UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA FACTORS INFLUENCING THE QUALITY OF FRESH ASPARAGUS AFTER IT IS HARVESTED C. S. BISSON, H. A. JONES and W. W. ROBBINS BULLETIN 410 October, 1926 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1926 Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://www.archive.org/details/factorsinfluenci410biss FACTORS INFLUENCING THE QUALITY OF FRESH ASPARAGUS AFTER IT IS HARVESTED C. S. BISSON,i H. A. JONES2 and W. W. KOBBINS3 INTRODUCTION Within the past few years California has taken a leading place in carlot shipments of fresh asparagus. Nearly all of these shipments originate in the Sacramento, San Joaquin, and Imperial valleys at about the same time of the year. Asparagus is shipped from the Imperial Valley until about May 1, a date at which the eastern asparagus is usually moved in considerably quantity. Most of the growers in the Sacramento and San Joaquin valleys stop cutting for eastern shipment when the canneries open, usually in the early part of April. Cuttings are made whenever the spears are sufficiently long. It may be necessary to harvest each day, or every second or third day, depending upon the temperature. The cut spears are laid on the ridges and gathered in lug boxes which are carried in horse-drawn sleds or carts. In the Imperial Valley the asparagus is graded, bunched, and packed on the individual ranches. In the delta region of the San Joaquin and Sacramento valleys, however, most of it is transported by truck or boat to central packing houses, where it is handled by a few large shippers. Most of the asparagus packed for eastern shipment is bunched. When brought to the packing sheds, the spears are usually sorted by hand into four or five different grades, which are distinguished mainly on the basis of size. The spears are then tied in bunches of approxi- mately two and one-half pounds each. These are then trimmed to a length of about eight and one-half inches. The trimmed bunches, until packed, are usually stood on the basal end in shallow pans in an inch or two of water, which may or may not be iced. When removed from the pan, each bunch is rolled in a stamped parchment paper wrapper. The wrapped bunches are then packed in pyramidal-shaped crates with the butts resting on a layer of wet moss. It is current i Professor of Chemistry, Chemist in Experiment Station. 2 Associate Professor of Truck Crops, Plant Breeder in Experiment Station. 3 Associate Professor of Botany, Botanist in Experiment Station. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION practice also to place parchment paper on the bottom of the box, so that the moss rests upon this paper rather than upon the dry boards of the box. In early spring when cuttings are light and before it is possible to obtain a sufficient number of crates to make carlot shipments, most of the asparagus is shipped by express without refrigeration. In the Imperial Valley, as soon as carlot shipments begin, the asparagus is pre-cooled before being loaded into iced cars. In northern California, pre-cooling is not necessary, the crates being loaded into iced cars as soon as packed. The crates are stacked in braced tiers in the car. Bunker icing is practiced. The bunkers are filled with ice several times during transit to eastern points. No ice is placed either in the container or on top of the load. OBJECTS OF EXPERIMENT In the main, the present methods of handling and shipping asparagus are satisfactory, but there are instances in which asparagus has reached the eastern markets in an unsatisfactory condition. Excessive wilting, elongation of the spears accompanied by an open- ing up of the heads, decay due to bacterial and fungous infection, and general deterioration in quality, have all caused a certain amount of loss. These losses have occasioned a general demand by some of the growers and shippers for additional information as to the factors that influence the keeping of asparagus and its edible qualities after harvest. The experiments reported in this bulletin were started primarily to determine the influence of different storage temperatures upon the amount of water absorbed by the spears ; upon their rate of growth (elongation) ; and upon those chemical changes taking place within them which are most responsible for their quality. MATERIALS AND GENERAL METHODS OF PROCEDURE The asparagus used for these studies was grown in the Delta, near Clarksburg. The spears were harvested early in the morning and brought promptly into a field packing shed where they were loosely placed in lug boxes. The crates were covered with moist burlap and removed to a cold storage cellar. About four hours elapsed between the time the spears were cut and the time they were placed under the storage conditions indicated in the experiments. In the cold Bull. