Pacific shrimp (Pandalus jordani) was washed repeatedly and the eluted bacteria were enumerated and identified. Selected isolates were tested for their adhesive properties. Washing reduced the microbial load by 3.84 to 42.04%. The bacteria which most resisted wash-off were Staphylococcus and Pseudomonas spp. The easiest to wash off was Flavobacterium spp. In higher-count samples, Moraxella and/or Lactobacillus spp. washed off readily, but they still constituted large proportions of the residual bacteria on shrimp. Adhesiveness, measured by hydrophobic interaction with octane, showed 43.3% change in absorbance by Staphylococcus spp., followed by 21.5% by Moraxella spp., and Arthrobacter spp. at 13.5%. Pseudomonas spp. showed only 5.7% change in absorption. Attachment, measured by hanging glass cover slips in broth, however, showed Pseudomonas and Staphylococcus spp. to have the greatest ability to adhere, with 0.47 and 0.46% attachment, respectively. Moraxella spp. showed the least ability to adhere to glass (.02%), followed by Lactobacil lus spp. at 0.11%. Arthrobacter and Flavobacterium spp. adhered at 0.30 and 0.37% levels, respectively. Attachment of Pseudomonas spp. to glass was the least affected by media composition, temperature, or presence of a surface-active agent (sodium hexametaphosphate). Staphylococcus spp., on the other hand, attached most strongly under optimum growth conditions but were most affected by varying growth conditions, temperature, and presence of a metabolic inhibitor (sodium hexametaphosphate). This indicates that the adhesive ability of Staphylococcus spp. is directly related to its metabolic activity, while Pseudomonas spp. is less sensitive to changes in metabolism and may depend on motility for adhesion. Bacteria that could adhere strongly on solid surfaces (Pseudomonas and Staphylococcus spp.) tend to be found in greater proportions and, hence, contribute more to the spoilage of shrimp. / Graduation date: 1983

Assessment of freshness and quality of meat and fish is a major activity of both food regulatory agencies and the food industry. Various methods are used for measuring fish and meat quality, each with its particular advantages and limitations. However, methods based on monitoring the products of proteolysis have received relatively little attention. The objective of the present study was to identify specific protein and peptide products of proteolysis as indicators of freshness and quality during chilled storage of fresh fish and meat. / Samples of meat and fish were subjected to chilled storage; at intervals of 0, 2, 4, 8, 12 and 16 days, samples were subjected to protein and peptide extraction, and separation of individual sarcoplasmic and myofibrillar proteins by SDS and native electrophoresis. These extracted proteins along with acid soluble nitrogen (ASN) were separated by RP-HPLC, fractions were collected and identified by electrospray ionization mass spectrometry (ESI-MS). / RP-HPLC separated at least thirty fractions from the ASN extract of fresh fish. ESI-MS revealed the presence of at least twenty-five polypeptides with molecular weights (MW) ranging from 2 to 32 kDa. The relative area % of the polypeptides with MW 32.8 kDa and 42.8 kDa decreased during the storage while polypeptides of MW of 10.9 kDa and 16.7 kDa increased during storage. Changes in polypeptides of MW 12, 34.2 and 42.8 kDa was also observed. The sarcoplasmic protein extracted from ground and whole meat contained at least 12 polypeptides with MW ranging from 11 to 42 kDa. The relative area % of polypeptide of MW of 35.7 kDa decreased during storage. The results suggest that changes in proteins and polypeptides of MW 10.9, 12, 16.7, 32.8, 34.2 and 42.88 kDa in fish and 35.7 kDa in meat could serve as indicators of spoilage.

