Traditional Fermented Shrimp Research Articles

Improving the safety and quality of fermented shrimp paste (terasi) through supplementation of betel leaf (Piper betle L.) essential oil

Terasi is a traditional fermented shrimp paste that has been an integral part of Indonesian cuisine and food culture. Despite its broad use and complex distinctive flavor, shrimp paste could be harmful for human consumption, particularly when its quality has deteriorated. Indeed, many chemical reactions and microbial activities taking place during shrimp paste fermentation could lead to a decrease in quality and the formation of toxic compounds that are potentially injurious to human health. Thus, this study aimed to explore to improve the safety and quality of shrimp paste by incorporating betel leaf (Piper betle L.) essential oil, known to exert antioxidant and antimicrobial properties. The supplementation of betel leaf essential oil (1% and 5%) reduced lipid peroxidation as well as the formation of toxic compounds, including histamine and acrylamide in the shrimp paste fermented for 30 and 60 days. This phenomenon was associated with the inhibition of microbial growth in shrimp paste supplemented with betel leaf essential oil. The sensory analysis revealed that the supplementation of 1% betel leaf essential oil did not affect the consumer’s preference for shrimp paste. Therefore, the present study highlights the potential of betel leaf essential oil as a food additive to improve the safety and quality of fermented shrimp paste.

Supplementation of Moringa oleifera leaves improves the safety and quality of fermented shrimp paste

Terasi is a traditional fermented shrimp paste popularly consumed in Indonesia. Despite its widespread popularity and distinctive flavor, terasi consumption should be approached with caution due to the presence of harmful compounds linked to its degradation and declining quality. These compounds, including allergenic histamine and potentially carcinogenic acrylamide, form during the fermentation of terasi as a result of various chemical reactions and microbial activities. The objective of the current research was to enhance the safety and quality of shrimp paste by introducing Moringa oleifera leaves, locally known as daun kelor, that are rich in antioxidants and antimicrobial compounds. The supplementation of M. oleifera leaves (5%(w/w) and 10%(w/w)) significantly reduced microbial growth, lipid peroxidation, as well as the formation of histamine and acrylamide in terasi fermented for 30 days. Moreover, the inclusion of M. oleifera leaves did not alter the sensory acceptance of terasi. Consequently, this study suggests that M. oleifera leaves have the potential to serve as an adjunct ingredient, enhancing both the safety and overall quality of terasi.

Supplementation of Torch Ginger (Etlingera elatior) Flowers Improves the Quality and Safety of Traditional Fermented Shrimp Paste

Terasi, a traditional fermented shrimp paste from Indonesia, is commonly made from salted planktonic shrimp (Acetes japonicus) undergoing spontaneous lactic acid fermentation. In spite of its broad use and appreciated distinctive flavor, consuming terasi could be injurious for human consumption due to the presence of toxic compounds that are related to its deterioration and quality decrease, such as the allergenic histamine and probably carcinogenic acrylamide. These compounds are formed during fermentation of terasi due to a plethora of chemical reactions and microbial activities. This study aimed to improve the quality and safety of shrimp paste by incorporating during its fermentation torch ginger (Etlingera elatior) flowers, locally known as bunga kecombrang, that are rich in antioxidants and antimicrobial compounds. These flowers are widely utilized in Indonesian cuisine. The supplementation of torch ginger flowers (5%(w/w) and 10% (w/w)) significantly reduced microbial growth, lipid peroxidation, as well as the formation of histamine and acrylamide in terasi fermented over a period of 30 days. In addition, the supplementation of 10% torch ginger flowers improved the sensory acceptance of terasi. Therefore, this study suggests the potential of torch ginger flowers as an additional ingredient to improve the safety and quality of terasi.

A multi-omics-based investigation into the flavor formation mechanisms during the fermentation of traditional Chinese shrimp paste

The fermentation process of traditional shrimp paste is closely associated with the production of flavor substances, but the formation mechanism of key aroma components is still unclear. In this study, a comprehensively flavor profile analysis of traditional fermented shrimp paste was carried out by E-nose and SPME-GC–MS. A total of 17 key volatile aroma components with OAV > 1 contributed greatly to the overall flavor formation of shrimp paste. In addition, high-throughput sequencing (HTS) analysis revealed that Tetragenococcus was the dominant genera in the whole fermentation process. Moreover, metabolomics analysis showed that the oxidation and degradation of lipids, protein, organic acids and amino acids produced a large number of flavor substances and intermediates, which laid the foundation for the Maillard reaction in term of generating the distinct aroma of the traditional shrimp paste. This work will provide theoretical support for the realization of flavor regulation and quality control in traditional fermented foods.

