Haejung An

University of Southern California, Los Angeles, California, United States

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Publications (25)50.19 Total impact

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    ABSTRACT: Isoelectric focusing (IEF) polyacrylamide gel containing an 80% pH 4–6.5 and 20% pH 3–10 ampholyte mixture greatly improved protein banding pattern for species identification of water extracts of raw pink, white and rock shrimp compared with the system using only the pH 3–10 range ampholyte. Identification of a specific species in mixture samples was achieved by the detection of water-extractable shrimp specific protein bands present in the gel. Sodium dodecyl sulfate (SDS) was a better protein extractant than water for cooked shrimp. Both water and SDS extracts of cooked shrimp showed specific protein banding patterns and improved resolution for species identification.
    No preview · Article · Feb 2007 · Journal of Food Biochemistry
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    ABSTRACT: Commonly used protease assays and substrates were compared for sensitivity and simplicity in analyzing proteolytic activity in Pacific whiting causing gel weakening of surimi during heat-setting. Assay based on detection of trichloroacetic acid (TCA)-soluble products, using azocasein as substrate, showed highest sensitivity. By that assay, optimal pH of the protease was 5.5, and optimal temperature, 55°. The validity of the assay for measuring activity was confirmed by pH profiles of residual proteolytic and autolytic activities of uncooked surimi. These analyses showed pH profiles similar to those of fish juice with a pH optimum of 5.5.
    No preview · Article · Aug 2006 · Journal of Food Science
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    ABSTRACT: ABSTRACTA proteinase in Pacific whiting surimi wash water (SWW) was characterized to be cathepsin L based on molecular mass (Mr), substrate specificity, and SDS-substrate gel electrophoresis. The proteinase was highly active on Z-Phe-Arg-NMec, and the native Mr was 27,400 based on size exclusion (SEC)-HPLC. Acidification of the SEC-HPLC fractions showed a two-fold increase in activity on Z-Phe-Arg-NMec. SWW proteolytic activity was found at Mr 54,200 on SDS-substrate gel. However, acidification shifted the activity zone to Mr 39,500 corresponding to cathepsin L. No evidence of activity by calpain or cathepsin B or H was found in Pacific whiting SWW.
    No preview · Article · Aug 2006 · Journal of Food Science
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    ABSTRACT: Cathepsin B was the most active cysteine protease in Pacific whiting fish fillets; cathepsin L was predominant in surimi. Cathepsin L showed highest activity at 55°C in both fish fillets and surimi, indicating its function in myosin degradation during conventional heating of fillets and surimi, gels. Washing during surimi processing removed cathepsin B and H but not cathepsin L. Myosin heavy chain was the primary substrate during autolysis of surimi paste and actin and myosin light chain showed limited hydrolysis during 2 hr incubation. Purified Pacific whiting cathepsin L hydrolyzed myofibrils, myosin and native and heat-denatured collagen. The degradation pattern of myofibrils by the protease was the same as the autolytic pattern of surimi.
    No preview · Article · Aug 2006 · Journal of Food Science
  • Shin-Hee Kim · Cheng-I Wei · Ywh-Min Tzou · Haejung An
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    ABSTRACT: Multidrug-resistant enteric bacteria were isolated from turkey, cattle, and chicken farms and retail meat products in Oklahoma. Among the isolated species, multidrug-resistant Klebsiella pneumoniae was prevalently isolated from most of the collected samples. Therefore, a total of 132 isolates of K. pneumoniae were characterized to understand their potential roles in the dissemination of antibiotic-resistance genes in the food chains. Multidrug-resistant K. pneumoniae was most frequently recovered from a turkey farm and ground turkey products among the tested samples. All isolates were resistant to ampicillin, tetracycline, streptomycin, gentamycin, and kanamycin. Class 1 integrons located in plasmids were identified as a common carrier of the aadA1 gene, encoding resistance to streptomycin and spectinomycin. Production of beta-lactamase in the K. pneumoniae isolates played a major role in the resistance to beta-lactam agents. Most isolates (96%) possessed bla(SHV1). Five strains were able to express both SHV-11 (pI 6.2) and TEM-1 (pI 5.2) beta-lactamase. Transfer of these antibiotic-resistance genes to Escherichia coli was demonstrated by transconjugation. The bacterial genomic DNA restriction patterns by pulsed-field gel electrophoresis showed that the same clones of multidrug-resistant K. pneumoniae remained in feathers, feed, feces, and drinking water in turkey environments, indicating the possible dissemination of antibiotic-resistance genes in the ecosystem and cross-contamination of antibiotic-resistant bacteria during processing and distribution of products.