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 5 cellar, the spears were graded, bunched, and trimmed to approxi- mately eight and one-half inches in length. All bunches were weighed, the length of individual spears being determined accurately, and then were placed with their butts in about one-half inch of water and stored at different temperatures. It was believed that more uniform results would be obtained if the spears were stood in water rather than upon wet moss, for the former procedure would eliminate the possibility of an uncertain water supply. Samples for chemical and microchemical analyses were taken from the lot as representative of the condition of the asparagus as it came from the field. The average temperature (Fahr.) of the different storage rooms was as follows : 33°, 41°, 56°, 77°, and 95°. The maximum deviations from these temperatures were about 2° P. for the 33° room and 1° F. for the 41°, 56°, 77°, and 95° rooms. The storage rooms were not ven- tilated to allow air to leave and enter freely, and furthermore, the air within them was not agitated. Increase in weight and length of green asparagus in storage at different temperatures. — When asparagus spears were stored with their butts in water or resting on moist moss, they gained in weight and in length for a number of days. The weight increase was due to the absorption of water, the length increase to actual growth of the living spear. Tables 1 and 2 show the results of two different tests. The spears stored at 77° and 95° became moldy after a few days, and therefore were discarded as soon as infection was noted. In Series II, spears were not stored at these higher temperatures. The data in tables 1 and 2 show that the rate of water absorption and of growth in length of spears increased as the temperature increased. However, at a temperature of 33° F. there was relatively little increase in weight and length of the spears. At all temperatures, the greates percentage of increase in weight and length occurred during the first twenty-four hours. After that, there was, with slight irregularities, a slowing down in the rate. These relations are graphically shown in figures 1 and 2. The differences between the corresponding columns in Series I and II are due in part, at least, to differences in the average sizes of the two lots of spears. A comparison of small and large spears showed that spears of small diameter grow more rapidly in length than those of large diameter. The average increase in length per spear of a certain lot of small spears for a seven day period was 20.7 mm., whereas that of a certain lot of large spears under similar storage conditions for the same period was 17.5 mm. UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE 1 Increase in Weight and Length of Green Asparagus Stored at Different Temperatures. Butts in Water. Series I. Date Tempera- ture Fahr. Num- ber of spears Total weight Gms. Per cent water Per cent increase in weight Total length mm. Total increase in length mm. Average increase in length per spear mm. May 2 33° 18 659.4 689.9 92.6 92.93 3979 4010 3 4.6 31 1.72 4 697.0 93.00 5.7 4022 43 2.38 5 702.1 93.05 6.5 4026 47 2.60 6 705.2 93.08 6.9 4026 47 2.60 7 709.7 93.12 7.6 4017 48 2.66 8 711.9 93.15 8.0 4039 60 3.33 9 713.5 93.16 8.2 4043 64 3.55 2 41° 20 714.2 92.60 4468 3 761.6 93.06 6.6 4597 129 6.45 4 769.1 93.13 7.7 4630 162 8.10 5 775.8 93.19 8.6 4676 203 10.40 6 777.3 93.20 8.8 4678 210 10.50 7 778.8 93.21 9.0 4698 230 11.50 8 780.0 93.24 9.2 4698 230 11.50 9 779.8 93.22 9.2 4701 233 11.6 2 56° 16 681.6 92.6 3532 3 757.1 93.34 11.0 3804 272 17.0 4 772.5 93.48 13.3 3841 319 19.9 5 776.8 93.51 14.0 3912 380 23.7 6 779.3 93.53 14.3 3930 398 24.9 7 779.1 93.53 14.3 3933 401 25.0 8 781.8 93.55 14.7 3933 401 25.0 9 778.1 93.52 14.1 3939 407 25.4 2 3 77° 20 689.5 92.60 4437 767.5 93.36 11.3 4765 328 16.4 4 767.7 93.36 11.3 4767 330 16.5 5 766.5 93.35 11.2 4808 371 18.5 6 712. 5 92.84 3.3 4807 370 18.5 2 95° 15 596.5 92.60 3355 3 671.1 93.41 12.4 3809 254 16.90 4 668.0 93.38 11.9 3617 262 17.45 5 650.0 93.20 8.9 3625 270 18.00 BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS TABLE 2 Increase in Weight and Length of Green Asparagus Stored at Different Temperatures. Butts in Water. Series II. Date Tempera- ture Fahr. Number of spears Total weight Gms. Per cent increase in weight Total length mm. Total increase in length mm. Average increase in length per spear mm. June 9 33° 16 754.1 3495 10 770.4 2.1 3519 24 1.5 11 772.8 2.4 3529 34 2.13 12 774.0 2.6 3530 35 2.19 13 781.1 3.5 3530 35 2.19 14 787.6 4.4 3532 37 2.31 15 795.3 5.5 3535 40 2.5 16 800.0 6.1 3535 40 2.15 9 41° 17 738.2 3726 10 785.6 6.4 3838 112 6.58 11 796.1 7.8 3866 140 8.23 12 800.0 8.3 3875 149 8.76 13 802.1 8.6 3888 162 9.52 14 802.2 8.7 3908 182 10.70 15 803.3 8.9 3910 184 10.82 18 804.0 10.2 3913 187 11.00 9 56° 18 773.2 3978 10 847.5 9.6 4218 240 13.33 11 858.5 11.3 4238 260 14.44 12 862.4 11.5 4254 276 15.33 13 862.8 11.6 4288 310 17.22 14 863.1 11.7 4288 310 17.22 15 863.4 11.7 4296 318 17.67 16 864.6 11.8 4298 320 17.77 In 1917, Morse 2 conducted experiments in keeping asparagus after cutting. The spears were stored under a variety of conditions, as follows : 1. Butts in shallow water, at laboratory temperatures (70° to 80° P.). 