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  • Author or Editor: William M. Walter Jr. x
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The sugar content of the sweetpotato cultivars Centennial, Coroner, Georgia Red, Jewel, and Sweet Red was measured by nign performance liquid chromatography (HPLC) and compared to the sugar content found by measuring the refractive index of cellular sap and converting the refractive index value to sugar concentration. The sugar content and refractive index values were measured for just-harvested, cured and stored roots. Changes in the sugar content as determined by refractive index were found to be linearly related to changes 1n sugar content measured by HPLC, indicating that this method can be used to monitor changes in postharvest sugar content.

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The sugar content of five sweetpotato [Ipomoea batatas (L.) Lam.] cultivars (`Centennial', `Cordner', `Georgia Red', `Jewel', and `Sweet Red') was measured by high-performance liquid chromatography (HPLC) and compared to the sugar content of the cellular sap measured by refractive index (RI). The HPLC and RI sugar contents were measured at harvest, after curing, and during storage. Changes in the sugar content, as determined by the RI, were found to be linearly related to changes in the sugar content of cell sap and tissue, as measured by HPLC, indicating that this method can be used to monitor changes in postharvest total sugar content.

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Abstract

Freshly harvested sweet potatoes [Ipomoea batatas (L.) Lam. c. Jewel] are cured by holding them at 80–95% relative humidity and 29.4°C for 5 to 7 days. Curing heals wounds inflicted during harvest, thus minimizing loss from microbial decay during subsequent storage. The wound healing process was followed by applying a saturated solution of phloroglucinol in strong acid (PG) to the underside of detached wound tissue and scoring the intensity of the color developed. Microscopic examination of companion tissue with PG showed that color intensity was due to the layers of cells in which PG positive material was deposited. Wound periderm formation was observed to occur simultaneously with development of the most intense color, indicating that the test may be useful in the evaluation of curing progress.

Open Access

Wound healing in cucumber fruit (Cucumis sativus L., cv. Calypso) was studied using histological and degradative techniques. A thick exudate appeared at the wounded surface shortly after wounding. This material retarded water loss and possibly aided in the formation of sclerified parenchyma observed 24 hours after wounding. The sclerified material was positive to a modified Weisner stain, indicating lignification was occurring. Wound periderm (cork) was initiated directly beneath the sclerified parenchyma cells within 48 hours after wounding. The cork layers were positive to Sudan IV stain, indicating suberin was being formed. The rate of phellem development decreased by 6 days after wounding. By day 7, younger phellem cells and sclerified parenchyma cells were stained by Sudan IV. Degradation of the wound tissue by chemical procedures demonstrated that relatively large amounts of lignin and suberin were deposited during healing. Fragments from the lignin degradation Indicated that lignin was composed mainly of gualacyl and p-hydroxyphenyl residues. Suberin was found to contain mainly 1,16-hexadecane and 1,18-osctadecene decarboxylic acids detected as the silylated diol derivatives.

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Abstract

Protein and dry matter contents were determined for 16 cultivars of sweet potatoes (Ipomoea batatas (L.) Lam.) planted May 28 and harvested on 4 different dates. Means of protein contents of cultivars differed significantly and ranged from 4.17% to 6.51%, dry basis. Protein content decreased at the rate of 0.0067% per day and dry matter decreased at the rate of 23% per day.

Open Access

Abstract

Roots of three sweet potato [Ipomoea batatas (L.) Lam] cultivars, Centennial, Jewel, and Pope, were harvested at three soil temperature ranges, cured for 1 to 7 days at 30°C and 90% to 95% RH, and stored at 13° to 13.5° and 90% and 95% RH. Wound healing during curing was evaluated using a rapid color test and histochemical methods. The color test was a good indicator of the lignification phase of wound healing for ‘Centennial’ and ‘Jewel’, and a fair indicator for ‘Pope’. Wound healing rates for the cultivars were similar. Roots harvested from the warmest soils (22° to 25°) had higher color scores (most wound lignification) up to 3 days of curing. After 5 days, there were ≈2.7 layers of lignified cells and one layer of wound periderm. After 16 weeks of storage, roots harvested at soil temperatures of 10° to 12° and 22° to 25° had lost more weight and developed more rots than did roots harvested at 15° to 17°, despite the fact that wound healing progress was similar. Thus, factors other than wound healing strongly influence storage stability.

Open Access

Abstract

A population of 100 sweet potato seedlings from 7 parent clones was grown for one season in order to evaluate root protein quantity and quality. Protein content of the 100 seedlings ranged from 4.38% to 8.98% with a mean of 6.29%; the 7 parents ranged from 4.96% to 6.53% with a mean of 5.72%. The mean of the seedlings was not significantly different from that of the parents. The 10 seedlings with highest protein (7.40% to 8.98%) were selected for further study of protein quality. Levels of nonprotein nitrogen (NPN) in these high protein selections were not significantly different from those of the parents. The correlation between the percentage of protein and the percentage of NPN was low (r = 0.30). The amino acid pattern in the high protein selections differed significantly from the parents with lower levels of valine, cysteine, methionine, tyrosine, and phenylalanine. Trypsin inhibitor activity (TIA) levels in the selected seedlings did not vary significantly from the parents. TIA and the percentage of protein were not significantly correlated (r = 0.15). The results indicate it is possible to obtain high protein cultivars without increasing the percentages of NPN and TIA. With the exception of valine, the aromatic and sulfur-containing amino acids, the overall protein quality was not changed in the seedlings with increased protein content.

Open Access