Inactivation of Escherichia coli K12 on raw almonds using supercritical carbon dioxide and thyme oil.

Raw almonds could be contaminated by pathogens, but the current pasteurization practice using propylene oxide in the U.S. has flammability and carcinogenicity concerns. Supercritical carbon dioxide (scCO2) is a water-free technology and is a solvent of essential oils that are effective antimicrobial preservatives. The objective of this study was to investigate the possibility of combining scCO2 and thyme oil (TO) to reduce Escherichia coli K12 inoculated on raw almonds. Raw almonds inoculated with ∼6 log CFU/g E. coli K12 were batch-treated with scCO2 alone or the combination of presoaking in pure TO followed by scCO2 treatments at different combinations of temperature, pressure, and duration. Compared to scCO2 alone treatments, the combination of TO and scCO2 treatments significantly improved the disinfection effectiveness. Temperature had the most significant effect on the log reduction. At 70 °C, the log reduction by the combination treatment was over 4-log CFU/g and the maximum reduction was 5.16 log CFU/g. The findings suggest that the combination of TO and scCO2 may be a potential water-free technology to meet the requirement of over 4-log reduction of target microorganism for almond and other tree nut products.

Enhancing bioaccessibility of resveratrol by loading in natural porous starch microparticles.

Resveratrol (RSV) is a lipophilic polyphenol susceptible to photo- and thermal degradation, and strategies are to be studied to enable its distribution in food matrices, prevent its degradation during storage, and increase its bioaccessibility during digestion. In this study, the porous matrix of natural starch, in the form of milled freeze-dried potato microparticles (FDPMs), was studied as an absorbent to load RSV. The binary solvent of ethanol and polyethylene glycol 400 (40:60 v/v) was used to dissolve 30% w/v RSV for diffusion into FDPMs. After ethanol was evaporated, the loading capacity was 112 mg RSV/g FDPMs and was maintained at 104 mg RSV/g FDPMs (92.9% retention) after 110-day ambient storage. The RSV stability under UV irradiation at 253 nm was improved by 32% due to shielding effect of FDPMs, and the ferric reducing power was 25% higher than the pristine RSV. The release of RSV in FDPMs was significantly higher than pristine RSV during simulated gastric and intestinal digestions (82.3% vs 51.4% bioaccessibility). The increased reducing power and bioaccessibility were supported by the amorphous state of RSV in FDPMs. The present study illustrates the potential of porous vegetable microparticles as natural matrices to load lipophilic bioactive compounds in functional foods.

Natural Products in the Prevention of Metabolic Diseases: Lessons Learned from the 20th KAST Frontier Scientists Workshop.

The incidence of metabolic and chronic diseases including cancer, obesity, inflammation-related diseases sharply increased in the 21st century. Major underlying causes for these diseases are inflammation and oxidative stress. Accordingly, natural products and their bioactive components are obvious therapeutic agents for these diseases, given their antioxidant and anti-inflammatory properties. Research in this area has been significantly expanded to include chemical identification of these compounds using advanced analytical techniques, determining their mechanism of action, food fortification and supplement development, and enhancing their bioavailability and bioactivity using nanotechnology. These timely topics were discussed at the 20th Frontier Scientists Workshop sponsored by the Korean Academy of Science and Technology, held at the University of Hawaii at Manoa on 23 November 2019. Scientists from South Korea and the U.S. shared their recent research under the overarching theme of Bioactive Compounds, Nanoparticles, and Disease Prevention. This review summarizes presentations at the workshop to provide current knowledge of the role of natural products in the prevention and treatment of metabolic diseases.

Gluconic acid as a chelator to improve clarity of skim milk powder dispersions at pH 3.0.

Clear acidic protein beverages have a niche market. Acidification of skim milk powder (SMP) dispersions to pH 3.0 using citric acid (CA) lowers turbidity but the dispersion remains translucent. The present study aimed at comparing physicochemical properties of 5% w/v SMP dispersions acidified to pH 3.0 using chelating gluconic acid (GA) and CA and non-chelating hydrochloric acid. GA was the most effective in reducing the dispersion turbidity to 394 NTU at pH 3.0, which was further reduced to 248 NTU after heating at 90 °C for 2 min resulting in transparent dispersions. The better chelating ability of GA than CA was supported by the higher extent of dissolved CCP in serum phase. The aggregation of dissociated caseins was not observed for the GA treatment based on transmission electron microscopy. The findings from this study may be used to produce clear casein-based protein beverages.