2. Butts in shallow water, in refrigerator (45° to 50° P.). 3. Wrapped loosely in paper, and laid on shelf, at laboratory temperature (70° to 80° P.). 4. Wrapped loosely in paper, and laid on shelf in refrigerator (45° to 50° P.). UNIVERSITY OF CALIFORNIA EXPERIMENT STATION /s ) ^° /4- /3 ta tt ,4t° 1 y S 7 Q3 6 1, >JJ° / 0, 12 3 4^67 Days Fig. 1. — Percentage increase in weight of green asparagus. BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS AVERAGE /NCPEA3E //V LENGTH PEP 3PEAP £6 >SG° a4 2B EO IS If) < Si \4/° | 10 3 6 4 33° a o < O / 8 3 4 S 6 Ool/3 Fig. 2. — Average increase in length per spear 7 3 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 5. Laid directly on cake of ice (no temperature indicated). 6. Stood upright in tin box with a tight cover, and with no water ; box and contents placed in refrigerator (45° to 50° F.). Morse's results show that all spears, except those with the butts in water, lost in fresh weight during the storage period. Even those laid directly on ice or kept in a tin box with a tight cover, lost from 2 to 5 per cent in fresh weight. The data also show that the growth rate of the spears when stored with the butts in water increases with an increase in the temperature. For example, the average increase in length per spear for a 10-hour period was 2.6 mm. at 45° F., 4.0 mm. at 49°-54° F., 12.3 mm. at 75°-76° P., and 18.6 mm. at 80° F. INFLUENCE OF DIFFERENT STORAGE TEMPERATURES UPON STRUCTURAL CHANGES OF GREEN ASPARAGUS It is well to have in mind the structure of the edible asparagus spear before discussing the morphological changes which it undergoes after it is harvested. Structure of the spear. — The general structure of the asparagus shoot may be seen from a study of figure 3. The following are the principal anatomical regions : 1. Epidermis. 2. Cortex. 3. Pericyclic fibers. 4. Ground parenchyma tissues. 5. Vascular bundles, scattered through the parenchyma. Epidermis. — This consists of a single layer of cells. The outer wall of the epidermal cells is thicker than the inner and side walls; it is somewhat cutinized, thus rendering it impervious to the passage of water. In the epidermis of a shoot are found numerous pores or stomata. Each stoma is bordered by two kidney-shaped epidermal cells, the guard cells. These differ from all other epidermal cells not only in shape, but in that they possess chlorophyll, and in the ability to change shape. It is through these pores that the gases, carbon dioxide, and ox3 r gen, pass into and out of the shoot, and the water vapor moves outward. Cortex. — The cortex is a zone of tissue of varying width, consist- ing of rather large, thin-walled cells, which do not fit closely together but have air spaces between them. It is these cells of the green stem which possess the green coloring material (chlorophyll). BULL. 410] FACTORS influencing quality of asparagus 11 Pericyclic fibers. — The pericyclic fiber zone is composed of long, tapering thick-walled cells (fibers), which fit closely together, leaving no intercellular spaces between them. The fiber cells have flat sur- faces, with sharp angles. The walls of old pericyclic fibers have deposited within them a material known as lignin, which gives hard- ness to this tissue. It should be mentioned at this point that the toughness of an asparagus shoot is in large part due to the hardness of the lignified Fig. 3. — Cross-section near the tip of an asparagus spear, e, epidermis ; c, cortex; p, pericycle; v, vascular bundles; g, ground tissue. walls in these fibers. In most canneries a grade known as ' ' stripped ' ' or "peeled" asparagus is canned. Only the very large spears are used in this grade. Each spear is scraped with a knife, in which process, the epidermis, cortex, and pericyclic fibers are removed. The removal of the pericyclic fibers eliminates the principal structural elements responsible for toughness. It will be observed from figure 3 that in the tip of the asparagus shoot, the walls of the fibers are thin ; moreover, no lignin is deposited within them. Also it will be noted that there is no sharp line of demarkation between the parenchyma tissue of the cortex and that 12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION which is destined to develop into pericyclic fibers. As the stem grows older, the fiber region becomes more and more distinct from the adjoining parenchyma (fig. 4). Fig. 4. — Cross-section near the base of an asparagus spear. Labelling as under fig. 3, above. Ground parenchyma. — This name is applied to the central part of the stem inside the pericyclic fiber zone. The cells composing this tissue are large and thin-walled, and are separated by large inter- cellular spaces. The vascular bundles are scattered throughout this area, except for a central region with indefinite boundaries, in which BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 13 bundles are