Determining the Maturity of Frozen Vegetables A Rapid Objective Method for Whole-Kernel Corn F. A. LEE, DOMENIC DEFELICE, AND R. R. JENKINS' New York State Agricultural Experiment Station, Geneva, N. Y.
A rapid objective method for determining maturity of whole-kernel corn, involving the determination of specific gravity by difference in weight in air and in a weak salt solution of specific gravity 1.000, was found successful. Coefficients of correlation of these results with corresponding organoleptic tests and tentative standards are listed.
I11 shows the several coefficients of correlation. I n calculating these coefficients of correlation for the 1939 series, the immature samples were not included in the calculation, in order t o get a straight-line relationship. I n making the calculations for the 1940 series, the overmature were omitted for the same reason. TABLE I. DATAFOR 1939 SEASON Specific Gravity of Thawed Corn in Xylene-CClr 1.0590 1.0660 1.0680 1.083 1.088 1.088
T
HE three essential factors in the quality grading of frozen
vegetables are maturity, absence of defects, and color. Maturity is very important. An objective test tends to obviate the personal element always present in organoleptic tests, and, therefore, a rapid objective test for maturity is desirable. I n a recent paper ($), one of the authors showed that specific gravity is a reliable index of the maturity of frozen
1.088
1,090 1.091 1.092 1.093 1.093 1.094 1.095 1.095 1.095 1.095 1.096 1.096 1.096 1.096 1 097 1.097 1.097 1.097 1,098 1.100 1.101 1.101 1.101 1.101 1.102 1 * 102
peas.
At the present time there are no recognized methods for frozen whole-kernel corn, such as exist for frozen peas (4). The work reported in this paper is the result of a n effort to promulgate a standard method for the measurement of maturity of frozen whole-kernel corn. The determinations were made on whole-kernel Golden Cross frozen corn packed under commercial conditions during the 1939 and 1940 seasons. The corn was blanched on the cob for 7.5 minutes at 210" to 212" F., the standard commercial practice. Duplicate lots of the same samples were saved for organoleptic testing by qualified disinterested groups. The maturity was determined by means of specific gravity, which was determined by the difference in weight in air and in a mixture of xylene and carbon tetrachloride adjusted to a specific gravity of 1,000, an adaptation of a method described before ( 3 ) . During the season of 1940, the same liquid was used for this purpose, and, in addition, another set of determinations was run making use of a weak salt brine of specific gravity 1.000. This brine was made to have a constant specific gravity, regardless of the temperature at which the determination was being run, and, therefore, the amount of salt in the brine varied with the temperature of the liquid used. Water has been used ( 1 ) in the determination of the specific gravity of potatoes as an index of the starch and solids content. weight in air X specific gravity of liquid Specific gravity difference of weights in liquid and in air The following equipment is used: A suitable balance weighing to 0.1 gram can be supported on a stand or shelf and the basket can be attached to the hook under the pan. The sample basket is made of 16-mesh brass screen 8.125 cm. (3.25 inches) high and 5.625 cm. (2.25 inches) in diameter, and conveniently holds a 100gram sample. The samples of corn are thawed and then drained for 2 minutes on an 8-mesh sieve before starting the work. The specific gravity can be found as follows. The corn is weighed in air. The weight in the liquid mixture is determined by subtracting the weight of the basket in the liquid used from that of the corn and basket in this same liquid. The weight in air minus the weight in the liquid mixture gives the difference of weight in this liqud.
a
Specific Gravity of Thawed Corn in Xylene-CCh 1.102 1.102 1.102 1.102 1.103 1.103 1.104 1,105 1.105 1.105 1.106 1.107 1 109 1.109 1.110 1,111 1.111 1.112 1.115 1.116 1.1?0b 1.121b 1.128b 1.128b 1.137b 1,1376 1.138b l.lR9b 1.1416 1.142b 1.143, 1.149b 1.149b 1.150b
Organoleptio, Based on 50 47 47 47 43 49 47 49 49 49 43 49 43 49 47 47 49 49 49 49 49 39 39 41 35 33 33 33 33 33 33 33 33 33 33
Immature.
b Overmsture.
Discussion The organoleptic ratings for maturity after cooking, together with the values assigned to them for use in the calculation of coefficients of correlation for the 1939 series are: A, satisfactory; B, satisfactory but not first grade; C, low quality; A = 49; A- = 47; A-B+ = 45; B+ = 43; B = 41; B- = 39; B-C+ = 37; C+ = 35; C = 33. Samples were added to one-half cup of boiling water and removed 2 minutes after the second boil. The organoleptic ratings after cooking (2) for the 1940 series are based upon a numerical basis of 100 points. Scores of 0 t o 40 are designated as C grade or unfit for food, 40 to 70 as B grade or good food but not the highest quality, and 70 to 100 as A grade or high quality.. This difference in scoring is accounted for by the fact t h a t two different, disinterested groups judged the samples. The point will always arise in the determination of maturity of whether the seasonal variation affects the quality of the product. This work on corn was done in two successive seasons of opposite climatic conditions. I n 1939 the season was hot and dry, while in 1940 it was cool and wet. Little variation, if any, was found in the indexes of quality for the two seasons. Although the length of ripening periods may vary from season t o season, the specific gravity determinations
si
Table I gives the data accumulated on this test during the 1939 semon. Table I1 gives the same for t,lie year 1940, and in addition, the specific gravity data in which brine was used in place of the xylene-carbon tetrachloride mixture. Table 1
Organoleptic Based on 50' 33 33 33 49 49 49 49 49 45 49 49 49 49 49 49 49 43 49 47 47 47 47 47 45 43 49 47 49 49 49 47 49 49
Died October 9, 1940.
