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few fish are landed, h o w e v e r , a few hours after they a r e c a u g h t and when they are just entering rigor mortis; these fish might remain in rigor until sold to the consumer so that a carbon d i o x i d e atmosphere would be of uncertain value. The results of the fillet series were graphed in the same way as the whole-fish series. Table VI shows the difference in these series more clearly. When the freshness index is 22 or leds, the condition of the fish is still quite good; and when it reaches 30, the fish are barely edible. The number of days required for this value to reach 22 and 30 has been calculated for the various series and t a b u l a t e d in Table V I in the order of their keeping q u a l i t i e s . Table V I shows that all three series of fillets stored in a carbon dioxide atmosphere kept better than the three in air. iMoreover, the fillets prepared in the laboratory kept much better than
VOL. 27, NO. 12 those prepared by the fish dealer. This was especially marked in t h e series kept in the carbon dioxide. Some of these results are depicted in Figure 4. These experiments show that the utmost care must be taken in preparing fillets if t h e products are to be kept for t h e maximum length of time.
Literature Cited (1) illekseieff, P. 8., Intern. Bull. Inf o r m a t i o n Refrigeration, 1934, RQ.?
(2) Coyne, F. P., J . SOC.Chem. Ind., 51,
I
I
I I L L C T S PREPARED TREATED COMMERCIAL UNTREATEOCOMHEICIAL IN LABORATORY FILLETS FILLETS
FIGURE 4. EFFECTOF STORAGEIN CARBON DIOXIDEUPOX KEEPINGQUALITY OF HADDOCK FILLETS PREPARED IN VARIOUS WAYS
119T (1932). (3) Ibid., 52, 19T (1933). (4) Griffiths. F.P..and Stansbu, M .E.. Trans. Am. Fisheries Soc., 64, 401 (1934). (5) Killeffer, D.H., IND. ENG. CHEM., 22, 140 (1930). (6) Reay, G.A, J . SOC.Chem. Ind., 54, 145 (1935). (7) Stansby, M. E., and Lemon, J. M., IND.ESG. CHEM.,Anal. Ed., 5, 208 (1933). RECEIVED iMay 24, 1935. Published with t h e permission of the Commissioner, U. S. Bureau of Fisheries.
Extraction of Pectin from
Apple Thinnings H. W. GERRITZ
College of Agriculture and Experiment Station, The State College of Washington, Pullman, Wash.
STIMATES have been made that 10 per cent by volume of the total apple crop is lost each year as June drop and thinnings. This immature fruit contains large quantities of pectinyielding material which is referred to by Fremy (3) as pectose and by the A M E R I C - ~ NCHEMICAL SOCIETYnomenclature ( I ) as protopectin. B y treating this immature fruit with 0.5 per cent hydrochloric, sulfuric, or tartaric acid, a large portion of the insoluble pectic substance is converted to soluble pectin of good gelling quality.
Experimental Procedure Rome Beauty and Jonathan ap les thinned from trees in the Yakima valley about the middle ofJune and others thinned from trees at Pullman about the middle of July were picked off the ground for use in the experiment. The apples were wei hed and washed, then ground, sliced, or frozen, and different met%ods of extraction were employed. The plan of each extraction was to obtain a yield of good-quality pectin of such nature that by filtering and concentrating, a liquid pectin sufficiently pure for jelly
ma Ing would be obtaine The jelling strength of the pectin solution was determined by Rooker’s method ( 4 ) ,and crude pectin in the extract was determined according to official methods (9) except that no allowance was made for ash. Since Rooker’s method gives the direct gelling value, rather than chemical pectin content, it offers the more valuable information to jelly manufacturers. (Rooker considers a pectin solution to contain 100 units when 100 grams of solution containing 0.41 gram of lactic acid will gel 100 grams of sugar in 24 hours to give a firm gel weighing 165 grams.) Apple thinnings were ground through a food chopper and suspended in hot water. The filtered press juice contained almost no pectin as indicated by gelling tests. Boiling in an open kettle gave similar results. Ground pressed thinnings heated to 15-20 pounds per square inch (1.1-1.5 kg. per sq. cm.) pressure in an autoclave gave a brown press liquor of no gelling value. Allowing this mixture to stand for several days did not increase its gelling power. Heating the thinnings with very dilute solutions (approximately 0.1 per cent) of h drochloric, sulfuric, or citric acid, as used for extracting pectin $om ripe apple pomace, was unsuccessful with these thinnings. When, however, ground or sliced apple thinnings were mixed with 0.5 per cent hydrochloric acid and allowed to stand for several days, a thick viscous pectin solution of light green color was obtained. The pectin in apple thinnings appears to be in a very insoluble form which cannot be extracted b y methods used on the more mature fruit. The long period of extraction with hydrochloric acid in the cold showed these apple thinrings to be rich in material yielding pectin of good gelling quality. The yield was about 1 per cent, compared to 0.4 per cent or less for ripe apples.
