Halophilic bacteria as starter cultures: A new strategy to accelerate fermentation and enhance flavor of shrimp paste.

Retaining the traditional flavor while shortening the fermentation cycle is the current research focus for shrimp paste fermentation technology. The present study investigated the effect of combined use of halophilic bacteria as starters on the sensory and flavor characteristics of rapidly fermented shrimp paste. Sensory evaluation indicated that the starter-inoculated samples had high texture, appearance, and overall quality scores. Headspace gas chromatography-ion mobility spectrometry/mass spectrometry (HS-GC-IMS/MS) identified 95 volatile compounds, the fingerprint profiles of the starter-inoculated samples were similar to those of the traditional sample. Notably, the content of benzaldehyde, phenylethylaldehyde, and 3-methylbutyraldehyde increased significantly in the starter-inoculated samples (p < 0.05), which may provide an intense malt, caramel, and pleasant odor. Although the content of certain flavor substances in the starter-inoculated samples was lower than those of traditional sample, the use significantly reduced the fermentation time and mimicked the flavor profile of traditional shrimp paste to some extent.

Effect of carboxymethyl chitosan on the detoxification and biotransformation of paralytic shellfish toxins in oyster Ostrea rivularis.

Economic bivalve ingested toxic algae causes frequent human poisoning events. To explore new compounds that can accelerate the depuration of toxins in shellfish, we investigated the detoxification of the paralytic shellfish toxins (PSTs) and the biotransformation pathway of PSTs during detoxification by the application of three treatments to a toxic bloom, Alexandrium minutum (A. minutum). The detoxification effect of Platymonas subcordiformis (PS) mixed with carboxymethyl chitosan (CMC) group is significantly better than the starving group in each oyster tissues. The toxicity of viscera which occupied 78.95% of total toxicity reduced to 155 MU/100g after 13 days' depuration experiment. And adding CMC could significantly achieve rapid detoxification and effectively reduce the STX to 0.07 µmol/100 g in viscera. Meanwhile, PSTs underwent biotransformation during the depuration process, which mainly manifested as GTX1/4→GTX2/3→STX, GTX2→dcGTX2. This study explored a new strategy for toxin depuration in shellfish.

Efficient extraction of chitin from shrimp waste by mutagenized strain fermentation using atmospheric and room-temperature plasma.

Chitin extraction from shrimp waste by protease-producing microorganisms was a positive and simple method. To improve the protease activity of microorganism used for the extraction of chitin, atmospheric and room temperature plasma technology was adopted to induce mutations in Exiguobacterium profundum, a protease-producing bacterium, which was isolated from traditional fermented shrimp paste. After several rounds of screening, the mutant numbered 10017 was screened. The hereditary properties of the mutant were found to be stable after a series of passages. This strain was subsequently used in the deproteinization process, which could remove 91.48% ± 2.60% protein, and the chitin recovery was 70.18 ± 2.68%. Fourier transform infrared spectrometry, X-ray diffraction, and scanning electron microscopy was adopted to compare the characteristics of the chitin extracted from mutagenized and wild-type strain fermentation. The crystallinity indices were 80.72% and 82.46%, and the degrees of deacetylation were 15.78% and 27.84%. These results indicated that the deproteinization by mutagenized strain fermentation might be applied to the production of chitin. Thus, the present study provides an appropriate strategy to develop an efficient method to improve protease activity in microbial fermentation.

Synthesis, Antimicrobial, Moisture Absorption and Retention Activities of Kojic Acid-Grafted Konjac Glucomannan Oligosaccharides.

Kojic acid (KA) with antibacterial activities produced by fermentation was grafted onto konjac glucomannan oligosaccharide (KGO) composed of glucose and mannose linked by ß-1,4 glycosidic bonds. A novel KGO derivative, konjac glucomannan oligosaccharide kojic acid (KGOK) possessing both moisture retention and antibacterial activities was synthesized. The structure of KGOK was characterized and analyzed by thermogravimetric analysis (TG), XRD, UV-vis absorption, FTIR, and 1H NMR. The analysis results suggest that KA was linked to the KGO molecular chain through a covalent bond, and the reaction site of KA was the methylol group. The studies demonstrate that KGOK maintained the excellent moisture absorption and retention properties of KGO and the good antibacterial activities of KA. The minimum inhibitory concentration (MIC) of KGOK is 2 mg/mL for Staphylococcus aureus, Staphylococcus epidermidis, Shewanella putrefaciens, and Salmonella enterica, while its MIC is 3 mg/mL for Escherichia coli. The multi-functionality of the KGOK synthesized from natural sources provides a theoretical foundation for their potential applications in the preservation of food, beverage, aquatic, and cosmetic products.

Characterization and application of enterocin RM6, a bacteriocin from Enterococcus faecalis.

Use of bacteriocins in food preservation has received great attention in recent years. The goal of this study is to characterize enterocin RM6 from Enterococcus faecalis OSY-RM6 and investigate its efficacy against Listeria monocytogenes in cottage cheese. Enterocin RM6 was purified from E. faecalis culture supernatant using ion exchange column, multiple C18-silica cartridges, followed by reverse-phase high-performance liquid chromatography. The molecular weight of enterocin RM6 is 7145.0823 as determined by mass spectrometry (MS). Tandem mass spectrometry (MS/MS) analysis revealed that enterocin RM6 is a 70-residue cyclic peptide with a head-to-tail linkage between methionine and tryptophan residues. The peptide sequence of enterocin RM6 was further confirmed by sequencing the structural gene of the peptide. Enterocin RM6 is active against Gram-positive bacteria, including L. monocytogenes, Bacillus cereus, and methicillin-resistant Staphylococcus aureus (MRSA). Enterocin RM6 (final concentration in cottage cheese, 80 AU/mL) caused a 4-log reduction in population of L. monocytogenes inoculated in cottage cheese within 30 min of treatment. Therefore, enterocin RM6 has potential applications as a potent antimicrobial peptide against foodborne pathogens in food.

Antimicrobial properties of milkfat globule membrane fractions.

Milkfat globule membranes (MFGMs) were prepared from bovine cream according to standard procedures. These membranes and peptide hydrolysates, which were generated by proteolysis with immobilized digestive enzymes, were screened for antibacterial activity against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica Typhimurium, Pseudomonas fluorescens, Bacillus cereus, Lactobacillus acidophilus, and Lactobacillus gasseri. Assays were first performed on beef heart infusion (BHI) plates spotted with test protein-peptide fractions and then seeded with lawns of indicator cells to monitor the zone of growth inhibition. Under these experimental conditions, MFGMs were most active against Salmonella Typhimurium and P. fluorescens. However, antibacterial activity was not seen after plating on Luria-Bertani (LB) medium. We determined that the antimicrobial effects observed on BHI plates were due to the generation of H2O2 by xanthine oxidase, a major protein constituent of the MFGMs, as a result of purine catalysis. This substrate is present in BHI but lacking in LB medium. Evaluation of purified xanthine oxidase alone resulted in analogous data trends. The growth of probiotic Lactobacillus strains were affected only marginally when grown on lactobacilli deMan Rogosa Sharpe plates, suggesting the decreased sensitivity of these bacteria to H2O2. In this study, several MFGM hydrolysates exhibited variable antibacterial activity against test food pathogens on agar plates prepared with M9 minimal media, and this variation was not attributable to xanthine oxidase enzymatic activity. The probiotic microorganisms were mostly resilient to these antibacterial fractions. Bovine MFGM fractions may represent an excellent resource material from which to generate native, naturally occurring biodefensive proteins and/or peptides.