Encapsulation of vitamin D3 in gum arabic to enhance bioavailability and stability for beverage applications.

Delivery of vitamin D3 (VD3 ) in foods should exhibit desirable physicochemical characteristics and improves absorption. In this study, gum arabic (GA) was investigated as a VD3 carrier to encapsulate VD3 . VD3 dissolved in 5 mL ethanol corresponding to 0.3 to 6.0% mass of GA, was blended in 5.0% w/v GA solution, followed by freeze drying. The encapsulation efficiency decreased while loading capacity increased with an increased amount of VD3 . At the highest VD3 level, the loading capacity (3.47%) was the highest, and the encapsulation efficiency (61.24%) was satisfactory, and the treatment was further studied. The magnitude of negative zeta-potential increased from 3.1 to 31.0 mV at pH 2.0 to 7.4. During the 100-day storage at 3 °C of capsules reconstituted at pH 2.0 to 7.4, the hydrodynamic diameter decreased at all pH conditions, most evident for reduction to 81.3 nm at pH 7.4, and no precipitation was observed, indicating the significance of steric repulsion on capsule stability. Bioaccessibility of VD3 in capsules (95.76%) was significantly higher than the nonencapsulated VD3 (68.98%). The in vivo pharmacokinetic study in Sprague-Dawley rats after a single-dose of 300 µg VD3 showed the area-under-curve of serum 25(OHD) level in 48 hr of the encapsulation treatment was 4.32-fold of the nonencapsulated VD3 and more than twice higher than the VD3 -GA physical mixture. During 2-week supplementation of 60 µg VD3 /d, rats receiving capsules or physical mixture had 25(OH)D levels of at least 81 ng/mL higher than that of the nonencapsulated VD3 group. The studied encapsulation system holds great potential as a value-added ingredient to supplement VD3 in beverages with a wide pH range. PRACTICAL APPLICATION: The findings of this study demonstrated the improved dispersion stability and absorption of vitamin D3 after encapsulation in gum arabic. The capsules exhibited good dispersion stability across a pH range between 2.0 and 7.4, showing potential application in beverages. Furthermore, the enhanced absorption of VD3 after encapsulation highlights the nutritional benefits of the studied encapsulation system.

Physical and antimicrobial properties of neutral nanoemulsions self-assembled from alkaline thyme oil and sodium caseinate mixtures.

The objective of this study was to utilize self-assembly properties of sodium caseinate to prepare nanoemulsions after neutralization of alkaline mixtures with 2% w/v caseinate and up to 3% v/v thyme oil. The encapsulation efficiency was >90% at a surfactant-to-oil ratio of up to 1:1.25. The nanoemulsions had structures smaller than 75 nm according to atomic force microscopy and stable hydrodynamic diameters of ~90-200 nm during 20-day storage at room temperature. When tested against Escherichia coli O157:H7 ATCC 43895 and Staphylococcus aureus ATCC 25923 in tryptic soy broth and milk, the encapsulated thyme oil was more active than free thyme oil. Additionally, S. aureus was more resistant than E. coli O157:H7, requiring 11.7 and 5 g/L of encapsulated thyme oil, respectively, to completely deactivate bacteria in milk in 4 h. The findings suggest that thyme oil nanoemulsions can be potentially used as natural preservatives to improve food safety.

Formulation and Characterization of Quercetin-loaded Oil in Water Nanoemulsion and Evaluation of Hypocholesterolemic Activity in Rats.

Due to poor water solubility and high susceptibility to chemical degradation, the applications of quercetin have been limited. This study investigated the effects of pH on the formation of quercetin-loaded nanoemulsion (NQ) and compared the hypocholesterolemic activity between quercetin and NQ to utilize the quercetin as functional food ingredient. NQ particle size exhibited a range of 207⁻289 nm with polydispersity index range (<0.47). The encapsulation efficiency increased stepwise from 56 to 92% as the pH increased from 4.0 to 9.0. Good stability of NQ was achieved in the pH range of 6.5⁻9.0 during 3-month storage at 21 and 37 °C. NQ displayed higher efficacy in reducing serum and hepatic cholesterol levels and increasing the release of bile acid into feces in rats fed high-cholesterol diet, compared to quercetin alone. NQ upregulated hepatic gene expression involved in bile acid synthesis and cholesterol efflux, such as cholesterol 7 alpha-hydroxylase (CYP7A1), liver X receptor alpha (LXRα), ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette sub-family G member 1 (ABCG1). These results suggest at least partial involvement of hepatic bile acid synthesis and fecal cholesterol excretion in nanoemulsion quercetin-mediated beneficial effect on lipid abnormalities.

