Eric Karangwa

An Overview of Ultrasound-Assisted Food-Grade Nanoemulsions

Nanoemulsions are considered a very important tool for the delivery of bioactive compounds to the human body through food systems. Application of low-frequency ultrasound, a high-energy method, facilitates the homogenization and dispersion process under the influence of cavitation phenomena. Frequency, time, power, oil phase and aqueous phase are major parameters governing the cavitation process, concomitantly influencing the size and polydispersity index of nanoemulsion droplet. Additionally, hydrostatic pressure, gas content and temperature may also have profound effects on the process. Present review highlights the principles and production technology of high-intensity ultrasound and discusses the role of acoustic cavitation in the preparation of food-grade O/W nanoemulsions. Finally, it indicates technical hurdles, issues and future prospects of the technology.

Fabrication of polymeric nanocapsules from curcumin-loaded nanoemulsion templates by self-assembly.

In this study, biodegradable polymeric nanocapsules were prepared by sequential deposition of food-grade polyelectrolytes through the self-assembling process onto the oil (medium chain triglycerides) droplets enriched with curcumin (lipophilic bioactive compound). Optimum conditions were used to prepare ultrasound-assisted nanoemulsions stabilized by octenyl-succinic-anhydride (OSA)-modified starch. Negatively charged droplets (-39.4 ± 1.84 mV) of these nanoemulsions, having a diameter of 142.7 ± 0.85 nm were used as templates for the fabrication of nanocapsules. Concentrations of layer-forming cationic (chitosan) and anionic (carboxymethylcellulose) biopolymers were optimized based on the mean droplet/particle diameter (MDD/MPD), polydispersity index (PDI) and net charge on the droplets/capsules. Prepared core-shell structures or nanocapsules, having MPD of 159.85 ± 0.92 nm, were characterized by laser diffraction (DLS), ζ-potential (ZP), atomic force microscopy (AFM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Furthermore, physical stability of curcumin-loaded nanocapsules in suspension was determined and compared at different storage temperatures. This study may provide information regarding the formation of ultrasound-assisted polymeric nanocapsules from the nanoemulsion templates which could be helpful in the development of delivery systems for lipophilic food bioactives.

Contribution of beef base to aroma characteristics of beeflike process flavour assessed by descriptive sensory analysis and gas chromatography olfactometry and partial least squares regression

Descriptive sensory analysis and gas chromatography-mass spectrometry (GC-MS) analysis were conducted to investigate changes in aroma characteristics of beeflike process flavours (BPFs) prepared from enzymatically hydrolyzed beef (beef base) of different DH (degree of hydrolysis) with other ingredients. Five attributes (beefy, meaty, simulate, mouthful and roasted) were selected to assess BPFs. The results of descriptive sensory analysis confirmed that BPF2 from beef base of moderate DH 29.13% was strongest in beefy, meaty and simulate characteristics; BPF4 and BPF5 from beef base of higher DH (40.43% and 44.22%, respectively) were superior in mouthful and roasted attributes respectively; while BPF0 without beef base gave weaker odour for all attributes. Twenty six compounds from GC-MS were selected as specific compounds to represent beef odour based on their odour-active properties assessed by a detection frequency method of GC-O and correlation of their contents with sensory attributes intensity. Correlation analysis of molecular weight (MW) of peptides, odour-active compounds and sensory attributes through partial least squares regression (PLSR) further explained that beef base with DH of 29.13% was a desirable precursor for imparting aroma characteristics of beeflike process flavour.

Stable nanoparticles prepared by heating electrostatic complexes of whey protein isolate-dextran conjugate and chondroitin sulfate.

A simple and green method was developed for preparing the stable biopolymer nanoparticles with pH and salt resistance. The method involved the macromolecular crowding Maillard process and heat-induced gelation process. The conjugates of whey protein isolate (WPI) and dextran were produced by Maillard reaction. The nanoparticles were fabricated by heating electrostatic complexes of WPI-dextran conjugate and chondroitin sulfate (ChS) above the denaturation temperature and near the isoelectric point of WPI. Then, the nanoparticles were characterized by spectrophotometry, dynamic laser scattering, zeta potential, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. Results showed that the nanoparticles were stable in the pH range from 1.0 to 8.0 and in the presence of high salt concentration of 200 mM NaCl. WPI-dextran conjugate, WPI, and ChS were assembled into the nanoparticles with dextran conjugated to WPI/ChS shell and WPI/ChS core. The repulsive steric interactions, from both dextran covalently conjugated to WPI and ChS electrostatically interacted with WPI, were the major formation mechanism of the stable nanoparticles. As a nutrient model, lutein could be effectively encapsulated into the nanoparticles. Additionally, the nanoparticles exhibited a spherical shape and homogeneous size distribution regardless of lutein loading. The results suggested that the stable nanoparticles from proteins and strong polyelectrolyte polysaccharides would be used as a promising target delivery system for hydrophobic nutrients and drugs at physiological pH and salt conditions.

