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D.H. Picha

Horseradish (Armoracia rusticana) has one of the highest rates of postharvest weight loss among all vegetable crops. Postharvest studies were conducted to identify improved methods of extending the market life of fresh horseradish roots. Postharvest treatments included submerging or coating thoroughly washed and dried roots in chlorine (150 ppm), hydrogen dioxide (Storox), 2,6-dichloro-4-nitroaniline (Botran), carnauba-based wax, shellac-based wax, paraffin wax, and polyolefin shrink film (75–100 micron thickness). Two treatments, shrink wrapping and paraffin waxing, were superior in reducing postharvest weight loss and extending horseradish root market life. Roots from the non-paraffin waxed and nonshrink-wrapped treatments lost an average of 20% weight after only 4 days of ambient temperature storage. This resulted in significant root shriveling and unacceptable market appearance. Roots from the shrink wrapped treatments lost an average of 1% weight after 4 days of ambient temperature storage, while paraffin waxed roots lost about 3% weight. It is important to thoroughly dry the roots before shrink wrapping, to avoid moisture condensation on the inner surface of the film and subsequent microbial growth. All of the shrink-wrapped roots and paraffin waxed roots were marketable after 14 days of ambient storage, and no surface mold was detected. Less than 3% weight loss occurred after 14 days of ambient storage in all shrink-wrapped roots, while paraffin-waxed roots lost about 9% weight. Weight loss in the unwrapped roots from the other postharvest treatments ranged from an unacceptably high 44% to 48% after 14 days.

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D.H. Picha

The use of heat shrinkable plastic film for wrapping individual sweetpotato roots was evaluated as a form of value-added packaging. Individual shrink wrapping of sweetpotatoes is a recently adopted but increasingly used retail marketing technique. The shrink wrapping process involves enclosing individual roots in shrink film which is cut and heat sealed followed by transfer through a heat tunnel to create a tightly sealed package. Film thickness ranges from 40 to 100 microns (gauge). Manual, semi-automatic, and automatic application methods are available. Fully automated commercial methods approach a speed of 1 wrapped root per second. Shrink wrapping adds value to fresh market sweetpotatoes by enhancing appearance, reducing weight loss, and allowing for individual root labeling. Various film types and thicknesses were tested under simulated retail conditions. Root weight loss from shrink wrapped roots was significantlyreduced during storage, ranging from a total of 0.5% in wrapped roots to 2.5% in unwrapped roots after 3 weeks of ambient storage. There was an inverse relationship between film thickness and root weight loss, with the thicker gauge films showing the least amount of weight loss. Film type and thickness did not influence overall root flavor and sweetness perception. In order to reduce the incidence of surface mold, the root must be completely dry before wrapping. This form of packaging offers significant potential for enhancing retail consumer demand.

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D.H. Picha

A course entitled “Plantation, Beverage, and Tropical Nut Crops” was developed in order to expand the content and diversity of the horticulture curriculum at Louisiana State University. The course was designed for both upper division undergraduates and graduate students in the plant sciences. The course was intended to broaden the exposure of both domestic and international students to the world's most important plantation, beverage, and tropical nut crops. These crops are generally not commercially grown in the United States, but include some of the world's most economically significant commodities. The selected crops are typically not covered in existing horticulture or agronomy classes. Details of the individual crop cultural practices, harvesting methods, postharvest care, agro-processing, and international marketing are provided. The instructional materials were formatted for delivery via compressed video and transmitted to off-campus sites to afford the opportunity of long-distance learning to nontraditional students. The course was successful in attracting nonhorticulture students and facilitated interdisciplinary interaction among students from diverse curricula.

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M.S. Padda and D.H. Picha

Antioxidant activity and phenolic content in sweetpotato root and leaf tissues were quantified at different developmental stages. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical method was used to measure antioxidant activity and total phenolic content was quantified by spectrophotometry using Folin-Denis reagent. Individual phenolic acids were quantified using reversed phase high performance liquid chromatography. Antioxidant activity and phenolic content decreased with root development and leaf maturity. Roots at the initial stages of development (about 4 g root weight) had a higher antioxidant activity and phenolic content compared to fully developed roots. Phenolic content in fully developed roots was significantly higher in the cortex tissue than internal pith tissue. The highest total phenolic content and antioxidant activity was found in cortex tissue at the initial stage of development (10.3 mg chlorogenic acid eq/g dry tissue weight and 9.7 mg Trolox eq/gdry tissue weight, respectively). Sweetpotato leaves had a significantly higher phenolic content and antioxidant activity than roots. Immature unfolded leaves had the highest total phenolic content (88.5 mg chlorogenic acid eq/g dry tissue weight) and antioxidant activity (99.6 mg Trolox eq/g dry tissue weight). Chlorogenic acid was the major phenolic acid in root and leaf tissues with the exception of young immature leaves in which the predominant phenolic acid was 3,5-dicaffeoylquinic acid.

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B.K. Chegeh and D.H. Picha

Cured and non-cured `Beauregard' and `Jewel' sweet potato roots were exposed to 0, 1, 10, 100, and 1000 ppm ethylene for 15 days at room temperature (21°C). Sucrose and total sugar content increased with increasing ethylene. Fructose, glucose, and maltose content had little or no change, while alcohol insoluble solids decreased with increasing ethylene concentration. Roots exposed to ethylene for 10 days and then chilled at 4.4°C for 15 days developed chilling injury symptoms sooner than those free of ethylene. Chilling injury increased with increasing ethylene concentration. Non-cured roots suffered more chilling injury than cured ones. `Jewel' was more susceptible to chilling injury than `Beauregard'. Sprout yield was higher in ethylene exposed roots and increased with increase in ethylene concentration. Cured `Beauregard' roots exposed to ethylene sprouted more than non-cured roots. `Beauregard' non-cured roots were not stimulated in sprouting by low ethylene concentrations while `Jewel' (cured and non-cured) roots were stimulated in sprouting by all ethylene concentrations.