Core-Shell Nanoencapsulation of α-Tocopherol by Blending Sodium Oleate and Rebaudioside A: Preparation, Characterization, and Antioxidant Activity.

Nanoencapsulation of α-tocopherol (α-TOC) by blending sodium oleate (NaOl) and rebaudioside A (RebA) was successfully prepared by self-assembly method under mild conditions. The optimized nanoemulsion showed the loading capacity of α-TOC was 30 wt% of sodium oleate. FTIR analysis suggested that hydrogen bonds and hydrophobic interactions were the major forces in α-TOC-NaOl/RebA complexes that were spherical and possessed well-distinguishable core-shell structures. The freeze-dried α-TOC-NaOl/RebA complexes had great stability under ambient conditions. The release profile of α-TOC showed a first-order kinetics reaching around 67.9% after 90 h at 25 °C. Nanoencapsulation improved dispersibility and greatly increased the antioxidant activity of α-TOC. Therefore, the stable α-TOC-NaOl/RebA core-shell complexes prepared from "generally recognized as safe" (GRAS) ingredients have great potential to supplement α-TOC in food and cosmetic products.

Nanoemulsions of thymol and eugenol co-emulsified by lauric arginate and lecithin.

Lauric arginate (LAE) is a cationic surfactant with excellent antimicrobial activities. To incorporate essential oil components (EOCs) in aqueous systems, properties of EOC nanoemulsions prepared with a LAE and lecithin mixture were studied. The LAE-lecithin mixture resulted in stable translucent nanoemulsions of thymol and eugenol with spherical droplets smaller than 100nm, contrasting with the turbid emulsions prepared with individual emulsifiers. Zeta-potential data suggested the formation of LAE-lecithin complexes probably through hydrophobic interaction. Negligible difference was observed for antimicrobial activities of nanoemulsions and LAE in tryptic soy broth. In 2% reduced fat milk, nanoemulsions showed similar antilisterial activities compared to free LAE in inhibiting Listeria monocytogenes, but was less effective against Escherichia coli O157:H7 than free LAE, which was correlated with the availability of LAE as observed in release kinetics. Therefore, mixing LAE with lecithin improved the physical properties of EOC nanoemulsions but did not improve antimicrobial activities, especially against Gram-negative bacteria.

Antimicrobial properties of microemulsions formulated with essential oils, soybean oil, and Tween 80.

It was previously found that blending soybean oil with cinnamon bark oil (CBO), eugenol or thyme oil, Tween 80, and equal masses of water and propylene glycol could be used to prepare microemulsions. In the present study, the objective was to determine the antimicrobial activity of the microemulsions in tryptic soy broth (TSB) and 2% reduced fat milk. In TSB, the minimum inhibitory concentration (MIC) of CBO solubilized in microemulsions was up to 625 ppm against cocktails of Listeria monocytogenes, Salmonella enterica or Escherichia coli O157:H7, which was equal to or higher in concentration than free CBO dissolved in ethanol. However, MICs of eugenol or thyme oil in microemulsions were much higher than that of free antimicrobials. Therefore, microemulsions of CBO were chosen to do further study. Inactivation curves of L. monocytogenes or E. coli O157:H7 in TSB or 2% reduced fat milk were tested and fitted using the Weibull model. In TSB, a gradual decrease in cell viability of L. monocytogenes and E. coli O157:H7 was observed with the microemulsion treatments at 625 ppm CBO, which was in contrast to the more rapid and greater inactivation by free CBO. Gradual inactivation of L. monocytogenes in 2% reduced fat milk was also observed in the treatment with 10,000 ppm free or microemulsified CBO. When fitted using the Weibull model, the predicted time to obtain a 3-log decrease of L. monocytogenes and E. coli O157:H7 in TSB or 2% reduced fat milk increased with an increased amount of soybean oil in microemulsions. Additionally, increasing the amount of Tween 80 in mixtures with different mass ratios of Tween 80 and essential oils significantly decreased the log reductions of L. monocytogenes in TSB. Our study showed that microemulsions can be used to dissolve EOs and control the rate of inactivating bacteria, but the composition of microemulsions is to be carefully chosen to minimize the reduction of antimicrobial activities.

