This research aims to provide a more complete understanding of almond seed coats, including microscopic development and structure, the relationship of measurable properties to surface area, and the kinetics of seed coat separation from the underlying almond kernel in response to a range of temperatures.
Immature almond samples of Nonpareil and Padre varieties were microscopically examined in the 16th-20th weeks after flowering (13 through 7 weeks prior to commercial harvest). The highly vacuolate and thin-walled diploid maternal tissues and triploid support tissue that sustain the embryo during development begin to rupture and compress down above a base monolayer of distinctly intact cells to form the mature seed coat. Over the course of blanching, no substantial swelling or dissolution of microscopic tissue layers was visible, however the junction between the base layer of the seed coat and the underlying almond cotyledon moved apart until they were no longer in contact with one another.
Surface areas of Nonpareil, Monterey, and Butte-Padre almonds were measured by manually peeling rehydrated nuts and analyzing images of their seed coats. Ninety-five percent of the 1,545 almonds measured in this study had surface areas between 515.96 mm2-942.24 mm2. Surprisingly, individual dimensions (length, width, and thickness) did not increase with increasing surface area, nor they did scale in proportion to one other. An empirical model was created to predict surface area (r2=0.74), which depends on the almond variety, as well as length, width, and mass after rehydration.
The progression of blanching was examined by quantifying the degree of seed coat separation at dozens of intermediate time-points during the blanching process, using this empirical model. Experimental temperatures were 70°C, 80°C, 90°C, and 100°C; at each temperature, seed coat separation occurred in a sigmoidal logarithmic fashion. Rates of blanching were calculated using non-linear two-parametric regression. Rates of blanching at 100°C and 90°C were not significantly different, however, blanching rates decreased semi-logarithmically with decreasing blanching temperature between 70°C and 90°C. D-values representing 90% seed coat separation were calculated as 30 seconds at 100°C, 35 seconds at 90°C, 120 seconds at 80°C, and 443 seconds at 70°C. From these, a z value for decimal reduction times between 70°C and 90°C was calculated at 18.48C degrees.
The novel empirical model for surface area could be used to improve the accuracy of mass transfer and energetic transfer calculations in almond processing. Quantifying the rate of seed coat separation could be used to explore any aspect of almond physiology dependent on or resultant from seed coat integrity, such as germination, rehydration kinetics, processing damage, or blanching efficacy. It could also potentially be used to compare the relative blanching propensity of different almond varieties, as well as evaluating the impact on skin separation of various growing, harvesting, and processing conditions. D- and z values characterizing the almond blanching process may be useful in optimizing almond processing conditions to reduce the chances of accidental seed coat separation, or to more efficiently achieve it.
|Advisor:||Barrett, Diane M.|
|Commitee:||Gradziel, Thomas, Jernstedt, Judy|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 74/10(E), Dissertation Abstracts International|
|Keywords:||Almond, Blanching, Integument, Prunus dulcis, Seed coat, Surface area|
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