[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to investigate the effect of infrared (IR) heating and tempering treatments on disinfection of Aspergillus flavus in freshly harvested rough rice and storage rice. Rice samples with initial moisture contents (IMCs) of 14.1 to 27.0% (wet basis) were infected with A. flavus spores before the tests. The infected samples were heated by IR radiation to 60°C in less than 1 min, and then samples were tempered at 60°C for 5, 10, 20, 30, 60, or 120 min. High heating rates and corresponding high levels of moisture removal were achieved using IR heating. The highest total moisture removal was 5.3% for the fresh rice with an IMC of 27.0% after IR heating and then 120 min of tempering. IR heating followed by tempering for 120 min resulted in 2.5- and 8.3-log reductions of A. flavus spores in rough rice with the lowest and highest IMCs, respectively. To study the effect on disinfection of rewetting dried storage rice, the surface of the dry rice was rewetted to achieve IMCs of 14.7 to 19.4% (wet basis). The rewetting process for the dry rice had a significant effect on disinfection. IR heating followed by tempering for 60 min resulted in 7.2-log reductions in A. flavus on rewetted rough rice. The log-linear plus tail model was applied to estimate the tempering time needed to achieve a 5-log reduction of A. flavus in rice of different IMCs. At least 30 and 20 min of tempering were needed for fresh rice and rewetted rice, respectively, with the highest IMCs. The recommended conditions of simultaneous disinfection and drying for fresh rice was IR heating to 60°C followed by tempering for 120 min and natural cooling, resulting in a final MC of 16.5 to 22.0%, depending on the IMC. For the rewetted dry rice with an IMC of 19.4%, the recommended condition for disinfection and drying involved only 20 min of tempering. The final MC of the sample was 13.8%, which is a safe MC for storage rice.
Journal of food protection 09/2014; 77(9):1538-1545. · 1.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tree nuts are responsible for many cases of severe food allergies. The 7S seed storage protein vicilin has been identified as a food allergen in many kinds of tree nuts. The vicilin protein consists of an N-terminal low-complexity region with antimicrobial activity and a C-terminal domain that forms a trimeric structure that belongs to the cupin superfamily. In this study, vicilin from pecan (Carya illinoinensis) was isolated and was expressed in bacteria for the first time. The cupin structural core of the protein, residues 369-792, was purified by metal-affinity and gel-filtration chromatography to high purity. Vicilin crystals were obtained and the best crystal diffracted to 2.65 Å resolution in space group P212121.
Acta Crystallographica Section F Structural Biology and Crystallization Communications 08/2014; 70(Pt 8):1049-1052. · 0.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Characterization of physical properties of fruits represents the first vital step to ensure optimal performance of fruit processing operations and is also a prerequisite in the development of new processing equipment. In this study, physical properties of engineering significance to processing of three popular cultivars of clingstone peaches were evaluated, including dimensional parameters, mass, dimensional ratios, aspect ratio, elongation index, sphericity, bulk density, texture, color, and flavor. Based on these physical properties, multivariate analysis of variance (MANOVA), canonical variate analysis (CVA), principal component analysis (PCA), and partial least squares and linear discriminate analysis (PLS-LDA) were applied to qualitatively and quantitatively discriminate the cultivar difference. Results showed that the studied peach cultivars had significantly different (p < 0.05) geometric characteristics. The peaches can be classified based on the cheek diameter (Dc) into three different size categories, including small- (Dc less than 60 mm), medium- (Dc between 60 mm and 70 mm), and large- (Dc higher than 70 mm) sized peaches. The peach flesh firmness significantly (p < 0.05) decreased with the increase of peach size, while the pit dimensions were independent of peach size. There were no apparent distinctions in color characteristics, bulk density, and sugar content among the three cultivars. The measurements and quantitative discrimination of peach properties in this study would benefit equipment design and process innovation to enhance the processing efficiency and quality of processed peaches.
Food and Bioprocess Technology 06/2014; 7(6). · 4.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Microwave (MW) almond roasting was investigated as an alternative to hot air (HA) roasting. Nonpareil almonds (Prunus dulcis) were roasted at 140C in a convection oven for different times to achieve light, medium and dark roasting levels. Several instrumental measurements were taken, establishing targets for each roasting level. To determine the MW time/power combinations necessary to match the HA targets, a response surface experiment was conducted. Additional MW-roasted samples prepared using the optimal time/power combinations underwent both instrumental and sensory analyses. The overall sensory difference test showed that, at the medium roasting level, the MW-roasted almonds were indistinguishable from their HA-roasted counterparts. At all three roasting levels, the HA- and MW-roasted samples were not significantly different in terms of sensory roasted flavor and crunchiness. Instrumental measurements supported the sensory results. When optimized, MW roasting yields results similar to HA roasting in a fraction of the time.Practical ApplicationThe findings of this work can be used by industrial almond processors to develop large-scale microwave (MW) roasting unit operations. Also, consumers could use the optimal MW time and power combinations found in this work as guidelines for at-home preparation of roasted almonds.
