Macromolecular acidic coating increases shelf life by inhibition of bacterial growth.

The sensitivity of microorganisms to low pH can be utilized in food protection by preparing coatings based on macromolecular acids. Due to limited diffusivity of macromolecules low pH occurs primarily at the surface, while the interior parts of the food remain unaffected. This principle is demonstrated using food approved alginic acid in various types of coatings (aqueous, emulsions, dispersions, dry coating) on a wide range of foods including meat, fish, chicken, shrimp and boiled rice. Significant delay or inhibition of the natural flora is generally demonstrated, particularly when exposed to 'temperature abuse'. Specifically, we show that the coatings reduce or inhibit regrowth of pathogens (Bacillus cereus, B. weihenstephanensis, Listeria monocytogenes serotype 1 and Staphylococcus aureus). In special cases like boiled rice, alginic acid may largely replace acetic acid for acidification and preservation, as demonstrated studying regrowth of added spores of B. cereus. Most formulations allow easy removal prior to further processing (cooking, frying). Temporary side effects such as 'acid cooking' obtained for high acid concentrations on sensitive surfaces (e.g. salmon) disappear during processing, recovering the normal taste and texture. The coating is hence suitable for a large variety of foods.

Cooperative Order-Disorder Transition of Carboxylated Schizophyllan in Water-Dimethylsulfoxide Mixtures.

Carboxylated schizophyllan ("sclerox") is a chemically modified polysaccharide obtained by partial periodate oxidation and subsequent chlorite oxidation of schizophyllan, a water-soluble neutral polysaccharide having a ß-1,3-linked glucan backbone and a ß-1,6-linked d-glucose residue side chain at every third residue of the main chain. The triple helix of schizophyllan in water has a cooperative order-disorder transition associated with the side chains. The transition is strongly affected by the presence (mole fraction) of dimethylsulfoxide (DMSO). In the present study, the solvent effects on the order-disorder transition of sclerox with different degrees of carboxylation (DS) in water-DMSO mixtures were investigated with differential scanning calorimetry and optical rotation. The transition temperature ( Tr) and transition enthalpy (Δ Hr) strongly depended on the mole fraction of DMSO ( xD). Data were further analyzed with the statistical theory for the linear cooperative transition, taking into account the solvent effect, where DMSO molecules are selectively associated with the unmodified side chains. The modified side chain does not contribute to the transition; hence, Δ Hr decreases with increasing DS. The dependence of Tr on the DMSO content becomes weaker than that for unmodified schizophyllan. The theoretical analyses indicated that the number of sites binding with the DMSO molecule and the successive ordered sequence of the ordered unit of the triple helix are changed by carboxylation.

Degradation kinetics of peptide-coupled alginates prepared via the periodate oxidation reductive amination route.

Biomaterials based on peptide-coupled alginates must provide both optimal biological environments and tuneable stability/degradation profiles. The present work investigates the degradation pattern and kinetics of peptide-coupled alginates prepared via the periodate oxidation reductive amination route. Alginates degrade slowly (non-enzymatically) under physiological conditions by acid-catalysed hydrolysis and alkali-catalysed ß-elimination, both operating simultaneously but dominated by the latter. While periodate oxidation alone largely increases the rate of ß-elimination, substitution restores the susceptibility towards ß-elimination to that of the parent alginate. For acid hydrolysis the rate of depolymerization is proportional to the degree of substitution, being approximately one order of magnitude larger than the parent alginate, but still lower than for the corresponding materials with fully reduced dialdehydes. Results also suggest a composition-dependent preference for substitution at C2 or C3. These results demonstrate how the various chemistries introduced by the coupling provide useful means to tune the biodegradability profiles.

Conformation of carboxylated schizophyllan in aqueous solution.

Carboxylated schizophyllan (sclerox) samples of different degrees of oxidation were molecularly characterized by size exclusion chromatography equipped with a multi-angle light scattering detector (SEC-MALS) in 0.10 M aqueous NaCl solution. The molar mass distribution obtained by SEC-MALS shows that sclerox of low degree of oxidation is dissolved mainly as the trimer, whereas the trimer and single chain coexist in solution of sclerox of high degree of oxidation. The trimer of sclerox is much more flexible than the fully ordered triple helix of the parent schizophyllan and easily dissociates into single chains upon heating.

Inter-laboratory evaluation of SEC-post-column calcofluor for determination of the weight-average molar mass of cereal ß-glucan.

Even though size exclusion chromatography (SEC) with post column addition of calcofluor (SEC-calcofluor) has been used for the determination of cereal ß-glucan molar mass in foods for many years, there is a lack of systematic evaluation of the method. To address this issue a set of suitable ß-glucan standards were generated by preparative SEC and their molar mass characteristics were determined by analytical multi-detection SEC (refractive index (RI), light scattering). Each standard was then analysed by SEC-calcofluor at three different labs. As a direct comparison, the analyses were repeated with a RI detector. For SEC-calcofluor accurate measurements of weight average molar mass (Mw) can be made for ß-glucan populations within 10-500×10(3)g/mol. Above this molar mass threshold there is an increasing tendency for underestimation of Mw. Precipitation of some ß-glucan-calcofluor complexes may have delayed their transport into the detector.

Influence of amino acids, buffers, and ph on the γ-irradiation-induced degradation of alginates.

Alginate-based biomaterials and medical devices are commonly subjected to γ-irradiation as a means of sterilization, either in the dry state or the gel (hydrated) state. In this process the alginate chains degrade randomly in a dose-dependent manner, altering alginates' material properties. The addition of free radical scavenging amino acids such as histidine and phenylalanine protects the alginate significantly against degradation, as shown by monitoring changes in the molecular weight distributions using SEC-MALLS and determining the pseudo first order rate constants of degradation. Tris buffer (0.5 M), but not acetate, citrate, or phosphate buffers had a similar effect on the degradation rate. Changes in pH itself had only marginal effects on the rate of alginate degradation and on the protective effect of amino acids. Contrary to previous reports, the chemical composition (M/G profile) of the alginates, including homopolymeric mannuronan, was unaltered following irradiation up to 10 kGy.

Cross-linking and depolymerisation of gamma-irradiated fish gelatin and porcine gelatin studied by SEC-MALLS and SDS-PAGE: a comparative study.

gamma-Irradiation of gelatin and collagen hydrogels can be used for sterilization and mechanical stabilization, providing biomaterials suitable for both tissue engineering and drug-delivery systems. Controversial results have been reported regarding the extent of irradiation-induced cross-linking and degradation, which depend on both protein concentration and irradiation dose. In this work the relative contributions of these processes were studied for irradiation doses between 0 and 1.0 kGy and concentrations between 0.3% and 5% using size-exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS) and viscosity detection, as well as SDS-PAGE. It was demonstrated that chain degradation and cross-linking occur simultaneously in fish gelatin (FG), porcine gelatin (PG) and porcine collagen (PC), by the gradual appearance of protein fragments (10-80) x 10(3) concomitant with the formation of structures of high molecular weight. FG and PG behaved rather similarly, despite the fact they were irradiated and analyzed above and below their denaturation temperatures, respectively, suggesting little or no influence of molecular ordering under the conditions used. PC showed an increasing amount of degradation products following heat treatment prior to SEC-MALLS, suggesting that chain cleavage may occur within ordered collagen structures without complete release of the protein fragments.