    No preview · Article · Nov 2005 · Journal of food protection
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    ABSTRACT: An immunoassay system was developed for efficient detection of prohibited meat and bone meal (MBM) in animal feed. Monoclonal antibodies (MAbs) were raised against bovine smooth muscle autoclaved at 130 degrees C for 20 min. Among the 1,500 supernatants of hybridoma cells screened, MAbs 3E1, 1G3, and 3E10 were selected and characterized in this study. The first set of MAbs produced, 3E1 and 1G3, had stronger reactivity against MBM than against smooth muscle that was heat treated at 90 degrees C for 10 min. However, reactivity gradually increased against smooth muscle that was autoclaved at 130 degrees C for up to 1 h. The enzyme-linked immunosorbent assay for detection of MBM in animal feed was optimized with the MAb 3E10 because of its superior performance. MAb 3E10 diluted to 100-fold was used to differentiate bovine MBM from that of other species in ingredients used for commercial animal feeds and could detect down to 0.05% MBM mixed in animal feed.
    No preview · Article · Oct 2005 · Journal of food protection
  • Shin-Hee Kim · Cheng-I Wei · Haejung An
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    ABSTRACT: Sixty-four multidrug-resistant isolates of Proteus mirabilis were collected from retail meat products in Oklahoma. The isolates showed four different patterns of antibiotic resistance based on their resistant phenotype and genotypes. Most of these isolates were resistant to ampicillin, tetracycline, gentamycin, and kanamycin. Class 1 integrons were detected as a common carrier of the antibiotic-resistant genes, such as aadA1, aadB, and aadA2. A few isolates (9%) contained class 2 integrons with three gene cassettes included: dhfr1, sat1, and aadA1. These isolates were even resistant to nalidixic acid due to mutations in gyrA and parC. All ampicillin-resistant isolates contained blaTEM-1. Plasmids that contained class 1 or 2 integrons and blaTEM-1 were able to be transferred from P. mirabilis isolates into Escherichia coli by conjugation, indicating that conjugal transfer could contribute to the dissemination of antibiotic resistance genes between the Enterobacteriaceae species.
    No preview · Article · Aug 2005 · Journal of food protection
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    ABSTRACT: An antimicrobial peptide was purified from fermented skate skin extract using the solid-phase extraction and separation on HPLC reversed-phase chromatography. Amino acid sequence of the purified peptide (Peak A) having an antimicrobial activity revealed the presence of many cationic residues of the total 28 amino acids. Its molecular mass was found to be 3059 Da. This result was in excellent agreement with the theoretical molecular mass calculated from the amino acid sequence. The synthetic kenojeinin I had inhibitory effects on B. subtilis (MIC, 12 microg/ml), E. coli (28 microg/ml), and S. cerevisiae (12 microg/ml). These results indicate that fermented skate skin is potentially antimicrobial.
