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J. Creighton Miller Jr.

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J. Creighton Miller Jr. and Douglas C. Scheuring

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Lavanya Reddivari and J. Creighton Miller Jr.

Antioxidants have been widely reported to play an important role in disease prevention. In addition to preventing cancer, stroke, heart diseases, and inflammation, they are also involved in immune surveillance. Since the per capita consumption of potatoes in the U.S. is about 137 lb, even moderate levels of antioxidants in this most important vegetable crop probably have an important human health benefit. About 75% to 80% of antioxidant activity in specialty potatoes is due to phenolics and carotenoids. The objectives of this investigation were to evaluate antioxidant activity and total phenolic and carotenoid content of specialty potato selections from the Texas Potato Variety Development Program, and to identify candidate compounds for cancer cell culture investigations. Potato tubers were also used to identify and quantify individual phenolics and carotenoids. Some 320 specialty selections were screened for antioxidant activity (AA), total phenolic content (TP) and carotenoid content (CC) using DPPH (2,2-Diphenyl-1-picrylhydrazyl), FCR (Folin-Ciocalteu Reagent) and colorimetric assays, respectively. After the initial screening, the top 10% were used for analysis of individual phenolics and carotenoids using HPLC. Wide variability for antioxidant activity, phenolic content, and carotenoid content was found among specialty potato selections, providing evidence for genetic control of theses traits. The specialty selection CO112F2-2P/P (purple flesh, purple skin) had the highest AA (832 μg trolox equivalents/g fw), TP (1553 μg chlorogenic acid equivalents/g fw) and CC (590 μg lutein equivalents/100 g fw). Chlorogenic acid (55% to 60%), caffeic acid (≈5%), gallic acid (18% to 20%), and catechin (18% to 20%) were found to be the most prevalent phenolic acids, and lutein and zeaxanthin were the most prominent carotenoids contributing to antioxidant activity. Gallic acid was identified as the candidate compound for use in cancer cell culture investigations.

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Peng Hwang, J. Creighton Miller Jr., and B. Greg Cobb

Field studies were conducted at two Texas locations: Lubbock, near the major production area for Texas potatoes, and College Station which is hotter and more humid. Early and late plantings were established at each location to compare cool and hot growing conditions. Nine genetically diverse cultivars, including those previously reported to be heat resistant or susceptible, were used in this study. Results indicated that the distribution of soluble carbohydrate and starch differed significantly among plant parts. In leaves and stems, glucose and fructose were the major soluble carbohydrates, while sucrose was the major soluble carbohydrate in tubers. Total soluble carbohydrate and starch content in leaves, stems and roots from the early plantings were significantly higher than those from the late plantings. Inositol increased significantly in the College Station late stress environment.

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Douglas C. Scheuring, J. Creighton Miller Jr., and David W. Walker

Two cowpea cultivars, Pinkeye Purple Hull and Royal Blackeye, were evaluated for their ability to produce a ratoon crop. Dry weight and pod yield were measured following harvest from two different cutting heights (second and fourth node), and stages of pod maturity (green and dry). The cultivar Royal Blackeye produced more green manure or returned biomass following ratooning than did Pinkeye Purple Hull. Cutting height and sampling at different pod maturities influenced ratooning potential. These results suggest that cowpea ratooning appears to be economically feasible and that further screening of cowpea cultivars for ratooning ability is warranted.

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Armando Campos Cruz, Douglas C. Scheuring, and J. Creighton Miller Jr.

The effect of Biozyme™, a commercial germination stimulant, on emergence of bean and sweet corn seeds, treated with four levels of Carbofuran and Chlorothalonil, and grown under suboptimal field temperatures, was evaluated. Half the seeds from each treatment were treated with Biozyme™ Two planting dates were selected to provide suboptimal temperatures during emergence. Pesticide overdoses caused significant detrimental effects to all emerging seedlings. These effects were magnified under the low temperatures of the first planting. Biozyme™ treatment significantly improved emergence rate, percent emergence, final stand and number of ears of sweet corn in the first planting, and the percent emergence final stand, plant dry weight, and number of ears in the second planting. In beans, however, Biozyme™ treatment significantly reduced emergence rate, percent emergence. and final stand in the first planting, while significantly increasing percent emergence, plant dry weight, and seed dry weight in the second planting. The beneficial effects of Biozyme™ appeared to be independent of the negative effects of pesticide overdoses.

