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  • Author or Editor: Niels Maness x
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The mechanism of softening was studied in a rapidly softening peach cultivar `Belle of Georgia' by assessing changes in pectins and hemicellulose from enzymically inactive cell walls. Cell wall preparations were sequentially extracted with imidazole and sodium carbonate (pectin extracts), and potassium hydroxide (hemicellulose extracts). The pectin extracts were particularly enriched in galacturonic acid, arabiiose and rhamnose, and contained only small amounts of hemicellulose associated sugars. Hemicellulose extracts were enriched in xylose, glucose, mannose, and fucose. More tightly bound hemicellulose fractions contained considerable amounts of pectin associated sugars. The proportion of pectin associated sugars in hemicellulose extracts was greater for cell wall extracts of softened fruit. Some possible relationships between pectin/hemicellulose solubility and fruit softening will be presented. Work was supported by USDA grant 90-34150-5022 and the Oklahoma Agricultural Experiment Station.

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Peach fruit softening appears to be associated with changes in cell wall polymers, particularly pectins and hemicelluloses. To determine changes of cell wall polymers associated with peach fruit softening, we conducted sequential extractions of pectin and hemicellulose from softening fruit. A more tightly bound hemicellulose fraction contained considerable amounts of pectin associated sugars. This fraction was separated into charged and neutral fractions, using anion exchange chromatography, and then fractionated into two apparent molecular weight classes by size exclusion chromatography. Virtually all of the charged fraction eluted in the higher apparent molecular weight fraction. The neutral sugar fraction segregated into both apparent molecular weight size classes, with a redistribution from the large to the small size class during softening. This redistribution was accompanied by changes in neutral sugar composition. A possible relationship between changes in this fraction and fruit softening will be discussed. Supported by USDA grant 92-34150-7190 and the Oklahoma Agricultural Experiment Station.

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Changes in cell wall polysaccharides associated with peach fruit softening were characterized over two harvest seasons. Enzymically inactive cell walls were prepared from mesocarp tissues of peach fruit harvested at three stages of softening. Pectin-associated and hemicellulose-associated polysaccharides were extracted from the cell walls sequentially, and glycosyl residue compositions were determined by GLC. Pectin extracts from both years were richest in galacturonosyl, arabinosyl, and rhamnosyl residues. Hemicellulose extracted with 1 m potassium hydroxide contained a high mole percentage of xylosyl, glucosyl, and fucosyl residues. Hemicellulose extracted with 4 m potassium hydroxide contained a substantial amount of pectin-associated sugar residues in addition to hemicellulose-associated sugar residues. During softening in both years, sugar compositions for cell walls, aqueous phenol-soluble polysaccharides, and imidazole extracts reflected a decrease in galacturonosyl residues and a concomitant increase in arabinosyl residues on a mole percent basis. The degree of change for galacturonosyl residues in these fractions depended on season, with greater variation exhibited from fruit at earlier stages of softening. With the notable exception of the seasonal variation exhibited for galacturonosyl residues in cell walls, the relative stability of other glycosyl compositional changes over seasons indicates conserved changes for pectins and hemicelluloses occur during peach fruit softening.