Proteolysis of myofibrillar proteins in Pacific whiting surimi occurs when the 50- 70°C temperature range is reached during standard cooking procedures (e.g. 90°C for 15 min). This proteolytic activity results in the softening of surimi gels. Bovine plasma protein (BPP) is the most effective of the food-grade inhibitors used to prevent this reaction, and enhance gel strength in PW surimi. The objective of this study was to determine the effective components of bovine plasma that enhance gel strength in PW surimi. Five bovine plasma fractions were evaluated for components that contribute to gel strength enhancement in PW surimi. Fraction I, which consists mostly of fibrinogen and albumin, was found to also contain plasma transglutaminase (PTGase) activity. Part of fraction I gel-enhancing ability may be attributed to an unknown component which inhibited papain independently of Ca²⁺ and inhibited 40% of surimi proteolytic activity. Fibrinogen or albumin did not inhibit papain activity or enhance gel strength of surimi. For fraction I-S, which is a more concentrated PTGase fraction, gel-enhancement of PW surimi was completely dependent on the presence of Ca²⁺. Autolytic inhibitory activity of fraction I-S in surimi was completely eliminated by the presence of Zn²⁺. Fraction II+III (1%) inhibited over 50% of surimi autolytic activity and displayed a small amount of PTGase activity. Fraction II+III (1%) gel enhancing abilities were low when compared to the other fractions and BPP, and only slightly effected by EGTA. Fraction IV (1%), which contains approximately 50% albumin and 15% α₂-macroglobulin, inhibited over 70% of surimi autolytic activity. It enhanced gel strength at a 1% (w/w) concentration when set for 20 hr at 4°C before cooking, and was not affected by EGTA. This fraction displayed no apparent PTGase activity. Fraction IV-1 (1%), which contains approximately 20-30% α₂-macroglobulin, gel strength enhancement surpassed the other fractions and BPP when set for 20 hr at 4°C and 2 hr at 25°C before being cooked at 90°C for 15 min. The gel strength enhancing abilities of fraction IV-1 were significantly affected by EGTA. Fraction IV-1 (1%) inhibited over 80% of surimi proteolytic activity. The gel strength of 1 mM (0.03%) E-64, which is a cysteine protease inhibitor, was equivalent to that of BPP (1%) after setting at 4°C for 20 hrs before cooking. E-64 (1 mM) inhibited 83% of the autolytic activity of PW surimi and BPP (1%) inhibited 78%. These data indicate that a cysteine protease inhibitor can increase gel strength, and suggests that BPP is acting as a cysteine protease inhibitor. Ca²⁺ dependent gel strength enhancement was attributed to transglutaminase (TGase) activity, both added PTGase and endogenous TGase. Gel strength enhancement that was Ca²⁺ independent was attributed to cysteine protease inhibitors, specifically α₂-macroglobulin. Overall, it was determined that gel strength in PW surimi was greatly enhanced by both concentrated PTGase (I and I-S) and concentrated α₂-macroglobulin (IV-1) fractions, with a combination of these fractions being most effective in gel strength enhancement, when the surimi is first set at 4°C or 25°C before cooking at 90°C for 15 min. These data suggest that the mechanisms of gel strength enhancement of BPP are from cysteine protease inhibition, possibly from α₂-macroglobulin, and from crosslinking of myosin in surimi from both added (PTGase) and endogenous TGase activity. / Graduation date: 1996

No description available.

No description available.

Eight samples of varying qualities and ages of surimi were used in the development of a new method for testing the quality of surimi. The effects of salt, pH, concentration, heating temperatures and times, and cooling times were observed. These results were used in the development of the McRae-Manning Test. By employing this method, it was possible to determine the difference between fresh high quality surimi, fresh low quality surimi, and old surimi. For this test, surimi was mixed at a 15% concentration, heated at 90 C for 20 minutes in plastic syringes, cooled and evaluated. The surimi was evaluated by emptying the samples onto prepared transparent sheets and measuring how far the sample spreads with time. The transparent sheets had circular measurements which indicated the amount of spread. Best results were obtained when the sheets were elevated at one end.

Listeria monocytogenes is a common post-processing contaminant in ready-to-eat vacuum packaged (VP) cold smoked salmon. Since this psychrotrophic pathogen can grow at refrigerated temperatures (~4°C), other safety barriers in addition to temperature are needed to ensure the continued safety of VP cold smoked salmon. One such novel barrier could be the pulsed light (PL) treatment of the product prior to packaging or treating the product through a transparent package. / Pulsed light destruction kinetics of L. monocytogenes were evaluated while dispensed into a liquid media, on the surface of a general purpose agar and on the surface of cold smoked salmon. Results showed that PL technology was an effective surface sanitation method (a decimal reduction time or D-value of 0.91, 1.37 and 2.25 s exposure of PL at 800, 700 and 600 V, respectively, and a resulting z value of 500 V) on the agar plate. However, it had only a limited success when applied to liquid samples as well as directly on the surface of cold smoked salmon (D-value ranged from 93 s to 24 min). / Sensory quality of VP cold smoked salmon subjected to selected PL treatments was monitored during storage for 14 days at 4°C. Both color and odor scores remained within acceptable limits over the 14 day storage period. Subsequent challenge studies were carried out with L. monocytogenes applied on VP cold smoked salmon. An overall reduction in counts was observed in samples stored at 4°C over 28 days; however, after PL treatment (day 0), there was no significant reduction in counts. Color and odor scores maintained acceptable values over 14 days. Additional experiments were carried out to determine the effects of (1) 1.5% salt, (2) 6% oil, (3) a representative salmon media and (4) background microflora (lactic acid bacteria) on the PL inactivation of L. monocytogenes. All of these factors significantly affected the destruction of L. monocytogenes by increasing the D-value (adding resistance to pulsed light destruction). / Overall, these studies have shown that PL treatment in combination with low temperature storage (4°C) has the potential to extend the shelf-life of VP cold smoked salmon products without compromising sensory quality. However further investigation into higher treatment voltages is necessary in order to achieve a higher target kill of L. monocytogenes.