Effect of enzymatic hydrolysis with subsequent mild thermal oxidation of tallow on precursor formation and sensory profiles of beef flavours assessed by partial least squares regression.

Effects of different pretreatments of tallow on flavour precursor development and flavour profiles of beef flavours (BFs) were evaluated. Analysis of free fatty acids and volatiles of tallow by GC and GC-MS indicated that the enzymatic hydrolyzed-thermally oxidized tallow formed the most characteristic flavour precursors compared with others. The results of descriptive sensory analysis confirmed that beef flavour 4 from enzymatic hydrolyzed-thermally oxidized tallow had the strongest beefy, meaty and odour characteristics, followed by beef flavour 2 from oxidized tallow. Electronic nose data confirmed the accuracy of the sensory analysis results. The correlation analysis of 51 volatile compounds in tallow and sensory attributes of BFs showed that some compounds, especially aldehydes, made a significant contribution to sensory attributes. Correlation analysis of free fatty acids and sensory attributes through partial least squares regression (PLSR) confirmed that the moderate enzymatic hydrolysis-thermal oxidation pretreatment of tallow was necessary to achieve the characteristic beef flavour.

Cardioprotective effects of lipoic acid, quercetin and resveratrol on oxidative stress related to thyroid hormone alterations in long-term obesity ☆ ☆☆

This study investigated possible mechanisms for cardioprotective effects of lipoic acid (LA), quercetin (Q) and resveratrol (R) on oxidative stress related to thyroid hormone alterations in long-term obesity. Female C57BL/6 mice were fed on high-fat diet (HFD), HFD+LA, HFD+R, HFD+Q and normal diet for 26weeks. Body weight, blood pressure, thyroid hormones, oxidative stress markers, angiotensin converting enzyme (ACE), nitric oxide synthase (NOS) and ion pump activities were measured, and expression of cardiac genes was analyzed by real-time polymerase chain reaction. HFD induced marked increase (P<.05) in body weight, blood pressure and oxidative stress, while plasma triidothyronine levels reduced. ACE activity increased (P<.05) in HFD mice (0.69±0.225U/mg protein) compared with controls (0.28±0.114U/mg protein), HFD+LA (0.231±0.02U/mg protein) and HFD+Q (0.182±0.096U/mg protein) at 26weeks. Moreover, Na(+)/K(+)-ATPase and Ca(2+)-ATPase activities increased in HFD mice whereas NOS reduced. A 1.5-fold increase in TRα1 and reduction in expression of the deiodinase iodothyronine DIO1, threonine protein kinase and NOS3 as well as up-regulation of AT1α, ACE, ATP1B1, GSK3β and Cja1 genes also occurred in HFD mice. Conversely, LA, Q and R inhibited weight gain; reduced TRα1 expression as well as increased DIO1; reduced ACE activity and AT1α, ATP1B1 and Cja1 gene expression as well as inhibited GSK3β; increased total antioxidant capacity, GSH and catalase activity; and reduced blood pressure. In conclusion, LA, resveratrol and quercetin supplementation reduces obesity thereby restoring plasma thyroid hormone levels and attenuating oxidative stress in the heart and thus may have therapeutic potential in heart diseases.

Controlled formation of flavor compounds by preparation and application of Maillard reaction intermediate (MRI) derived from xylose and phenylalanine

An effective method for preparing Maillard reaction intermediate (MRI) derived from xylose (Xyl) and phenylalanine (Phe) in aqueous medium was proposed in this study. Maillard reaction products (MRPs) were prepared by Maillard reaction performed under stepwise increase of temperature, and cysteine was added as an indicator. The formation conditions of MRI generated from Xyl and Phe were determined through MRPs browning analysis. The MRI prepared under the determined formation conditions was purified using RP-HPLC, and characterized using UPLC-ESI-mass spectra and NMR. The molecular mass (297.1 Da) and formula (C14H19O6N) were proposed. The capacity of flavor formation of heated MRI was evaluated through GC-MS. Results showed that flavor compounds were formed during the subsequent heat treatment, and MRI could be a great potential substitute of MRPs in preparation of fresh process flavors. Therefore, controlled formation of process flavors could be achieved by preparation and application of MRI.