Journal of Food Processing and Preservation 06/2014; 38(3). · 0.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Critical behaviors of peeling tomatoes using infrared radiation heating are thermally induced peel loosening and subsequent cracking. Fundamental understanding of the two critical behaviors, peel loosening and cracking, remains unclear. This study aimed at investigating the mechanisms of peel separation for tomatoes subjected to a newly developed infrared dry-peeling process. Microstructural changes in tomato epidermal tissues under infrared heating were compared with those of fresh, hot lye and steam treated samples. Theoretical stress analyses coupled with the experimentally measured failure stress of tomato skin were combined to interpret the occurrence of peel cracking within a framework of elastic thin shell theory. With the use of light microscopy and scanning electron microscopy, it was observed that peel loosening due to infrared heating appeared to result from reorganization of extracellular cuticles, thermal expansion of cell walls, and collapse of several cellular layers, differing from samples heated by hot lye and steam. Crack behaviors of tomato skin were attributed to the rapid rate of infrared surface heating which caused the pressure build-up under the skin and strength decrease of the skin. In order to achieve a sufficient skin separation for effective peeling using infrared, promoting rapid and uniform heating on the tomato surface is essential. The findings gained from this study provide new insights for developing the sustainable infrared dry-peeling technology.
Journal of Food Engineering 05/2014; 128:79–87. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thyme essential oil (TEO) and apple skin polyphenols (ASP) are natural compounds considered as generally recognized as safe by FDA, with biological effects against bacteria and fungi. This work aimed to evaluate physical and antimicrobial properties of açaí edible films formulated with TEO and ASP at 3% and 6% (w/w) individually or combined at 3% (w/w) each. Physical properties studied include mechanical resistance, water vapor permeability (WVP), color, and thermal resistance. Antimicrobial activity against Listeria monocytogenes was determined using the overlay diffusion test. Addition of ASP resulted in improved mechanical properties. TEO at 6% (w/w) resulted in increased elongation. ASP films had significant higher WVP than control film. ASP films were lighter and had more red color than other films. Incorporation of ASP resulted in improved film thermal stability, whereas TEO caused rapid thermal decomposition. Presence of clusters was observed on the surface of films. Addition of ASP resulted in a smother surface, whereas addition of TEO led to the formation of crater-like pits on the film surface. Açaí edible film incorporated with 6% (w/w) TEO presented the highest antimicrobial activity. However, both antimicrobials are necessary in the açaí films in order to obtain edible films with suitable physical-mechanical properties. The results of the present study showed that TEO and ASP can be used to prepare açaí edible films with adequate physical-mechanical properties and antimicrobial activity for food applications by direct contact.Practical ApplicationDeveloped açaí edible films presented antimicrobial activity against L. monocytogenes and good physical-mechanical properties, showing the potential use of açaí edible films in food preservation.
Journal of Food Science 04/2014; · 1.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A vicilin-like globulin seed storage protein, termed convicilin, was isolated for the first time from Korean pine (Pinus koraiensis). SDS-PAGE analysis revealed that Korean pine convicilin was post-translationally processed. The N-terminal peptide sequences of its components were determined. These peptides could be mapped to a protein translated from an embryo abundant transcript isolated in this study. Similar to vicilin, native convicilin appeared to be homotrimeric. Differential scanning calorimetry (DSC) analyses revealed that this protein is less resistant to thermal treatment than Korean pine vicilin. Its transition temperature was 75.57 °C compared with 84.13 °C for vicilin. The urea induced folding-unfolding equilibrium of pine convicilin monitored by intrinsic fluorescence could be interpreted in terms of a two-state model, with a Cm of 4.41 ± 0.15 M.
Plant Physiology and Biochemistry 03/2014; 80C:97-104. · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of carvacrol and methyl cinnamate vapors incorporated into strawberry puree edible films on the postharvest quality of strawberry fruit (Fragaria × ananassa) was investigated. Fresh strawberries were packed in clamshells and kept at 10 °C for 10 days with 90% RH. Strawberry puree edible films, applied in the clamshell, served as carriers for the controlled release of natural antimicrobial compounds without direct contact with the fruit. Changes in weight loss, visible decay, firmness, surface color, total soluble solids content, total soluble phenolics content and antioxidant capacity of strawberries during storage were evaluated. A significant delay and reduction in the severity of visible decay was observed in fruit exposed to antimicrobial vapors. Carvacrol and methyl cinnamate vapors released from the films helped to maintain firmness and brightness of strawberries as compare to the untreated strawberries. The natural antimicrobial vapors also increased the total soluble phenolics content and antioxidant activity of fruit at the end of the storage period.
