460,000 bushels; and the yield in bushels per acre increased from 87.2 to 107.5. During the same period acreage in

224 FLORIDA STATE HORTICULTURAL SOCIETY, 1958 Georgia dropped from 98,000 to 19,000, and yield dropped from 7,180,000 to 1,672,000 bushels; while acreage in Florida dropped from 18,000 to 9,000 and yield dropped from 1,182,000 to 675,000 bushels. Sweet potatoes are processed by canning, freezing or manufacturing them into specialty products. Among the problems encountered are, selecting the most suitable method of processing, choosing the variety of sweet po tatoes, whether to use uncured or cured po tatoes, what kind and amount of sweetener to use and selecting the most suitable con tainers. Other problems are how to obtain the desired qualities in the product, such as color, texture, appearance and flavor. Sweet potatoes are nutritious and high in energy value. They generally are liked when served as a vegetable, in breadstuffs, as des serts, or in meat combinations. When canned they have the sweetness of a fruit and body of a vegetable, and may be served as a part of any meal. Very few commodities may be served in as many ways, on as many occasions, or as often as sweet potatoes. While composed chiefly of starch and su gar, they also contain calcium, phosphorus, and iron, as well as carotene, thiamine, riboflavin, niacin and ascorbic acid. Canning Sweet Potatoes Size is important. Grading sweet potatoes before peeling according to size, shape, color, variety, and degree of curing is essential for minimum peeling losses and uniformity of product. Also, the style and type of pack depends largely upon the size of potatoes. Commercial plant data for cured Porto Rico potatoes, show 45% yield of prepared product from 12,740 pounds of potatoes of 1-2 inch diameter, and 58.3% yield from 5,400 pounds of sweets of 2-5 inch diameter. Curing effects. During curing, sweet po tatoes undergo many changes, most of which improve the quality of the canned product. Curing involves the special treatment given soon after harvesting, the potatoes being held about 10 days at 85-90 F. and 90% relative humidity. After curing, the temperature should be lowered to 55-60 F. and a humidity low enough (about 80%) to prevent condensa tion and sprouting. During storage, physical and chemical changes continue as a result of enzymatic action, respiration, and tran spiration. Uncured vs. cured. There is no single ans wer to determining optimum degree of curing of sweet potatoes before canning. Some va rieties are more suitable if canned freshly dug, some improve in flavor and lose in tex ture during curing, and others are equally good if canned uncured or cured. Among the varieties preferred uncured (based on an equal evaluation of color, tex ture, and flavor) was Easter Porto Rico. Those preferred cured are Allgold and Geor gia Bunch Porto Rico. There was little pre ference for Early Port, Goldrush, Sunnyside, Leeland Bunch, Oklahoma 26, and B-5999. Quality points appearance, color, aroma, texture, and flavor increased during curing and storage up to four weeks, then gradually decreased. At no time during a 22-week per iod of investigation were they below that of potatoes canned fresh. Syrup on canned cured potatoes was clearer than on those un cured. Amount of suspended material was inversely proportional to the amount of cur ing (conversion of starch to sugars). Most marked difference was in texture. Force in grams required to crush potatoes canned uncured, was 194.19; for freshly cured 108.1; two week old, 65.8; four weeks old, 39.90. Texture remains practically con stant throughout rest of 22 weeks. Yellow color decreases slightly in potatoes during curing and storage, while units of red color almost double during storage before canning. Freshly dug potatoes with a high moisture content (72.7%) peeled easiest in the shortest time. After seven days, both the moisture content and alkali required for peeling de creased, while time and temperature needed increased. At 21 days' storage, the moisture content continued to decrease, and the alkali required for peeling changed only slightly. After 45 days' storage, the moisture content continued to decrease and lye needed for peeling and the difficulty of peeling greatly increased. Also, alkali used for peeling varied with the size of the potatoes, and whether they were freshly dug or cured was a further factor. Results show: (1) That potatoes peeled easier with lye when freshly dug, and that peeling difficulties increased with length of

WOODROOF: SWEET POTATOES 225 storage and higher storage temperatures; (2) amount of alkali required for peeling freshly dug potatoes was high, decreasing as the peel became slightly thinner due to drying of stor age potatoes, but increasing markedly as peel got hard. Peeling. Peeling resulted in 10-to-60% losses depending upon the method of peeling, size of potatoes, degree of curing, length of stor age period, and variety. Two methods of peel ing were successful lye (10% solution at 210-215 deg. F. for 6 min. for uncured, and 10 min. for cured potatoes), or steam pressure (up to 90 pounds for 30 to 360 sec.) that is released suddenly. Sweet potatoes peeled with lye were im proved by dipping in 2% citric acid solution to neutralize traces of lye and to stabilize the yellow color. Traces of citric acid (enough to lower the ph of the syrup to 4.95) ab sorbed from the acid bath improved the ap pearance, color, and