Texture and Storage Stability of Processed Beefsticks as Affected by Glycerol and Moisture Levels

Ground beef-based beefsticks were produced with glycerol levels of 0, 2, and 4%, and dried to water activity levels of 0.90 and 0.85. Samples were analyzed by uniaxial compression and colorimetry after production and after 52°C storage for 1, 2, 3 or 4 wk. Deformability modulus, percent recoverable work, relaxation properties, and relative lightness were calculated. Glycerol, as well as water, acted as an effective textural plasticizer. Reductions in modulus and relaxation parameters due to glycerol addition were in the range of 30–40%. Glycerol can thus effectively be used to adjust physical properties without compromising stability. Higher moisture samples were relatively more elastic, as determined by recoverable work. High temperature storage reduced modulus, solidity and percent recoverable work (20–70%) in all samples.     

BTN1, a Yeast Gene Corresponding to the Human Gene Responsible for Batten's Disease,is Not Essential for Viability,Mitochondrial Function,or Degradation of Mitochondrial ATP Synthase

The Saccharomyces cerevisiae gene BTN1, encodes a 408 amino acid putative integral membrane protein, which is 39% identical and 59% similar to the human Cln3p, whose mutant forms are responsible for Batten's disease and for a diminished degradation of mitochondrial ATPase synthase subunit c. Disruption experiments established that Btn1p is not essential for viability, mitochondrial function, or degradation of mitochondrial ATP synthase in yeast. © 1997 John Wiley & Sons, Ltd.     

Effect of Oxygen on Thermal Degradation of 5-Methyl-5,6,7,8-Tetrahydrofolic Acid

Previous studies of thermal degradation of folic acid have not given consistent rate expressions or activation energies. The present study employed a model system which eliminated oxygen mass transfer limitations to examine degradation as a result of heating. A pseudo first-order reaction rate constant (k_365.K) and an activation energy (E_a) for thermal degradation due to an oxidative mechanism were estimated to be 0.154 ± 0.044 min^?1 and 16.3 kcal/mol, respectively. In the presence of N₂, these parameters were estimated to be 0.094 ± 0.009 min^?1 and 23.3 kcal/mol, respectively. While elimination of oxygen will not ensure folic acid retention, the overall degradation rate will be reduced significantly.     

Chemical Modification of Egg White with 3, 3-Dimethylglutaric Anhydride

SUMMARY— Egg white, near its normal concentration, was reacted at 25°C, pH 9.0, with levels of 3,3-dimethylglutaric anhydride (DMGA) from 0 to 60 mol/mol egg white protein (EWP) (assuming egg white to have an average mol wt of 50,000). Analysis for amino acids and functional groups showed about 26% of the lysine residues reacted at 15 mol DMGA/mol EWP. Sulfhydryls are more resistant to reaction with 60% unreacted at 150 mol DMGA/mol EWP. Electrophoresis indicates significant changes in net charges on the protein, particularly on lysozyme which migrates anodically in six separate bands at higher DMGA levels. Ultracentrifugation sedimentation data suggest no hydrolysis or aggregation changes. Foam formation is not seriously altered, but the heat coagulation properties, as evidenced by angel cake failures, are changed. As measured by viscosity, light transmission and aerating ability, DMGA exerts a protective action against the effect of heat on these properties.     

COLD GELATION OF WHEY PROTEIN EMULSIONS

Stable and homogeneous emulsion‐filled gels were prepared by cold gelation of whey protein isolate (WPI) emulsions. A suspension of heat‐denatured WPI (soluble WPI aggregates) was mixed with a 40% (w/w) oil‐in‐water emulsion to obtain gels with varying concentrations of WPI aggregates and oil. For emulsions stabilized with native WPI, creaming was observed upon mixing of the emulsion with a suspension of WPI aggregates, likely as a result of depletion flocculation induced by the differences in size between the droplets and aggregates. For emulsions stabilized with soluble WPI aggregates, the obtained filled suspension was stable against creaming, and homogeneous emulsion‐filled gels with varying protein and oil concentrations were obtained. Large deformation properties of the emulsion‐filled cold‐set WPI gels were determined by uniaxial compression. With increasing oil concentration, the fracture stress increases slightly, whereas the fracture strain decreases slightly. Small deformation properties were determined by oscillatory rheology. The storage modulus after 16 h of acidification was taken as a measure of the gel stiffness. Experimental results were in good agreement with predictions according to van der Poel's theory for the effect of oil concentration on the stiffness of filled gels. Especially, the influence of the modulus of the matrix on the effect of the oil droplets was in good agreement with van der Poel's theory.     

