In California, off-ground almond harvesting offers significant potential to reduce dust generation, microbial contamination, and insect damage, issues commonly associated with conventional harvesting method. However, freshly off-ground harvested almonds have high moisture content, making them vulnerable to postharvest quality deterioration if not properly dried. The drying process is energy-intensive, which directly impacts profitability. Therefore, the overall goal of this research was to investigate the drying mechanisms of off-ground harvested almonds and develop efficient drying methods to reduce drying time and energy consumption while maintaining product quality and safety. Several important aspects of the drying process of the off-ground harvested almonds, including the initial characteristics of almonds (moisture content distributions, dimensions, chemical compositions, and thermophysical properties), moisture diffusivity, theoretical heat, and moisture transfer modeling, the feasibility of commercial dryer systems, and quality attributes of the dried product, as well as the impact of insect infestation, were investigated.To investigate insect infestation of almonds, eight almond varieties were collected from 17 orchards across northern and southern California during three consecutive harvesting seasons (2019, 2020, and 2021). A total of 44 samples were analyzed, consisting of 11 off-ground harvested samples collected immediately after shaking and 33 conventionally harvested samples collected at various times during on-ground drying. Results indicated that off-ground harvested almonds were cleaner and had a significantly lower rate of insect infestation (2.0±1.7%) compared to those from conventional harvest (4.2±3.7%). Among conventionally harvested samples, those from northern California showed a higher infestation rate (6.0±3.4%) than those from the southern region (2.6±3.4%), likely due to the cooler, more humid climate in the north, which favors insect proliferation. Additionally, the insect damage ratio increased with prolonged on-ground drying. For example, Nonpareil almonds from Nickels and Frank farms had infestation rates ranging from 0.3% to 3.7% and 1.3% to 2.3%, respectively, after drying on the orchard floor for one week. These findings highlight the quality and safety benefits of adopting off-ground harvesting methods for almonds. Samples were collected at two harvest timings, early harvest (EH) and standard harvest (SH) to comprehensively examine the initial characteristics of off-ground harvested almonds. EH typically begins 3-4 weeks earlier than SH, a timeline traditionally based on regional practices. Key attributes, including moisture content (MC) distributions, dimensions (length, width, and thickness), shapes (sphericity), chemical compositions (dry matter, protein, fat, crude fiber, and carbohydrate), and thermophysical properties (true density, thermal conductivity, and specific heat capacity) of three different almond components (hull, shell, and kernel) were analyzed. Results showed that EH almonds were composed entirely of in-hull almonds, while SH almonds consisted of three fractions: in-hull almonds, in-shell almonds, and loose hulls. The overall average MC for EH almonds was approximately 63% (wet basis), compared to 22% for SH in-hull almonds and 8% for SH in-shell almonds. Specifically, for EH in-hull almonds, the MC values of hull, shell, and kernel were 76.3%, 46.8%, and 28.5%, respectively. In contrast, SH in-hull almonds exhibited lower MC values of 27.1% for hulls, 15.3% for shells, and 13.0% for kernels. In both EH and SH almonds, the hull consistently had the highest MC, followed by the shell and kernel. Regarding dimensions, the average length, width, thickness, and sphericity for EH in-hull almonds were 32.8 mm, 25.2 mm, 24.4 mm, and 83%, respectively, compared to 35.9 mm, 24.1 mm, 24.5 mm, and 77% for SH in-hull almonds. Observations also revealed the presence of air gaps between the hull and the shell and between the shell and the kernel for both EH and SH almonds. Distinct thermophysical properties were noted among the hull, shell, and kernel, with variations observed between EH and SH almonds. EH hulls and shells exhibited lower true densities but higher thermal conductivities and specific heat capacities than SH samples. A similar trend was observed for the kernels, though the true density was slightly higher in EH almonds. These findings demonstrated the significant differences between EH and SH almonds, which is helpful in designing the drying process for different purposes. Moreover, the results offer valuable data for accurately determining the moisture diffusivity of almonds and identifying essential parameters for model development. For SH almonds, drying loose hulls results in unnecessary energy consumption, while drying in-hull almonds and in-shell almonds together can lead to over- or under-drying. To address this issue, a dimension- and terminal velocity-based sorting approach was developed to efficiently separate loose hulls while minimizing product loss. The results indicated that in-shell almonds had significantly smaller thicknesses compared to in-hull almonds and loose hulls. Using a cut-off thickness of 21.1 mm, 100% of the in-shell almonds were successfully separated. Additionally, the terminal velocity (TV) range for in-hull almonds was much higher than that of loose hulls. By selecting a critical