lacking*. The vascular bundles near the fibers are the youngest and smallest ; they increase in age and size as the center of the stem is approached. Vascular bundle. — Each vascular bundle appears in cross section as a V-form (fig. 5), with the apex directed toward the center of the stem. The tracheal tubes form the arms of the bundle, and between them are the phloem elements. The tracheal tubes of a bundle are smallest at the point of the bundle, usually becoming larger as the Fig. 5. — Cross-section of single vascular bundle from asparagus spear. Note the large lignified (shaded) water conducting tubes. ends of the arms are approached. Associated with the tracheal tubes are thick-walled wood fibers. The tracheal tubes are chiefly of the reticulate type ; a few of the smaller have spiral thickenings. Anatomical changes which take place as the stem grows older. — One may follow the anatomical changes which take place in the aspar- agus spear b}^ a study of successive sections from the tip towards the butt (fig. 6). Normally, under field conditions, the following struc- tural changes occur as the spear grows older : (a) The outer wall of the epidermis becomes thicker and more heavily cutinized, and hence probably more impervious to loss of water. 14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION (&) The fiber zone becomes more distinct from the adjoining parenchyma tissue, and the fiber walls become thicker and more heavily lignified. Fig. 6. — A, cross-section of asparagus spear near tip; B, same, at about the middle; C, same near the base; D, vascular bundle bordering pith from section A; E, same from section B; F, same from section C. In D, E, and F, the shaded portions indicate lignified elements. (c) There is an increase in the number of lignified tracheal tubes and a thickening of their walls. If sections are taken at various dis- tances from the tip of an asparagus shoot, it will be observed that the BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 15 nearer the base they are taken, the greater is the number of lignified elements in the vascular bundles (fig. 6). For example, in freshly harvested shoots, the average number of lignified elements in the innermost vascular bundles of sections near the tip (young portion of shoots) was found to be 9 ; in sections of the same shoot taken about half way between the tip and the butt, 11.5 ; and in sections taken at the base (oldest portion of shoots) 17.6. Duplicate lots of asparagus spears similar to those used in Series I and II, were stored at different temperatures, with the butts in about one-half inch of water. Spears were taken from each storage tem- perature at 24-hour intervals and examined anatomically. Transverse sections of three different parts of representative spears were taken, as follows : Section I about 1 cm. from the tip in the tender, green part of the spear ; section II about 10 cm. from the tip in the purple part of the spear; and section III, approximately 15 cm. from the tip in the more mature, fibrous, and white portion of the spear. The sections, cut free hand, were placed immediately in an alcoholic solution of phloroglucin (phloroglucin 1 gm., 95 per cent alcohol 100 cc), and left five minutes. They were then transferred to 25 per cent hydrochloric acid for a period of ten to fifteen minutes. All lignified membranes stained red. The degree of lignification was roughly indicated by the shade of red ; membranes slightly lignified were pink or light red, and those heavily lignified dark red. Safranin was also tested as a lignin stain, but it proved less satis- factory than phloroglucin. Safranin stains cellulose walls as well as lignified walls, but with alcohol, washes out of the former much more readily than from the latter. However, unless differentiation is uniform in all sections, there is danger of being misled. The degree of lignification was determined by counting the number of lignified tracheal tubes in the oldest vascular bundles, which are those bordering the central parenchyma tissue; also, by noting the color of the pericycle, and of the cells bordering the tracheal tubes. In each section examined, of which there were many hundreds, the number of lignified tracheal tubes in from five to ten vascular bundles was ascertained. This variation resulted from the fact that the num- ber of vascular bundles of the inner ring was not always the same, and also that only those bundles were considered in which the lignified elements could be counted with accuracy. It will be seen from these figures that under the conditions of storage, lignification took place the full length of the shoot and at all temperatures, in general being less at low temperatures than at high, 16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION g «5 fr £ w M t> CO ^ s a. 03 S a .2 o 01 m "5 OS * * * * CO CM IO rjn N O0 O0 N -t" HM CO ■* -H-* t~- * * * * -M CO CO N CO C i> eo «d tj< a; h CO CO co ■* H 1 1— CO «5 * * * * ++++++++ ©©^OOOTfioOlN N h © to N H ■* CO CO CO O 00 CM Tt< M ■* 3 * # * * -M- +-t- -H- ++ COcOCOCO©TttQ0CM N CO O0 M CC -—l CM CM CM CO CO i— I i> "* "t 1 "* co ***** ©O Tf H C CO CO o NiO O N OC h M CO CO CO t^ CO ^ CO -tf ^ 3g s c .2 o 03 w OS to 00 rH >0 r-H r-H O 00 H CO CO CO H 1 1— t^ * * * * IO CO© H C h © CO © CO H CO CO CO ^t -t — - to U3 * * # * IO CM Tt< CM CO * * * O ^ H i-H CO o ^ cc i-h CM CO CM Cn CO 00 00 CM CO CO «# * * * * lO CO 00 o cc h 6 io co cc —l CM CM CM CN © © © CD N 'O CM CM CO CO CO * * >o O CO O C\ ^ 00 CO i— i IO OS CO CC iH rH i-H CM C\ IO CO >o CO CO CO ■ft £ .2 "5 02 as o oo co co OS 00 1-- t^ .