The effect of sucrose on the oxygen uptake kinetics of ascorbic acid (A) in a closed aqueous system was studied at different temperatures (26.5,30, and 33 "C) and pH levels (3.0-5.0). The reactions generally followed a pseudo-first-order reaction with respect to dissolved oxygen. The activation energy of A oxidation in sucrose solutions was greater than that in solutions containing no sucrose at all pH levels. Approximately 1 mol of oxygen was used per mole of A at the early stage of the noncatalyzed oxidation of A in various solutions. Two effects of sucrose on the A oxidation in the closed homogeneous system were suggested. First, a pH-independent physical hindrance effect retarded A oxidation and, second, a pH-dependent catalytic effect accelerated oxidation due to metal impurities found even in analytical grade sucrose.Sucrose is commonly present as a sweetening ingredient in fruit juices and drinks containing ascorbic acid. The effect of sugar on the stability of ascorbic acid in liquid media has been studied. Sucrose has long been reported to inhibit ascorbic acid oxidation in Cu-catalyzed or noncatalyzed reactions, and the mechanism of this protective effect was attributed to either the viscosity or the Cu-binding power of the sugar (Birch and Pepper, 1983;Lin and Agalloco, 1979;Kyzlink and Curda, 1970; Miller and Joslyn, 1949a,b;Chamrai, 1941). Recently, Hsiehand Harris (1987a) found that in an open-air system a t pH 3.2 sucrose accelerated the degradation of ascorbic acid when ita viscosity effect was diminished by vigorous shaking. This destructive effect of sucrose was attributed to the trace amounts of metal impurities found in sucrose because metal ions, e.g., cupric ion, have been shown to have great catalytic effect on the oxidation of ascorbic acid even a t trace levels (Silverblatt et al., 1943) and it is very difficult to completely eliminate the metal impurities and their catalytic effect from water and food ingredients in liquid systems. Furthermore, the study (Hsieh and Harris, 1987a) shows that the destructive effect of sucrose on ascorbic acid was much more pronounced in coppercatalyzed solutions containing 1-5 ppm of added copper. Sucrose (10%) did not show any Cu-binding ability, as was postulated in early literature, but enhanced the catalytic effect on ascorbic acid oxidation by its physical bulking effect and decreased water activity in solutions which increased cupric ion activity (Hsieh and Harris, 1987b). These results shed new light on former studies that illustrated the effect of sucrose on ascorbic acid oxidation in a heterogeneous oxygen-diffusion mediated system. To clearly define the reaction mechanism of the effect of sucrose on ascorbic acid oxidation, it is also important to investigate the effect of sucrose in a closed homogeneous nondiffusion mediated aqueous system. Therefore, the present research was designed to study oxygen uptake in the early stages of ascorbic acid oxidation in a closed homogeneous aqueous system which simulated the practical quiescent condition o...

No abstract

No abstract

No abstract

Regulations aimed to control the epidemic of bovine spongiform encephalopathy have banned the use of certain animal products, i.e., ruminant meat and bone meals, in ruminant animal feeds. A sensitive enzyme-linked immunosorbent assay has been developed to detect prohibited bovine and ovine muscles in feedstuffs. The assay utilizes a pair of monoclonal antibodies (MAbs) against skeletal troponin I (TnI). MAb 5G9, specific to bovine and ovine TnI, was used as the capture antibody and the biotin-conjugated MAb 2G3, reacting to all heterologous TnI, was used as the detection antibody. Quantitative procedures were applied to samples containing 5, 0.5, and 0.05% (wt/wt) of heat-treated (132 degrees C/2 bar, 2 h) bovine and ovine meat meals in three different feeds, coexisting with porcine, chicken, or turkey meat meal. The presence of these nonprohibited species did not affect the detection of bovine and ovine meat meals in the feed samples (P > 0.05). Quantitative determinations of extractable bovine and ovine TnI, with a detection limit of 5.0 and 4.0 ng/ml, respectively, were achieved when the matching feed matrixes were used in the calibration curves. This new assay provides a rapid and reliable way to detect animal protein products containing a trace amount of bovine or ovine muscle tissue in feedstuffs.