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Tyann Blessington, Douglas C. Scheuring, and J. Creighton Miller Jr.

Potatoes are stored to ensure a continuous supply; however, losses due to shrinkage and sprouting can be large. It is believed that ionizing irradiation will become more prominent for sprout inhibition due to the increasingly higher operating costs of low-temperature storage and possible phase-out of chemical sprout inhibitors. The effects of storage and ionizing irradiation (gamma and electron beam) on antioxidant activity (AOA), phenolic content, and carotenoid content were analyzed using the potato cultivar Atlantic. Tubers were subjected to 0, 75, and 200 Gy γ-irradiation doses, stored at 20 °C, and analyzed after 0, 10, 20, 75, and 110 days. Tubers from another harvest were subjected to a surface dose of 0 or 200 Gy e-beam irradiation, stored at 20 °C, and analyzed after 0, 10, 20, 75, and 110 days. AOA was measured via the DPPH method; phenolic content via the Folin-Ciocalteau method and individual phenolics via HPLC; and carotenoid content via absorbance at 445 nm and individual carotenoids via HPLC. During early storage, higher doses resulted in higher AOA, while, during longer storage, lower doses produced greater AOA. Phenolic content increased in storage during the γ-irradiation study, but decreased in the e-beam study, partly due to increases in chlorogenic acid in the former and decreases in caffeic acid in the latter. The e-beam dose of 200 Gy resulted in significantly greater total phenolics than 0 Gy. Total carotenoids and lutein decreased with storage, but were not affected by irradiation. Storage exerted a much greater influence on AOA, phenolic content, and carotenoid content than either irradiation treatment.

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M.N. Nzaramba, Douglas C. Scheuring, and J. Creighton Miller Jr.

Antioxidants are important to human health, as they are responsible for reduced risk of diseases such as cancer, hence motivating researchers to examine crop plants for available antioxidant compounds. There is also increasing interest in the use of antioxidants from plants instead of synthetic products. In order to evaluate variability of antioxidant activity (AOA) in cowpea, 697 cowpea accessions from the U.S. Cowpea Core Collection obtained from the Regional Plant Introduction Station, Griffin, Ga., were analyzed for AOA expressed as μg trolox equivalents/gdw. Two grams of dry seed from each accession were ground, extracted in methanol and analyzed for AOA using the free radical, 2,2-Diphenyl-1-picrylhydrazyl (DPPH), method. A large variation in AOA within the core collection, ranging from 1859 μg·g–1 dw (PI 180355, pigmented seed coat) to 42.6 μg·g–1 dw (PI 583100, cream seed coat), was observed. A least significant difference of 131.5 (p =0.05) was obtained. Higher AOA was manifested by accessions with pigmented seed coats. Accessions that were speckled, striped or had a pigmented eye were moderate in AOA, while the cream types were generally low. Variability in AOA observed among cowpea accessions suggests that breeding for high AOA can be successfully conducted. Accessions with high AOA could also be used to extract antioxidants for industrial purposes. Some accessions were a mixture of various colors and patterns, making it difficult to classify them into a particular category. Therefore, there is need to ensure purity of these accessions by ascertaining whether the mixtures are physical, i.e., combination of different varieties, or are composed of segregating material.

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Peter J. Mes, B. Gregory Cobb, Douglas C. Scheuring, and J. Creighton Miller Jr.

The major markets for cowpea are seed sales and processing. During the storage period prior to sales, some seedcoats of `Mississippi Silver' darken from tan to varying shades of brown. This darkening is undesirable for the processing market, since it results in an unattractive product lacking uniformity. A series of studies was undertaken to investigate this problem. It was noted that darkening proceeded at a rapid rate when seed were left in the field after drying. Selection against darkening was unsuccessful, and attempts at extracting the colored compound with polar and nonpolar solvents were inconclusive. A method of screening for the darkening trait was devised. It was found that darkening could be induced by exposing seed to a high-oxygen environment, suggesting that oxidation is involved in the darkening process. In support of this, it was found that the lowest rate of darkening occurred when the seed were placed in an enriched nitrogen chamber after harvest.