    No preview · Article · May 2005 · Peptides
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    ABSTRACT: Histamine and biogenic amine contents in retail canned anchovies were determined. Bacterial strains were isolated, and their histamine-producing capability was determined. The majority of canned anchovy products (80%) had histamine levels below the FDA guideline of 50 ppm. The sensory quality of products was relatively good. A few samples contained high levels of histamine (>1000 ppm). Overall, histamine contents in the products showed great lot-to-lot variations. Spermine and tyramine were commonly detected in all samples analyzed, regardless of their histamine contents. Bacterial counts in the products were mostly below the detection limit (102 CFU/g), and bacteria were frequently recovered with the enrichment of test samples in tryptic soy broth supplemented with 0.5% or 5% NaCl. Only Bacillus spp., the nonhistamine formers, were isolated from these test products. Prolific histamine-forming bacteria were not detected in these canned anchovies.
    Preview · Article · Feb 2005 · Journal of Food Science
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    ABSTRACT: For the detection of prohibited meat and bone meal (MBM) in animal feed, monoclonal antibodies (MAbs) were raised against heat-stable h-caldesmon purified from bovine intestinal smooth muscle. The obtained hybridoma cells were screened against extracts of the bovine MBM and heat-treated smooth muscle, and MAb 5E12 was identified as having the best performance. Antibody 5E12 did not react with animal feed, milk product, plant proteins, and other ingredients used for commercial animal feed except for the gelatin. This antibody diluted to 100-fold was able to detect MBM mixed in animal feed at 0.05% in an ELISA, and it showed strong affinity toward bovine smooth muscle autoclaved at 130 degrees C. Therefore, this antibody can be used in the ELISA system for field testing of the presence of MBM in animal feed.
    No preview · Article · Jan 2005 · Journal of Agricultural and Food Chemistry
  • Article: Review

    No preview · Article · Jan 2004 · Journal of Aquatic Food Product Technology
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    ABSTRACT: A polymerase chain reaction (PCR) assay for the rapid and sensitive detection of the most prolific histamine former, Morganella morganii, was developed. 16S rDNA targeted PCR primers were designed, and the primer specificity and sensitivity of the PCR assay were evaluated. The 16S rDNA sequence (1,503 bp) for M. morganii showed 95% identity to those for enteric bacteria, i.e., Enterobacter spp., Klebsiella spp., Citrobacter spp., Hafnia alvei, Proteus spp., and Providencia spp. The unique primers for M. morganii were designed on the basis of the variable regions in the 16S rDNA sequence. The primers showed positive reactions with all M. morganii strains tested. However, PCR amplification was not detected when the primers were tested with other enteric or marine bacteria. When the sensitivity of the assay was evaluated, M. morganii was detected at levels ranging from 10(6) to 10(8) CFU/ml in albacore homogenate after the PCR amplification. The sensitivity of the assay was greatly improved with the enrichment of samples, and 9 CFU of M. morganii per ml of albacore homogenate was detected after 6 h of enrichment at 37 degrees C.
    No preview · Article · Sep 2003 · Journal of food protection
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    ABSTRACT: A reverse dot-blot DNA/DNA hybridization method coupled with a non-radioactive nucleic acid detection system was evaluated for the direct detection of the emerging pathogen Stenotrophomonas maltophilia in albacore tuna, a fish species of high commercial value in Europe and the US. Probes consisting of total genomic DNA of S. maltophilia, when used in dot-blot hybridization assays, differed in a sufficient way with respect to Morganella morganii, Enterobacter aerogenes Enterobacter agglomerans, Klebsiella planticola, Acinetobacter baumani and other bacteria frequently isolated from spoiled tuna fish species, as to allow its specific detection in extracts of albacore tuna. The introduction of an enrichment step prior to DNA isolation and labelling allowed the successful detection of 102 viable cells of S. maltophilia in 1 ml of artificially-contaminated albacore muscle extracts with no cross-hybridization with other Gram-negative competing microflora being observed. The detection strategy described in this work may be useful for the detection and control of S. maltophilia in tuna fish species and seafood products.