+- H 1— -*— o »h i-h cm io oi h ■*' oi co CO to . O CO © 00 oc 00 CO © OS CM t^ i-H C\ CO t^ 00 ■"*< O CX) ■* H Tf OS- CM CM OC 00 ^H © © .id co co CO O 00 CO r- >o CO IO CO OS o o o <- CO CM CO *c (-. cv E s O o 03 >> O h (N CO "1 IO CC > t^ s I o I II — bl O C C O co a.jl S3 o o _Q OJ - •3 -S s S3 jS .2P Ph Q j BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 17 and less at the tip of the spear than at the butt. The discrepancies occasionally appearing in the figures are believed to be due partly to individual variation, partly to the inability to select shoots which are of exactly the same age, and partly to the difficulty of making sections at comparable parts of the spear. In addition to lignification which takes place in the bundles, there was also progressive lignification of the fibers in the pericycle, and of the elements immediately surrounding the vascular bundles. In these cases, also lignification progressed more rapidly at high than at low temperatures, and at the TABLE 4 Average Number Lignified Tracheal Tubes in Inner Vascular Bundles of Asparagus Spears Stored at Different Temperatures. Degrees F. (Series II) Number of Section I (Tip) Section II (Middle) Section III (Base) days stored 33° 41° 56° 33° 41° 56° 33° 41° 56° 12.6 12.6 12.6 21.1 21.1 21.1 29.9* 29.9* 29.9* 1 13.8 11.4 11.6 24.4 24.6 23.8* 32.6* 33.6* 32.8* 2 14.0 12.6 13.0 23.0 27.6* 21.2* 33.2* 32.0* 35.2* 3 11.0 8.2 10.4 12.8* 25.6* 24.6* 33.4* 35.2| 31.8J 4 14.2 14.2 13.2 24.6* 26.8* 27.8* 31.2* 35. 2\ 33. 7J 5 14.2 14.4 15.4 34.0* 27.4* 26.6* 32.4* 35. 0| 38. 6J 6 14.8 14.0 15,2 33.6* 28.8* 28.8* 43.6| 39. 2t 39. 8 J * Pericyclic fibers lignified. % Lignification of cells surrounding the vascular bundles in addition to that of pericyclic fibers. base of the shoots than at the tip. Attention is called to the fact that the most pronounced lignification took place the first 24 hours after the spears were placed in. storage. It should also be noted that at the end of the seventh day of storage, although an increase in toughness was evident, no pronounced bitterness had developed in any of the lots stored at 33°, 41°, and 56° F. . Bitting 1 studied the anatomical changes in white asparagus after .harvest. The results obtained are, in general, similar to those reported herein. However > it is of interest to note that Bitting finds in a com- parison of "etiolated" (white) and "green" spears, that the former "showed more lignification, indicating that the green stalks are in better condition to resist the traumatic effects resulting from the cutting, at least for the first days." Considering the data cited above, and the results obtained by Bitting, it is seen that asparagus spears begin to deteriorate in quality, 18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION as evidenced by the degree of lignification, immediately after they are cut, and that deterioration is most rapid during the first 24 hours, after which time the process continues at a decreased rate. Deteriora- tion progresses at all temperatures, even at 33° F ; it is less, however, at low than at high temperatures. INFLUENCE OF DIFFERENT STORAGE TEMPERATURES UPON THE CHEMICAL COMPOSITION OF GREEEN ASPARAGUS General Methods Preparation and storage of samples. — The bulk composite sample of asparagus as obtained from the field was divided into lots contain- ing from 18 to 20 spears, and cut to a length of about eight and one- half inches. Care was taken to make the lots as nearly alike in all respects as possible. They were then placed in 800 cc. beakers with the butt ends resting in about one-half inch of distilled water. One of the lots was preserved shortly after harvesting. The remaining lots were placed in the different storage rooms. Preparation of the samples for analysis. — One of the lots of asparagus was removed from each storage room every 24 hours and preserved immediately. Before preserving, the spears were wiped to remove grit and water. Samples were removed every 24 hours for four days except from the 95° F. room. The spears stored at the latter temperature were starting to rot by the fourth day and there- fore were not preserved. The spears were cut into one inch lengths and placed in storage flasks. They were weighed, 0.25 gm. of CaC0 3 added, and then enough redistilled 95 per cent alcohol added to make the final solution about 60 per cent alcohol by volume. The flasks were placed in a water