Effect of alginate coatings with cinnamon bark oil and soybean oil on quality and microbiological safety of cantaloupe.

The quality and microbiological safety of cantaloupes can potentially be improved using antimicrobial coatings that are able to maintain effectiveness throughout storage. The objective of this work was to study the effect of coating mixtures containing sodium alginate and cinnamon bark oil (CBO) on the quality of cantaloupes and the survival of inoculated bacterial pathogens and naturally occurring yeasts and molds during ambient storage at 21 °C. Cantaloupes were dipped in mixtures containing 1% sodium alginate with or without 2% CBO and 0 or 0.5% soybean oil (SBO). Weight loss and total soluble solids content of the flesh were not significantly different among coating treatments. However, changes in color and firmness of cantaloupes were delayed to different extents after coating, most significantly for the CBO+SBO treatment. Cocktails of Salmonella enterica, Escherichia coli O157:H7, or Listeria monocytogenes inoculated on cantaloupes were reduced to the detection limit (1.3 log CFU/cm(2)) and completely inhibited during the 15-day storage by the CBO+SBO treatment, while L. monocytogenes and S. enterica reached populations of 2.9 log CFU/cm(2) and 2.4 log CFU/cm(2), respectively, on cantaloupes coated with CBO alone. Antimicrobial coatings, especially with SBO, also reduced yeast and mold counts on cantaloupes by 2.6 log CFU/cm(2). SBO improved the retention of CBO during storage suggesting it is related to the enhancement of quality and microbiological safety. Findings demonstrated the potential of the antimicrobial coating system studied to improve microbiological safety and quality of cantaloupes.

Antimicrobial activity of thyme oil co-nanoemulsified with sodium caseinate and lecithin.

Emulsions of essential oils are investigated as potential intervention strategies to improve food safety and are preferably prepared from generally-recognized-as-safe emulsifiers. Stable thyme oil nanoemulsions can be prepared using combinations of sodium caseinate (NaCas) and soy lecithin. The objective of the present research was to study the antimicrobial activity of these nanoemulsions and understand the impacts of emulsifier concentrations. 10 g/L thyme oil was emulsified using combinations of (A) 4% w/v NaCas and 0.5% w/v lecithin or (B) 2% w/v NaCas and 0.25% w/v lecithin by high shear homogenization. Combination A resulted in a transparent emulsion with a mean droplet diameter of 82.5 nm, while it was turbid for the Combination B with an average diameter of 125.5 nm. Nanoemulsified thyme oil exhibited quicker initial reductions of bacteria than free thyme oil in tryptic soy broth (TSB) and 2% reduced fat milk at 21 °C, due to the improved dispersibility of thyme oil. In TSB with 0.3 g/L thyme oil, it took less than 4 and 8 h for two nanoemulsions and free oil, respectively, to reduce Escherichia coli O157:H7 and Listeria monocytogenes to be below the detection limit. The emulsified thyme oil also demonstrated more significant reductions of bacteria initially (4 and 8 h) in 2% reduced fat milk than free thyme oil. Especially, with 4 g/L thyme oil, the nanoemulsion prepared with Combination A reduced L. monocytogenes to be below the detection limit after 72 h, while the free thyme oil treatment was only bacteriostatic and the turbid nanoemulsion treatment with Combination B resulted in about 1 log CFU/mL reduction. However, E. coli O157:H7 treated with 3 g/L emulsified thyme oil and Salmonella Enteritidis treated with 4 g/L emulsified thyme oil recovered to a higher extent in milk than free thyme oil treatments. The increased concentration of emulsifiers in Combination A apparently reduced the antimicrobials available to alter bacteria membrane permeability as tested by the crystal violet assay at low antimicrobial concentrations and short time (1 h). The findings suggest that nanoemulsions can be potentially used to incorporate thyme oil for use as antimicrobial preservatives in foods.