TV value of 12.2 m/s, the in-hull almonds and loose hulls could be 100% separated. However, some in-hull almonds and loose hulls with smaller thicknesses were misclassified into the in-shell fraction, with misclassification rates of 6.7% and 23.3%, respectively. Despite this, these error rates are relatively low and acceptable for practical applications. To characterize the intrinsic moisture transfer mechanisms during the drying process, experiments were conducted to determine the effective moisture diffusivities of different almond components during hot air drying of in-hull almonds. Drying experiments were conducted at three air temperatures (45°C, 60°C, and 75°C) with a constant air velocity of 1.4 m/s, using a factorial experimental design. The process continued until the average moisture content of in-hull almonds reached approximately 9% on a wet basis. Due to natural variations in moisture content, weight, and dimensions of freshly harvested almonds, a single almond could not represent the entire batch. To minimize this variability, 10 almonds with similar weights and dimensions were carefully selected and marked for each drying experiment. At each sampling point, 10 marked almonds were removed from the dryer for dimensional and moisture content measurements. Effective moisture diffusivities were calculated using the slope method derived from the first term of the analytical solution to Fick’s second law of diffusion for spherical geometry. A geometry factor was applied to integrate the ellipsoidal dimensions and correlate the intrinsic diffusivity of an ellipsoid to that of an equivalent sphere with a corresponding radius. Non-linear regression analysis in MATLAB software was used to establish mathematical relationships between effective moisture diffusivity and sample moisture content, as well as shrinkage and moisture ratio (MR). Results showed that the drying behavior of the hull and shell followed typical patterns in most food and agricultural materials. However, the kernel differed significantly, with its moisture content beginning to decrease notably after 180 minutes at 60°C and 75°C while remaining relatively unchanged for about 720 minutes at 45°C. In terms of shrinkage, the hull and kernel experienced pronounced dimensional reductions, while the shell displayed minimal shrinkage, with the maximum reduction being 3.1% across all tested temperatures. The length, width, and thickness of the almond components showed different extents of shrinkage. The deformation of almond components was not observed, as the shape (i.e., sphericity) remained relatively unchanged during drying. Additionally, hull splitting was not detected throughout the process. The effective moisture diffusivities of almond components increased with rising air temperatures. Specifically, as the air temperature increased from 45C to 75C., the average Deff for the almond hull, shell, and kernel increased from 9.70 × 10-10 to 2.05 × 10-9 m2/s, 4.71 × 10-10 to 9.24 × 10-10 m2/s, and 5.82 × 10-11 to 1.45 × 10-10 m2/s, respectively. Polynomial equations were developed to correlate Deff with moisture content, which effectively captured the dynamic variations in Deff during in-hull almond drying, with adjusted R-squared (R_adj^2) values greater than 0.973 for the hull, 0.926 for the shell, and 0.978 for the kernel. The findings provided critical insights into the non-isotropic shrinkage of almond components, the absence of hull splitting or deformation during drying, and established mathematical relationships linking effective moisture diffusivity with moisture content. This information is essential for the development of a comprehensive theoretical heat and moisture transfer model for in-hull almonds. To further study the heat and moisture transfer mechanisms and visualize the spatial moisture and temperature profiles within in-hull almonds during drying, a single in-hull almond was modeled. The model identified the presence of air gaps between the hull and shell and between the shell and kernel, with thickness ranging from 0.1 to 0.25 mm. For simplification, a uniform average air gap thickness of 0.2 mm was used. The in-hull almond was represented as an ellipsoid with five distinct layers: the hull, the air gap between the hull and shell, the shell, the air gap between the shell and kernel, and the kernel. In addition to validated assumptions of non-isotropic shrinkage, negligible shell shrinkage, and absence of deformation or hull splitting, the model incorporated multiphase moisture transfer (involving liquid water and water vapor), variable moisture diffusivity, and a non-equilibrium approach to phase change between liquid water and water vapor. Conservation equations for liquid water, water vapor, and energy were derived from Fick’s second law of diffusion and Fourier’s law. A local evaporation/condensation rate term was integrated into the energy balance equation to capture the thermal effects of moisture evaporation more accurately. Three scenarios were modeled for comparative analysis: Scenario 1 (nsh_CD) assumed a constant moisture diffusivity coefficient and no shrinkage; Scenario 2 (nsh_VD) considered moisture-dependent diffusivity without shrinkage; and Scenario 3 (sh_VD) included both moisture-dependent diffusivity and shrinkage effects. This comparative approach allowed for a comprehensive evaluation of how shrinkage and variable moisture diffusivity influence the drying kinetics of