Nitrite at the level found in turkey frankfurter formulations vii did not interfere in the hydrazone test as developed by Andrews (1975). The aldehyde levels of frankfurters made principally from MD turkey meat were, on the average, twice as high as the levels in the raw meat. Aldehyde levels generally increased as the frozen storage time of the raw meat increased. There were some variations from this trend due to variation in the fat content of the raw meat. Sixty days was recommended as a maximum frozen storage time. However, because of variation in the fat content from sample to sample , assaying t he level of aldehyde in the raw meat was recommended as a more reliable method of predicting acceptability of further processed products than length of frozen storage. Aldehyde levels of less than two ppm in the raw meat and less than four ppm in the frankfurters were acceptable. The aldehyde measured by Andrews' hydrazone test was identified as formaldehyde.

This study investigated the effect of cold, heat, or osmotic shock treatment on the resistance of L. lactis subsp. cremoris MM160 and MM310 and Lactococcus lactis subsp. lactis MM210 and FG2 cheese starter bacteria to freezing and freeze-drying. The ability to withstand freezing at -60°C for 24 h was variable among lactococci, but resistance to this treatment was significantly improved (P < 0.05) in most strains by a 2-h cold shock at l0°C or a 25-min heat shock at 39°C (L. lactis subsp. cremoris) or 42°C (L. lactis subsp. lactis). Stress treatments that improved lactococcal freeze resistance were also found to significantly (P < 0.05) enhance the resistance of most strains to lyophilization. Increased resistance to freezing or lyophilization was not detected when stress treatments were performed in broth that contained erythromycin, which indicated stress-inducible proteins were involved in cell protection. Membrane fatty acid analysis of stress-treated cells suggested that enhanced resistance to freezing and lyophilization may be related to heat or cold shock-induced changes in cell membrane composition. Heat-shocked cells had a higher 19:0 cyclopropane fatty acid content than did control cells, and cold-shocked cells contained a lower ratio of saturated to unsaturated fatty acids. Other factors must also be involved in cell protection, however, because similar changes in membrane composition were also detected in strains whose resistance to freezing and lyophilization was not improved by heat or cold shock.

It has been shown that iron binds strongly to the proteins in milk, and our aim was to determine whether or not this binding was affected by lowering pH in the manufacture of yogurt. Iron-protein complexing was studied using two different techniques. 1) Skim milk was fortified with 10 mg iron/100 ml and the pH of the milk was adjusted to 6.7, 6.2, 5.8, 5.3, 4.5, and 4.0. The milk was fractionated by ultracentrifugation at 52,000 x g for 60 minutes. The pellets and serum were then analyzed for iron, calcium, and phosphorus content by inductively coupled plasma spectroscopy. SOS-PAGE gels were used to determine protein profiles in the pellets and serum. 2) Yogurt was made from milk fortified with FeCl3, iron complexed with casein, and iron complexed with whey proteins. Small samples of the yogurt were then freeze-dried on carbon coated grids and examined by transmission electron microscopy at 80 KV. Affinity of iron for milk proteins was independent of pH. Iron fortification of milk did not cause loss of calcium or phosphorus from casein micelles. Electron spectroscopic imaging (ESI) showed that iron was bound to casein when yogurt was fortified with FeC13 or iron-casein complex. When fortified with iron-whey protein complex, the iron was distributed throughout the non-micellar portion of the yogurt. To determine effects of iron on yogurt quality, low-fat (2%) and nonfat iron fortified yogurt was made with three sources of iron: FeCl3, iron complexed with casein, and iron complexed with whey protein, at three levels (10, 20, 40 mg/kg). Iron content and lipid oxidation were determined over one month of storage at 4°C. Iron fortification had no effect on the rate of fermentation by the lactic cultures. There was no significant increase in oxidation levels between iron-fortified yogurt and unfortified yogurt (P > .05). No differences in the appearance, mouth feel, flavor, and overall quality ,between iron-fortified yogurt and unfortified yogurt were detected in consumer sensory analysis. Our study showed that high quality iron-fortified yogurt could be manufactured without added food safety risks.

The Mozzarella cheese market is growing rapidly. Major concerns with cheese meltability and color have arisen in the fast food industry. Pre starter culture was used in this study to improve the physical properties of Mozzarella cheese. Three tests (stretch test, melt test, and browning test) were modified to evaluate the quality of cheese. A stretch test using the Brookfield helipath viscometer to stretch the cheese sample at 60°C was successful in distinguishing cheeses from different make procedures and from different proteolytic strains. A melt test using a glass tube to hold the cheese flow at 110°C for 60 min was used to determine meltability of cheese. A chroma meter was used to measure color change after the cheese sample was subjected to boiling water for 60 min. The b* value was used to indicate the color change. Cheese made with Pre strains of Lactobacillus bulgaricus stretched less but showed longer melting flow than that from Prt+ strains. Cheese made with Pre strains was lighter in color than cheese from Prt+ strains. An inverse relationship existed between stretchability and meltability. When mixed cultures of L. bulgaricus and Streptococcus thermophil us were used, the symbiotic interaction in acid production of Prt+ strains was more effective than mixed cultures of Prt- strains. Stretchability of...

