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  • Author or Editor: Gerald Brusewitz x
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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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Variability in mesocarp firmness for peach (Prunus persica L. Batsch) fruit halves cut either parallel or perpendicular to the suture was determined for three cultivars (Halehaven, Ranger, and Topaz). Firmness evaluations were conducted using an Instron Universal testing instrument with a 3.2-mm rounded tip probe. Firmness of the inner, middle, and outer regions of the mesocarp at four angular positions around each peach half was determined at four maturity stages. Average mesocarp firmness declined with advanced stages of fruit maturity. Inner mesocarp was firmest for fruit from all three cultivars. Internal variation in firmness for the middle and outer regions of the mesocarp was highly cultivar dependent. Firmness decreased longitudinally from the stem end to the blossom end and latitudinally from the suture to the cheeks.

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Impact testing was used to assess the variables related to bruise resistance for four peach [Prunus persica (L.) Batsch] cultivars. The effects of cultivar, ripeness, drop height, and firmness on fruit bruise incidence, bruise volume, respiration, and ethylene evolution rates of freshly harvested peaches were determined. The impact variables peak impact force, contact time, absorbed energy, and percent absorbed energy were measured at three stages of fruit ripeness and at three fruit drop heights. Each of the impact variables changed with fruit ripeness. Cultivars differed in their characteristic response to impact. Fruit impact, under the low to moderate impact energies used, had negligible effects on fruit respiration and ethylene production for the cultivars studied. Bruise incidence and volume increased with drop height and especially with advancing stage of ripeness. Under conditions we used, peach fruit bruise severity could be determined by either bruise incidence in or bruise volume of mesocarp tissue.

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Irrigation schedules were evaluated on `Cresthaven' peach [Prunus persica (L.) Batsch.] to determine if water application could he reduced or omitted without affecting fruit size or yield. Tensiometers were used to schedule trickle irrigation during 1984-M. Treatments were no irrigation or irrigation when soil pressure potential at a 30-cm depth reached 40 or 60 kPa, respectively. When production began in 1986, trees were either irrigated until harvest (1-7 Aug.) or until October. Beginning in 1989, class A pan evaporation was used to schedule irrigation by replacing 60% of evaporation. Trees were irrigated from budbreak to harvest or October, from beginning of stage III fruit growth until harvest or October, or trees were not irrigated. The irrigation treatments were in factorial combination using sod middles, with annual ryegrass (Lolium multiforum Lam.) seeded under the trees or a sod-herbicide strip. The ryegrass was seeded in October, then killed at the onset of stage III fruit growth. Water application was reduced 32% to 57% when irrigation was discontinued after harvest compared to irrigation until October. Irrigation before stage III fruit growth did not affect fruit yield, size, or pruning weights compared to trees irrigated at the onset of stage III fruit growth. Trunk size was increased by irrigation; however, there were no differences in trunk size among irrigation treatments. Irrigation occasionally increased fruit size and yield compared to no irrigation. There were few differences in flower bud density, fruit set, yield, or fruit size among trees with reduced irrigation schedules compared to trees receiving irrigation from budbreak until October. Annual ryegrass decreased shoot growth in 1990 and flower bud density in 1991; however, fruit set was not affected. Annual ryegrass depleted excess soil moisture during the spring in some years, then conserved soil moisture after it was killed. Using sod with annual ryegrass under the trees may be a viable alternative to management with sodherbicide strips.

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Partial oil extraction is being investigated as a means to increase oxidative stability and provide reduced fat pecan halves. Supercritical extraction with carbon dioxide provided a means to extract twenty to thirty percent of resident oil, with little to no kernel damage and leaving no harmful residues in the kernel or the extracted oil. Variances in extraction time, temperature, pressure and total carbon dioxide volume used for extraction with a continuous flow extractor will be discussed. Fatty acid composition of oils extracted using supercritical carbon dioxide was essentially the same as oils obtained by solvent extraction and by cold press. Fatty acid yield in the oils was greater for supercritical extraction compared to the other two methods. Oxidative stability for extracted and unextracted pecans, determined using an accelerated aging technique, will be compared. Supported by USDA grant 92-34150-7190 and the Oklahoma Agricultural Experiment Station.

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Shelf life is a major problem in the marketing of pecans, particularly at the retail level. A procedure to extend the shelf life of pecans was described. The full-oil and supercritical carbon dioxide extracted (22% and 27% reduced-oil) native pecan kernels packaged in standard air mixture (21% O2, 79% N2), stored for up to 37 weeks at 25 °C and 55% RH, were subjected to hexanal analysis, sensory analysis, and determination of lipid class changes, that occur as the pecans age. Hexanal concentration of reduced-oil pecans was negligible throughout the storage, while full-oil pecans reached excessive levels by 22 weeks. Hexanal analysis was in agreement with the sensory scores. Free fatty acid lipid class was selectively extracted during the partial oil extraction process. Reduction in free fatty acids, and an overall reduction in lipid content on a per kernel basis, decreased the sites for oxidative deterioration and contributed to enhanced shelf-life of pecans. Work was supported by OCAST grant AR4-044 and the Oklahoma Agricultural Experiment Station.

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Techniques to reduce the oil content of shelled pecans using supercritical CO2 have been developed, and the effect of partial oil extraction on kernel quality is being investigated. Extraction conditions induce little kernel damage and allow for up to 30% oil reduction. Extraction temperature, at 40 or 80C, influenced kernel color. Regardless of temperature, extracted nut meat was lighter in color. Testa color increased in redness for kernels extracted at 80C compared to kernels extracted at 40C. Extracted oil was amber. Fatty acid composition of oil obtained with supercritical CO2 was essentially the same as oil obtained by organic solvent extraction and by cold press. Investigations to determine the effect of oil reduction on pecan shelf life are described. This research was supported by U.S. Department of Agriculture grant 92-34150-7190, Oklahoma Center for Advancement of Science and Technology grant AR4-044, and the Oklahoma Agricultural Experiment Station.

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This study examined the effects of high humidity (>95%) and airflow on fresh peach [Prunus persica (L.) Batsch.] quality. Peaches were stored in high airflow at 98%, 88%, and 67% relative humidity (RH) (6, 5.6, and 4.3C, respectively) and negligible airflow at 100%, 95%, and 81% RH (6, 5.6, and 4.3C, respectively). Fruit weight loss, penetrometer force, impact variables, and bruise occurrence from a single 15-cm drop impact were measured over 20 days of storage. Fruit stored at a low vapor pressure deficit had a lower rate of weight loss, with drop impact values characteristic of firmer fruit than fruit stored at higher vapor pressure deficits. High airflow increased weight loss and decreased fruit firmness, but had only a secondary effect on localized humidity. Penetrometer force and bruise occurrence were less sensitive than drop impact variables in detecting differences in fruit firmness due to treatments.

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