Qixin Zhong

Enhanced dispersibility and bioactivity of curcumin by encapsulation in casein nanocapsules.

In this work, a novel encapsulation method was studied by spray-drying a warm aqueous ethanol solution with codissolved sodium caseinate (NaCas) and lipophilic food components, using curcumin as a model compound. The encapsulation caused the loss of crystallinity of curcumin. After hydration of spray-dried powder and centrifugation, 137 μg/mL curcumin was dispersed in the transparent dispersion, which was 4 decades higher than its water solubility. Dynamic light scattering and atomic force microscopy results showed that curcumin-loaded casein nanoparticles were bigger than those of NaCas processed at encapsulation conditions but were smaller than those of the native NaCas. The increased nanoparticle dimension, together with fluorescence and FTIR spectroscopy results, suggested that curcumin was entrapped in the nanoparticle core through hydrophobic interactions. The curcumin encapsulated in casein nanoparticles had higher biological activity, as assessed by antioxidant and cell proliferation assays, than pristine curcumin, likely due to the improved dispersibility. This simple approach may be applied to encapsulate various lipophilic bioactive compounds.

Long-Term Stabilization of Foams and Emulsions with In-Situ Formed Microparticles from Hydrophobic Cellulose

We report a simple method to produce foams and emulsions of extraordinary stability by using hydrophobic cellulose microparticles, which are formed in situ by a liquid-liquid dispersion technique. The hydrophobic cellulose derivative, hypromellose phthalate (HP), was initially dissolved in water-miscible solvents such as acetone and ethanol/water mixtures. As these HP stock solutions were sheared in aqueous media, micron sized cellulose particles formed by the solvent attrition. We also designed and investigated an effective and simple process for making HP particles without any organic solvents, where both the solvent and antisolvent were aqueous buffer solutions at different pH. Consequently, the HP particles adsorbed onto the water/air or water/oil interfaces created during shear blending, resulting in highly stable foams or foam/emulsions. The formation of HP particles and their ability for short-term and long-term stabilization of interfaces strongly depended on the HP concentration in stock solutions, as well as the solvent chemistry of both stock solutions and continuous phase media. Some foams and emulsion samples formed in the presence of ca. 1 wt% HP were stable for months. This new class of nontoxic inexpensive cellulose-based particle stabilizers has the potential to substitute conventional synthetic surfactants, especially in edible, pharmaceutical and biodegradable products.

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.

Purification and characterization of a novel angiotensin-I converting enzyme (ACE) inhibitory peptide derived from enzymatic hydrolysate of grass carp protein.

Peptides inhibiting angiotensin-I converting enzyme (ACE, EC. 3.4.15.1) are possible cures of hypertension. Food-derived ACE-inhibitory peptides are particularly attractive because of reduced side effects. Previously, we reported ACE-inhibitory activity of grass carp protein hydrolysates. In this work, we report steps for purifying the ACE-inhibitory peptide from the hydrolysate and its biochemical properties. Following steps of ultrafiltration, macroporous adsorption resin, and two steps of reversed phase high performance liquid chromatography (RE-HPLC), a single Val-Ala-Pro (VAP) tripeptide was identified. The tripeptide with excellent ACE-inhibitory activity (IC(50) value of 0.00534 mg/mL) was a competitive ACE inhibitor and stable against both ACE and gastrointestinal enzymes of pepsin and chymotrypsin. This is the first report of food-derived VAP. The identified unique biochemical properties of VAP may enable the application of grass carp protein hydrolysates as a functional food for treatments of hypertension. The developed purification conditions also allow the production of VAP for pharmaceutical applications.

Nanodispersed eugenol has improved antimicrobial activity against Escherichia coli O157:H7 and Listeria monocytogenes in bovine milk.

There has been great interest in intervention strategies based on plant essential oils to control pathogens such as Escherichia coli O157:H7 and Listeria monocytogenes (Lm). However, the poor solubility of essential oils in water makes it difficult to disperse evenly in food matrices, impacting food quality and antimicrobial efficacy. In the present study, eugenol was dispersed in nanocapsules prepared with conjugates of whey protein isolate (WPI) and maltodextrin (MD, of various chain lengths). When eugenol was encapsulated in the conjugate made with MD40 at a WPI:MD mass ratio of 1:2, the nanodispersion was transparent and was characterized for antimicrobial efficacy against E. coli O157:H7 strains ATCC 43889 and 43894, and Lm strains Scott A and 101 in tryptic soy broth (TSB) and milk with different fat levels (whole, 2% reduced fat, and skim) at 35 or 32 °C, with comparison to the same levels of free eugenol. In TSB, antimicrobial efficacy of nanodispersed eugenol against E. coli O157:H7 and Lm was not improved, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values being 0.25 g/L higher than those of free eugenol. Free eugenol performed better in TSB because there was no interfering compound and the MIC and MBC were below the solubility of eugenol. In milk, nanodispersed eugenol was consistently observed to be more effective than free eugenol, with MIC and MBC values above the solubility limit of eugenol. The nanodispersed eugenol was speculated to be evenly distributed in food matrices at concentrations above the solubility limit and supplied the antimicrobial locally when the binding caused eugenol level below the inhibition requirement. Nanodispersed eugenol thus provides a novel approach for incorporation in foods to improve antimicrobial efficacy without changing turbidity.