Casein/pectin nanocomplexes as potential oral delivery vehicles.

Delivery systems prepared with natural biopolymers are of particular interests for applications in food, pharmaceutics and biomedicine. In this study, nanocomplex particles of sodium caseinate (NaCas) and pectin were fabricated and investigated as potential oral delivery vehicles. Nanocomplexes were prepared with three mass ratios of NaCas/pectin by acidification using glucono-δ-lactone and thermal treatment. NaCas/pectin at 1:1 mass ratio resulted in dispersions with the lowest turbidity and the smallest and most uniform nanocomplexes. Thermal treatment at 85 °C for 30 min facilitated the formation of stable, compact, and spherical nanocomplexes. Heating not only greatly increased the yield of nanocomplexes but also significantly improved the encapsulation capability of rutin studied as a model compound. Pectin in nanocomplexes delayed the hydrolysis of NaCas by pepsin at gastric conditions and enabled the controlled release of most rutin in simulated intestinal conditions. The nanocomplexes based on food-sourced biopolymers have promising features for oral delivery of nutrients and medicines.

Microemulsions based on a sunflower lecithin-Tween 20 blend have high capacity for dissolving peppermint oil and stabilizing coenzyme Q10.

The objectives of the present study were to improve the capability of microemulsions to dissolve peppermint oil by blending sunflower lecithin with Tween 20 and to study the possibility of codelivering lipophilic bioactive compounds. The oil loading in microemulsions with 20% (w/w) Tween 20 increased from 3% (w/w) to 20% (w/w) upon gradual supplementation of 6% (w/w) lecithin. All microemulsions had particles of <12 nm that did not change over 70 d of storage at 21 °C. They had relatively low Newtonian viscosities and were physically and chemically stable after 50-200-fold dilution in water, resulting from similar hydrophile-lipophile-balance values of the surfactant mixture and peppermint oil. Furthermore, the microemulsions were capable of dissolving coenzyme Q10 and preventing its degradation at UV 302 nm, more significant for the microemulsion with lecithin. Therefore, natural surfactant lecithin can reduce the use of synthetic Tween 20 to dissolve peppermint oil and protect the degradation of dissolved lipophilic bioactive components in transparent products.

Thermal and UV stability of ß-carotene dissolved in peppermint oil microemulsified by sunflower lecithin and Tween 20 blend.

Microemulsions are suitable for simultaneous delivery of flavour oils and lipophilic bioactive compounds in transparent beverages. In the present study, the feasibility of delivering ß-carotene in microemulsions formulated with peppermint oil and a blend of Tween® 20 and various amounts of sunflower lecithin was investigated. The poorly water- and oil-soluble ß-carotene was dissolved in the transparent microemulsions that had particles smaller than 10nm and were stable during ambient storage for 65 d. The inclusion of ß-carotene did not change the flow-behaviour and Newtonian viscosity. The degradation of ß-carotene in microemulsions during ambient storage, ultraviolet radiation, and thermal treatments at 60 and 80 °C followed first order kinetics and was greatly suppressed when compared to the solution control. The antioxidant potential of peppermint oil and a greater content of lecithin in microemulsions enabled the better protection of ß-carotene. The studied microemulsions may find various applications in manufacturing transparent beverages.

Thyme oil nanoemulsions coemulsified by sodium caseinate and lecithin.

Many nanoemulsions are currently formulated with synthetic surfactants. The objective of the present work was to study the possibility of blending sodium caseinate (NaCas) and lecithin to prepare transparent thyme oil nanoemulsions. Thyme oil was emulsified using NaCas and soy lecithin individually or in combination at neutral pH by shear homogenization. The surfactant combination improved the oil content in transparent/translucent nanoemulsions, from 1.0% to 2.5% w/v for 5% NaCas with and without 1% lecithin, respectively. Nanoemulsions prepared with the NaCas-lecithin blend had hydrodynamic diameters smaller than 100 nm and had significantly smaller and more narrowly distributed droplets than those prepared with NaCas or lecithin alone. Particle dimension and protein surface load data suggested the coadsorption of both surfactants on oil droplets. These characteristics of nanoemulsions minimized destabilization mechanisms of creaming, coalescence, and Ostwald ripening, as evidenced by no significant changes in appearance and particle dimension after 120-day storage at 21 °C.

