冰藏三文鱼品质变化及菌相分析

以感官、物理(质构、色差)、化学(TVB-N、TMA-N、K值)及微生物(菌落总数、嗜冷菌落数、致病菌数)为指标,研究三文鱼冰藏期间的品质变化,并对三文鱼冰藏期间的菌相变化及优势腐败菌进行分析。结果表明:三文鱼在冰藏期间品质变化明显,第4天到达高品质期终点,第10天感官即已不可接受。冰藏过程中,色差变化很小,质构变化中剪切力与咀嚼性逐渐减小,硬度与弹性先增加后减小,黏附性在贮藏后期上升,前期波动较大。TVB-N、TMA-N、TVC和K值变化明显,冰藏到第10天已分别达到17.36 mg/100 g、7.62 mg/100 g、7.64 lg(CFU/g)和68.7%。菌相分析表明假单胞杆菌属(Pseudomonas spp.)为冰藏三文鱼的特定腐败菌。     

大菱鲆冷藏过程中的鲜度变化与货架期

以感官、化学和微生物为指标,对大菱鲆(Scophthalmus maximus)在0(冰藏)、3、7℃和10℃贮藏过程中的鲜度变化和货架期进行研究,并探讨菌落总数、嗜冷菌、假单胞菌、产H2S 菌、TVB-N、TMA-N 与感官评价的一致性。结果表明,在0 、3 、7 、10℃贮藏过程中,大菱鲆较好品质期分别为433、197、93h 和68h, 货架期分别为602、362、165h 和116h。各温度较好品质期终点和货架期终点时菌落总数分别为(5.74 ± 0.31)、(6.99 ± 0.39)lg(CFU/g),假单胞菌数分别为(5.48 ± 0.24)、(6.26 ± 0.71)lg(CFU/g),TVB-N 均值分别为(15.66 ± 1.93)、(31.81 ± 1.94)mg/100g,TMA-N 均值分别为(2.73 ± 0.12)、(10.71 ± 0.81)mg/100g,各温度下较好品质期终点和货架期终点时各指标均值均无显著差异(P ＞ 0.05),表明菌落总数、假单胞菌、TVB-N 和TMA-N 作为大菱鲆低温贮藏的鲜度指标与感官评价有较好的一致性。     

Evaluation of an ozone–slurry ice combined refrigeration system for the storage of farmed turbot (Psetta maxima)

The use of ozonised slurry ice was investigated as a new refrigeration system for the storage of farmed turbot (Psetta maxima). With this purpose in mind, an ozone generator device was coupled to a slurry ice system working subzero at −1.5 °C. The ozone concentration was adjusted to a redox potential of 700 mV, and the slurry ice biphasic mixture was prepared at a 40% ice/60% water ratio and 3.3% salinity. Certain biochemical parameters indicative of fish freshness, such as the rate of nucleotide degradation or TMA-N formation, were not significantly affected by the presence of ozone in the slurry ice mixture. However, storage in ozonised slurry ice significantly slowed down the mechanisms responsible for lipid hydrolysis and lipid oxidation in farmed turbot. Storage in ozonised slurry ice also led to significantly (p < 0.05) lower counts of both total aerobes and psychrotrophic bacteria in both turbot muscle and skin, as compared with the control batch stored without ozone. Sensory analyses confirmed an extended shelf life of turbot specimens stored in ozonised slurry ice; these maintaining “A” sensory quality up to day 14, while the counterpart batch stored in slurry ice kept this quality only up to day 7. The combination of ozone and slurry ice may be recommended for the chilling and storage of farmed turbot with a view to extending its shelf-life.     