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Malkeet S. Padda and D.H. Picha

Phenolic acids are considered important antioxidants that may help to prevent many human chronic diseases. The antioxidant activity and phenolic content of sweetpotato [Ipomoea batatas (L.) Lam.] roots and leaves of different sizes and ages, respectively, were quantified. Small roots (≈4 g root weight) had a higher antioxidant activity and phenolic content compared with full-sized marketable roots (≈300 g root weight). Phenolic content in marketable roots was significantly higher in the cortex tissue than in the internal pith tissue. The highest total phenolic content [chlorogenic acid equivalents (10.3 mg·g−1 dry weight)] and antioxidant activity [Trolox equivalents (9.7 mg·g−1 dry weight)] was found in cortex tissue of small-sized roots. Sweetpotato leaves had a significantly higher phenolic content and antioxidant activity than roots. Young, immature unfolded leaves had the highest total phenolic content (88.5 mg·g−1 dry weight) and antioxidant activity (99.6 mg·g−1 dry weight). Chlorogenic acid was the major phenolic acid in root and leaf tissues with the exception of young immature leaves in which the predominant phenolic acid was 3,5-dicaffeoylquinic acid. The results suggest that small-sized roots, which are typically discarded in the field, and young immature leaves may be concentrated sources of phenolic antioxidants.

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M.S. Padda and D. H. Picha

Phenolic acids are one of several classes of naturally occurring antioxidant compounds found in sweetpotato. Simplified but reliable methodologies were developed to quantitate total and individual phenolic acids in sweetpotato roots. Total phenolic acid content was measured using both Folin-Denis and Folin-Ciocalteu reagents. The Folin-Ciocalteu reagent gave an overestimation of total phenolic acids due to the absorbance of interfering compounds (i.e., reducing sugars and ascorbic acid). The average total phenolic acid content in `Beauregard' sweetpotatoes was 60.9 mg/100 g fresh weight. Individual phenolic acids were separated with two reversed-phase C18 columns of different dimensions and particle size. The columns tested were a 7 × 53 mm, 3 μm, Alltima Rocket (Alltech Assoc.) and a 3.9 × 150mm, 4 μm, Nova-Pak (Waters Corp.). Different mobile phases were also evaluated. The Alltima C18 column using a mobile phase of 1% (v/v) formic acid aqueous solution: acetonitrile: 2-propanol, pH 2.5 (70:22:8) provided the best separation of individual phenolic acids. Total analysis time was less than 5 minutes. Chlorogenic acid was the major phenolic acid found in sweetpotato root tissue (15.8 mg/100 g fresh weight). In a comparison of different tissue preparation states (fresh, frozen, freeze-dried), fresh tissue gave the highest concentration of total and individual phenolic acids. Among the 3 extraction solvents tested (80% methanol, 80% ethanol, and 80% acetone), 80% methanol and 80% ethanol gave higher, but similar, phenolic acid extraction efficiency.

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M.S. Padda and D.H. Picha

Sweetpotatoes may be potentially high in concentration of certain phytochemical compounds, including phenolics. Low temperature stress-induced phenolic compounds may enhance the nutraceutical value of sweetpotatoes. However, extended exposure to low temperature results in chilling injury. Cured and non-cured roots of `Beauregard' sweetpotatoes were exposed to low temperature storage (5 °C) for up to 4 weeks. The total phenolics and individual phenolic acid contents were determined at weekly intervals using Folin-Denis reagent and reversed-phase HPLC, respectively. Total phenolics and individual phenolic acids increased with length of low temperature exposure. Non-cured roots had a higher phenolic content than cured roots after 4 weeks. A 3-day exposure period to room temperature (22 °C) following removal from low temperature storage typically resulted in increased phenolics. In a comparison of different tissue locations, the highest phenolic content was found in peel tissue and the lowest in the pith tissue. The major individual phenolic acid in all root tissues was chlorogenic acid.

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M.S. Padda and D.H. Picha

Antioxidant activity and phenolic content of sweetpotato root and leaf tissues were quantified at different developmental stages. 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical method was used to measure antioxidant activity and total phenolic content was quantified by spectrophotometry using Folin-Denis reagent. Individual phenolic acids were quantified using reversed phase high performance liquid chromatography. Antioxidant activity and phenolic content decreased with root development and leaf maturity. Roots at the initial stages of development (about 4.0 g root weight) had a higher antioxidant activity and phenolic content compared to fully developed roots. Phenolic content in fully developed roots was significantly higher in the cortex tissue than internal pith tissue. The highest total phenolic content and antioxidant activity was found in cortex tissue at the initial stage of development (10.3 mg chlorogenic acid eq/g dry tissue weight and 9.7 mg Trolox eq/gdry tissue weight, respectively). Sweetpotato leaves had a significantly higher phenolic content and antioxidant activity than roots. Immature unfolded leaves had the highest total phenolic content (88.5 mg chlorogenic acid eq/g dry tissue weight) and antioxidant activity (99.6 mg Trolox eq/g dry tissue weight). Chlorogenic acid was the major phenolic acid in root and leaf tissues with the exception of young immature leaves in which the predominant phenolic acid was 3,5-dicaffeoylquinic acid.

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C.E. Johnson, J.T. Payne, W.A. Young, D.H. Picha, and W.R. Okie