Formulating essential oil microemulsions as washing solutions for organic fresh produce production.

Applications of plant-derived organic essential oils (EOs) as antimicrobials for post-harvest produce operations are limited by their low water solubility. To dissolve EOs in water, microemulsions were studied using two surfactants permitted for organic production, sucrose octanoate ester (SOE) and soy lecithin that were mixed at various mass ratios before dilution with water to 40% w/w. EOs were then mixed with the surfactant solution by hand shaking. Based on visual transparency, intermediate lecithin:SOE mass ratios favoured the formation of microemulsions, e.g., up to 4.0% clove bud oil at ratios of 2:8 and 3:7, and 4.0% cinnamon bark oil and 3.0% thyme oil at ratios of 2:8 and 1:9, respectively. Microemulsions with intermediate lecithin:SOE mass ratios had a relatively low viscosity and better ability to wet fresh produce surfaces. The microemulsions established in this work may be used as washing solutions to enhance the microbial safety of organic fresh produce.

Self-emulsification of alkaline-dissolved clove bud oil by whey protein, gum arabic, lecithin, and their combinations.

Low-cost emulsification technologies using food ingredients are critical to various applications. In the present study, a novel self-emulsification technique was studied to prepare clove bud oil (CBO) emulsions, without specialized equipment or organic solvents. CBO was first dissolved in hot alkaline solutions, added at 1% v/v into neutral solutions with 1% w/v emulsifier composed of whey protein concentrate (WPC), gum arabic, lecithin, or their equal mass mixtures, and adjusted to pH 7.0. The self-emulsification process did not affect UV-vis absorption spectrum, reversed-phase HPLC chromatogram, or antimicrobial activity of CBO against Escherichia coli O157:H7, Listeria monocytogenes Scott A, and Salmonella Enteritidis. The entrapment efficiency after extraction by petroleum ether was determined to be about 80%. Most emulsions were stable during 7 days of storage. Emulsions prepared with WPC had smaller particles, whereas emulsions prepared with emulsifier mixtures had more stable particle dimensions. The studied self-emulsification technique may find numerous applications in the preparation of low-cost food emulsions.

Blending lecithin and gelatin improves the formation of thymol nanodispersions.

Delivery systems of lipophilic antimicrobials such as thymol prepared with generally recognized-as-safe ingredients are needed to enhance the microbiological safety of low-acid (pH > 4.6) foods. Nanodispersions with particle diameters below 100 nm are particularly demanded because of the low turbidity and physical stability. In this study, thymol dispersions were prepared by gelatin and soy lecithin on an individual basis or in combination. Dispersions prepared with the lecithin-gelatin blend were translucent and stable at pH 5.0-8.0, contrasting with turbid and unstable dispersions when the emulsifiers were used individually. The synergistic surface activity of gelatin and lecithin was due to complex formation that effectively prevented particle size change due to coalescence and Ostwald ripening. Electrostatic interactions were observed to be the colloidal force responsible for preventing particle aggregation. The studied generally recognized-as-safe nanodispersions have great potential to deliver lipophilic antimicrobials such as thymol in low-acid foods to enhance food safety.

Thymol nanoencapsulated by sodium caseinate: physical and antilisterial properties.

In this work, thymol was encapsulated in sodium caseinate using high shear homogenization. The transparent dispersion at neutral pH was stable for 30 days at room temperature as determined by dynamic light scattering and atomic force microscopy, which agreed with high ζ potential of nanoparticles. The slightly decreased particle dimension during storage indicates the absence of Ostwald ripening. When molecular binding was studied by fluorescence spectroscopy, thymol was observed to bind with tyrosine and possibly other amino acid residues away from tryptophan of caseins. At pH 4.6 (isoelectric point of caseins), the stabilization of thymol nanoparticles against aggregation was enabled by soluble soybean polysaccharide, resulting from the combined electrostatic and steric repulsions. The encapsulated thymol showed the significantly improved antilisterial activity in milk with different fat levels when compared to thymol crystals, resulting from the quicker mixing and increased solubility in the milk serum. The transparent thymol nanodispersions have promising applications to improve microbiological safety and quality of foods.