in-hull almonds. The governing partial differential equations were solved using the finite element method in COMSOL Multiphysics software. The “Transport of Dilute Species” module was employed to simulate liquid water and water vapor transfer, while the “Heat Transfer in Solids” module handled heat transfer simulations. The “moving mesh” feature, based on the Arbitrary Lagrangian-Eulerian (ALE) method, was used to account for hull and kernel shrinkage during drying. Results showed that all three models demonstrated good agreement with experimental data, achieving R_adj^2 values greater than 0.942 for temperature predictions and 0.946 for moisture content predictions. Of the three, the sh_VD model showed the closest alignment with experimental moisture content data, with R_adj^2 values of 0.966, 0.990, and 0.974 at drying air temperatures of 45°C, 60°C, and 75°C, respectively. For final overall moisture content predictions, the nsh_CD model produced large deviations of 17.4%, 7.4%, and 17.4% at 45°C, 60°C, and 75°C, respectively, whereas the sh_VD model yielded errors of 5.6%, 0.6%, and 0.2%. A sensitivity analysis was also conducted to evaluate the impact of the evaporation rate constant (K) on the model performance. Results indicated that the evaporation rate constant had less impact on the temperature profile compared to its effect on the moisture profile. Using different K values for the hull, shell, and kernel, improved the accuracy of the model predictions compared to using a uniform K value, which is commonly used in existing literature. The spatial moisture profile results revealed that moisture loss primarily occurred from the hull surface, leading to relatively low surface moisture levels, while higher moisture concentrations persisted within the almond kernel. This discrepancy suggested that the drying process may appear complete when observing only the hull surface, but elevated moisture content within the kernel could still pose a risk of microbial growth and spoilage. The developed model successfully visualized spatial temperature and moisture profiles within the in-hull almond during drying, providing a valuable tool for estimating optimal drying time and optimizing and designing of drying process. To evaluate the feasibility of using commercial dryers for drying off-ground harvested almonds and address knowledge gaps in both drying techniques and product quality assessment, three types of commercial dryers: tunnel dryers, stadium dryers, and trailer dryers, were tested under different drying conditions. Tunnel drying was conducted using six tunnels to dry the independence almond variety under three conditions: ambient air drying starting during the daytime, ambient air drying starting at nighttime, and hot air drying at 46°C. The air velocity for all three conditions was 1 m/s. Stadium drying used four bins (three assigned to Monterey and one to Fritz) with an air temperature of 35°C and an air velocity of 0.7 m/s. Trailer drying was conducted using four trailers to dry Monterey almonds under two conditions (two trailers per condition) at 43°C and 54°C, with an air velocity of 1.2 m/s. The quality attributes of the dried product were evaluated based on the incidence of kernel cavities, concealed damage, whiteness index, and oil quality (peroxide value and free fatty acids). For energy use and cost, the utility use of each drying test, consisting of electricity use for the blowers and natural gas or propane used for the burners, was calculated using the numbers obtained from the drying facilities. The dryer performance indicators assessed were drying rate, throughput, specific energy consumption (SEC), specific moisture extraction rate (SMER), and coefficient of performance (COP). Results showed that all tested dryers were capable of drying off-ground harvested almonds in a short period without compromising product quality. Final moisture content distributions of almonds varied widely across dryers: 3.6-31.1% for Independence almonds after tunnel drying, 3.2-9.7% for Monterey almonds after stadium drying, 3.2-16.6% for Fritz almonds after stadium drying, and 1.6-11.9% for Monterey almonds after trailer drying. Across all conditions, the dried almonds showed no cavities, concealed damage, or notable color changes in the kernels. Only almonds dried using trailer dryers exhibited higher peroxide values (1.33-1.83 meq/kg oil) and free fatty acid levels (0.26-0.31%). However, these values remained well below the industry standards of 5 meq/kg oil for peroxide values and 1.5% for free fatty acid levels. Energy use and costs varied based on the initial moisture content, dryer type, and drying conditions. Among the evaluated dryers, trailer dryers presented superior performance with higher SMER (0.34-0.83 kg/MJ) and COP (4.5-9.6) and lower energy costs (¢0.52-¢1.34/lb of dried product). Besides, trailer dryers were also preferred due to their ease of temperature control and larger drying capacity. In summary, this research comprehensively characterized various aspects of hot air drying for off-ground harvested almonds using experimental and modeling approaches. The findings provide valuable insights into the drying behavior of almonds, spanning from bench-scale studies to commercial-scale applications. The improved understanding of heat and moisture transfer mechanisms can inform the optimization and design of efficient drying processes in future investigations.

