Oxidative damage to turkey white muscle myofibrillar proteins (MP) was investigated by measuring changes in chemical, physical, and functional properties after exposure to iron or copper (25 mM) and ascorbate. Both ironand copper-oxidized MP exhibited increased absorbance at 265 nm and carbonyl content compared to controls. Increasing the ascorbate concentration from 0 to 25 mM increased the absorbance 6.8-and 4.0-fold and the carbonyl content 2.6-and 1.9-fold for MP in the presence of iron and copper, respectively. The ironand copper-oxidized MP showed lower solubility, gel strength, and gel water-holding capacity than controls. SDS-polyacrylamide gel electrophoresis demonstrated that both ironand copper-catalyzed oxidation resulted in a major loss of myosin and actin with concomitant formation of protein polymers. These data suggest that the decreased functionality of proteins in muscle foods exposed to oxidative environments could be due to chemical and physical changes resulting from oxidative reactions.
Abstract. The change in polyphenol content in the primed leaves of burley, flue-cured, and Turkish tobaccos during air-curing was related to the activities and isozymes of polyphenol oxidase and peroxidase. The quantity of chlorogenic acid was rapidly reduced during the first week of curing. The decrease in rutin content during curing was less significant, especially when the concentration of chlorogenic acid was high in leaf tissues. This result was further confirmed by in vitro assays with partially purified tobacco polyphenol oxidase.The polyphenol oxidase activity did not differ at any stage of curing in the 3 tobaccos. When the activity was measured by the oxidation of 3,4-dihydroxyphenylalanine it rose rapidly during the first day of curing and then decreased sharply so that in the fully cured leaf only 15 %/c activity remained. The increase in activity was not observed when chlorogenic acid was used as the substrate. A similar level of peroxidase activity was found in the 3 tobaccos before curing. Peroxidase activities increased rapidly during the first 24 hr of curing. declined thereafter, and remained highest in the flue-cured tobacco, less in the Turkish line, and least in the burley at the end of curing process.By polyacrylamide gel block electrophoresis, 10 peroxidase isozyme bands, 2 cationic and 8 anionic, appeared identical in all 3 tobaccos. When catechol replaced benzidine-2 HCI as the electron donor, 1 cationic and 2 anionic peroxidase isozvmes did not form. Of interest is that the same 10 peroxidase isozyme bands also exhibited polyphenol oxidese activities when treated with 3,4-dihydroxyphenylalanine or chlorogenic acid.
The effects of three levels of N fertilization on polyphenol content and polyphenoloxidase and peroxidase activities in the juvenile plants of hurley and dark tobaccos, Nicotiana tabacum L. were studied in solution culture. Large amounts of polyphenols were accumulated in the leaf; smaller amounts accumulated in the root. Chlorogenic acid and two isomers were the predominant fractions of polyphenols in the leaf, but the isomer neochlorogenic acid was absent in the root. Roots contained high concentrations of scopolin and scopoletin. The latter was not detected in seedling leaves. The amount and kind of N fertilizer greatly influenced the accumulation of polyphenols. Polyphenols were lowest on medium N, whereas they accumulated in large concentrations on both high and low N solutions. As a result, quantitative difference between the high and low polyphenol strains became less significant. Plants grown in high nitrate N solution contained more polyphenols than those fed with high ammonium nutrition. Polyphenoloxidase and peroxidase activities were higher in root than in leaf extracts and in plants cultured under medium N rate than in either extreme N environment. However, in high ammonium N fertilization the activity of both oxidases increased in the leaf but polyphenoloxidase decreased in the root. The results suggest that a medium rate of N fertilization increases oxidase in roots, polyphenoloxidase in particular, accompanied by a decrease of soluble polyphenol content in leaves, and produces a maximal phenotypic contrast for leaf polyphenol concentration among tobacco strains.
7he antioxidant activity of 0.5% camosine alone and in combination with selected antioxidants was investigated in uncooked ground turkey stored at 4C. A combination of tocopherol (0.05 %) and camosine exhibited additive antioxidant activity in salted and unsalted ground turkey. An ascorbyl palmitate (0.05%)/camosine combination decreased TBARS 1 .5 fold in salted ground turkey but was less effective in unsalted muscle (0.15 % ascorbyl palmitate). Combining carnosine with STP (0.5 %) or citrate (0.01 or 0.05 %) did not increase the antioxidant activity of camosine in ground turkey. n e s e data suggest that tocopherol and ascorbyl palmitate could enhance the antioxidant activity of carnosine.
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