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  • Author or Editor: David H. Picha x
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Abstract

Concentrations of the major sugars and organic acids within ripe ‘Charleston Gray’ and ‘Jubilee’ watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] flesh were quantified in 5 different regions. The percentage of soluble solids (%SS) in both cultivars and the percentage of sucrose in ‘Charleston Gray’ were highest in the heart region, followed by the blossom end, and lowest in the stem end. Glucose, malic acid, and citric acid were generally higher in the heart and blossom end compared to the stem end, while fructose was higher in the blossom end than stem end. No significant differences between the top side and the soil side were found for any of the sugars or organic acids. Fructose was the major sugar in all regions in ‘Jubilee’, whereas the major sugar in ‘Charleston Gray’ (sucrose or fructose) depended on the region. Malic acid was the primary organic acid in all regions of both cultivars.

Open Access

Abstract

Sugars and organic acids in ripe ‘Charleston Gray’ and ‘Jubilee’ watermelons [Citrullus lanatus (Thunb.) Matsum & Nakai] were measured at harvest and after 14 or 19 days of storage at 0°, 7°, 16°, 23°, or 27°C. Soluble solids content (SSC), sucrose, fructose, and glucose concentrations mostly did not change during storage at 0°, but all generally were reduced at the higher temperatures. ‘Charleston Gray’ contained about 3% to 4% sucrose, 2% to 3% fructose, and 1.0% to 1.5% glucose. Fructose was the major sugar in ‘Jubilee’, followed by sucrose and glucose. Malic acid was the major organic acid in both cultivars. Temperature of storage had little effect on malic acid concentration. The concentration of citric acid decreased during storage at 23° or 27°, but not consistently at low temperatures.

Open Access

The glucose-6-phosphate dehydrogenase (G-6-PDH) and glucose oxidase methods are commonly adapted for plant invertase assay. A disadvantage of the G-6-PDH assay is the relatively high cost of the coupling enzymes and cofactors. A disadvantage of the glucose oxidase method, which uses a glucose kit (Sigma, 510-A), is the presence of high activities of acid invertase and alkaline invertase in the PGO enzyme formula (peroxidase and glucose oxidase), which gives a falsely high invertase activity value. An alternative and inexpensive coupled assay was developed for enzymatic assay of plant invertases. In this assay, ADP produced from phosphorylation of glucose and fructose (hydrolysis products of invertases) is coupled to oxidation of NADH by the enzymes pyruvate kinase and lactate dehydrogenase in presence of phosphoenolpyruvate and NADH. This method was compared with the glucose-6-phosphate dehydrogenase method by using protein preparations derived from plant materials of three different species. Statistical analysis indicated that the alternative assay was similar in accuracy to the glucose-6-phosphate dehydrogenase method, with an advantage of reducing the cost from $0.85 to $0.35 per assay.

Free access

`Beauregard' sweetpotato (Ipomoea batatas L. Lam) roots were maintained under different controlled atmospheres ranging from 0% to 21% O2 at 22 °C in two separate trials for 14 days to study changes in activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH). Trial I showed no difference in activities of PDC and ADH between 0% and 1% O2, or among 2%, 5%, and 21% O2. Both PDC and ADH activities were significantly higher at 0% and 1% O2 compared to the 2%, 5%, and 21% O2 atmospheres. In trial II, both enzyme activities were lower at 1.5% O2 than at 0% O2, but higher than at 10% and 21% O2 atmospheres. The combined data of the two trials showed a very strong correlation between PDC and ADH activities (R 2 = 0.86). In addition, a strong correlation existed between PDC activity and acetaldehyde concentration (R 2 = 0.95). The maximal activities were at pH 6.5 for PDC and at pH 8.5 for ADH in the direction of acetaldehyde-to-ethanol. The results suggest that 1.5% O2 is the critical point for the transition from aerobic to anaerobic metabolism in CA storage of sweetpotato roots, and PDC is the key enzyme in alcoholic fermentation.

Free access

Changes in fructose, sucrose, and glucose were investigated in cured roots of `Beauregard', `Jewel' and `Travis' sweet potatoes stored at 15°C and 1.5°C for 8 wk. Samples of 6 roots each in triplicate were analyzed at 2 wk intervals. At each interval, samples were also heated for 5, 10, 20 or 40 min. at 100°C to determine changes in rate of maltose conversion. Roots stored at 15°C displayed gradual or no increase in sugars over the 8 wk. Roots stored at 1.5°C increased more rapidly in sugars, especially fructose, over the same time. `Jewel' had the greatest increase in the sugars when stored at 1.5°C. There was no consistent pattern of maltose conversion in roots stored at 15°C over the 8 wk storage time. Roots stored at 1.5°C displayed a reduction in ability to convert starch to maltose upon heating. Less maltose was produced with increasing time of storag at 1.5°C. `Beauregard' and `Jewel' changed the most, while `Travis' changed only slightly.

Free access