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Hydrochloric Acid Extraction
was clarified as milch a.i: possible by centrifuging. Fourteen
A light green pectin solution with gelling quality of at least 135 units was obtained by extracting apple thinnings with 0.5 per cent hydrochloric acid at room temperature. The solution was transparent but slightly turbid. Sliced apples were later found to give a less turbid solution than ground ap les. Two kilograms of apples were ground through a coarse g o d chopper and suspended in 3 liters of 0.5 per cent hydrochloric acid. After standing 2 days, the mixture became thick and slimy. On pressing through a crude fiber filter cloth a thick, turbid solution resulted. The solution TTas filtered with difficulty through a pulped paper mat in a Biichner funnel. About 100 cc. of the solution were heated to 70" C. and poured into a filter paper in an ordinary gravity funnel. On allowing to stand overnight, only 50 cc. of filtrate were collected. Treating with charcoal, centrifuging, and filtering proved unsuccessful because of the improper grade of decolorizing carbon used. The pectin solution obtained was rich in pectin, hoivever, as was shown by its high viscosity. On pouring the filtered solution into an equal volume of 95 per cent alcohol, a voluminous coagulate of clear tough pectin was obtained. On centrifuging, part of the pectin rose to the top of the alcohol but the remainder settled to the bottom of the tube. The pectin was filtered out on a crude fiber filter cloth and dried. One gram of the dried pectin was dissolved in 100 cc. of water containing 65 grams of sucrose and 0.5 gram of citric acid. The solution was brought to boiling and boiled for 20 minutes. A stiff gel formed. Seventy-five cubic centimeters of the pectin solution made to 100 cc. with distilled mxter, when treated in t'he above manner, set to a stiff gel in 3 hours, showing it to contain at least 135 units, The pulp was covered with hot water and again pressed. The press juice contained about half as much pectin as the first extraction. Apple thinnings from Jonathan trees in the Yakima valley were extracted with 0.5 per cent hydrochloric acid and in two trials yielded more than one per cent of their weight in pectin in the first extraction. Eight hundred grams of apples lvere frozen, to facilitate pressing, and were then thawed and pressed. The pomace, weighing 255 grams, was cut into 1500 cc. of hydrochloric acid (pH about 2). The mixture was boiled 30 minutes, then rapidly cooled in running water, and allowed to stand for 46 hours, The pomace was pressed and the pectin liquor clarified as much as possible by centrifuging.
hundred cubic centimeters of solution were obtained. One hundred cubic centimeters of solution poured into an equal volume of 95 per cent alcohol yielded 0.42 gram of dried pectin. This is a yield of 0.74 per cent on the basis of fresh apples taken, as contrasted to a 1.07 per cent yield wit11 hydrochloric acid.