Postharvest Biology and Technology 03/2014; 89:11–18. · 2.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The increasing strawberry consumption has led to a growing safety concern since they are not washed after harvest. Antimicrobial edible coating could be an effective postharvest technique to assure microbial safety and, at the same time, retain overall quality of the fruits. Response surface methodology was used to optimize the antimicrobial activity against Escherichia coli O157:H7 and Botrytis cinerea and several physical properties (turbidity, viscosity and whitish index) of alginate coating. A full factorial design was used to select the concentrations of carvacrol and methyl cinnamate based on their effect against E. coli and B. cinerea. A central composite design was then performed to evaluate the effects/interactions of the two antimicrobials on the coating characteristics. The results from analysis of variance showed the significant fitting of all responses to the quadratic model. Considering the desirable responses, the optimal concentrations were at 0.98% (w/w) carvacrol and 1.45% (w/w) methyl cinnamate.
Journal of Agricultural and Food Chemistry 01/2014; · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of ultraviolet-B (UV-B) light treatment on total soluble phenolic (TSP) contents of various whole and fresh-cut specialty crops was evaluated. Whole fruits (strawberries, blueberries, grapes), vegetables (cherry tomatoes, white sweet corn) and root crops (sweet potatoes, colored potatoes), and fresh-cut fruit, vegetables and root crops (apple wedge, iceberg lettuce, broccoli floret and stem, and sliced radish, daikon, and parsnip) were treated with increasing UV-B dose levels (1.3–5.9 kJ m−2) and followed by incubation to allow for the samples to respond. TSP levels were measured. The changes in TSP were species-dependent. Whole grapes, blueberries, pink and red cherry tomatoes, white sweet corn, colored potatoes and sweet potatoes did not benefit from UV-B exposure. Strawberries showed a slight, but significant increase in TSP at the highest UV-B dose. UV-B exposure did not affect TSP of apple wedge, broccoli floret and stem, sliced radish and daikon after incubation. Fresh-cut lettuce and parsnip showed significant 1.2 and 2.3 times increase, respectively, in TSP mostly due to the combination effect of wounding and UV-B light exposure after 3 d of incubation. UV-B light exposure (1.3–5.9 kJ m−2) can be used as an additional processing step on selected specialty crops to enhance their soluble phenolic contents.
Postharvest Biology and Technology 01/2014; 93:72–82. · 2.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Salinity and wastewater disposal problems associated with the conventional wet-lye method for peeling clingstone peaches result in considerable negative environment impacts. The efficacy of using infrared (IR) heating as an alternative method for peach peel removal was investigated to eliminate the use of water and chemicals. Peaches sorted into three size categories were double-sided heated under IR with three emitter gaps for a range of heating times from 90 s to 180 s. Wet-lye peeling was used as a control. Results showed that 180 s IR heating for medium sized peaches under an emitter gap of 90 mm yielded 84 mm2/100 mm2 peelability and 90 g/100 g peeling yield, produced peeled products with comparable firmness and color to wet-lye peeled peaches. Surface temperature increased rapidly (> 00 °C) during IR heating whereas the flesh temperature at 16 mm beneath skin remained relatively low (<45 °C). Thermal expansion of cell walls and collapse of cellular layers adjacent to skins were found in IR heated peaches and differed from the micro-structural changes observed in lye heated samples, indicating their mechanistic difference. Promoting uniform and rapid surface heating is essential to further develop IR heating as a non-chemical method for peach peeling.