Effects of fermentation time on chemical, microbiological, antioxidant, and organoleptic properties of Indonesian traditional shrimp paste, terasi

Terasi is a traditional fermented shrimp paste from Indonesia. It is commonly used in the preparation of sambal terasi, a traditional chili sauce. This study aimed to: (1) investigate the microbiological and chemical changes occurring during the fermentation of terasi for 90 days and (2) analyze the antioxidant activity and sensory acceptance of sambal terasi prepared from shrimp paste fermented for different durations. The microbial load increased during fermentation and was highly dominated by halophilic bacteria. The number of lactic acid bacteria decreased at the final stage of fermentation. While the pH fluctuated, the moisture content and water activity did not change during fermentation. According to its water activity (0.634–0.663), terasi is considered as an intermediate moisture food. Protein degradation and lipid oxidation took place during fermentation, as shown by the increase in TCA-soluble peptides and TBARS. Such processes contributed to the flavor development in terasi. In addition, the formation of potential toxic compounds also occurred during the fermentation of terasi, including histamine from protein degradation and acrylamide from the Maillard reaction. Terasi had a negligible antioxidant activity. However, sambal terasi had a strong antioxidant activity due to the presence of chili peppers and other spices rich in antioxidants. The sensory testing revealed consumer preference for sambal terasi prepared with shrimp paste fermented for a longer period (60–90 days). However, due to food safety reasons, it is preferred to opt for a shorter fermentation time of terasi (7–21 days).

The analysis of volatile compounds through flavoromics and machine learning to identify the origin of traditional Chinese fermented shrimp paste from different regions

Traditional Chinese fermented shrimp paste is a national geographical indication product with a distinctly regional flavor. The great commercial value and highly appreciated aroma urgently require establishing reliable methods to define the origin of shrimp paste and dissect the aroma essence. Therefore, in this study, flavoromics, chemometrics, and data augmented machine learning were performed to analyze shrimp paste from different regions of Bohai Bay, China. The results showed that shrimp paste contained several volatile compounds, including sulfur-containing compounds, nitrogen-containing compounds, aldehydes, and alcohols. In addition, chemometric and flavor association networks indicated that higher salt content produces some volatile compounds, such as 2-heptanone and phenylethanol. Furthermore, the prominent fruitiness and fermented aromas were associated with some key aroma substances, such as (E)-2-octenal and phenylethanol. Finally, a classification model for the origin identification of shrimp paste was developed. The results showed that seven trained machine learning models, including random forest (RF), support vector machine (SVM), and artificial neural network (ANN), were able to accurately (100%) identify the origin of shrimp paste. In summary, this study provides a theoretical support and application basis for identifying the origin and protection of the characteristic geographical flavor of shrimp paste.

New insights from flavoromics on different heating methods of traditional fermented shrimp paste: The volatile components and metabolic pathways

Traditional Chinese fermented shrimp paste is popular with consumers for its unique seafood flavor and fermented aroma. However, different heating methods exerted various flavors, which directly affect consumer choice and the industrialization of shrimp paste. In this study, the effect of four heating methods (steaming, frying, microwaving, and infrared) on volatile components of shrimp paste were compared by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC–MS), gas chromatography–ion mobility spectrometry (GC-IMS) and chemometrics. Results showed that 96 volatile components were identified; The volatile components such as pentanal, ethyl acetate, dimethyl disulfide, and propanal were the characteristic volatile components that could be distinguished between different heating methods. The concentration of phenols and alcohols decreased, and the concentration of ketones and aldehydes increased after heating. The effect of microwave heating on volatile components is closer to that of steaming and frying, while infrared heating had the most significant impact on volatile components of shrimp paste. In addition, steaming, frying, microwaving, and infrared heating improve the aroma quality of shrimp paste by promoting fat oxidation, protein degradation, the Strecker pathway, and the escape of sulfur-containing compounds. Therefore, our results can provide theoretical support for improving shrimp paste quality and consumer choice.