    No preview · Article · Jun 2002 · Food Control
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    ABSTRACT: Cystatins are a superfamily of low Ki cysteine proteinase inhibitors found in both plants and animals. Cystatin C, a secreted molecule of this family, is of interest from biochemical and evolutionary points of view, and also has biotechnological applications. Recently we cloned and sequenced the cDNA for rainbow trout (Oncorhynchus mykiss) cystatin C [Li et al., 1998. Molecular cloning, sequence analysis and expression distribution of rainbow trout (Oncorhynchus mykiss) cystatin C. Comp. Biochem. Phys. B 121, 135-143]. To explore the relationship between protein structure and function of trout cystatin C, we established a bacterial system for expression of the protein. Trout cystatin C expressed in the cytoplasm of bacterial cells did not have detectable protease inhibitory activity. Activity was regained by Ni-NTA chromatography under denaturing conditions followed by dialysis-based refolding. Titration of purified cystatin C preparations with papain indicated that approximately 20% of the total protein had been converted to the active form after one refolding cycle. Expression levels were 3-5 mg/l. The protease-inhibitory properties of recombinant trout cystatin C were similar to those of human and chicken cystatin C derived from biological sources and recombinant cystatin C derived from rat and mouse genes. The Ki for papain was 1.2 x 10(-15) M, exhibiting the high affinity binding unique to this family of protease inhibitors.
    No preview · Article · May 2000 · Comparative Biochemistry and Physiology Part B Biochemistry and Molecular Biology
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    ABSTRACT: Cystatin C is one of a family of proteinase inhibitors of cathepsins and other cysteine proteinases. Among warm-blooded vertebrates, small functional regions of cystatin amino acid sequences are well conserved among species, but major portions of cystatin amino acid sequences vary evolutionarily. Although considerable attention has been given to mammalian and avian cystatins, little data exist on cystatins from other vertebrates. A cDNA clone for trout cystatin C was isolated from a lambda gt11 cDNA library of rainbow trout (Oncorhynchus mykiss) liver. An apparently full-length cDNA clone of 674 bp encoding 132 amino acid residues was obtained. Sequence analysis indicated that trout cystatin C contains an N-terminal signal sequence extension of 21 amino acids and a mature sequence of 111 amino acid residues, with amino acid residues conserved in functional regions relative to mammalian and avian cystatin C. Using cloned cDNA as a probe, we investigated expression of the cystatin C gene in trout tissues, several cell lines of trout liver or liver tumor, and cell cultures of liver tumor origin. Cystatin C mRNA was in high abundance in trout embryo tissue, a tumor-derived liver cell line and some normal adult tissues. Southern hybridization analysis indicated one copy of the trout cystatin C gene per haploid genome, and sequence comparisons indicated considerable divergence in large portions of the coding region of the trout cystatin C gene relative to a variety of species.
    No preview · Article · Nov 1998 · Comparative Biochemistry and Physiology Part B Biochemistry and Molecular Biology
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    ABSTRACT: Gel strength enhancement of Pacific whiting surimi was studied by using an α2-macroglobulin (α2-M)-enriched plasma fraction (FIV-1) and a transglutaminase (TG)-enriched plasma fraction (FI-S). Fluorescent amine-incorporating activity was detected in FIV-1, FI-S, and bovine plasma protein (BPP), indicating potential protein cross-linking activity by α2-M and TG. Inhibition of autolytic activity was observed with FIV-1 and BPP. FIV-1 in combination with bovine serum albumin, fibrinogen, or FI-S enhanced gelation more than FIV-1 alone. These results indicate various components in BPP function both to enhance gelation of Pacific whiting surimi and to inhibit proteolysis. Keywords: Plasma protein; transglutaminase; α2-macroglobulin; surimi; gelation
    No preview · Article · Aug 1997 · Journal of Agricultural and Food Chemistry
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    ABSTRACT: No changes in actomyosin Ca2+-, Mg2+-, or Mg2+-Ca2+-ATPase activities were observed during iced storage of Pacific whiting fillets, but Mg2+-EGTA-ATPase increased with a loss of Ca2+-sensitivity. Surface hydrophobicity of actomyosin increased substantially within 2 days, but not total sulfhydryl (SH) content. During longer storage, the SH content decreased gradually, but surface hydrophobicity remained constant. Autolytic degradation products increased in fish muscle with storage time. Myosin heavy chain (MHC) was degraded by 45% within 8 days, but no noticeable difference was observed in actin. Results indicated that autolysis may be the main cause of physicochemical changes in Pacific whiting muscle proteins during iced storage.