flavor of the canned product. Styles of packs. According to the U. S. Standards for Grades of Canned Sweet Po tatoes, the following styles of packs are recog nized : when approximate original confor mation of the prepared sweet potatoes is re tained. Pieces consisting of cut or broken units of prepared sweet potatoes. Mashed when prepared product is wholly comminuted or crushed. Combination of two or more of the above. Style of pack depends upon: (1) Grade of the raw potatoes, especially the size; (2) manner of serving candied, pies, souffles, and with meats; (3) variety, especially re ferring to firmness. Different styles of packs require different grades of potatoes, slightly different preparation equipment, different pro cessing times, and are priced differently. Whenever practical, canning potatoes whole is desirable because this utilizes potatoes too small to be otherwise marketed, and at a price higher than that for cut or mashed potatoes. Also canned whole potatoes remain more solid and the syrup is clearer. This is especial ly true for potatoes held in storage for two or more months, and they are preferred to cut potatoes for serving in the home or in stitution, since the size and shape are more uniform. Other than being slightly softer and more irregular in shape, quality of the cut product is equal to that of whole potatoes. In many commercial packs whole and cut potatoes are mixed in the can and so labeled. Mashed sweet potatoes are prepared from any size of raw, sound potatoes, without thoroughly mixing or removing the strings. They are preferred for pies, souffles, and pud dings. or modifications of this style include baby foods to which sufficient water is added to render the product soupy, and pie stock to which syrup, spices, and fruit, such as raisins or coconut, are added. Sweet potato puree is improved in con sistency and flavor by the addition of 20% by weight of 50% syrup containing 0.2% cit ric acid. There are several advantages in packing high quality sweet potato puree: (1) Pro duct can be rapidly and efficiently prepared from cooked peeled potatoes by stainless steel finishers; (2) puree is easily standardized in color and consistency, irrespective of the size of potatoes; (3) fibers, hard areas, and strings are completely removed or disinte grated. A large proportion of canned sweet potatoes are consumed in the form of puree. Kind of sugar. Concentration of syrup used influenced appearance, flavor, texture, and color of the canned product. If the total of soluble solids in the syrup was less than about 25%, the product became soft, water logged, and lacked flavor. When the syrup concen tration was 30% or higher, the sweets retained firmness and improved in flavor. Addition of enough 40-45% sucrose syrup to cover the product in the cans was most satisfactory. Corn syrup was satisfactory for canning sweet potatoes. A two-year experiment was conducted in cooperation with the Corn In dustries Research Foundation to determine the effect, if any, on the acceptability of canned sweet potatoes when sucrose was re placed by various kinds and amounts of corn syrup. The sweeteners used in these packs were (1) sucrose; (2) regular conversion corn sy rup, 42 D.E.; (3) intermediate conversion corn syrup, 52 D.E.; high conversion corn syrup, non-ion exchange, 62 D.E.; and (5)

226 FLORIDA STATE HORTICULTURAL SOCIETY, 1958 high conversion corn syrup, ion exchange, 62 D.E. Corn syrups were used in 0, 25, 50, 75 and 100 percents replacements of sucrose. In 1955, Porto Rico and Jersey Orange varieties of sweet potatoes were cured, care fully selected and processed. After preheating in water at 180 F. for eight to ten minutes, the potatoes were peeled in 10 percent lye solution at 200 F., thoroughly washed, dip ped in a two percent citric acid solution, trimmed, and packed in No. 2/2 cans. Each can contained 21 ounces of potatoes and 11 ounces of syrup, and was marked by code as to the variety of potatoes, kind of syrup, and corn syrup replacement. After exhausting the filled cans in live steam for ten minutes, they were sealed at 180 F. and processed at ten pounds steam pressure for 45 minutes. After one and nine months' storage at 70 F. the canned product was examined and evalu ated. This same packing plan and procedure was repeated in 1956 except that Goldrush variety sweet potatoes was used in place of the Jersey Orange variety and the examinations were performed after three and nine months storage. The results of these experiments were: (1) Potatoes of three varieties packed in corn syrup were equal in United States Depart ment of Agriculture grades and sheen to those packed in 100 percent sucrose. (2)There was no significant difference in texture between potatoes packed with corn syrup and those packed in 100 percent sucrose. (3) In gen eral, the color of the three varieties of po tatoes packed in corn syrup was preferred or equal to those packed in 100 percent suc rose. (4) The type of cover syrup had no effect upon ph of the product. (5) The cut out Brix reading was influenced more by va riety than by cover syrup composition when the ingoing Brix of the cover syrup was con stant. (6) There were only slight differences in the consistency of the potatoes packed in corn syrup and those packed in sucrose, the indication being that those packed in corn syrup were slightly heavier. Three types of discoloration are recognized in canning sweet potatoes. 