Spray-Dried Zein Capsules with Coencapsulated Nisin and Thymol as Antimicrobial Delivery System for Enhanced Antilisterial Properties

Food grade antimicrobial delivery systems were studied in this work to enhance the effectiveness of antimicrobials inhibiting the growth of Listeria monocytogenes during storage. Corn zein was used as a carrier biopolymer and nisin and thymol as antimicrobials. Capsules produced by spray drying demonstrated different microstructures and release characteristics of nisin at different usage levels of thymol. Better release profiles were achieved when glycerol was additionally used to prepare capsules. Capsules showing sustained release of significant amounts of both antimicrobials effectively inhibited the growth of L. monocytogenes at pH 6.0 and 30 °C in the growth medium. Capsules were also more effective than free antimicrobials in inhibiting the growth of L. monocytogenes in 2% reduced fat milk at 25 °C. Our work showed that engineered delivery systems have promise to fulfill the antimicrobial effectiveness during shelf life storage of foods to ensure microbiological safety.

Antimicrobial properties of lauric arginate alone or in combination with essential oils in tryptic soy broth and 2% reduced fat milk

The objective of this study was to evaluate the antimicrobial activity of lauric arginate (LAE) when used alone or in combination with the essential oil (EO) from cinnamon leaf and EO components, thymol and eugenol. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) for Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella Enteritidis were determined by the microbroth dilution method in tryptic soy broth (TSB) at their optimal growth temperatures. The MIC for LAE was 11.8ppm against L. monocytogenes and E. coli O157:H7 and 23.5ppm against S. Enteritidis. Synergistic antimicrobial activity was demonstrated against L. monocytogenes with combinations of LAE and cinnamon leaf oil or eugenol, while the LAE and thymol combination showed additive antimicrobial activity. Conversely, antagonistic effects were shown for all combinations against E. coli O157:H7 and S. Enteritidis. Beef extract, at 2 or 5% w/v in TSB, showed no effects on the MIC and MBC of LAE against L. monocytogenes, while soluble starch from potato, at 2-10% w/v in TSB, increased the MIC and MBC. When tested in 2% reduced fat milk, significantly higher levels of antimicrobials were required to achieve similar inhibitions as in TSB. The growth curves of bacteria at 21°C followed similar trends as in TSB, showing synergism against the Gram-positive L. monocytogenes and antagonism against the two Gram-negative bacteria. Findings suggest that application of LAE could enhance microbial food safety, especially when used in combination with EO to inhibit the growth of Gram-positive bacteria.

Nanocapsular Dispersion of Thymol for Enhanced Dispersibility and Increased Antimicrobial Effectiveness against Escherichia coli O157:H7 and Listeria monocytogenes in Model Food Systems

ABSTRACT Essential oils are marginally soluble in water, making it challenging to evenly disperse them in foods and resulting in an increased tendency to bind with food lipids and proteins, resulting in lowered antimicrobial efficacy. In the current study, free and nano-dispersed (ND) thymol were compared in terms of their antimicrobial efficacies against Escherichia coli O157:H7 ATCC 43889 and 43894 and Listeria monocytogenes strains Scott A and 101 in apple cider and 2% reduced-fat milk. Apple cider was adjusted to pHs 5.5 and 3.5, and antimicrobial tests were performed at 0.3-, 0.5-, 0.75-, and 1.0-g/liter thymol concentrations at 35, 32, 25, and 4°C. Overall, 0.5 and 1.0 g/liter thymol in nano-dispersion and along with free thymol were inhibitory and bactericidal, respectively, against bacterial strains under all treatment conditions. At pH 5.5, 0.5 g/liter ND thymol was bacteriostatic against L. monocytogenes and E. coli for up to 48 h. At pH 3.5, L. monocytogenes controls did not survive beyond 12 h but E. coli survived and was inhibited by 0.5 g/liter ND thymol after 12 and 48 h in apple cider. E. coli strains were significantly sensitive to 4°C and pH 3.5 (P < 0.05). When bacteria were tested in 2% reduced-fat milk at 35 or 32°C, ND and free thymol demonstrated inhibition at 4.5 g/liter. Thus, the current technology seems to be promising and novel, enabling thymol-containing nano-dispersions that are not only transparent but also effective against pathogens in food applications, especially in clear beverages.

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 as Nanoreactors To Produce Whey Protein Nanoparticles with Enhanced Heat Stability by Sequential Enzymatic Cross-Linking and Thermal Pretreatments

Sequential enzymatic cross-linking and heat pretreatments were used in this work to enhance the heat stability of whey protein isolate (WPI). In the first route, WPI was cross-linked by transglutaminase before incorporation in microemulsions for heat pretreatment at 90 degrees C for 20 min. In the second route, WPI was cross-linked by transglutaminase within microemulsions before thermal pretreatment. Particles produced from the two routes were different in dimension and heat stability and were also affected by the ratio of WPI and enzyme and cross-linking duration. At appropriate conditions, for example, 10 h of cross-linking by transglutaminase equivalent to 5% mass of WPI using the first route, a 5% dispersion (pH 6.8 and 100 mM NaCl) of the produced nanoparticles remained clear after heating at 90 degrees C for 20 min. In comparison, nanoparticles produced by thermal pretreatment only in a microemulsion corresponded to a translucent, flowable dispersion, whereas native WPI formed a gel. This novel approach can be used to manufacture heat-stable whey protein ingredients for clear beverage applications.