EVALUATION OF PROCESSING TOMATOES FROM TWO CONSECUTIVE GROWING SEASONS: QUALITY ATTRIBUTES, PEELABILITY AND YIELD

Peelability is an important quality parameter in the selection of tomato cultivars (cvs.) for whole peeled and dice processing. Six processing tomato cvs. were evaluated in two consecutive years to examine the effects of cv., maturity and physical attributes on peelability and yield. Physical attributes of the raw tomatoes (size, weight, pericarp wall thickness, color) and processed paste quality (pH, titratable acidity, soluble solids, Bostwick consistency, serum viscosity, color) were determined. Large variations in physical attributes and paste quality were observed in selected tomato cvs. and maturities. In general, most of the attributes indicative of paste quality were more desirable at the less mature (e.g., pink) stage and declined with maturity. Statistical analysis suggests that there were significant differences in percentage of peeled tomatoes, peel index, and yields of whole peeled and diced tomatoes between two consecutive growing years.     

ASSESSING LYCOPENE CONTENT IN CALIFORNIA PROCESSING TOMATOES

Tomatoes constitute the main source of lycopene in the U.S. diet. Growing interest in the potential health‐protective role of lycopene is bringing attention to the content of lycopene in tomatoes. A wide range of lycopene content (55–181 mg/kg) was observed in juice prepared from selected cultivars of tomatoes grown in nine California counties. A comparison of cultivars H 8892, H 9665 and Halley 3155 grown in Colusa, Fresno, San Joaquin and Yolo counties during three seasons concludes that mean lycopene concentrations were significantly greater (P < 0.01) in 2000 (106 mg/kg) than in 1999 (101 mg/kg) and 2001 (88 mg/kg). An evaluation of nine processing tomato cultivars harvested in one season on four separate dates indicated that lycopene concentration of tomatoes decreases with maturation on the plant. Lycopene concentration of tomatoes is dependent on the growing season, location, cultivar and maturity.     

Rapid Methods for Lipoxygenase Assay in Sweet Corn

Potential methods for rapid assay of sweet corn lipoxygenase (LPO) were evaluated and compared by visual inspection. Both model system (partially purified) and vegetable (LPO extract) system studies were carried out. Model system studies indicated that LPO had maximum activity at pH 6.0 and 2.0 mM linoleic acid. Methylene blue bleaching (MBB), carotene bleaching (CB), and potassium iodide-starch (KI-S) methods were evaluated both spectrophotometrically and visually. Both MBB and KI-S methods were effective for the model system. For the vegetable LPO extract systems (sweet corn and green beans), the MBB method indicated positive results for both, the CB method was not effective for either, and the KI-S method was very effective for green beans but not for sweet corn.     

Lipoxygenase in Sweet Corn Germ: Isolation and Physicochemical Properties

Off-flavor and off-aroma development, which may be catalyzed by lipoxygenase (LPO), are common in frozen stored sweet corn. Lipoxygenase activity in the germ fraction of sweet com (Zea nruys L. cv. Jubilee) was determined and compared with that in the degermed fraction. Lipoxygenase activity/g germ was about three times greater than that of the degermed fraction, Optimized procedures for isolation of lipoxygenase from the germ fraction were developed. Lipoxygenase was isolated by preparation as an acetone powder, extraction with 0.2M TrisHCI, pH 8.0 (4°C), fractionation with 40–60% saturated ammonium sulfate and dialysis. Optimum pH was 6–7 and temperature 50°C for activity of partially purified lipoxygenase. The enzyme appeared stable at pH 5–8 and ～90% of original activity was inactivated after heating in pH 7 buffer at 70°C for 3 min.