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- Author or Editor: Laurence Sistrunk x
Previous work in this lab has shown that drying temperatures above 35°C will cause excessive loss of the kernel's natural light color and less oleic (18:1) oxidation to linoleic (18:2) fatty acid. The former is undesirable because of poor consumer appeal and the latter is desirable because of superiority of oleic acid in reducing low density lipoprotein in the blood plasma of consumers and a longer shelf life. The drying temperature of 35°C and an air volume of 45 CFM was superior in 1989 to 75 CFM at the same temperature and an air dried control. Lower air volumes in 1990 proved to be no better than 45 CFM at 35°C The best compromise drying regime was determined to be 45 CFM at 35°C.
Five Texas orchards were selected in Spring 1993 in commercial pecan counties for testing three types of soil aeration equipment. Mechanical aeration spikes were either 20 or 46 cm long, and a pneumatic spike was 20 cm long. The mechanical spikes are on a rolling cylinder that can be manufactured in sufficient lengths to fit the tree spacing in different orchards. The pneumatic probe is manually inserted into the soil so that a quick burst of 130-psi air can be delivered to effect soil profile fracturing. The fourth replicated treatment was an nontreated control. There were no differences in trunk diameter increases and yield in 1993 between May-applied replicated treatments. The May treatments and November measurements will continue for two more years to allow for differences in soil aeration to influence growth and yield. Shoot growth measurements will be taken in Spring 1995. Irrigation water has penetrated the soil under aerated trees more readily than in nonaerated controls.
Four cultivars of pecan [Carya illinoinensis (Wangenh.) K. Koch] were studied for 3 years to determine if variations in yield influence fatty acid composition of kernels. Trees used in the study are part of the U.S. Dept. of Agriculture, Agricultural Research Service Historical Block, a test orchard planted in randomized block design with four blocks, having one single-tree replication per block and containing 36 cultivars. Four trees of each of four cultivars (`Cheyenne', `Mohawk', `Pawnee', and `Osage') were used in this test. Trees were in their 5th to 7th leaf from grafting and showed patterns of increasing yield over time for each cultivar. `Osage' was earliest to mature nuts each year and produced nuts with the lowest linoleic acid content. `Cheyenne' was latest to mature nuts and had nuts with the highest linoleic acid content. Oleic acid composition varied with yield in `Osage' and `Pawnee': as yield (kilogram/square decimeter trunk area) increased, oleic acid content decreased. Kernel color, as determined by a Hunter LabScan 5100 Spectrocolorimeter, varied in relation to fatty acid composition for `Osage' and `Pawnee': as oleic acid content increased, kernel lightness decreased. High oleic acid content and light kernel color are associated with high-quality pecans. The pattern of decreasing oleic acid content associated with increasing kernel lightness raises questions concerning the role kernel color evaluation should play in selecting high-quality pecan cultivars.