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Pectin and hemicellulose were solubilized from cell walls of peach [Prunus persica (L.) Batsch] fruit differing in firmness by extraction with imidazole and sodium carbonate (pectin extracts), followed by a graded series of potassium hydroxide (hemicellulose extracts). The extracts were subjected to size exclusion chromatography. In imidazole extracts, as fruit softened, there was an increase in proportion of a large apparent molecular mass peak, with a galacturonosyl to rhamnosyl residue ratio resembling a rhamnogalacturonan-like polymer. A smaller apparent molecular mass peak was enriched in galacturonic acid and probably represented a broad polydisperse peak derived from more homogalacturonan-like polymers. In sodium carbonate extracts, a homogalacturonan-like polymer appeared to elute primarily as a higher apparent molecular mass constituent, which increased in quantity relative to other constituents as fruit softened. In cold 1 mol·L-1 KOH extracts three peaks predominated. A xyloglucan-like polymer appeared to elute predominantly in the second peak and fucose was strongly associated with it. In 4 mol·L-1 KOH extracts (tightly bound hemicellulose) the higher apparent molecular mass peak was predominantly acidic and presumably of pectic origin. The smaller apparent molecular mass peaks were composed primarily of neutral sugars, the second peak became smaller and the third peak larger as fruit softened. The ability to separate pectin and xyloglucan-like polymer as two separate fractions based on charge suggests that the nature of any pectin-hemicellulose interaction in this fraction is probably one of physical entrapment of pectin fractions by hemicellulose and not principally by covalent crosslinking between the two polysaccharide classes in peach. Flesh firmness serves as an important determinant of quality in peaches. Our results indicate that apparent molecular mass of both pectins and hemicelluloses changed as peaches softened, resulting in alteration of cell wall structure and associated with decreased tissue cohesion.

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Factorial combinations of two row arrangements on 1.8-m-wide beds (either four rows, each 30 cm apart, or eight rows, each 15 cm apart) and two in-row seeding rates (either 48 or 96 seeds per 30 cm of row) were compared on ‘Santo’ cilantro (Coriandrum sativum L.) in five experiments at Bixby, OK. Plots were harvested once per experiment by cutting at a height of ≈7 cm with a small-plot greens harvester, and fresh weight yields were taken. Treatments minimally affected canopy height at harvest. Eight rows resulted in higher yields than four rows in three of five experiments. Main effects of seeding rate or interactions of row number and seeding rate on yield were rare. Of the four combinations tested, the eight-row arrangement sown at 48 seeds per 30 cm would be recommended. This arrangement was used in three other experiments to test effects of a single preharvest spray application of gibberellic acid (GA). Treatments were a water control and GA at either 10 or 20 g·ha−1. Treatment with GA increased bolting in a 17 Apr. planting and increased canopy height at harvest in two of three experiments. However, GA treatments did not affect yield. Treatment with GA would not be recommended for a spring cilantro crop and may have limited impact on increasing machine recovery of raw product in a fall crop.

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The Stonyhard peach fruit mutation has been used to study softening and textural changes during ripening. Without ethylene exposure, firmness of Stonyhard remains fairly constant at room temperature. When exposed to 1 or 100 ppm C2H2 for 48 hours, fruits soften at a rate consistent with control fruit (`Cresthaven') to a similar firmness. However, 1 ppm—treated fruit attains a normal juicy texture, while 100 ppm—treated fruit attains a pasty texture. Control fruit softened to a normal juicy texture with either ethylene treatment. Cell wall endopolygalacturonase (endo-PG) was not detectable in Stonyhard fruit without C2H2 exposure; it increased at a rate similar to control fruit when exposed to 1 ppm C2H2, and was double that of 1 ppm for fruit exposed to 100 ppm for up to 48 hours. Low levels of endo-PG were detected in control fruit not exposed to C2H2; 1 ppm treatment led to a normal increase, which was comparable to that in Stonyhard. However, endo-PG in 100 ppm—treated fruit was very similar to that of 1 ppm for up to 24 hours, though high levels of endo-PG were observed at 48 hours. Attainment of the pasty texture in 100 ppm—treated Stonyhard fruit may have been related to release of large quantities of pectic polysaccharides as a result of the sudden increase in endo-PG activity. Work was supported by USDA grant 96-34150-2540 and the Oklahoma Agricultural Experiment Station.