Quality and shelf life assessment of Pacific white shrimp (Litopenaeus vannamei) freshly harvested and stored on ice

Pacific white shrimps (Litopenaeus vannamei) are an important shrimp aquaculture species worldwide. To quantify the quality and shelf life of untreated shrimp is imperative prior to the application of preservative treatments. In this paper, the quality and shelf life of Pacific white shrimp freshly harvested from three different farms and stored on ice for up to 12 days was investigated. The titratable acidity (TA) of shrimp specimens exhibited significant decreases (P < 0.05) whereas the metric chroma (C), total colour difference (TCD), aerobic plate count (APC), trimethylamine (TMA-N) and total volatile basic – nitrogen (TVB-N), peroxide value (PV) and p-anisidine value (AnV) exhibited significant increases during iced storage (P < 0.05). The TMA-N and TVB-N were significantly correlated whereas temporal TMA-N/TVB-N ratio increased considerably (P < 0.05). While the PV and AnV significantly correlated (P < 0.05), the temporal PV/AnV ratio depicted how primary and secondary lipid oxidation of Pacific white shrimp could relate during iced storage of 12 days. The shelf life of ice stored Pacific white shrimps was determined to be 8 days. The information gained by this study could serve as baseline for preservative treatments applied to fresh shrimps.     

冷冻处理的熟制虾肉在保鲜条件下的货架期

以熟制克氏原螯虾(Procambarus clarkia)虾肉为原料,分别进行缓慢冷冻和快速冷冻处理后,于4℃下贮藏,通过感官评价、理化指标和微生物指标的测定,研究冷冻处理的熟制虾肉的货架期和品质。研究发现:快速冷冻处理虾肉的品质优于缓慢冷冻处理,但两者的货架期均为5d,6d为可接受的限值,未经冷冻处理的虾肉货架期为2d。感官评分值与TVB-N,MDA含量和菌落总数均有极显著的负相关,R2均在-0.947以上(P<0.01)。快速冷冻组虾肉在贮藏期间失重率和pH值稳定。TVB-N和菌落总数有望作为评价熟制虾肉品质的化学指标,TVB-N值为30mg/100g和菌落总数为6logcfu/g可作为熟制虾肉可接受的限值。冷冻处理有效的延长了熟制虾肉在4℃贮藏条件的货架期,可作为一种处理手段应用于熟制水产品的保鲜。     

Biochemical changes and quality loss during chilled storage of farmed turbot (Psetta maxima)

Changes in three of the major biochemical components – nucleotides, lipids and proteins – related to quality loss in farmed turbot, were determined during 29 days of iced storage; results were complemented with sensory analysis. Nucleotide degradation, as estimated by the K value, underwent a gradual increase until day 19, in agreement with the loss of freshness observed for the sensory scores (high quality: days 0–2; good quality: days 3–14; fair quality: days 15–19). After day 19, the fish was judged unacceptable and the K value did not show differences until the end of storage. Lipid hydrolysis and oxidation occurred at slow rates, free fatty acid contents and the peroxide value being below 20.0 g kg⁻¹ lipids and 4.00 meq active oxygen kg⁻¹ lipids, respectively, during the whole storage. The content of fluorescent compounds did not increase significantly until day 19, when a sharp increase was detected. The electrophoretic protein profiles of turbot muscle did not point to any major protein degradation event or any significant change in protein during storage. However, a new band, corresponding to 22 kDa, could be observed at day 2 in the low-ionic strength buffer extract, whose concentration seemed to increase at days 9 and 14 and was present until the end of the chilled storage. The results obtained in this work indicate slow and gradual biochemical changes and long shelf life and good quality times (19 and 14 days, respectively) for iced turbot; these long times would be very profitable when turbot commercialisation is carried out in places distant from production farms.     