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to investigate the antimicrobial effects of carvacrol and cinnamaldehyde incorporated into apple, carrot, and hibiscus-based edible films against Salmonella Newport in bagged organic leafy greens. The leafy greens tested included organic Romaine and Iceberg lettuce, and mature and baby spinach. Each leafy green sample was washed, dip inoculated with S. Newport (10(7) CFU/mL), and dried. Each sample was put into a Ziploc® bag. Edible films pieces were put into the Ziploc bag and mixed well. The bags were sealed and stored at 4 °C. Samples were taken at days 0, 3, and 7 for enumeration of survivors. On all leafy greens, 3% carvacrol films showed the best bactericidal effects against Salmonella. All 3 types of 3% carvacrol films reduced the Salmonella population by 5 log10 CFU/g at day 0 and 1.5% carvacrol films reduced Salmonella by 1 to 4 log10 CFU/g at day 7. The films with 3% cinnamaldehyde showed 0.5 to 3 log reductions on different leafy greens at day 7. The films with 0.5% and 1.5% cinnamaldehyde and 0.5% carvacrol also showed varied reductions on different types of leafy greens. Edible films were the most effective against Salmonella on Iceberg lettuce. This study demonstrates the potential of edible films incorporated with carvacrol and cinnamaldehyde to inactivate S. Newport on organic leafy greens.
Journal of Food Science 01/2014; 79(1):M61-6. · 1.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The prevalence of food allergy has increased in recent years and Korean pine vicilin is a potential food allergen. We have previously reported the crystallization of Korean pine vicilin purified from raw pine nut. Here we report the isolation of vicilin mRNA and the crystal structure of Korean pine vicilin at 2.40 Angstrom resolution. The overall structure of pine nut vicilin is similar to the structures of other 7S seed storage proteins and consists of an N-terminal domain and a C-terminal domain, each assumes a cupin fold and they are symmetrically related about a pseudo-dyad axis. Three vicilin molecules form a doughnut shaped trimer through head-to-tail association. Structure characterization of Korean pine nut vicilin unexpectedly showed that in its native trimeric state, the vicilin has three copper ligands. Sequence alignments suggested that the copper coordinating residues were conserved in winter squash, sesame, tomato, and several tree nuts, while they were not conserved in a number of legumes including peanut and soybean. Additional studies are needed to assess whether the copper coordinating property of vicilins has a biological function in the relevant plants. The nutritional value of this copper coordinating protein in tree nuts and other edible seeds may be worth further investigations.
Journal of Agricultural and Food Chemistry 12/2013; · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Infrared heating was recently used to develop a more efficient roasting technology than traditional hot air roasting. Therefore, in this study, we evaluated the shelf-life of almonds roasted with three different approaches, namely infrared (IR), sequential infrared and hot air (SIRHA) and regular hot air (HA). Nine medium roasted almond samples produced by the aforementioned heating methods were processed at three different temperatures (130, 140 and 150°C), packed in paper bags and then stored at 37°C for three, six or eight months. Shelf-life of the roasted almonds was determined by measuring the changes in colour, peroxide value, moisture content, water activity, volatile components and sensory quality. No significant difference was observed in moisture content and water activity among the almond samples processed with different roasting methods and stored under the same conditions. GC/MS analysis showed that aldehydes, alcohols, and pyrazines were the main volatile components of almonds. Aliphatic aldehydes such as hexanal, (E)-2-octenal, and nonanal were produced as off-odours during storage. Although the overall quality of roasted almonds produced with SIRHA and HA heating was similar during the first three months of storage, their peroxide value and concentration of aliphatic aldehydes differed significantly for different roasting methods and increased significantly in all roasted samples during storage. We postulate that hexanal and nonanal might be better indicators of the shelf life of roasted almonds than the current standard, peroxide value.
[Show abstract][Hide abstract] ABSTRACT: Profilins from numerous species are known to be allergens, including food allergens, such as peanut (Arachis hypogaea) allergen Ara h 5, and pollen allergens, such as birch allergen Bet v 2. Patients with pollen allergy can also cross-react to peanut. Structural characterization of allergens will allow a better understanding of the allergenicity of food allergens and their cross-reactivities. The three-dimensional structures of most known food allergens remain to be elucidated. Here, we report the first crystallographic study of a food allergen in the profilin family. The structure of peanut allergen Ara h 5 was determined and the resolution of the final refined structure was 1.1 angstrom. Structure alignment revealed that Ara h 5 is more similar to Bet v 2 than to Hev b 8 although sequence alignment suggested that Ara h 5 is more closely related to Hev b 8 than to Bet v 2, indicating that homology model-based prediction of IgE epitopes needs to be interpreted with caution.
Journal of Agricultural and Food Chemistry 01/2013; · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effectiveness of using infrared (IR) dry-peeling as an alternative process for peeling tomatoes without lye and water was studied. Compared to conventional lye peeling, IR dry-peeling using 30 s to 75 s heating time resulted in lower peeling loss (8.3%–13.2% vs. 12.9%–15.8%), thinner thickness of peeled-off skin (0.39–0.91 mm vs. 0.38–1.06 mm), and slightly firmer texture of peeled products (10.30–19.72 N vs. 9.42–13.73 N) while achieving a similar ease of peeling. IR heating increased the Young's Modulus of tomato peels and reduced the peel adhesiveness, indicating the tomato peels to loosen, become brittle, and crack more easily. Also, IR heating resulted in melting of cuticular membrane, collapse of several cellular layers, and severe degradation of cell wall structures, which in turn caused peel separation. These findings demonstrated the effectiveness of the novel IR dry-peeling process for tomatoes.
