Diacetyl Test as a Quality Control Tool in Processing Frozen Concentrated Orange Juice

One subjective and two objective methods were used to determine the color of reconsti tuted frozen concentrated orange juice. The USDA color scores for 21 samples ranged from 32 to 37 points when this subjective method was used. Two objective methods were used: (a) the Hunter Color and Color Difference Meter to ob tain tristimulus color values and (b) the Bausch and Lomb Spectronic 505 recording spectrophotometer to obtain spectral curves. Hunter Rd values ranged from 20.3 to 27.1; the a values values from —7.5 to —2.8; and the b values from 28.1 to 29.8. Dominant wavelengths computed from the spectral curves for the reconstituted juices, ranged from 576 to 581 m^; purity from 59 to 90%; and brightness from 20.3 to 33.8%. As the visual color score increased, the Hunter a value increased and the Rd value decreased; also, brightness decreased but no trend was evi dent between either the dominant wavelength or purity and the color score. Florida Agricultural Experiment Stations Journal Ser ies No. 2529. lCooperative research by the Florida Citrus Experiment Station and Florida Citrus Commission. 2Florida Citrus Experiment Station, Lake Alfred. 3Florida Citrus Commission, Lake Alfred. Introduction Color to different disciplines of science means various things. To the chemist it is dye and pigments. To the physicist color is a phenomena in the field of optics and electromagnetc radia tion. To the physiologist and psychologist color denotes a sensation to the human observer. There are many procedures in use today that compare the color of one object with that of another or give a value for the color difference between them. Such methods are either sub jective or objective, the former depending upon a visual evaluation while the latter uses differ ent instruments. Subjective methods.—The Maerz and Paul Dictionary of Color (5) contains examples of many colors. Plate 10 on page 43 of this book shows various colors that could apply to orange juice. The Macbeth-Munsell Disk Colorimeter (3, 4) can be used so that overlapping color wedges are spun and the resulting color compared to that in samples of orange juice. By varying the amount of white, gray, yellow, and orange, the color of orange juice may be matched. Another example of a subjective method is the use of USDA color comparator tubes to obtain a color score for orange juice. A trial set at such tubes consisted of colored viscous plastic in capped glass tubes. These were avail-