bath, heated to boiling, and the material boiled slowly with a reflux condenser for five minutes. The flasks were stoppered white hot. The samples were then stored in this condition at room temperature until they were analyzed. The preserved samples were analyzed for dry matter, reducing substances (chiefly sugars), total sugars, and crude fiber. Dry matter. — The weights of the dry material from the samples were obtained in the following manner. The alcoholic extract was evaporated on a water bath until a thick syrupy liquid remained in the dish. The spears were cut lengthwise into strips and then placed in the evaporating dishes containing the residue from their alcoholic extracts. By cutting the solid material into thin strips much time was Bull. 410 FACTORS INFLUENCING QUALITY OF ASPARAGUS 19 saved in drying the samples, and also in grinding the material after it was dry. The dishes containing the solid material were again placed on the water bath and heated until most of the water and alcohol were evaporated. The dishes were then placed in an electric oven, operated at 55° C. (131° F.). After 48 hours in the oven, the samples were taken out, and the last traces of volatile substances removed in a vacuum oven at 60° C. (140° F.). The dishes and contents were brought to constant weight. The weight of the dry matter was then corrected for the added CaC0 3 . The percentage of dry matter in the total sample of asparagus for each day at the various storage tempera- tures is given in table 5. These results are represented graphically in figure 7. TABLE 5 Percentage of Dry Matter Period of storage Original sample Storage temperatures (Fahr.) in hours 33° 41° 56° 77° 95° Per cent Per cent Per cent Per cent Per cent Per cent 7.45 24 7.17 6.87 6.31 6.39 6.25 48 7.06 6.56 6.18 5.99 6.01 72 6.91 6.55 6.07 5.85 5.86 96 6.87 6.56 6.25 5.89 •- •— *j~=.— . , ^Ay' ^ -95° 77 , BA 43 72 Period of storage in hours 96 Fig. 7. — Percentage of dry matter. 20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The values given in table 6 for the percentage decrease of dry matter at the end of each 24-hour period for each storage temperature were calculated from the data in table 5 by dividing the differences between the percentage of dry matter at the end of each 24-hour interval and the percentage of dry matter in the original sample, by the percentage of dry matter in the original sample. These values are plotted in figure 8 against the period of storage in hours. TABLE 6 Percentage Decrease of Dry Matter Storage period Storage temperatures (Fahr.) in hours 33° 41° 56° 77° 95° Per cent Per cent Per cent Per cent Per cent 24 3.8 7.8 15.3 14.2 16.1 48 5.2 11.9 17.0 19.6 19.3 72 7.3 12.1 18.5 21,5 21.3 96 7.8 11.9 16.1 20.9 O £A 46 7E 96 Period of storage in hours Fig. 8. — Percentage decrease of dry matter. It will be observed that the rate of decrease of dry matter is smallest in the samples stored at 33° F. and that this rate increases with considerable uniformity as the temperature becomes higher. The decrease in the percentage of dry matter is due to the absorption of water and probably to the destruction of sugars by respiration, the former probably being chiefly responsible. BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 21 Sugars. — Sugars are important constituents of asparagus, deter- mining to a degree its food value and edible quality. Moreover, the reducing sugars are the chief substances from which cell wall mate- rials and other more complex plant substances are made; and, too, the foods mainly used in respiration are sugars. Consequently, sugar values at intervals are probably a partial measure of the edible quality and of the food value of the spears, and show the trend of important chemical transformations going on in the plant. After the dry weights were obtained, the samples were ground and passed through an 80-mesh sieve, dried again for 12 hours in a vacuum oven, and stored in tightly stoppered tubes in a desiccator until analyzed. The determinations of free reducing substances (chiefly sugars) and total sugars w T ere made on alcoholic extracts of the original pre- TABLE 7 Percentage of Free Reducing Substances (On Dry Weight Basis) Period of Original sample Storage temperatures (FatnO storage in hours 33° 41° 56° 77° 95° Per cent 23.1 Per cent Per cent Per cent Per cent Per cent 24 23.30 22.53 21.35 19.87 21.21 21.93 21.08 17.70 19.62 19.92 18.89 16.27 18.82 18.36 17.36 14.90 18 27 48 14.87 72 14.90 96 24 46 72 Per/od of~ storage in hours Fig. 9. — Percentage of free reducing substances (chiefly sugars). 