Increasing consumer demand for fresh fishery products with minimized loss of their nutritional properties is forcing food industry to look for alternative technologies to maintain the fresh attributes, stability and safety of foods. Demand for fresh tuna fish is no exception, being a valuable source of nutrients with immense health benefits. However, this product is highly perishable and has been commonly implicated in scombroid (histamine) poisoning caused by microbial decarboxylation of histidine contained in high levels in the tissues of scombroid fishes. Current techniques are inadequate for the prevention of histamine formation in fresh fishery products and high pressure processing is a potential alternative for it can inactivate microorganisms and enzymes, without affecting (or only minimally altering) the quality characteristics of foodstuffs. Previous studies have shown a decrease in histamine formation after a high pressure treatment and this study focuses on the effect of high pressure on the histidine decarboxylase enzyme and selected histamine forming microorganisms involved in histamine formation. / Commercial histidine decarboxylase suspended in different media (buffer solution and fish slurry with and without added histidine) was submitted to different high pressure treatments (200--400 MPa) with distinct time durations (0--60 min) at room temperature (20°C--25°C). Enzymatic activity of pressure treated and control samples were then compared by measuring histamine formation. Results were similar in all media; a 200 MPa treatment increased the enzymatic activity a little more than 20% as time increased; a 300 MPa treatment increased activity over 20% at first, followed by a decrease in activity as time increased only to reach a level of residual activity similar or only slightly lower than control samples; and a 400 MPa treatment reduced enzyme activity as time increased to a level of 55% residual activity in a buffer solution where the greatest inactivation was observed. / Enzyme activation and inactivation were affected by a dual effect attributed to a pulse effect, which caused a shift in activity and was independent of the length of the treatment, and a pressure-hold effect, during which activation or inactivation followed first order kinetics. The enzyme appeared highly resistant to pressure in all media as observed from D-values (>2700 min) and pressure sensitivity of destruction rate (zp) values (>500 MPa). / Inactivation of non-pathogen histamine forming bacteria (HFB) Escherichia coli K12 and Bacillus megaterium was evaluated by inoculating cultures in a fish tissue homogenate. Surviving colonies were enumerated after the treatments observing inactivation described by the same dual effect described earlier. Pressures above 300 MPa achieved a significant destruction of E. coli K12 (> 4 log-cycles) while B. megaterium appeared highly resistant for only a 2 log-cycle reduction was observed after at the highest pressure treatment conditions (400 MPa, 20 min). / D-values for both microorganisms decreased as pressure increased being significantly smaller for E. coli K 12, which also appeared to be more sensitive to pressure changes as observed from the zp values (zp = 151.51 MPa and zp = 909.10 MPa for E. coli and B. megaterium respectively. Inactivation caused by the pulse effect appeared very effective for both microorganisms as pressure increased, particularly at 400 MPa (PE > 1.25).

No description available.

A number of crab processors in the Maryland and Virginia region experienced an abnormally high incidence of spoilage in their pasteurized product in the fall of 1989. The spoilage was only seen in cans that were processed either shortly before or after hurricane Hugo and the majority of spoilage occurred in machine picked meat only. All processors pasteurized the meat at least to an Fi~5 of 32 minutes, which is the minimum National Blue Crab Industry Association (NBCIA) recommendation. Spoiled pasteurized crabmeat, processed in 1989 and 1990, were analyzed for their microbial content. Several cans that had spoiled in 1972 were also analyzed for microbial content Isolated organisms were tested for heat tolerance, and those organisms able to survive an F11~5 of 32 minutes or longer were identified. Can seams were evaluated to determine if the spoilage was due to post processing contamination. Approximate D-values were determined for the heat tolerant organisms. A psychrotrophic Clostridium sp. was found in all cans tested from a Maryland processor, Processor B. This processor only had spoilage in machine picked meat pasteurized after hurricane Hugo. Spoilage was seen in cans which had received a F 16/185 of 80 to 100 minutes. Spores from this organism had an approximate D-value of 6.5 minutes at 85 C in brain heart infusion broth (BHI). Cans from Processor B did not show any seam defects, and it was concluded that spoilage was due to the survival of spores, during pasteurization, from the Clostridium sp. that were able to outgrow at the temperature at which crabmeat is stored commercially. A Bacillus sp., possibly Bacillus pasteuranii, was found in one can from Processor B. Spores from this organism have an approximate D-value of 26.5 minutes in BHI broth at 85 C. This organism is unable to grow at refrigeration temperatures and it is not felt to have caused spoilage in the crabmeat. The Clostridium sp. found in cans from Processor B, pasteurized in 1989 and 1990, was also found in a can of jumbo lump meat from Processor D, processed in 1989, and a can of claw meat from Processor E, pasteurized around 1972. Cans from Processor A, who saw small amounts of spoilage before hurricane Hugo and in some hand- picked meat as well as machine piced meat had can seam measurements which did not meet specifications. It was concluded that spoilage from this processor was due to post-processing contamination. Crab processors must be aware that spores, from organisms that are able to outgrow at refrigeration temperatures, are able to survive pasteurization. The Clostridium sp. isolated in this study is one example. Processors will need to make sure their product is receiving sufficient heat to kill all spores of these organisms, while still maintaining a product with good sensory characteristics. It appears, from this study, that crab processors may want to increase the F-value that a lot of crabmeat receives after major storms, since the Clostridium sp. seemed to show up after hurricanes. Finally, crab processors need to be stringent in their sanitation and cleanliness so as to minimize the numbers of these types of organisms in their product. / Master of Science