1. Enzymatic evidenced by black streaks or areas during curing, storage, or early stages of canning. It was controlled by careful se- TABflfc _L QUAUTY OF FROZEN SWEET POTATOES Fora Preparation Additives. Baked Peeled Candied 5:1(80 Brix) Quality after freezing Comments storage for: U Months: 8 Months: 12 Months Poor Poor Poor Very soft, discolored, frost-bitten aroma and flavor Good Good Fair Slightly dry and bland, warmed-over flavor after eight months Good Fair Fair When baked in foil the texture, aroma and flavor ware like boiled; when baked unwrapped the surface was crusty, texture dry and normal flavor. Remained in excellent condition for more than two years Blanched Blanched Blanched Blanched Slices Candied Strips Blanched X2") Pies Pies Uncooked 5:1 (50c Brix) syrup 5:1 (50 Brijc) syrup (2/3 su crose 1/3 corn syrup) 5:1 dry sugar 80 Brix syrup 50 Brix syrup 5:1 (50 Brix) syrup (2/3 su crose 1/3 corn syrup) 5*1 dry sugar Good Good Good Excellent Very good Good Remained very good for more than two years Excellent sheen, texture and flavor for more than two years Appearance fair, sugar unevenly distributed Progressive drying and dulling of surface Remained excellent for more than two years Remained good for more than two years. Excellent sheen, texture and flavor for more than two years Very good Good Good Became progressively dull and dark Excellent Good Good Became progressively dry and dull Excellent Good Fair Became progressively dry, dull and dark 5:1 (50 Brix) No quality loss in two years syrup and 0.l citric acid Good Good Good Too stiff to handle, slight color and flavor loss after 24 months Pie Ingredients Excellent Very good Good Excellent Very good Good Excellent Very good Good

MURDOCK: -FEED INSECT CONTROL 227 lection of the potatoes and preheating prior to peeling. 2. Metallic indicated by black areas after coming in contact with iron, controlled by use of stainless steel equipment. 3. Rrowning seen after heating and re sulting from the browning reaction. The cara mel-like color and flavor thus caused in the finished product grows worse during storage. This was controlled by rapid processing, care ful selection of sweeteners, and storage of canned potatoes in a cool place. No off-flavor has been found to be im parted to the canned product when certain insecticides toxapene, isotox, chlordane, or aldrin were applied to the leaves of the plants at the strength recommended for insect con trol, or are used in transplanting water, put in the soil with the fertilizers, or broadcast over the soil. Freezing Sweet Potatoes Sweet potatoes have been frozen commer cially and in the home since about 1950. However, a procedure has not been standard ized. This is due to (a) lack of a specific /ariety proven suitable for freezing; (b) lack of a knowledge of the specific qualities desired in frozen sweet potatoes, by the homemaker, or other end-users; (c) lack of proven superiority in quality of frozen over canned sweet potatoes; (d) lack of data on the eco nomics of freezing as compared with can ning sweet potatoes; and (e) lack of data on the demand for frozen sweet potatoes as com pared with other frozen products, such as pumpkins and fruits. The information given in Table 1 is an evaluation of the Porto Rico variety of sweet potatoes prepared for freezing 18 ways. These results were summarized as follow: (1) Excellent results were obtained by freezing sweet potatoes whole, sliced, as puree, as pie stock, or in prepared baked or unbaked pies. (2) It was found necessary to partially (blanch) or completely cook sweet potatoes for freezing to stabilize the texture, color, aroma and flavor. (3) Raked sweet potatoes retained the initial qualities well but pre paration and packaging were difficult. (4) The addition of one part sugar or syrup to five parts prepared potatoes was an advan tage in preventing drying, browning and a dull appearance of whole or sliced potatoes; dry sugar was difficult to distribute evenly, while corn syrup increased the sheen. (5) or sliced sweet potatoes, or puree, re mained excellent for more than two years when frozen with either heavy or medium syrup; for eight months when not protected with syrup or sugar; and for six months when spices were added. (6) Replacement of onethird to two-thirds of the sucrose syrup with corn syrup improved the appearance; and the addition of one teaspoon of citric acid per 10 pounds of prepared potatoes accentuated the color and flavor. (7) The consistency of sweet potato puree was improved by the addition of one part of 50 Rrix syrup to five parts prepared potatoes. FACTORS TO CONSIDER IN CONTROLLING INSECTS IN A FEED WAREHOUSE D. I. MURDOCK Staff Bacteriologist Minute Maid Corporation Orlando Dried citrus pulp is the principal by-pro duct of the Florida citrus industry. It is used by the dairy and beef cattle industries as a source of carbohydrates. Over 300,000 tons are produced annually with a yearly monetary value of between 11 and 13 million dollars. Dried citrus pulp is manufactured from peel, pulp and seed of fresh citrus fruit, which remains after juice extraction or canning of fruit segments. A small amount of lime is added to the fresh pulp to release bound wa ter. The mixture is thoroughly agitated, press ed, dried and then shredded in a hammer mill. Citrus pulp, being a food commodity, is very susceptible to insect infestation. This situation has been aggravated by long term storage, which has created a serious ware-