California produces over 99% of US commercial almonds and walnuts. Conventionally, almonds are dried on the ground while walnuts are partially dried on ground and then dried in heated air dryers. Both drying methods are essential to increase product shelf-life and safety as well as ensure yearlong availability. However, these conventional drying practices are inefficient due to the slow process and intensive energy use, and on-ground drying often is associated with food safety risk of the finished products. This research investigated the drying and quality characteristics of almonds dried by stepwise high temperature air drying and walnuts dried by sequential infrared and heated air drying (SIRHA) as alternative methods to the conventional drying. The studied quality characteristics include kernel color change, concealed damage, and oil quality analysis. Almond in-hulls and in-shells of Nonpareil (NP) and Wood Colony (WC) varieties were dried with air velocity of 1.0 m/s (air flow rate of 1.75 m3/s per m3 of fresh almonds) under two approaches: at a constant temperature of 40°C, 50°C, and 60°C and at a stepwise high temperature with the first stage at 80°C and 90°C, a holding time of 1, 2, and 3 hours, and the second stage at 60°C. The almond samples were dried until the kernels reached a final wet basis moisture content of 6%. The total processing times of almonds dried by heated air at 40, 50, and 60°C ranged from 7 to 16 hours while the total processing time (including holding) of almonds dried by stepwise high temperature ranged from 7 to 10.5 hours, both of which were significantly less than the drying time of 36 hours for almonds dried at ambient temperature (p < 0.05). Under the same drying condition, almond in-shells required significantly less drying time than almond in-hulls. Overall, the drying curves for almonds were best represented by the Page model. To evaluate the almond kernel quality, the whiteness index (WI) of almond flesh was measured with a colorimeter, and the concealed damage after roasting at 135°C for 90 minutes was evaluated with the color development score (CDS). To determine the oil quality, the peroxide value (PV) and acid value (AV) of extracted almond oils were measured by titration methods. In general, the different drying conditions did not cause a significant color change in the almond kernels. The WI values of all dried almond samples were relatively similar at 77.1±2.3 for NP and 79.1±2.1 for WC. After roasting, the concealed damage scores appeared to be consistent regardless of the drying conditions and the variety, averaging at the CDS of 2.8±0.6 in which indicated no concealed damage. In terms of oil quality, both PV and AV of all almond samples increased along with the rising of drying temperature. However, the PVs of both varieties at different drying conditions were not significantly different, averaging at 0.585±0.100 meq/kg. Meanwhile, the AVs of NP samples were significantly lower than the WC samples at p < 0.05. Overall, the oil quality of almonds dried under all of the drying methods was far below the industry standards (PV < 5 meq/kg and AV < 3.0 mg KOH/g). In shell walnuts with low initial wet basis moisture content of 10.06±0.75 % (LMC) and high initial wet basis moisture content of 27.67±2.74 % (HMC) were acquired for this study. Both kinds of walnuts were cleaned by dipping and soaking in clean water for 2 minutes to mimic the industrial washing procedure. Then, the half of the walnut samples were infrared pre-dried for 25 seconds for LMC walnuts and 60 seconds for HMC walnuts, based on the time for the internal temperature of the walnuts to reach about 43°C. After the IR pretreatment, the walnuts were conditioned into in-shell, cracked shell, and kernel using a nut cracker. Then, the samples were dried by heated air at 45, 50 or 55 degrees Celsius with air velocity of 1.0 m/s to an average final wet basis moisture content of 7% for walnuts dried in in-shell and cracked-shell conditions and 3% for walnuts dried in kernel condition. The drying time of LMC walnuts ranged from 0.5 to 2 hours while the drying time of HMC walnuts ranged from 5 to 16 hours. Overall, walnut samples dried the fastest under heated air temperature of 55°C, followed by 50°C and 45°C, consecutively. When compared to in-shell walnuts, walnuts dried in cracked-shell and kernel only conditions could reduce the drying time by up to 28% and 54%, respectively. An accelerated shelf-life study was conducted by storing dried walnut samples in an incubator set at 35oC with relative humidity of 53% for 20 days, representing 2 years of storage at 4oC. Samples were collected after 0, 5, 10, 15, and 20 days of storage for quality analysis. To evaluate the product quality, the lightness value (L*) of the kernels was measured with a colorimeter, and the PV and AV of extracted walnut oils were determined by titration methods. Under all of the tested conditions, the L* values decreased over the storage time. The application of IR pretreatment and the different drying temperatures did not significantly alter the lightness values. However, the L* values of the kernels from dried in-shell walnuts were significantly different from that of direct kernel dryings at p <0.05. In terms of oil quality, the PVs were generally increased over the storage time, but the AVs were relatively stable over the storage time at 0.147±0.125 mg KOH/g. The application of IR pretreatment on LMC walnuts resulted in lower PVs, possibly due to the deactivation of catalytic pro-oxidant in the walnuts due to the high temperature heat treatment. However, the application of IR pretreatment on HMC walnuts significantly increased the AVs, indicating high lipid hydrolysis activities. Overall, the product qualities over storage time were within the industry standards (L* > 40, PV < 1.0 meq/kg oil, AV < 1.2 mg KOH/g). Based on the experimental data and analytical observation, almonds dried by stepwise high temperature air drying and walnuts dried by sequential infrared and heated air drying can be applied as alternative methods to the conventional drying practices without causing any quality concern. Also, this study showed that heated air drying can be used for walnuts in cracked-shell and kernel only conditions without affecting the quality and shelf-life of the dried products.

