HPLC Determination of Furfural and 5-Hydroxymethylfurfural in Citrus Juices

A rapid sample clean-up and chromatographic separation were devel- oped to determine both furfural and 5-hydroxymetbylfurfural (HMF) in citrus juices. Furfural and HMF were isolated by using a C-18 cartridge, and quantified by isocratic elution with acetonitrile/water (1Y85, v/v) as the mobile phase with a Radial-PAK C-18 column (100 × 8 mm i.d.). Detection was at 280 nm and the lower limit of detection for both compounds was 50 ppb. Recoveries between 94.0 and 101.2% were obtained for HMF added to orange juice. Recoveries of fmfural ranged between 96.8 and 103.9%.     

Bacterial Extracellular Ice Nucleator Effects on Freezing of Foods

Extracellular ice nucleators (ECINs) were incorporated into foods and subjected to subzero freezing. Time-temperature profiles, ice-formation patterns and textures were examined by thermocouple, microscopy and texture analyzer. Onset temperatures (initial freezing), enthalpies and freezing rates were measured by DSC. Addition of ECINs to liquid foods elevated ice nucleation temperatures and promoted freezing. Solid or semisolid products frozen with ECINs resulted in a fiber-like texture. These effects were more apparent at –10°C or higher. Differential scanning calorimetry revealed onset temperatures were increased 11°C by addition of ECINs, but length of time to complete the phase transition was extended at constant cooling rates. Results indicated that ECINs can be used instead of whole bacterial cells for efficient freezing and textural modification.     

Singlet Oxygen and Ascorbic Acid Effects on Dimethyl Disulfide and Off-Flavor in Skim Milk Exposed to Light

The light-induced off-flavor and dimethyl disulfide increased as fluorescent light exposure increased from 0,2,4,6, to 8h (p<0.05). Sensory evaluation and identified compounds suggest that dimethyl disulfide was mainly responsible for the light-induced off-flavor in skim milk. Dimethyl disulfide was formed by the singlet oxygen oxidation of methionine in milk. Gas chromatographic analysis and sensory evaluation showed that 200,500, and 1000 ppm ascorbic acid, which is a singlet oxygen quencher, lowered the formation of dimethyl disulfide and off-flavor in skim milk (p<0.05).     

A RESEARCH NOTE THE EFFECTS OF PRERIGOR SODIUM BICARBONATE PERFUSION ON THE QUALITY OF PORCINE M. SEMIMEMBRANOSUS

The effect of prerigor sodium bicarbonate (SBC) perfusion on the quality of porcine semimembranosus muscle was tested in 8 pigs, heterozygous for the halothane gene. Perfusion via the iliac artery was initiated at 15 min postmortem. For each carcass, one side was perfused with 4 L of 0.75 M SBC and one side with 0.7% saline. None of the sampled muscles was. PSE quality. SBC treatment resulted in a doubling of the muscle sodium content, indicating that about 5% of the perfused SBC was absorbed. Although the ultimate pH of SBC samples was higher (P<0.05) than the pH of controls, the difference was smaller than expected. L*-value and drip losses were lowered (P<0.05) by SBC treatment. These results suggest that it may be possible to reduce PSE by prerigor application of SBC. Further studies on optimum delivery (perfusion versus infusion) and SBC concentration are needed.     

Utilizing the R-Index Measure for Threshold Testing in Model Soy Isoflavone Solutions

ABSTRACT: Twenty-eight untrained panelists used the signal detection rating method to determine thresholds for daidzein and genistein. Five concentrations of genistein and daidzein were suspended in starch solutions. The starch solution represented the noise, and isoflavone suspensions represented the signal. Blindfolded panelists received 15 replicates of noise and signal. To determine group detection thresholds, the concentration at an R-index of 75% was calculated. The group thresholds for genistein and daidzein were 4.006 × 10⁻³ M and 2.921 × 10⁻³ M, respectively. These results indicate a much higher threshold value than reported in the literature and in soymilks. This strongly suggests that daidzein and genistein individually do not contribute to bitterness or astringency in soy food products.     

Prevention of Pinking, Off-odor, and Lipid Oxidation in Irradiated Pork Loin Using Double Packaging

ABSTRACT: Lipid oxidation, color, volatiles, and sensory evaluation of double-packaged pork loin were determined to establish a modified packaging method that can improve the quality of irradiated pork loins. Vacuum-packaged irradiated samples produced dimethyl sulfide and dimethyl disulfide responsible for irradiation off-odor, whereas lipid oxidation was promoted under aerobic conditions. Exposing double-packaged irradiated pork to aerobic conditions for 1 to 3 d was effective in controlling both lipid oxidation and irradiation off-odor, regardless of packaging sequence. Sensory panels could distinguish the decrease in irradiation off-odor intensities by modifying the packaging method. However, carbon monoxide heme pigments, responsible for the increased redness by irradiation, were not effectively controlled by double packaging alone.     

Standardized Failure Compression Test of Protein Gels from a Collaborative Study

A failure compression test with a standardized procedure for protein gelation was developed. Using whey protein concentrate, egg white protein and soy protein isolate as representative proteins, a highly reproducible procedure for sample preparation and gel testing was developed after refinements. Gels of varying protein concentrations were prepared with 0.1 M NaCl at pH 7. Force (N) and strain (Δh/h) at failure were the main parameters measured. Variability of results was found due to uncontrolled conditions for protein hydration and pH adjustment and air incorporation during hydration. After corrective steps to avoid potential errors, the procedure was recommended for a routine analysis of failure properties of protein gels.     

BIOCHEMICAL AND ANTIBACTERIAL PROPERTIES OF LYSOZYME PURIFIED FROM THE VISCERA OF SCALLOPS (PATINOPECTEN YESSOENSIS)

A lysozyme was purified from the viscera of scallops by ion exchange, gel permeation and affinity chromatographies. The yield of the purified lysozyme was 1.52%, and its purification ratio was 411.9 folds. The molecular weight of the scallop lysozyme was about 14.5 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The optimal temperature for lysozyme activity was 20C, but the optimal stability temperature was between 20 and 30C.
The optimal pH for lysozyme activity was 5.0, but the optimal stability pH was between 5.0 and 6.0. Scallop lysozyme had antibacterial activities against both gram-positive and gram-negative bacteria in which gram-negative bacteria, Escherichia coli and Vibrio vulnificus, were inhibited more effectively than gram-positive bacteria. Egg white lysozyme inhibited gram-positive bacteria better than the scallop lysozyme, whereas the reverse was true for gram-negative bacteria. The N-terminal sequence of the scallop lysozyme consisted of 10 amino acids: proline, cysteine, valine, tyrosine, alanine, phenylalanine, methionine, asparagine, glutamic acid and aspartic acid.

PRACTICAL APPLICATIONS

Egg white lysozyme (EWL) has been used as a preservative or antibacterial agent in the pharmaceutical and food industry, but is limited to broaden its application because of poor antibacterial activity against gram-negative bacteria. Scallop viscera lysozyme has two times higher antibacterial activity against gram-negative bacteria ( Escherichia coli and Vibrio vulnificus ) than EWL. Therefore, scallop viscera lysozyme shows a promise as a bacteriostatic or prophylactic agent in food preservation and specialty product.