The effects of ambient temperature storage on the chemical and nutritional characteristics of phosphoric and sorbic acid-stabilized fish autolysates were determined. Variations in sample composition due to autolysis, deboning, and acidification were also evaluated. Autolysates of English sole (Parophrys vetulus), true cod (Gadus macrocephalus), Dover sole (Microstomus pacificus), and orange rockfish (Sebastodes pinniger) carcass wastes, whole Pacific hake (Merluccius productus) and dogfish shark (Squalis acanthias), and a hake/tuna viscera (70/30 wt/wt) mixture were utilized in the investigation. Samples were acidified to ca. pH 3.25 with phosphoric acid (85% w/v) and contained potassium sorbate at the 0.2% (wt/wt) level. Screen separation of bone reduced the ash levels of samples, with the exception of dogfish shark. Loss of bone minerals, specifically calcium and phosphorus, was responsible. Phosphoric acid addition elevated ash and phosphorus contents to higher levels than for raw materials. Acid-stabilized autolysates were stable to microbial outgrowth throughout 8 months of ambient temperature storage. Slight increases in pH levels were generally observed. Sorbate levels decreased at an apparently exponential rate with respect to time (r=-.9146, P [greater than or equal to] .005). Hydrolytic rancidity did not proceed during storage. Stability towards microbial outgrowth, inactivation of endogenous lipases during pasteurization, and maintenance of acidic environmental conditions enhanced fat stability. Oxidative rancidity, as measured by 2-thiobarbituric acid (TBA) numbers, progressed during storage. Carcass wastes showed higher rates and overall levels of oxidation. Initial free fatty acid levels correlated in a linear manner with 0 and 4 month TBA numbers (r=.9548, P [greater than or equal to] .005; r=.9187, P [greater than or equal to] .005, respectively). The regression of TBA numbers at 4 months on zero time values increased in a linear manner (r=.9346, P [greater than or equal to] .005). Proteolysis during storage, as monitored by free amino groups, was not detected. Inactivation of native proteases during processing and the microbial stability of samples were responsible. Levels of available e-amino lysine and tryptophan were stable throughout storage. The protein quality of acidified hake, dogfish shark, orange rockfish, and English sole autolysates, stored for 0, 4, and 8 months, was evaluated using protein efficiency ratio (PER) determinations. Protein quality was not affected by storage in samples of acidified hake, English sole, and orange rockfish (P=.05). Ratios for all samples of hake and the 0 and 8 month samples of dogfish shark did not vary significantly (P=.05) from the casein control. English sole and orange rockfish samples yielded PER values that were inferior to casein and round fish samples (P=.05). The regression of feed consumption and PER values on TBA numbers decreased in a linear manner (r=-.7999, P [greater than or equal to] .005; r=-.8424, P [greater than or equal to] .005, respectively). Higher contents of nutritionally inferior visceral proteins and increased rates of oxidative rancidity in the carcass waste samples probably were responsible for their reduced protein qualities. / Graduation date: 1978

This study was undertaken to determine the sensory differences in high pressure vs. heat processed food systems after storage at ambient and refrigerated temperatures as determined by a trained sensory panel. Spanish rice and spaghetti with meat sauce were prepared and treated with heat and with high pressure processing (HHP). A citrus fruit mix consisting of pieces of orange, grapefruit, and pineapple was processed by mild heat and HHP, and heat alone. One day after processing, treated products were tested along with untreated controls. Products were stored at either 22°C or 3°C, and tested at 10, 30, 60, 90, and 120 days. Sensory testing was done by a panel trained in a QDA-type method, and data was analyzed by univariate and multivariate methods. For spaghetti with meat sauce, significant differences (p>0.05) were found between processing methods stored at the same temperature in appearance and texture attributes, with the high pressure processed samples closer to unstored product than those treated by heat. Differences in treatments first appeared in 'dry appearance' at 10 days, and by 120 days there were differences in 'tomato integrity', 'pasta integrity', 'brightness of color', and 'firmness of pasta' as well. Most of these differences were due to the stickiness caused by the extra amylose leaking out of the heat treated pasta over time. For Spanish rice, there were no statistically significant differences between samples processed by the two methods and stored at the same temperature. The Spanish rice was formulated with parboiled rice, which allows very little amylose leakage, so it did not show amylose-related effects as the spaghetti with meat sauce did. The fruit mix processed with HPP and mild heat had significantly higher ratings in appearance attributes 'brightness of color' and piece integrity', and lower ratings in 'cooked' descriptors than product treated with heat alone stored at the same temperature. / Graduation date: 2000