Correlating Enzymatic browning inhibition and antioxidant ability of Maillard reaction products derived from different amino acids

BACKGROUND Up to now, only limited research on enzymatic browning inhibition capacity (BIC) of Maillard reaction products (MRPs) has been reported and there are still no overall and systematic researches on MRPs derived from different amino acids. In the present study, BIC and antioxidant capacity, including 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and Fe2+ reducing power activity, of the MRPs derived from 12 different amino acids and three reducing sugars were investigated. RESULTS The MRPs of cysteine (Cys), cystine, arginine (Arg) and histidine (His) showed higher BIC compared to other amino acids. Lysine (Lys)-MRPs showed the highest absorbance value at 420 nm (A420 ) but very limited BIC, whereas Cys-MRPs, showed the highest BIC and the lowest A420 . The A420 can roughly reflect the trend of BIC of MRPs from different amino acids, except Cys and Lys. MRPs from tyrosine (Tyr) showed the most potent antioxidant capacity but very limited BIC, whereas Cys-MRPs showed both higher antioxidant capacity and BIC compared to other amino acids. Partial least squares regression analysis showed positive and significant correlation between BIC and Fe2+ reducing power of MRPs from 12 amino acids with glucose or fructose, except Lys, Cys and Tyr. The suitable pH for generating efficient browning inhibition compounds varies depending on different amino acids: acidic pH was favorable for Cys, whereas neutral and alkaline pH were suitable for His and Arg, respectively. Increasing both heating temperature and time over a certain range could improve the BIC of MRPs of Cys, His and Arg, whereas any further increase deteriorates their browning inhibition efficiencies. CONCLUSION The types of amino acid, initial pH, temperature and time of the Maillard reaction were found to greatly influence the BIC and antioxidant capacity of the resulting MRPs. There is no clear relationship between BIC and the antioxidant capacity of MRPs when reactant type and processing parameters of the Maillard reaction are considered as variables.

Direct determination of 3-chloro-1,2-propanediol esters in beef flavoring products by ultra-performance liquid chromatography tandem quadrupole mass spectrometry

A sensitive ultra-performance liquid chromatography tandem quadrupole mass spectrometry (UPLC-TQ-MS) method coupled with amino solid-phase extraction was developed for the direct determination of 3-chloro-1,2-propanediol (3-MCPD) esters which were firstly detected in the natural beef flavoring products. The analyzed 3-MCPD esters in this paper contain three monoesters and six diesters. The validation data indicated that the proposed method provided good linearity, repeatability and sensitivity. The method showed a good linearity within the range of 40–200 μg kg−1 for monoesters and 20–100 μg kg−1 for diesters with the determination coefficients (R2) ranging from 0.9912 to 0.9993. The limits of detection (LODs) for monoesters and diesters of 3-MCPD were in the range of 0.04–5.0 μg kg−1 and 0.13–16.0 μg kg−1, respectively. The method accuracy was confirmed by higher sample recovery which ranged from 80.5 to 113.7%. The repeatability expressed as intra-day precision ranged from 0.8 to 9.9% and inter-day precision varied from 2.8 to 13.8%. The validated method was successfully applied for determination of 3-MCPD esters in beef flavoring products.

Mechanism of Formation and Stabilization of Nanoparticles Produced by Heating Electrostatic Complexes of WPI–Dextran Conjugate and Chondroitin Sulfate

Protein conformational changes were demonstrated in biopolymer nanoparticles, and molecular forces were studied to elucidate the formation and stabilization mechanism of biopolymer nanoparticles. The biopolymer nanoparticles were prepared by heating electrostatic complexes of whey protein isolate (WPI)-dextran conjugate (WD) and chondroitin sulfate (ChS) above the denaturation temperature and near the isoelectric point of WPI. The internal characteristics of biopolymer nanoparticles were analyzed by several spectroscopic techniques. Results showed that grafted dextran significantly (p < 0.05) prevented the formation of large aggregates of WD dispersion during heat treatment. However, heat treatment slightly induced the hydrophobicity changes of the microenvironment around fluorophores of WD. ChS electrostatic interaction with WD changed the fluorescence intensity of WD regardless of heat treatment. Far-UV circular dichroism (CD) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopies confirmed that glycosylation and ionic polysaccharide did not significantly cause protein conformational changes in WD and ChS (WDC) during heat treatment. In addition, hydrophobic bonds were the major molecular force for the formation and stabilization of biopolymer nanoparticles. However, hydrogen bonds slightly influenced their formation and stabilization. Ionic bonds only promoted the formation of biopolymer nanoparticles, while disulfide bonds partly contributed to their stability. This work will be beneficial to understand protein conformational changes and molecular forces in biopolymer nanoparticles, and to prepare the stable biopolymer nanoparticles from heating electrostatic complexes of native or glycosylated protein and polysaccharide.