Instrument for Measuring Changes in Texture of
Fish
Dehydrated
CHARLES F. SHOCKEY, LYNNE G. McKEE, AND WILLIAM S. HAMM Fishery Technological Laboratory,
U. S. Fish and Wildlife Service, Seattle, Wash.
A
NUMBER of mechanical devices for the measurement of tenderness of various kinds of food products such &s peas and beefsteak have been described but none seems exactly suitable for dehydrated fish. The undeairahle feature, inherent in an organoleptic method, is that the tester cannot accurately carry over from one testing period to another the standards far the degrres of texture evaluation. Thus any observations regarding the course of change occurring during an extended period of storage might he subject to considerable emor. I n order to eliminate the irregularities to which organoleptic tests are so susceptible and to he more directly applicable to the need, an instrument has been devised t o record numerical values proportional to the changes in texture occurring in dehydrated fish during storage. The new instrument consists essentially of a set of shearing plates or jaws, a s u p p o r t i n g stand, a spring scale of 54.5-kg. (120- pounds) capacity, and a gearedFigure 1. General View of Indown winch (Figure 1). The shearing jaws canstrument sist of 5 unner and fi lower too1 'steel plates with sau®round edges, 0.47 cm. ( a h . inch) think bv 3.75 em.
matelv 0.026-mm. (0.001-inch) clearanoe. so that B positive' ;hear-
plates df the lower jiw and provibing a s h l d dn e&h side. The cut-away portion of the top jaw exactly coincides with that of the lower 'aw when they are closed. Thus the sample compartment can b e easiky cleaned by raising the shields a t the sides and brushing out the sample residue. The sample to he tested is placed loosely and evenly in the Compartment with the jaws open and the shields lowered into position. The upper jaw is then lowered until it rests on the sample, the sprin so& is hooked to it, and a pulling force is applied to the scaqe hy means of a oahle fastened to the winch beluw. The forre nnPswry to hhwr rhr mmplP is read direrrly irr pounds from the dial. A s the sxmplr is slienred the nupper j 3 w drui.9 suddpnlv. thus rrleasin~the nrrscurc on rhe s~aie.mid rlip maiimum readihg is registera hy Iheans of a friction haid. The scale is then unhooked, the shields are raised, and the sample residue is brushed out of the compartment into the waste can
located directly helow the jaws. The upper jaw is again rsi~wd, the shields are lowered into position, and the instrument is ready for another sample. Preliminary tests indicated that to get uniform data the sample must he of uniform size and a uniform rehydration procedure must he followed in its preparation.
Ten grams of the dehydrated fish are allowed to rehydrate in
60 ml. of water at room temperature for 30 minutes.
Temperature of rehydration &s shown hy Hamm, Butler, aud Heerdt (1) is not critical, so that exact control of temperature during rehydration is not necessary. The reoonstituted sample is then drained free of water on an inclined screen for 2 minutes and 10gram samples of the reconstituted material are used for the measurement&
I.
Change in Texture of Dehydrated Fish upon Storage as Indicated by Instrument Readings Original After 14 Days After 30 Dai-s
Table
Av.
14.0 14.5 16.0 16.0 13.5 17.5
23.6 24.6 28.0 24.0 22.8 25.8
32.8 38.8 36.2 35.4 38.2 35.4
15.2
24.8
'36.1
Extensive tests with samples of various lots of dehydrated fish gave standard deviations of 1 pound for samples of the order of 10 pounds' toughness and 4 pounds for samples measuring 50 pounds. From these data. i t may he inferred that the average toughness value of 4 to 6 samples will he measured with B precisionof less than * 5 % . Tahle I is an example of the' data obtsined under actual operation. Organoleptic tests for texture changes made parallel with tests on the instrument, have shown that the samples are placed in the same order in relation one to another hut that small differences shown bv Figure 2. Shearing Jaws the instrument are not always detected organoleptically. This instrument is not designed to evaluate the quality of an unknown sample of dehydrated fish, but is of value in following the change in texture that occurs on storage. While no tests have been made on products other than dehydrated fish, it might he adapted for use with other such dehydrated products where alteration in texture during &orage is a problem. LRERATURE CITED (1)
Hamrn, W. S.. Butler, C.. and Heerdt, M., Food hfwtn'es, 16. 4R9 (1944).
638