The microorganisms present determine to a great extent the quality of cured meat. Some of them may have unfavorable effects on the color and flavor, whereas others are known to have beneficial effects on these quality factors. Yeasts, bacilli, and streptococci were found to be predominately present in a cover pickle which had been recently used for curing hams in a commercial meat packing plant. They were isolated and their characteristics studied. All three organisms rapidly reduced resazurin and litmus milk, but failed to reduce nitrates. They were salt-tolerant and grew best at about 21°C. The yeasts did not produce carbon dioxide when grown in lactose or glucose fermentation tubes. The effect of these organisms on the rate of color development during curing of pork was studied. Ham from a freshly slaughtered hog was cut aseptically and ground. It was blended with a sterile curing solution and inoculated with each of the test organisms. It was then incubated at 60°F. for 24 hours and finally heated at 120°F. The color development throughout curing was studied with the Photovolt Spectrophotometer with a reflectance attachment. The pH, oxidation-reduction potentials, and plate counts were determined during curing at 60°F. The results indicated that the organisms tested improved the color of cured meats by reducing the oxidation-reduction potential of the meat during curing. / Graduation date: 1955

The biochemical and organoleptic changes that took place in raw whole Pacific shrimp and in the cooked meat during eight days of iced storage were investigated. A steady increase of both microbial numbers on the raw shrimp and pH in the raw shrimp and cooked meat was observed. The levels of total and non-protein nitrogen and total carotenoid pigment decreased during the storage period. Tyrosine levels showed a. decrease in the raw shrimp, but a progressive increase in the cooked meat was observed. Although proteolytic and polyphenolase activity in the raw shrimp decreased during storage, the losses in nitrogenous components was probably related to a combination of the autolytic degradation of the shrimp coupled with the washing action of melting ice. Trimethylamine oxide levels were shown to decrease in raw shrimp daring storage due to the washing action of melting ice and its reduction to dimethylamine and formaldehyde and in lower amounts, to trimethylamine. The latter, probably is the result of bacterial activity, while the former is due to the action of enzyme systems in the shrimp. Levels of dimethylamine and formaldehyde increased in a parallel manner during the storage period. Trimethylamine levels also increased, but at a much slower rate. Organoleptic quality as shown by taste panel evaluations progressively declined during the storage period. Dimethylamine and formaldehyde levels appeared to be more sensitive indices of cooked shrimp quality than microbial numbers, pH and trimethylamine levels. / Graduation date: 1973

Pectinmethylesterase (PME) activity in fresh cucumber fruit was determined. The effects of several cationic species, temperature, pH, and acetic acid on the activity of cucumber PME was investigated. The efficacy of blanching, infiltration with CaCl₂ or acetic acid, and fermentation with 0 and 40 mM CaCl₂ on inhibition of cucumber PME activity were evaluated. Over 50% of PME activity was present in the skin and 75% occurred within the outer 3 mm of the fruit. Maximum stimulation of PME occurred at 125 mM NaCl, 200 mM KCl, and 5 mM CaCl₂. Higher levels of each cation demonstrated inhibition of PME activity. 50% inhibition was observed at 750 mM NaCl, 800 mM KCl, and 200 mM CaCl₂. Optimum pH was 8.0 and acid pH conditions greatly reduced activity. PME exhibited no activity at pH 4.0. PME activity responded typically to temperature variations with maximum activity occurring at 50°C. The temperature coefficient Q¹⁰ for PME activity between 10 and 40°C was 1.24. PME activity was slightly stimulated by increased levels of acetic acid and reached its maximum at 1.5% acetic acid at pH 7.5. No inhibitory effect on PME was detected at acetic acid levels of 0 to 2.0%. Inhibition of PME by NaCl and CaCl₂ was reversible. High levels of NaCl (1 M) stabilized PME activity while incubation of PME activity in low levels of NaCl (0.24 M) resulted in loss of activity over time. Both high (500 mM) and low (5 mM) levels of CaCl₂ imparted stability to PME activity. No detectable PME activity remained in cucumbers after 15 days of fermentation. Addition of CaCl2 (40 mM equilibrated) to the fermentation brine caused a rapid reduction in PME activity during the first 6 to 12 hours after brining. After 24 hours of brining there was no difference in PME activity due to CaCl₂ addition. Acetic acid infiltration at high levels (>10%) effectively reduced the pH of skin tissue to near 4 and resulted in complete inhibition of PME activity. The most effective treatment for controlling cucumber PME activity was rapid pH reduction by acetic acid infiltration and resulting in PME inhibition. Infiltration with very high CaCl₂ levels (>500 mM) may also be beneficial toward accomplishing PME inhibition. Rapid inactivation prior to brining or within 6 to 12 hours after brining is necessary to achieve effective control of cucumber PME activity. / Graduation date: 1989