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Marigold flower pigments can be extracted and used as a natural source of food colorants in the poultry and dairy industry. These pigments impart an orange color to egg yolks and a yellowish color to dairy products. We examined four African marigold cultivars for their ability to be commercially grown and harvested mechanically. `E-1236' yielded the highest quantity of lutein (22 kg/ha), a carotenoid pigment, using a spectrophotometer for quantification. `E-1236' and `A-975' were the earliest flowering cultivars, 11 June 1998 for transplants and 9 July 1998 for direct-seeded, at 8 weeks after sowing regardless of field establishment method. `E-1236' produced the greatest number of flowers in a production season, both as transplants (68 flowers/plant) and direct-seeded (57 flowers/plant) at 363,290 plants/ha. Transplants resulted in two more harvests in a single season than direct-seeded plants. Subsequently, more flowers and petal material were produced for pigment extraction than with direct-seeded plants. A one-time application of ammonium nitrate (28.02 kg/ha) at mid-season did not significantly effect flower number, flower weight, or pigment yield. Experiment was repeated in 1999 with four cultivars, two field establishment methods, seven harvest dates, and five nitrogen applications.

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Softening to a normal melting flesh texture in peaches involves a combined participation between polymers located in the middle lamella and primary cell wall. Pectins located in the primary cell wall polysaccharide matrix which cosolubilize when hemicellulose is extracted with KOH have received less attention than the chelator or sodium carbonate soluble pectin likely to be associated with the middle lamella. We conducted a series of extractions for cell walls prepared from softening peach fruit (47, 30, and 15 N firmness) using 0.5 m imidazole, sodium carbonate and a graded series of KOH. Hemicellulose-associated pectin was a substantial proportion of most KOH extracts (30 to 50 mole percent) and fractionated on size exclusion chromatography as a high apparent molecular weight peak which became more prominent as fruit softened and could be separated from two lower apparent molecular weight peaks by anion exchange chromatography. The nature of a hemicellulose-pectin interaction in peach was apparently by physical entrapment, versus covalent cross-linking. Softening related changes in hemicellulose-associated pectin will be addressed.

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The pungency in hot peppers [Capsicum annuum (L.) var. annuum] is mostly due to two capsaicinoids, capsaicin (CAP) and dihydrocapsaicin (DC), which are amide derivatives of vanillylamine and 8-methyl-6-nonenoic acid (E) or 8-methyl-nonanoic acid (A), respectively. During our investigation of the mechanism of capsaicinoid-specific metabolism in pepper fruit, we have developed a method to extract, purify, and quantitate these fatty acids from the free fatty acid pool in placental tissue. Fresh placenta was ground using a mortar and pestle and extracted with diethyl ether. Fatty acids were methanolysed and fatty acid methyl esters were quantitated using GC with capric acid as internal standard. Capsaicinoids accumulated in the same placenta were extracted with N,N-dimethylformamide (DMF) and quantitated using HPLC. The lipid fraction had to be separated from capsaicinoids, since capsaicinoids yielded about 10% of their respective fatty acids during methanolysis. An aminopropyl column was used to separate capsaicinoids from free fatty acids. Extraction recovery for both fatty acids was greater than 70%. This procedure is being used to quantitate fatty acid precursors for capsaicinoid biosynthesis in pepper placenta. We will demonstrate use of this procedure with pepper selections varying in CAP/DC ratio to evaluate the effect of metabolic precursors on capsaicinoid metabolism.

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Pecans, because of their high oil and polyunsaturated fatty acid content, have a relatively short shelf life due to oxidation of the oil. Using a nondestructive supercritical CO2 extraction process, we evaluated oil reduction as a means for pecan shelf life extension. Pecan halves were extracted under sufficient conditions for 22% and 28% oil reduction, and then stored in modified-atmosphere packages with 21% O2 at 22C for up to 37 weeks. Kernel hexanal content and sensory rancid flavor were monitored at various times throughout the study. The resistance of oils to oxidation, indicated by the onset of sustained hexanal production, was increased from 6 weeks for full-oil halves, to 18 weeks for 22% reduced-oil halves, to 22 weeks for 28% reduced-oil halves. Objectionable rancid flavor was detected by the 22nd week of storage for full-oil pecans. Reduced-oil pecans never developed objectionable rancid flavor. Supported by USDA grant 93-341508409, OCAST grant AR4-044, and the Oklahoma Agricultural Experiment Station.

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