Microbiological safety and microbiota of Kapi, Thai traditional fermented shrimp paste, from different sources

Kapi is traditional Thai shrimp paste and is usually used as a seasoning. Traditional fermented foods are considered safe due to their long-standing consumption history, despite not having been evaluated for hygiene and microbiologically safety. Since Kapi is produced by natural fermentation, the microbiota differs depending on the raw material and production method. To control the quality of Kapi to a certain level, it is important to understand the microbiota of the product. In the present study, 27 Kapi samples purchased from wet markets and supermarkets were evaluated for microbiological safety and their microbiota was analyzed using 16S rRNA gene amplicon sequencing analysis. From the physicochemical analysis, the Kapi sample purchased at the wet market had a larger variation in pH and sodium chloride. Moreover, Kapi purchased from the wet market had a higher detection rate of E. coli, coliforms, and Bacillus group than those purchased from the supermarket. Salmonella, Listeria sp., and Vibrio sp. were not detected in any sample. The results of 16S rRNA gene amplicon sequencing analysis revealed that the microbiota differed for each sample regardless of the place of purchase, with Lentibacillus sp., Tetragenococcus sp., Salinicoccus sp., and Alkalibacillus sp. as the predominant groups.

The Effects of Garlic and Red Chilli Pepper Powder on Physicochemical, Microbiological, and Sensory Properties of Cincalok.

Cincalok, a traditional fermented shrimp, is prepared by mixing rebon shrimps (Acetes sp) with coarse salt and granulated sugar in a certain ratio. This research was aimed at studying the effect of adding garlic and red chilli pepper powder on the physicochemical, microbiological, and sensory properties of cincalok. Cincalok was made to be three recipes, namely, original cincalok, A, consists of 2 kg of rebon shrimp, 400 g of granulated sugar, and 100 g of coarse salt; B (A ingredients plus 20 g of red chilli pepper powder); and C (A ingredients plus 20 g of garlic powder). Sensory analysis was conducted on recipe A, and the colour was observed by the naked eye on days 0, 2, 4, 6, 8, 13, 18, 23, 28, 33, 43, 60, 90, 120, 150, and 180. According to the highest criterion score on sensory results, the panellists chose day 6 as the best fermentation for recipe A. The colour of recipe A started changing from pink to a light brown colour on the surface on day 28. Therefore, the physicochemical, microbiological, and sensory properties of each recipe were analyzed for 28 days. Overall, the water, ash, and fat content; titratable acid (TA); total volatile base nitrogen (TVBN); and amino acid nitrogen (AAN) showed insignificant differences (p > 0.05) among the recipes during 28 days of the same observation. The crude protein, pH, and free fatty acid (FFA) of recipe C were significantly different (p < 0.05) from recipes A and B. All recipes contained the total count of mesophilic anaerobic bacteria (TMABs) and the lactic acid bacteria (LABs) except Bacillus cereus, Clostridium perfringens, Staphylococcus aureus, and Enterobacteriaceae for all observation times. The highest criterion score for consumer acceptability was awarded for recipe C followed by recipes B and A. The addition of garlic and red chilli pepper powder affected the physicochemical, microbiological, and sensory properties of cincalok.

Extraction of Chitin From Shrimp Shell by Successive Two-Step Fermentation of Exiguobacterium profundum and Lactobacillus acidophilus.

As an environmentally friendly and efficient method, successive two-step fermentation has been applied for extracting chitin from shrimp shells. To screen out the microorganisms for fermentation, a protease-producing strain, Exiguobacterium profundum, and a lactic acid-producing strain, Lactobacillus acidophilus, were isolated from the traditional fermented shrimp paste. Chitin was extracted by successive two-step fermentation with these two strains, and 85.9 ± 1.2% of protein and 95 ± 3% of minerals were removed. The recovery and yield of chitin were 47.82 and 16.32%, respectively. Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM) were used to characterize the chitin. The crystallinity index was 54.37%, and the degree of deacetylation was 3.67%, which was lower than that of chitin extracted by the chemical method. These results indicated that successive two-step fermentation using these two bacterial strains could be applied to extract chitin. This work provides a suitable strategy for developing an effective method to extract chitin by microbial fermentation.

Genome sequencing of cold-adapted Planococcus bacterium isolated from traditional shrimp paste and protease identification.

