SOURCES and DETECTION OF VOGES‐PROSKAUER REACTANTS IN CALIFORNIA VALENCIA ORANGE JUICE^a

Abstract

The utility of the Voges-Proskauer (17) reaction in detecting bacterial metabolites responsible for specific off-flavors in frozen concentrated Florida orange juice has been denionstrated by Hill, Wenzel, and Barreto ( 7 ) and Byer ( 3 ) . This report is concernecl with the application of their niethod to California Valencia orange juice, particularly as compositional differences may affect evaluation of data from different citrus prodnciiig areas.The Voges-Proskauer reaction was selected by the original citrus workers because of its sensitivity for the oxidation-reduction compounds diacetyl and acetoin (acetyliiiethylcarbinol) . Several methods are known for the detection of diacetyl. One of these, employing hydroxylamine, yields dimethylglyoxime, which subsequently condenses with urea to give a yellow coinpound (19). The method does not appear to be sensitive below 15 p.p.m.Other workers (12, 18,11, 13) have reacted the dimethylglyoxime with a nickel salt to produce soluble tetravalent nickel dimethylglyoxime having a red color. The method, used on beer, appears to be sensitive at 0.2 p.p.m.The hydroxylamiiie reaction, although highly specific for diacetyl, is time-consuming and requires meticulous technique. Other methods based on reaction with chromotropic acid or analine extraction (15) are either not specific or sufficiently sensitive.The Voges-Proskauer reaction as modified by Barritt (1) results froin the reaction of diacetyl and peptone with u napthol to produce a red color. The test also determines 2,3 butanediol (2,3 butylene glycol). The detectable limits appear to be 0.05 p.p.m. diacetyl, 0.5 p.p.m. acetylmethylcarbinol, and 40,000 p.p.ni. 2,3 butylene glycol.The Voges-Proskauer reaction, hereinafter referred to as the V-P reaction, although highly specific for the above three named substances, can be affected by other compounds, some of which are naturally occurring or degradation products in orange juice. The Byer modificatioii ( 3 ) for citrus juices affords concentration of the significant materials to an easily detectable level and removal of same from a substrate containing a heterogeneity of interfering compounds.

Orange juice quality with an emphasis on flavor components

“…3 Unfortunately, diacetyl exhibits a low flavor threshold in orange juice, and even a small amount formed during storage can easily be detected by the consumer. 94 The enzyme peroxidase is present in orange juice and can catalyze the oxidations of several juice constituents, ascorbic acid, pyridoxal-phosphate, and phenolic acids, to name a few." Citrus peroxidase is not detrimental to juice flavor if the orange juice is pasteurized within 4 hr after extraction."…”

Enzyme-mediated aldehyde change in orange juice

“…Kirchner and Miller (1957) reported that during storage of canned orange juice at room temperature (80-90°), acetaldehyde declined and diacetyl increased. Because diacetyl has a low flavor threshold in orange juice (0.25 ppm) (Beisel et al, 1954), even a small conversion from acetaldehyde during storage may be detected.…”

Enzymatic Removal of Diacetyl from Beer

“…Diacetyl in beer causes an off-flavor which has been described as "lactic-diacetyl, buttery, or sarcina-like" (28). In addition, diacetyl is considered to be an off-flavor in wines (10, 20) and in citrus juices (2,16). Different causes for this flavor defect have been suggested.…”