22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION pared samples. The alcoholic extracts were anatyzed for their sugar contents, using the gravimetric method of Munson and Walker 3 . The results of the analyses for free reducing substances are given in table 7 and are plotted in figure 9 against the storage period in hours. The data given in table 8, calculated from those given in table 7, show the total percentage decrease of reducing substances at each tem- perature at the end of every 24-hour interval. These values are represented graphically in figure 10. TABLE 8 Percentage Decrease of Free Eeducing Substances Period of Storage temperatures (Fahr.) storage in hours 33° 41° 56° 77° 95° Per cent Per cent Per cent Per cent Per cent 24 —0.8 8.2 15.1 18.5 20.9 48 2.5 5.1 13.8 20.5 35.6 72 7.6 8.7 18.2 24.9 35.5 96 14.0 23.4 29.6 35.5 24 48 72 Period of storage in hours Fig. 10. — Percentage decrease of reducing substances (chiefly sugars) It will be seen from the values given in tables 7 and 8, and from figures 9 and 10 that, with the exception of the samples stored at 33° F., all show a very rapid decrease in reducing substances during BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 23 the first 24 hours of storage. With the exception of the 95° F. curve, the rates of decrease in reducing substances are relatively large even during the last 24 hours in storage. At the end of 96 hours the sugar content of the samples stored below 95° F. did not drop below the percentage present in the 95° F. sample at the end of 48 hours. At 95° F., asparagus spears lost over 20 per cent of their reducing sub- stances during the first 24 hours, an amount which exceeds by about 7 per cent that lost by spears stored at 33° F. at the end of 96 hours. The results of the analyses for total sugars are given in table 9 and are represented graphically in figure 11. The curves (fig. 11) have nearly the same form as those (fig. 9) for reducing substances. The rate of loss of total sugars with increas- ing temperatures is also very similar to that of the reducing sub- TABLE 9 Percentage of Total Sugars (on Dry Weight Basis) Period of storage in hours Original sample 33° 41° 56° 77° 95° Per cent 24.91 Per cent Per cent Per cent Per cent Per cent 24 26.69 26.37 24.76 23.91 23.59 24.58 23.63 21.08 22.05 21.49 21.32 18.21 20.09 20.28 18.08 16.41 19.63 48 16.34 72 16.75 96 2A *a Period of sforoqe Jn hours Fig. 11. — Percentage of total sugars. 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION stances. It is worthy of note that at a storage temperature of 33° F., there is no loss, but rather a slight increase, in both the reducing substances and the total sugars during the first 24 hours, after which time there is a decrease. It will be observed that reducing sugars constitute approximately 90 per cent of the total sugar in the dry matter. Under the various storage conditions of his experiment, Morse (loc. cit.) found losses of the total sugar in the dry matter, the values being greater at room temperature than at those which prevailed in the refrigerator. Crude fiber. — The percentage of crude fiber gives an indication of the "toughness" of asparagus. The total percentages of crude fiber for each storage temperature are given in table 10 and are plotted in figure 12. TABLE 10 Percentage of Crude Fiber (On Dry Weight Basis) Storage period Original sample Storage temperatures (Fahr.) in hours 33° 41° 56° 77° 95° Per cent 8.88 Per cent Per cent Per cent Per cent Per cent 24 9.24 9.35 9.91 9.67 10.54 10.26 10.06 10.52 11.22 11.76 11.36 11.91 11.97 12.63 12.53 14.02 12.44 48 13.05 72 13.56 96 46 72 Period of storage /n hours Fig. 12. — Percentage of crude fiber. Bull. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 25 The curves indicate a very marked increase in the crude fiber in asparagus under different temperature conditions. The results in general are in accord with those obtained by microchemical tests, as shown on pages 16 and 17. The percentage increase of crude fiber under different storage conditions is given in table 11, and graphically represented in figure 13. TABLE 11 Percentage Increase of Crude Fiber (On Dry Weight Basis) Period of Storage temperatures (Fahr.) storage in hours 33° 41° 56° 77° 95° Per cent Per cent Per cent Per cent Per cent 24 4.1 18.7 26.4 34.8 40.1 48 5.3 15.5 32.4 42.3 47.0 72 11.6 13.3 27.9 41.1 52.7 96 8.9 18.1 34.1 49.0 £4 43 78 Period or storage in hours Fig. 13. — Percentage increase of crude fiber. The greatest percentage change takes place during the first 24 hours of storage, and for the higher temperatures the rate of change decreases with the length of time in storage. It will be noted that as the crude fiber increases, the sugar decreases. The development of the former is probably at the expense of sugar. Morse (loc. cit.) cites a positive gain in the absolute amount of crude fiber in asparagus 26 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION spears after they were harvested. At a temperature of 70° to 80° F., with the butts in water, the percentage of fiber in the dry matter changed from 10.54 to 15.51 in 72 hours, whereas at a temperature of 45° to 50°F. the change was from 10.54 to 12.71 during the same interval. DISCUSSION AND SUMMARY 1. After asparagus is harvested, changes occur in its structure and chemical composition, which affect its edible qualities. 