Microgard, a commercially-available pasteurized fermented milk, was found inhibitory to gram negative bacteria such as Pseudomonas putida, some well-known foodborne pathogens (e.g. Salmonella, Yersinia and Aeromonas) and some fungi as revealed by an agar incorporation assay method. Gram positive bacteria, however, were not inhibited. Rather, some bacteria in this group were stimulated by Microgard. The inhibitory activity of Microgard was optimum at pH 5.3 and below. Thermal stability and protease sensitivity were characteristic of Microgard. Addition of albumin or some emulsifying substances antagonized Microgard whereas treatment with proteases at an initial pH of 11.0 enhanced its inhibitory ability. Purified eluates of Microgard from a Sephadex Column (gel filtration) exhibited thermal stability and maximum UV absorbance. Furthermore, they gave positive results with the Biuret test, indicating the presence of protein type substance(s). Diacetyl, known to be inhibitory for psychotrophic bacteria, was present in Microgard as well as several organic acids. Filter-sterilized fermentation growth metabolites of Pediococcus spp., Propionibacterium spp., Bifidobacterium longum, Lactobacillus plantarum and a black-pigmented yeast were tested for antimicrobial activity as Microgard had been tested. Results revealed that some of these metabolites were inhibitory to Pseudomonas putida and Listeria monocytogenes, which represented food spoilage and pathogenic bacteria, respectively. / Graduation date: 1989

Approximately 200 raw prunes were harvested from each of five Italian prune trees near Corvallis every three days for nine consecutive harvest dates. Forty individual fruit from each tree were drawn at random and subjected to a series of fresh fruit quality tests. For each quality factor which was measured, the experiments were set up as nine by five factorial analysis of variance studies with the numbers of observations in a replication depending upon the factor being studied. The correlation of each objective and subjective test with canned fruit flavor was then calculated. The regression line, standard error of estimate, and 90 percent confidence limits were calculated for each tests which had a correlation of 0.80 or better with canned fruit flavor. Several objective tests were used on raw prunes such as soluble solids-acid ratio, pressure test, percent soluble solids, titratable acidity and color of raw prune flesh measured by the Hunter Color-Color Difference Meter in the order named are significantly correlated with the flavor of the canned Italian prune. Analysis of variance and L.S.D. was used to determine that the first two of these tests show good three-day precision as a guide to harvest maturity. The others appear suitable for longer time intervals. Certain objective tests such as pH values and fresh fruit weight are of little value to predict canned fruit flavor and show poor three-day precision as a guide to harvest maturity. The subjective grading of raw prunes by outer skin appearance does not seem to be a precise way to predict canned fruit quality. The three-day precision as a guide to harvest maturity is poor. Respiration of the fresh fruit shows a definite climacteric and the climacteric appeared at approximately the same time the fruit harvested exhibited optimum canned fruit flavor and color. The remaining lot of fruit after the fresh fruit samples were removed was placed in 32°F. cold storage and held for processing the next day. Fruit from each tree each harvest date were processed in twelve No. 2 fruit enameled cans for use in canned fruit analysis studies. Several canned prune quality factors such as percent transmittance of the canned juice, canned fruit skin color as measured by the Hunter Color-Color Difference Meter and titratable acidity of the canned prune pulp can be used to predict or specify the canned fruit flavor. Other objective tests used on canned prunes such as pH values, cut-out soluble solids and cut-out soluble solids-acid ratio are not highly correlated with canned fruit flavor. Subjective tests used on canned prunes were color and flavor of the fruit. These factors were judged by a statistically selected panel of judges. The correlation between color and flavor of the canned fruit was the highest of the study (r= -.9458). The subjective color measurement seems to be very precise in predicting canned fruit flavor. Every subjective and objective test carried out on the raw and canned prunes were correlated with canned fruit flavor because this factor was felt to be of singular importance in canned prune quality. Regression equations are given. / Graduation date: 1953

Growth of spoilage fungi in bread and other bakery products is currently controlled with the addition of weak acid preservatives. Consumers demand more natural products and thus there is a need to reduce the amount of chemical preservatives added to foods, or to identify alternative, more 'natural' antifungal compounds with strong biological activity. This thesis reports on several areas of research undertaken in the project: evaluation of sub-optimal concentrations of existing preservatives, under different environmental conditions, on growth and ochratoxin A (OT A) production by six bread spoilage moulds; efficacy of new/natural antifungal compounds for possible use in bread preservation; evaluation of the impact of preservation hurdles on ecophysiology of the spoilage fungi, including niche overlap; and mechanisms of action of preservatives on hydrolytic enzymes. It was found that the use of currently applied levels of the existing preservatives potassium sorbate, calcium propionate and sodium benzoate were effective, under low pH environments (pH 4.5) at completely controlling growth of spoilage moulds (Aspergillus ochraceus, Eurotium repens, Cladosporium herbarum, Penicillium corylophilum and Penicillium verrucosum) on wheat flour-based substrates over a period of 30 days. At higher pH levels, the efficacy decreased being almost nil at pH 7.5. The use of sub-optimal concentrations of weak acid preservatives led in most cases to reductions in lag times and/or stimulation of mould growth and ochratoxin A production by P. verrucosum strains. Cont/d.

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