Surface-enhanced Raman spectroscopy of soft-landed polyatomic ions and molecules

Surface-enhanced Raman spectroscopy (SERS) was used to detect and characterize polyatomic cations and molecules that were electrosprayed into the gas phase and soft-landed in vacuum on plasma-treated silver substrates. Organic dyes such as crystal violet and Rhodamine B, the nucleobase cytosine, and nucleosides cytidine and 2'-deoxycytidine were immobilized by soft landing on plasma-treated metal surfaces at kinetic energies ranging from near thermal to 200 eV. While enhancing Raman scattering 10(5)-10(6)-fold, the metal surface effectively quenches the fluorescence that does not interfere with the Raman spectra. SERS spectra from submonolayer amounts of soft-landed compounds were sufficiently intense and reproducible to allow identification of Raman active vibrational modes for structure assignment. Soft-landed species appear to be microsolvated on the surface and bound via ion pairing or pi-complexation to the Ag atoms and ions in the surface oxide layer. Comparison of spectra from soft-landed and solution samples indicates that the molecules survive soft landing without significant chemical damage even when they strike the surface at hyperthermal collision energies.     

Low-fat set yogurt made from milk subjected to combinations of high hydrostatic pressure and thermal processing

The combined use of high hydrostatic pressure (300 to 676 MPa, 5 min) and thermal treatment (85 degrees C, 30 min) in milk for the manufacture of low-fat yogurt was studied. The objective was to reduce syneresis and improve the rheological properties of yogurt, reducing the need for thickeners and stabilizers. The use of high hydrostatic pressure alone, or after thermal treatment, reduced the lightness and increased the viscosity of skim milk. However, milk recovered its initial lightness and viscosity when thermal treatment was applied after high hydrostatic pressure. The MALDI-TOF spectra of skim milk presented monomers of whey proteins after a treatment of 676 MPa for 5 min. Yogurts made from skim milk subjected to 400 to 500 MPa and thermal treatment showed increased yield stress, resistance to normal penetration, and elastic modulus, while having reduced syneresis when compared to yogurts from thermally treated or raw milks. The combined use of thermal treatment and high hydrostatic pressure assures extensive whey protein denaturation and casein micelle disruption, respectively. Although reaggregation of casein submicelles occurs during fermentation, the net effect of the combined HHP and thermal treatment is the improvement of yogurt yield stress and reduction of syneresis.     

Ligand and Flavor Binding Functional Properties of β-Lactoglobulin in the Molten Globule State Induced by High Pressure

ABSTRACT: β-lactoglobulin (β-LG) in the molten globule state induced by high hydrostatic pressure (HHP) at 500 MPa and 50 °C for 32 min exhibited a significant decrease in affinity for retinol and a significant increase in affinity for cis-parinaric acid (CPA) and 1-anilino-naphthalene-8-sulfonate (ANS) compared to native β-LG. The number of β-LG binding sites for retinol and CPA significantly decreased after HHP treatment. The HHP-induced molten globule state of β-LG exhibited less affinity for palmitic acid, capsaicin, or carvacrol ligands than native β-LG, and no detectable specific binding for α-ionone, β-ionone, cinnamaldehyde or vanillin flavors. HHP treatment resulted in changes in the hydrophobic calyx and surface hydrophobic sites of β-LG.     

Nonthermal pasteurization of liquid foods using high‐intensity pulsed electric fields

Processing foods with high‐intensity pulsed electric fields (PEF) is a new technology to inactivate microorganisms and enzymes with only a small increase in food temperature. The appearance and quality of fresh foods are not altered by the application of PEF, while microbial inactivation is caused by irreversible pore formation and destruction of the semipermeable barrier of the cell membrane. High‐intensity PEF provides an excellent alternative to conventional thermal methods, where the inactivation of the microorganisms implies the loss of valuable nutrients and sensory attributes. This article presents recent advances in the PEF technology, including microbial and enzyme inactivation, generation of pulsed high voltage, processing chambers, and batch and continuous systems, as well as the theory and its application to food pasteurization. PEF technology has the potential to improve economical and efficient use of energy, as well as provide consumers with minimally processed, microbiologically safe, nutritious and freshlike food products.     

Characterization of sol-gel transitions of food hydrocolloids with near infra-red spectroscopy

Near infra-red spectroscopy (NIR, 600-1100 nm) was used to characterize sol-gel transitions of food hydrocolloids including whey protein (WP), high acyl (HA) and low acyl (LA) gellan gums. Whey protein (20% w/w), LA and HA gellan (1% w/v) aqueous solutions with selected calcium concentrations (0-40 mM) were used. Principal components analysis (PCA) and principal component regression (PCR) were performed to analyze spectral data of gel dispersions at a series of controlled temperatures (20-95 °C). Gelling temperatures of gellan dispersions were determined directly based upon the PCA results without requiring for reference values. The gelling temperatures determined with the NIR method were similar to those obtained by dynamic rheological tests and dielectric property test. The PCR models showed a good predictability for temperatures of gellan dispersions with selected calcium concentrations during cooling or heating process. This study indicates that the NIR method has a great potential to detect structural change, and to monitor time and temperature dependant behaviour of food hydrocolloids during sol-gel transition period.     

Effects of combined exposure of micrococcus luteus to nisin and pulsed electric fields

Death and injury following exposure of Micrococcus luteus to nisin and pulsed electric field (PEF) treatment were investigated in phosphate buffer (pH 6.8, σ=4.8 ms/cm at 20°C). Four types of experiment were carried out, a single treatment with nisin (100 IU/ml at 20°C for 2 h), a single PEF treatment, a PEF treatment followed by incubation with nisin (as before) and addition of nisin to the bacterial suspension prior to the PEF treatment. The application of nisin clearly enhanced the lethal effect of PEF treatment. The bactericidal effect of nisin reduced viable counts by 1.4 log₁₀ units. Treatment with PEF (50 pulses at 33 kV/cm) resulted in a reduction of 2.4 log₁₀ units. PEF treatment followed by nisin caused a reduction of 5.2 log₁₀ units in comparison with a 4.9 log₁₀ units reduction obtained with nisin followed by PEF. Injury of surviving cells was investigated using media with different concentrations of salt. Sublethally damaged cells of M. luteus could not be detected by this means, following PEF treatment.     

Effects of novelty and familiarity on illness-induced aversions to food and place cues in coyotes (Canis latrans).

Two experiments investigated the effects of novelty and familiarity on illness-induced aversions to taste and place cues in 10 coyotes. Ss were made ill on familiar food laced with Li?CO? in a novel place and then received preference tests. In Exp I, Ss avoided the previously poisoned familiar food in the novel treatment place but readily ate the same familiar food in a familiar safe place. Exp II replicated the results of Exp I, and it was found that Ss would eat a different familiar food in the novel treatment place. A model for averting animals from places where they are not wanted is presented. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)