Recent studies suggest aromatic amino acid catabolism by starter lactococci and flavor adjunct bacteria have a significant impact on off-flavor development during Cheddar cheese ripening. We hypothesized that a flavor adjunct bacterium, Brevibacterium linens BL2, produces off-flavor compounds from aromatic amino acid metabolism that will have a detrimental impact on cheese flavor. The mechanism of tryptophan (Trp) catabolism in Brevibacterium linens BL2, was investigated in a chemically defined medium during incubation in laboratory conditions (no carbohydrate, pH 6.50, 220 rpm, 25°C) and cheese-like conditions (no carbohydrate, 4% NaCl, static incubation, l5°C). In laboratory conditions, metabolic studies and enzyme assays confirmed that Trp was converted to kynurenine and anthranilic acid. However, cells incubated in cheese-like conditions did not utilize Trp, indicating that these enzymes are not likely to be involved in formation of Trp compounds associated with off-flavors in Cheddar cheese. In an attempt to verify the metabolic activity of the cells during incubation by monitoring the amino acid metabolism in chemically defined medium inoculated with B. linens BL2, a capillary electrophoresis-laser-induced fluorescence method was developed that could separate, detect, and quantitate 18 amino acids within 38 min. The data indicated that B. linens BL2 was metabolically active. Presumably, the cells will be metabolically active and metabolize amino acids in cheese as well. The ability to determine the Trp metabolic activity of B. linens BL2 in cheese, and to quantify Trp catabolic compounds in cheese during ripening, requires a quantitative extraction procedure. An analytical method was developed to extract and quantify aromatic amino acids and Trp catabolites from cheese using capillary electrophoresis. Methanol was used to extract Cheddar cheese made with Lactococcus lactis S3 alone and in combination with B. linens BL2 to quantitatively determine the influence of BL2 on the occurrence of aromatic catabolites. All cheeses contained aromatic amino acids, indole acetic acid, and indole. The concentration and time taken for development of these compounds were significantly decreased or delayed by the addition of B. linens BL2. After 6 months of aging, the concentrations of Trp catabolites were significantly lower in cheese made with B. linens BL2. Addition of BL2 did not directly contribute to off-flavors derived from Trp catabolism in Cheddar cheese. Therefore, the hypothesis was rejected.

An automated continuous flow analysis for milk protein utilizing ultraviolet spectroscopy resulted in a correlation coefficient of 0.972 and a standard estimate of error of 0.082 percent protein when 30 samples were compared with the acid orange 12 dye binding method. Milk was solubilized in 95-105 volumes of acetic acid using the Technicon Auto Analyzer II and measured for absorbance at 274 nanometers. No deviation from the standard method due to mastitis and varying milk fat concentration was observed. A theoretical model indicated a possible standard estimate of error 0.059 percent protein due to inter- and intra-breed variation in milk protein fraction distribution. Potassium dichromate and other preservatives interfered with the results.

Commercial microbial milk clotting enzyme preparations were purified by immunoaffinity chromatography using purified antibody covalently coupled to porous glass beads as the column matrix. Commercial enzyme preparation diluted in 1 mM sodium acetate buffer at pH 5.0 was then biospecifically adsorbed to the column matrix by end-over-end mixing of the glass-antibody complex in the enzyme solution for 12 h at 5°C. The antibody bound enzyme adsorbed glass beads were soaked in .2 M glycine or ethanolarnine at pH 7.0 to block uncoupled reactive sites on the matrix. Following this, the column was washed with 1 mM sodium acetate buffer at pH 7 .0, followed by additional wash with .5 M NaCl, until absorbance at 280 nm returned to baseline. Elution of adsorbed enzyme was achieved with .2 M sodium acetate at pH 3.0, .2 M acetate at pH 3.5, containing .15 M NaCl and .5 M acetate at pH 4.0 containing .5 M NaCL At the same protein concentration, immunoaffinity chromatography purified enzymes had higher clotting activity than the commercial enzyme preparations. Amino acid analysis and OPA proteolysis tests of TCA soluble peptides liberated from casein hydrolysis showed purified enzymes to exhibit lower general proteolytic activity. Immunological reactivity of Mucor enzymes with calf rennet was determined with antibodies produced by intramuscular injections of Mucor miehei protease, Mucor pusillus protease and calf rennet emulsified in Freund's adjuvant into three New Zealand White rabbits . Harvested antisera were heated at 56°C for 30 min to inactivate complement factors and contaminating proteins then centrifuged at 1700 x g for 30 min. Ouchterlony double immunodiffusion method was used to test for presence of antibodies in the antisera, and for cross immunoreactivity. Antibodies against M. miehei were cross reactive with M. pusillus antigen and M. pusillus antibodies cross reacted with M. miehei antigen. Immunodiffusion assay did not show cross reactivity of calf rennet antibodies with either M. miehei antigen or M. pusillus antigen. Antibodies against the Mucor enzymes did not show cross reactivity with calf rennet antigen. Although their actions in milk differ, proteolytic enzyme preparations from M. miehei and M. pusillus are both used as calf rennet substitutes in cheese manufacture. Differences in the characteristics of the two Mucor enzyme preparations exist, even though they exhibit some immunological homology . From our results, at least one antigenic factor is common to both enzyme preparations.