Psychrophiles have evolved to adapt to freezing environments, and cold-adapted enzymes from these organisms can maintain high catalytic activity at low temperature. The use of cold-adapted enzymes has great potential for the revolution of food and molecular biology industries. In this study, four different strains producing protease were isolated from traditional fermented shrimp paste, one of which, named Planococcus maritimus XJ11 by 16S rRNA nucleotide sequence analysis, exhibited the largest protein hydrolysis clear zone surrounding the colonies. Meanwhile, the strain P. maritimus XJ11 was selected for further investigation because of its great adaptation to low temperature, low salinity and alkaline environment. The enzyme activity assay of P. maritimus XJ11 indicated that the optimum conditions for catalytic activity were pH 10.0 and 40 °C. Moreover, the enzyme also showed an increasing activity with temperatures from 10 to 40 °C and retained more than 67% activity of the maximum over a broad range of salinity (50-150 g L-1 ). Genome sequencing analysis revealed that strain XJ11 possessed one circular chromosome of 3 282 604 bp and one circular plasmid of 67 339 bp, with a total number of 3293 open reading frames (ORFs). Besides, 21 genes encoding protease, including three serine proteases, were identified through the NR database. Cold-adapted bacterium P. maritimus XJ11 was capable of producing alkaline proteases with high catalytic efficiency at low or moderate temperatures. Furthermore, the favorable psychrophilic and enzymatic characters of strain P. maritimus XJ11 seem to have a promising potential for industrial application. © 2020 Society of Chemical Industry.

Quality Improvement of Semi-Wet Terasi by Optimizing the Starter Culture Ratio of Controlled Fermentation

Terasi is a traditional fermented shrimp paste used in Indonesian dish as condiments. Due to its affordability, the paste is widely consumed among the general population, and thus has a great impact in Indonesia. Currently, small-scale or home industry is common for terasi production, and natural fermentation process is the traditional method. Fermentation process is considered complete when desired aromatic odors are obtained. However, this makes the fermentation process subjective, because the decision is solely dependent on the producer. Additionally, natural fermentation poses a higher risk for contamination of microbial pathogens. As a result, the quality of the final product varies greatly from region to region. Therefore, it is necessary to improve the quality of terasi by means of controlled fermentation. Hence, the objective of the research is to optimize the controlled fermentation condition of terasi by determining the most optimal ratio of mixed starter culture. Optimal fermentation conditions were determined by analyzing the effect of the various starter inoculum on the inner microbial community, and results indicated that mixed culture of Staphylococcus saprophyticus, Bacillus subtilis, and Lactobacillus murinus with ratio of 2:1:2 was the most effective for suppressing the growth of unwanted microorganisms. The difference in the microbial composition also resulted to a change in the metabolite profile of terasi.

Microbial diversity during processing of Thai traditional fermented shrimp paste, determined by next generation sequencing

Shrimp paste, one of the traditional Thai fermented food ingredients, is a mixture of small shrimp and salt fermented for 1–2 months which gives a unique and rich flavor to Thai dishes. Dynamics of microbial diversity during processing and its contribution to the flavor of shrimp paste was investigated by next generation sequencing. Bacteria containing aminopeptidase genes were analyzed to present the possibility relating to taste-enhancing di- and tripeptide generation. Furthermore, this study showed the difference of microbial community structure in shrimp pastes collected from various regions in Thailand. The microbial diversity structure dramatically changed from the raw materials since the first step of processing. Salimicrobium spp. (53.6%) and Salinicoccus spp. (44.0%) were the major population; however, they were decreasing during processing. Alkalibacterium, Macrococcus caseolyticus, Jeotgalicoccus psychophillus, and Staphylococcus spp. became visible. M. caseolyticus and J. psychrophilus were detected as the first time in shrimp paste products. Then in one-month fermented sample, Lentibacillus spp. was 3.3%. Although, as per our experimentation (water activity, salt and pH), we could not observe any significant difference among different products. In two-month fermented sample, Lentibacillus spp. was solely the most abundant microorganism. From aminopeptidase genes analysis, the abundance of Salinococcus spp. during preparation and Lentibacillus spp. during fermentation may relate to good flavor quality of shrimp paste.

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.

REDUCTION OF PATHOGENIC BACTERIA DURING FERMENTATION OF MASIN BY PROTEASE AND BACTERIOCIN-PRODUCING LACTIC ACID BACTERIA

Contamination of pathogenic and spoilage bacteria on fermentation process of seafood and fisheries product is a major concern on food safety. The aims of this study were isolating and applying the bacteriocin- and protease-producing lactic acid bacteria from the gastrointestinal tract of mud crab for starter culture of masin, a traditional fermented shrimp from East Java. This study consisted of characterization of lactic acid bacteria, the application on the fermentation process and microbial analysis. Ninety-four isolates were isolated from mud crab was screened for the bacteriocin and protease producing as well as characterized by pH, salinity and biochemical. Isolate IKP-29 was exhibited strong protease and bacteriocin activity. Application of Isolate IKP-29 on masin fermentation showed that sharp reduction of Escherichia coli, Vibrio sp. and lactic acid bacteria counted. This study suggested that the application of lactic acid bacteria which producing bacteriocin and protease improved the food safety of traditional fermented fish.