    No preview · Article · Jun 1997 · Journal of Food Science
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    ABSTRACT: Abstract. Cystatins are a superfamily of cysteine proteinase inhibitors found in both plants and animals. We were interested in the molecular cloning of rainbow trout (Oncorhynchus mykiss) cystatin, but were unable to identify cystatin-related sequences using a mammalian cystatin probe. In a second approach, highly degenerate oligonucleotide primers for polymerase chain reaction were designed from corresponding conserved amino acid sequences of cystatin family 2. First-strand cDNA was made from total RNA of rainbow trout liver. A prominent band of the predicted size was observed on agarose gel following electrophoresis of products generated by reverse transcription polymerase chain reaction. The amino acid sequence deduced from the corresponding cDNA sequence of this PCR product is 98% identical to the corresponding cystatin amino acid sequence of chum salmon (Oncorhynchus keta).
    No preview · Article · Feb 1997 · Journal of Marine Biotechnology
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    ABSTRACT: The gelation of surimi is largely dependent on appropriate interactions between adjacent myosin molecules. The development of myosin gels occurs at two stages during heating: at 30–40°C by unfolding of α-helices in the tail portion of myosin molecules, and above 50°C by interactions between hydrophobic regions, which are rich in the head portions of myosin molecules. Proteinases and transglutaminases can affect the gelation process and, consequently, the gel strength of surimi, by hydrolyzing or crosslinking myosin, respectively. Protein additives have been widely used to inhibit proteinase activity and enhance myosin crosslinking. Fish species with high proteolytic activity can be successfully utilized for surimi with the aid of protein additives.
    No preview · Article · Oct 1996 · Trends in Food Science & Technology
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    ABSTRACT: Commonly used food-grade inhibitors, beef plasma protein (BPP), egg white, and potato powder, were characterized for their inhibitory activity toward proteinases. BPP and egg white had the highest rate of cysteine and serine proteinase inhibition, respectively. Egg white, containing specific serine proteinase inhibitors, reduced trypsin activity by as much as 99%. Active inhibitory components in the proteinase inhibitors were detected by inhibitory activity staining on sodium dodecyl sulfate (SDS)-substrate gels. Egg white and potato powder contained more serine proteinase inhibitor bands than cysteine proteinase inhibitor bands. No specific cysteine proteinase inhibitory component was found in BPP. Serum albumin was detected on both papain and trypsin inhibitory activity-stained gels of BPP but was not inhibitory to the proteinases. A high molecular weight protein band (HMP) of BPP was also detected on both inhibitory activity-stained gels, but the protein was postulated to be polymerized plasma components resistant to proteolysis. Keywords: Activity staining; proteinase inhibitor; surimi
    No preview · Article · Sep 1996 · Journal of Agricultural and Food Chemistry

Publication Stats

994 Citations
50.19 Total Impact Points


  • 2004-2005
    • University of Southern California
      • School of Pharmacy
      Los Angeles, California, United States
  • 2002-2003
    • Auburn University
      Auburn, Alabama, United States
  • 1994-2000
    • Oregon State University
      • Department of Food Science and Technology
      Corvallis, Oregon, United States
  • 1997
    • Prince of Songkla University
      • Department of Food Technology
      Amphoe Muang Songkhla, Songkhla, Thailand