2. The principal changes reported in this paper concern growth in length, weight, dry matter, reducing substances, total sugars, and crude fiber. Crude fiber, which is reflected in the toughness of asparagus, was determined by chemical analysis, and by microscopic examination of the spears in order to ascertain the degree of lignifica- tion of structural elements. These changes are markedly influenced by the temperature at which the spears are stored and by the length of storage period. 3. The storage temperatures employed were 33°, 41°, 56°, 77°, and 95° F. All changes were observed at 24-hour intervals. 4. It is known that asparagus spears grow in length in the crate, if the butts are on moist moss. If the moss is uniformly moist and remains so throughout the period of storage, the chief factor deter- mining the growth rate is temperature. The growth rate of spears with the butts in water was found to be least at 33° F., and to increase as the temperature was raised (within the limits of the experi- ment). Mold appeared on the asparagus stored at temperatures of 77° and 95° F., after 5 and 4 days respectively, and consequently, the results obtained at these temperatures after mold appeared are discarded. The greatest percentage of increase in the length of asparagus occurred during the first 24 hours, after which there was a slowing down in the rate. 5. Asparagus spears stored with their butts in water or on wet moss absorb water and increase in weight. The rate of weight increase due to water absorption, which is also shown in a decrease in the per- centage of dry matter, was least at 33° F., somewhat greater at 41° F., and still greater at the higher temperatures. Here, again, the greatest percentage of increase in weight, or decrease in dry matter, occurred during the first 24 hours after the spears were harvested. 6. During the storage period represented in these experiments, there was a loss in reducing substances and in total sugars. These BULL. 410] FACTORS INFLUENCING QUALITY OF ASPARAGUS 27 losses were especially pronounced at the higher temperatures (56°, 77°, and 95° F.). The maximum rate of loss occurred during the first 24 hours. At a temperature of 33° F., however, there was a very slight gain in the amount of these substances during the first 24 hours, after which there was a decrease; and at 41° and 56° F., after an initial loss there was apparently a very slight gain in these substances during the second day, after which there was further decrease. It should be stated that sugars constitute but one group of substances which determine flavor ; among others may be mentioned esters, gluco- sides, ammo-acids, and proteins. The loss of sugar during storage is probably due to its transformation to cell wall material, chiefly lignin, and other substances. 7. Both microchemical and macrochemical studies showed a gen- eral increase in the amount of fiber of the spears at all storage tem- peratures. This was shown in the number of lignified elements both in the pericycle and in the vascular bundles, as well as in the per- centage of crude fiber as ascertained by chemical analysis. The greatest increase (with one exception) in fiber at all temperatures came during the first 24 hours after the asparagus was cut, but was least at the lowest temperature, and greatest at the highest tem- perature. In storage, lignification took place the full length of the spear. 8. It appears from the results above, that green asparagus should be bunched, packed, and placed under refrigeration as soon after harvest as is compatible with efficient handling. There is progressive deterioration, as shown in the reduction in sugar, and increase in fiber, even at a temperature slightly above the freezing point ; it is desirable, therefore, that the product reach the consumer in the shortest possible time. The results obtained show that green asparagus should be maintained at temperatures slightly above the freezing point. It is desirable that the crate and the parchment wrappers surrounding the individual bunches be clearly marked so as to indicate to retailers and consumers that fresh asparagus should be kept at a low temperature in order that its edible quality may be maintained. 28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION ACKNOWLEDGMENTS The writers desire to express their appreciation to Mr. J. Gordon Sewell of the Division of Chemistry, who helped in preparing the samples, tabulating data, and calculating the results from the chemical analyses ; to Mr. H. A. Borthwick of the Division of Botany, who assisted in the microchemical studies; and to Mr. H. W. Allinger of the Division of Chemistry and Mr. Oscar H. Pearson of the Division of Truck Crops for their careful work in making the analyses. LITERATURE CITED i Bitting, K. G. 1917. Deterioration in asparagus. Nat. Canners' Assoc. Bull. 11: 1-18. 2 Morse, F. W. 1917. Experiments in keeping asparagus after cutting. Massachusetts Agr. Exp. Sta. Bull. 172: 297-307. s Munson and Walker 1925. Methods of analysis A. O. A. C, p. 191. lOm-10,'26