Physicochemical and Microbiological Profiles of Commercial Cincalok from West Kalimantan

&lt;p&gt;Cincalok, a traditional fermented shrimp product, is prepared with mix small and fresh shrimp, salt, and sugar in a certain ratio incubated for 3-7 days. Different recipes of each the commercial cincalok products obtain different of quality and safety level. The aim of this study is to assess the quality and safety of the commercial cincalok products of West Kalimantan based on their physicochemical and microbiological properties. Seven commercial cincalok products collected from the traditional market of West Kalimantan were analyzed physicochemical (moisture content, pH, free amino nitrogen (FAN), titratable acidity, salt content, glucose content, sucrose content, ethanol content) and microbiological (total number of mesophilic aerobic bacteria (TMABs), total halotolerant bacteria (THBs), endospores bacteria, lactic acid bacteria (LABs), fungi, Enterobacteriaceae, &lt;em&gt;Bacillus cereus, Clostridium perfringen&lt;/em&gt;s, and &lt;em&gt;Staphylococcus aureus&lt;/em&gt;)&lt;br /&gt;properties. The mean of moisture content, pH, free amino nitrogen (FAN), titratable acidity, salt content, glucose content, sucrose content, ethanol content for 7 samples was 67.59%, 5.16, 0.60 mM/g, 1.75%, 10.56%,&lt;br /&gt;1.30%, 0.49% and 0.59%, respectively. The mean of TMABs, THBs, endospores bacteria, LABs, fungi, and Enterobacteriaceae for 7 samples was 1.19-5.18 log CFU/g and 1.76 log CFU/g, respectively, while &lt;em&gt;B. cereus,&lt;/em&gt;&lt;br /&gt;&lt;em&gt;C. perfringens,&lt;/em&gt; and&lt;em&gt; S. aureus&lt;/em&gt; were not detected for all of the samples. The results showed high variation of physicochemical and microbiological properties of the products. Some of the products are safe to ate without&lt;br /&gt;cooked but the other still contain pathogenic bacteria such as some of the enterobacteriaceae strains.&lt;/p&gt;

Reduction of tyramine accumulation in Thai fermented shrimp (kung-som) by nisin Z-producing Lactococcus lactis KTH0-1S as starter culture

Tyramine production of 20 strains of lactic acid bacteria and coagulase-negative staphylococci isolated from Thai traditional fermented shrimp (kung-som) was investigated by using chromatographic and molecular methods. Among 20 strains tested, Enterococcus faecalis 9Y, Enterococcus faecalis D0KS13 and Weissella cibaria D0KS11 were able to produce tyramine and also harbor the tyrosine decarboxylase (tdc) gene. This indicated a positive correlation existing between the presence of tdc gene and production of tyramine. The effectiveness of nisin Z-producing Lactococcus lactis KTH0-1S against tyraminogenic strains was evaluated in co-cultivation experiments. Both co-culture of E. faecalis D0KS13 and W. cibaria D0KS11 with L. lactis KTH0-1S significantly decreased the growth rate and the maximal cell concentration, depending on the initial inoculum level of tyraminogenic strain. The reduction of tyramine accumulation decreased strongly when tyraminogenic strain was inoculated at 4.0 log cfu/mL and, to a lesser extent, at 5.0 and 6.0 log cfu/mL. Additionally, the inoculated kung-som with L. lactis KTH0-1S as starter culture showed significantly lower (p < 0.05) of Enterobacteriaceae, Staphylococcus aureus and total viable bacteria count than those of spontaneous kung-som. The addition of L. lactis KTH0-1S as a starter culture in kung-som was markedly reducing accumulation of tyramine by about 100 mg/kg in comparison with naturally fermented kung-som. Hence, the use of bacteriocinogenic amine-negative strain as a starter culture is advisable for production of safer kung-som with minimalized pathogen contaminants and lowering the tyramine content.