240
ANALYTICAL EDITION
March 15, 1942
show no variation for the corn harvested in prime condition. It is evident, therefore, that restandardization is not necessary from year to year. Check tests indicate that the figures given here are applicable to all similar sweet corn varieties. Table I1 indicates that the specific gravities as determined by means of the xylene-carbon tetrachloride mixture are somewhat higher than those determined by means of the water containing enough sodium chloride to give a specific gravity of 1.000. This is possibly caused by the fact that water adhering to the vegetable is weighed when it is immersed in the xylene-carbon tetrachloride mixture because of its failure to dissolve in this mixture. When the vegetable is weighed in the aqueous mixture, only the vegetable itself is weighed. The final result would be a slight error in both methods, and a different set of standards would have to be prepared for each method. The brine method is somewhat the better of the two because of its low cost, because it is easier to prepare, and because it is less likely to change in use, although it should be tested with the hydrometer from time to time to be sure the specific gravity is 1.000.
TABLE11. 1940 SERIES Specifio Gravity of Thawed Corn In xylene-CClr In brine 1.042a 1.063 1.053 1.048" 1.051 1.050~ 1.062 1.053" 1.058" 1.065 1,0590 1.065 1.062" 1.059 1,066' 1.074 1.066' 1.081 1,070" 1.076 1.071* 1.078 1.073" 1.05s 1.074' 1.084 1.076a 1,052 1 os9 1.080 1.098 1,084 1.085 1.096 1.103 1.086 1.087 1,087 1.094 1.088 1.093 1.089 1.081 1.098 1,101 1.092 1.101 1.096 1.096 1.102 1.097 1.101 1.097 1.102 1.111 1.097 1,101 1,098 1.101 1.09s 1.106 1.098 1.09s 1.106 1.098 1.109 1.098 1.111 1.099 1.103 1,099 1.105 1,009 1.106 1.100 1.097 1.100 1.102 1,101 1.105 1.101 1 110 1.102 1.100 1.102 1.10.5 1.110 1.102 1,102 1.111 1.104 1.103 1.106 1.112 1.106 1.114 1.107 1.110 1.107 1.114 1,110 1.108 1.116 1.10s 1.109 1.111 1,109 1.112 1.116 1.109 1.110 1.120 1.112 1.116 1.113 1.110 1.113 1.115 1.113 1.117 1.118 1.117 1.121b 1.128 1.122b 1.122 1,130b 1.134 1.147 1 149b 1.154 1,150b 1,151b 1.155 a Immature. b Overmature.
Organoleptic, Based on 100 58 45 46
55 57 48 53 56 57 66
55 69 59 60 73 69 62
so
74 77 85 77 71 70 75 77 77 77 77 68 80 80 74 91 70 68 82 79 75 76 86 89 72 71 74 70 87 82 78 71 88 79 82 92 84 89 89 SO
80
SO
77 64 64 63 34 39 35
TABLE111.
241
COEFFICIENTS O F CORREL.4TION
FOR
SPECIFIC
GRAVITY OF THAWED COR?; Correlation between: Xylene-carbon tetrachloride method a n d organoleptic tests (1939) Brine method and organoleptic testa (1940) Xylene-carbon tetrachloride method a n d organoleptic tests (1940)
Coe5cient
t0.8456
* 0.0221 * 0.0246
4-0.8408
0.0253
-0.8592
The following tentative standards are suggested, based upon the results using the brine solution for the determination of the specific gravity: Fancy Reject, immature Reject, overmature
1.080 to 1.118 1.079and lower 1,119and higher
These standards can be revised if and when other grades are generally packed.
Acknowledgment The authors wish to thank the Frosted Foods Sales Corporation, New York, N. y., for financial assistance, and the Snider Packing Corporation, Rochester, N. Y., for making available facilit'es a t one of its plants for this work. They also wish to thank the group of tasters connected with this corporation for running the organoleptic tests for the 1939 set of samples, and to thank L. S. Fenn of the Agricultural Marketing Service, United States Department of Agriculture, and his associates for running the organoleptic tests for the 1940 set of samples.
Literature Cited (1) Behrend, P., Maeroker, M., and Morgen, A., Landw. Vets.-Stat., 25, 107 (1880). (2) Boggs, Mildred, Western Canner and Packer, 32, No.2, 47 (1940). (3) Lee, F. A , , IND.ENG.CHEM.,ANAL.ED., 13, 38 (1941). (4) U.S. Dept. of Agr., Bur. Agr. Econoniics, Proposed Tentative U. S. Grades of Frozen Peas (February 25, 1939). APPROVED b y the director of the New York S t a t e Agricultural Experiment Station for publication a8 Journal Paper No. 472.
Determination of the Maturity of Frozen Peas New
F. A. LEE York State Agricultural Experiment Station, Geneva, N. Y.
A
REVISION of the method for determining the maturity of frozen peas (1) has been worked out, in which the mixture of xylene and carbon tetrachloride is replaced by water containing enough sodium chloride to give a liquid of specific gravity 1.000. This liquid is considerably less expensive than the former, is easier to prepare, and has the added advantage of undergoing less change in specific gravity in use. The following set of standards is suggested to replace those published before: Fancy Standard Substandard
1.072 and lower 1.073 t o 1.084 1.085 and higher
These standards can be revised if and when an extra standard grade is generally packed.
Literature Cited (1) Lee, F.A., IND.ENG.CHEM.,ANAL.ED., 13, 38-9 (1941). APPUOVBDb y t h e director of t h e New York S t a t e Agricultural Experiment Station for publication as Journal Paper No. 480.