Eleven hundred and eighty cubic centimeters of solut'ion were obtained. T h e liquor produced a stiff gel of light color, and 100 cc. of clarified liquor gave 0.73 gram of crude pectin. On the basis of fresh apples used, the yield of crude pectin was 1.07 per cent. On the basis of wet pomace, the yield was about 3.3 per cent' crude pectin. A repetition of the procedure gave 1.07 per cent crude pectin on the fresh apple basis and 4.5 per cent on the basis of pressed pomace. Additional work showed that pressing the apples and extracting the pomace with hydrochloric acid resulted in an extraction comparable with that of extracting the total apple. Apples bleached in sodium sulfite before pressing gal-e an excellent quality of pectin but the yield appeared to be lowered. The appearance of the pectin solution was pleasing. Boiling t,he pomace in the acid for 30 minutes gave a slightly darker liquor than that obtained by soaking only a t room temperature, but also an average of several extractions appeared to give higher yields. Boiling alone did not extract the pectin and standing a t room temperature for 2 or 3 days mas necessary for profit,able extraction. A solution of 0.4 to 0.5 per cent hydrochloric acid gave best extraction. More dilute solutions were unsatisfactory. Extraction with 0.5 per cent sulfuric acid was less satisfactory than with the same concentration of hydrochloric acid.
Tartaric A4cidExtraction Eight hundred grams of frozen and thawed Jonathan thinnings from the Yakima valley were pressed, yielding 246 grams of pomace. The pomace was cut into a 0.5 per cent tartaric acid solution and allowed to stand for an hour. The pomace darkened appreciably. The mixture was boiled for 30 minutes, then cooled in running water, and allowed to stand for 3 days. During the boiling the pomace became light in color. The pomace was pressed and the pectin liquor
Concentrated Pectin from Apple Thinnings About 1500 grams of sliced apple thinnings mere extracted with 0.5 per cent hydrochloric acid. The pectin was precipitated with alcohol and filtered out on a crude fiber filter cloth. It was allowed to drain overnight. The stiff coagulum obtained above was triturated in warm water containing 6 grams of citric acid in 300 cc. until a suspension of that volume was formed. Homogenizing was necessary to obtain a uniform suspension. Twenty cubic centimeters of the concentrate were made u p to 100 cc. with distilled water, 65 grams of sugar m-ere added, and the solution mas boiled for 15 minutes. A stiff gel formed immediately on rooling. The jelly was light and quite clear in appearance.
Dried Pectin from Apple Thiniiings The crude pectin prepared from apple thinnings was airdried in a thin film. When ground it appeared as a green powder. This powder dissolved with slight difficulty in jelly sirup, and one grain dissolved in 100 cc. of mater containing 65 grams of sugar, and 0.5 gram of citric acid yielded a stiff gel on boiling and cooling.
Discussion of Results The apple thinnings were found to be rich in pectin-yielding material. Best results mere obtained by slicing turgid applc thinnings into 0.5 per cent hydrochloric acid and allowing t'hem to stand for 2 to 3 days a t room temperature before pressing. Similar results were obtained from the pomace aft'er freezing t'he apples, thawing and pressing to remove the juice. il quantity of acid solution equivalent to one and one-half times the weight of the unpressed apples was found to give a convenient volume of rich pectin solution. -4second extraction with hot water gave an additional yield of pectin. The p e c h obtained either as the original solution, as :L concentrated solution, or as a dried poTvdered pectin produced a n excellent gel. Solutions of 0.5 per cent sulfuric or tartaric acid were found to be about i 5 per cent as efficient as hydrochloric acid in extracting the pectin. More concentrated solution:; of tartaric acid niight give yields comparable to those obtained with hydrochloric acid. The nature of hydrochloric acid, which makes it an efficienthydrolyzing agent in sugar hydrolysis, is probably responsible for its efficiency in hydrolyzing the insoluble pectin material. The pecbin solution obtained by extraction with hydrochloric acid a t room temperature was of such color t h a t charcoal clarification was unnecessary in the preparation of pectin for jelly making.
Literature Cited (1) hmerican Chemical Society, Division of Agricultural and Food Chem., Rept. of Comm. on Nomenclature of Pectin, Sept. 6-11, 1926. (2) Assoc. Official Agr. Chem., Official and Tentative Methods, 3rd ed., 1930. (3) Fremy, J.pharm. chim., 26,368(1840). (4) Rooker, W.L., "Fruit Pectin," New York, Avi Pub. Co., 1928. RECEIVED M a y 24, 1935. This paper represent6 one phase of a project 011 the utilization of apple waste. Published as Scientific Paper No. 313, College of Agriculture and Experiment Station.