Pomegranate (Punica granatum L.) is an ancient fruit and a commodity favored by people worldwide for its unique shape and flavor. Pomegranate peel is a major by-product from the juicing process with rich health-promoting bioactive compounds (mainly polyphenol content) but remains underutilized or disposed of. The main goal of this dissertation was to study the extraction of functional ingredients from pomegranate peel waste, evaluate their nutritional benefits, and develop value-added nutritional products. A novel green process for antioxidant extraction from wet pomegranate peel (WPP) was developed. The effects of various extraction conditions on polyphenol yield and quality were investigated, including particle size, time, temperature, and solvent ratios. WPP extraction at 20°C for 6 min with a solvent (water) ratio of 4:1 is recommended as an economic and sustainable process, resulting in 10.53% total phenolic yield (TPY) with 6.35 g g-1 tannic acid equivalent (TAE) and 88.93% punicalagin (most unique and potent polyphenol in pomegranate) purity. Plant bioactive compounds have demonstrated promising effects in promoting health. Therefore, the hypolipidemic effects of pomegranate peel powder (PPP) and pomegranate peel extract (PPE) were researched via Lakeview Golden (LVG) Syrian hamsters with a high-fat (20%) diet. PPP and PPE significantly improve obesity-related indices, including adjusting microbiota composition, increasing the microbiota diversity towards a leaner type, and down-regulating the expression of 2 genes (HMG-CoAR and LDLR) to reduce cholesterol ingestion and LDL uptake. However, further research on potential toxicity was required, as adverse plasma LDL-elevating effects were observed at a higher dose of PPP and PPE intake. As functional food fortified with plant bioactive compounds became more popular, the potential of PPE as ingredients for fortified food supplementation was evaluated. A PPE-fortified Greek Style yogurt was developed using a top-down formulation method based on USDA dietary guidelines. According to the results from response surface methodology, the optimum formula for a 130 g (4.6 oz) product consisted of 10.4 g (8%) of protein and 77 g (59%) of PPE, which could satisfy the polyphenol daily need (1g per day) while maintaining pleasant product properties. An organic acid-based ultrasound-assisted co-extraction process of polyphenol and pectin was investigated for thorough WPP utilization and broader industry applications. Citric acid was applied for extraction since it’s a common GRAS acid in food applications. Process conditions, including pH, extraction temperature, extraction time, ultrasound intensity, and solvent ratio, were evaluated via Box-Behnken design to study the effects on extraction performance, including polyphenol/pectin yield, antioxidant activity, and pectin characteristics. High methylated (Degree of methylation up to 79.66%) pectin yield was as high as 13.99%, which demonstrated that WPP could be utilized as a reliable pectin source. The extraction kinetics were characterized for future industry application guidance. In conclusion, this dissertation demonstrated the potential of pomegranate peel to be utilized as a source of healthy and bioactive compounds.

The objective of this research was to characterize the qualities (mechanical properties and water resistance) of particleboard made from saline Jose Tall Wheatgrass (JTW), Agropyron elongatum. For the JTW particleboards made with 4% polymeric methane dipherryl diisocyanate (PMDI), the mechanical properties and water resistance improved with the increase of particleboard density from 0.71 to 0.75 g/cm(3). The particleboards with density of 0.74g/cm(3) had similar mechanical properties of wood-based particleboards, except for lower internal bond strength. Among the particleboards made with particles of different initial moisture contents from 2% to 10%, the particleboard with the particles of 8% initial moisture content had the highest qualities. The pretreatment using NaOH solution to wash the JTW particles reduced the qualities of finished particleboards bonded with both PMDI and urea formaldehyde (UF) resins. Particle-boards made with PMDI showed superior qualities than those made with UF, as shown by the measured contact angle results between the adhesives and JTW.