Ice cream mix (12% fat, 11% milk solids nonfat, 12.5% sugar, and 4.5% corn syrup solids) was fermented with Lactobacillus acidophilus and Bifidobacterium bifidum. Half of the mix was heat treated at 82°C for 30 minutes and cooled to 40-41°C. The other half was warmed to 40-41°C and inoculated with the starter cultures. Both were made into ice cream and stored at -29°C. Survival of L. acidophilus and B. bifidum and of β-galactosidase activity were monitored during 17 weeks of frozen storage. Reinforced clostridial medium was used to enumerate culture bacteria. Colony counts, after fermentation, for both L. acidophilus and B. bifidum were about 5 x 108. The population of cultures decreased less than one log cycle after initial freezing. After 17 weeks storage the bacterial counts were 1 x 107 for B. bifidum and were 4 x 106 for L. acidophilus. During the same period, β-galactosidase activity decreased only 31%. Therefore, frozen fermented dairy products provide a good vehicle to supply β-galactosidase enzymes to people who are lactose maldigestors. Frozen fermented ice cream was prepared at four different pH's (5.0, 5.5, 6.0, 6.5) by blending fermented mix with unfermented mix and then was frozen to produce samples for sensory evaluation. All samples were strawberry flavored. These were then evaluated by 88 judges. The preferred pH, based on overall acceptance, was 5.5. A second sensory evaluation was conducted to compare heat-treated with non-heat-treated ice cream. There were no significant differences in appearance, texture, flavor, and overall acceptance between the two samples. Our study shows that ice cream is a suitable vehicle for delivering these beneficial microorganisms and enzymes to consumers.

Clostridium sporogenes PA 3679 spores were inoculated into a meat-vegetable mixture before extrusion, cooking, and vacuum packaging into "stewsticks" to simulate Clostridium botulinum growth. The experiment was a 3 x 5 x 2 x 3 factorial which determined the influence of pH, water activity, initial spore load, and storage period on spore survival. Spore levels decreased throughout storage for all treatments. Spore levels decreased linearly (P = 0.02) as water activity increased, in samples that were heated to kill vegetative cells and activate spores. Other significant interactions of heat-treated samples were observed with inoculum level (P < 0.01) and storage time (P < 0.01). Spore levels in stored products were also significantly affected by water activity* inoculum level (P = 0.03), pH * time, water activity* time (P = 0.01), inoculum level * time (P < 0.01), and water activity * inoculum levels * time (P < 0.01). The interaction between pH * water activity * time tended towards significance (P = 0.06). Most probable number estimates in nonheated samples accounted for naturally occurring viable cells and spores, and added spores and were significantly affected by the main effects of inoculum level (P < 0.01) and time (P < 0.01). The two-way interactions of water activity * inoculum level (P = 0.04), pH * inoculum level (P < 0.01),water activity * time (P < 0.01), and three-way interaction of pH * inoculum level * time (P = 0.03) were significant. Spore levels approached 102, or less (compared to an inoculum level of 106 spores per gram) due to the effects of many treatments. Some stewstick packages were observed to become "gassy" or "loose" during storage. Subsequently the stewstick packages were used to isolate microorganisms that were able to grow at water activities of 0.96-0.86, in glycerol-adjusted Rogosa agar, and were acid tolerant to pH 4.4-4.2. One produced gas in pure culture, and some produced indole. These bacteria were not destroyed by heating to 74°C for at least 30 minutes, and lowered the pH in the stewstick during storage. In conclusion, in all stewstick samples, regardless of pH or Aw, inoculated clostridial spore levels decreased during storage, apparently because spores germinated and vegetative cells subsequently died. Thus, if stewsticks are cooked to 74°C throughout, have a Aw ≤ 0.86 and pH ≤ 4.8, they appear to be safe.

No description available.