Development of a sustainable and non-chemical peeling technique for food processing industry is urgent. Currently, industrialized peeling methods such as hot lye or steam peeling are water- and energy-intensive operation and result in a large amount of waste effluent. Disposal of these wastewater containing high salinity and organic solids poses negative environmental footprints. Tomato processors have long been interested in pursuing a sustainable and non7 chemical peeling alternative in order to minimize waste effluent containing high salinity and organic loads and reduce the negative environmental impacts associated with conventional hot lye peeling. The emerging infrared dry-peeling technique offers a novel approach to eliminate the usage of chemicals and water in the peeling process while maintaining high quality peeled products. The study explored several crucial and fundamental aspects of developing infrared radiation heating technology as a sustainable tomato peeling method. The findings of this research provide scientific evidence of the benefits of infrared dry-peeling in comparison to the conventional hot lye peeling and have been used for the development of a pilot scale tomato infrared dry-peeling system.
[Show abstract][Hide abstract] ABSTRACT: In this study, frozen restructured whole apple and strawberry bars were manufactured by partial dehydration, using infrared (IR) heating, followed by restructuring and freezing. The objective of this investigation was to determine the effect of IR partial dehydration on the quality of restructured frozen apple and strawberry bars. Apples and strawberries were cut into 6‐mm‐thick slices before being dried at 50C to various moisture levels: from 89.0 to 75.3% for apples and from 92.7 to 75.3% (wet basis) for strawberries. IR drying reduced the moisture in the fruits quickly and caused partial degradation of total phenolic and vitamin C. However, the concentration of total phenolic and vitamin C significantly increased in the finished fruit bars due to the moisture removal. Both frozen apple and strawberry bars had desirable appearance and hardness when their water activities were below 0.97. PRACTICAL APPLICATIONSThis research demonstrated a new processing method for manufacturing healthful frozen fruit bars by using infrared partial dehydration of sliced fruit slices, followed by restructuring and freezing.
Journal of Food Processing and Preservation 01/2013; 37(5). · 0.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Wounding stresses resulting from fresh-cut processing are known to enhance the antioxidant capacity (AC) of carrots by increasing the synthesis of phenolic compounds. Ultraviolet-B (UV-B) light exposure further promotes the formation of phenolic compounds. Changes in total soluble phenolics (TSP), 5-O-caffeoylquinic acid (5-CQA), total carotenoids, AC, and phenylalanine ammonia-lyase (PAL) activity of five commercial fresh-cut carrot products (baby carrots, carrot stixx, shredded carrots, crinkle cut coins, and oblong chips) were evaluated after exposure to UV-B dosage at 141.4mJ/cm(2). Significant increases in TSP, AC and 5-CQA levels were observed for each sample following UV-B exposure. Increases in PAL activity were also observed in all carrot products, except crinkle cut coins. Total carotenoids of the carrot products were unchanged by UV-B exposure. Increases in AC levels corresponded directly with increases in the area/weight ratio (exposure area) of the fresh-cut carrot products.
[Show abstract][Hide abstract] ABSTRACT: Cold- and warm-water fish gelatin granules were exposed to ultraviolet-B radiation for doses up to 29.7 J/cm(2) . Solutions and films were prepared from the granules. Gel electrophoresis and refractive index were used to examine changes in molecular weight of the samples. Also, the gel strength and rheological properties of the solutions as well as the tensile and water vapor barrier properties of the films were characterized. SDS-PAGE and refractive index results indicated cross-linking of gelatin chains after exposure to radiation. Interestingly, UV-B treated samples displayed higher gel strengths, with cold- and warm-water fish gelatin having gel strength increases from 1.39 to 2.11 N and from 7.15 to 8.34 N, respectively. In addition, both gelatin samples exhibited an increase in viscosity for higher UV doses. For gelatin films, the cold-water fish gelatin samples made from irradiated granules showed greater tensile strength. In comparison, the warm-water gelatin films made from irradiated granules had lower tensile strength, but better water vapor barrier properties. This might be due to the UV induced cross-linking in warm-water gelatin that disrupted helical structures.
Journal of Food Science 08/2012; 77(9):E215-E223. · 1.78 Impact Factor