Changes in Sensory, Physicochemical and Microbiological Properties of Ronto During Fermentation

Abstract Background and Objective: Ronto is a traditional Indonesian fermented shrimp product; however, there are very few reports on how its properties change during fermentation. The aim of this study was to study the changes in sensory, physicochemical and microbiological properties of ronto during fermentation. Materials and Methods: Shrimp (Acetes japonicus) was mixed with salt and rice to give a mixture that was 11.5% salt and 20% rice. The mixture was put into plastic bottles and incubated at room temperature for 18 days. Samples were taken after every 2 days and sensory, physicochemical and microbiological properties were analyzed. Results: It was found that the fermented shrimp developed a sour, savory flavor and bright pink color after 8 days of fermentation, both of which became stronger after 12 days. After 14 days of fermentation, the texture of the shrimp gradually became that of a porridge-like paste. The acidity of the fermented shrimp increased during fermentation, after 12 days of fermentation, the pH had decreased from 8.3-4.8. The total volatile bases increased from 25-150 mg N/100 g over 18 days of fermentation. Lactic acid, proteolytic and amylolytic bacteria were involved in the fermentation process. The concentrations of these three bacteria increased during the early phases of fermentation and decreased in the later phases. Conclusion: Ronto fermentation ended after 14 days when the color of the fermented material became bright pink and when it had developed a strong, sour and savory flavor. That product had a lightness (53.11), a redness (11.72), a yellowness (15.68), a pH (4.8) and the texture of porridge-like paste and was relatively low in total volatile bases. Key words: Ronto, fermented shrimp, sensory, physicochemical, microbiology

Occurrence of chitinolytic bacteria in shrimp rusip and measurement of their chitin-degrading enzyme activities

Puspita ID, Wardani A, Puspitasari ROA, Nugraheni PS, Putra MMP, Pudjiraharti S, Ustadi. 2017. Occurrence of chitinolytic bacteria in shrimp rusip and measurement of their chitin-degrading enzyme activities. Biodiversitas 18: 1275-1281. The objectives of this research were to isolate chitinolytic bacteria from shrimp rusip (an Indonesian traditional fermented shrimp product), identify bacterial isolates showing high chitinolytic activity, and determine the chitinolytic activity of these isolates. There were 44 chitinolytic bacteria isolated from shrimp rusip: 39 isolates of Gram-positive bacteria and 5 isolates of Gram-negative bacteria. The quantitative method we used to evaluate chitin-degrading enzyme activity measured the amount of N-acetylglucosamine produced from the reaction of crude enzyme and colloidal chitin. Seven isolates showing highest chitinolytic activity were Bacillus cereus (KKT 1, KKT 14, and KKT 19), Bacillus thuringiensis (KKT 6), Enterobacter cloacae (LCK 20), Pseudomonas stutzeri (LCK 17), and Stenotrophomonas maltophilia (THK1). The highest chitinolytic activity showed by KKT 1, KKT 6, KKT 14, KKT 19, and THK 1 were 0.0016 U/mL (at 72 hours); 0.0018 U/mL (at 48 hours); 0.0019 U/mL (at 48 hours); 0.0033 U/mL (at 48 hours); and 0.0032 U/mL (at 24 hours), respectively.

Analyzing the flavor compounds in Chinese traditional fermented shrimp pastes by HS-SPME-GC/MS and electronic nose

Shrimp paste is a type of condiments with high nutritional value. However, the flavors of shrimp paste, particularly the non-uniformity flavors, have limited its application in food processing. In order to identify the characteristic flavor compounds in Chinese traditional shrimp pastes, five kinds of typical commercial products were evaluated in this study. The differences in the volatile composition of the five products were investigated. Solid phase micro-extraction method was employed to extract the volatile compounds. GC-MS and electronic nose were applied to identify the compounds, and the data were analyzed using principal component analysis (PCA). A total of 62 volatile compounds were identified, including 8 alcohols, 7 aldehydes, 3 ketones, 7 ethers, 7 acids, 3 esters, 6 hydrocarbons, 12 pyrazines, 2 phenols, and 7 other compounds. The typical volatile compounds contributing to the flavor of shrimp paste were found as follows: dimethyl disulfide, dimethyl tetrasulfide, dimethyl trisulfide, 2, 3, 5-trimethyl-6-ethyl pyrazine, ethyl-2, 5-dimethyl-pyrazine, phenol and indole. Propanoic acid, butanoic acid, furans, and 2-hydroxy-3-pentanone caused unpleasant odors, such as pungent and rancid odors. Principal component analysis showed that the content of volatile compounds varied depending on the processing conditions and shrimp species. These results indicated that the combinations of multiple analysis and identification methods could make up the limitations of a single method, enhance the accuracy of identification, and provide useful information for sensory research and product development.