The effect of powdered thyme sprinkling on quality changes of wild and farmed gilthead sea bream fillets stored in ice

The effect of powdered thyme sprinkling on the quality characteristics of fresh and ice-stored wild and farmed gilthead sea bream fillets was assessed. Initially, significant differences in proximate composition and quality attributes were found between wild and farmed fresh sea bream flesh. Throughout ice storage, biochemical alteration appeared more pronounced in farmed fish fillets with significantly higher levels of TVB-N, TMA-N, and TBA; and a lower liquid-holding capacity (LHC). Thyme powder addition (1% w/w) exhibited a preservative effect in both fish lots since significant lower levels of TVB-N, TMA-N, free amino acids (NPS), TBA and LHC were observed in thyme-treated fillets during ice storage. However, thyme inhibitory effect was more marked in wild than farmed fish. As revealed by partial least square regression, LHC in both groups was positively influenced by storage time and trimethylamine accumulation factors, while it was negatively influenced by thyme treatment and fish origin. Hence, LHC was suggested to be related to spoilage bacterial growth. The use of dried thyme extended the shelf life of fish fillets by about 5 days and appeared to be highly valuable to the fish industry as a natural preservative.     

Effects of storage in ozonised slurry ice on the sensory and microbial quality of sardine (Sardina pilchardus)

The use of slurry ice, both alone and in combination with ozone, as compared with traditional flake ice was investigated as a new refrigeration system for the storage of sardine (Sardina pilchardus). Microbiological, chemical and sensory analyses were carried out throughout a storage period of 22 days. According to sensory analyses, sardine specimens stored in ozonised slurry ice had a shelf life of 19 days, while counterpart batches stored in slurry ice or flake ice had shelf lives of 15 and 8 days, respectively. Storage in ozonised slurry ice led to significantly lower counts of aerobic mesophiles, psychrotrophic bacteria, anaerobes, coliforms, and both lipolytic and proteolytic microorganisms in sardine muscle, and of surface counts of mesophiles and psychrotrophic bacteria in sardine skin as compared with the slurry ice and the flake ice batches. In all cases, the slurry ice batch also exhibited significantly lower microbial counts, both in muscle and skin, than the flake ice batch. Chemical parameters revealed that the use of slurry ice slowed down the formation of TVB-N and TMA-N to a significant extent in comparison with storage in flake ice. A combination of slurry ice with ozone also allowed a better control of pH and TMA-N formation as compared with slurry ice alone. This work demonstrates that the combined use of slurry ice and ozone for the storage of sardine can be recommended to improve the quality and extend the shelf life of this fish species.     

Rep-PCR characterization and biochemical selection of lactic acid bacteria isolated from the Delta area of Egypt

Samples of raw milk and traditional dairy products were collected from different rural areas in the Delta region. 170 isolates from these products were identified using repetitive genomic element-PCR (Rep-PCR) fingerprinting. The identified isolates were tested for efficiency of biomass production and separation, acidifying activity, autolytic and aminopeptidase properties, antagonistic activities and exopolysaccharide production. The obtained results revealed that the Lactobacillus delbrueckii subsp. lactis, Lactobacillus fermentum, Enterococcus faecium Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus paracasei subsp. paracasei, Lactobacillus plantarum and Lactococcus lactis subsp. lactis were the predominant species in Egyptian dairy products. Two percent of Lactococcus, 10% of Lactobacillus and 1% of Enterococcus isolates showed fast acidifying activity. Aminopeptidase and autolytic properties were generally higher for most Lactobacillus strains when compared to other strains. Among these species, lactobacillus paracasei subsp. paracasei was the highest in Aminopeptidase activity and autolytic properties. Antagonistic activity was detected in 40% of Lactococcus, 70% of Lactobacillus and 50% of Enterococcus isolates. Some isolates produced exopolysaccharides in milk and dairy products.     

The viability of three probiotic organisms grown with yoghurt starter cultures during storage for 21 days at 4°C

This study investigated the viability of probiotic ( Lactobacillus acidophilus LA5, Lactobacillus rhamnosus LBA and Bifidobacterium animalis subsp . lactis BL-04) in milk fermented with Lactobacillus delbrueckii subsp . bulgaricus LB340 and Streptococcus thermophilus TAO (yoghurt – Y). Each probiotic strain was grown separately in co-culture with Y and in blends of different combinations. Blends affected fermentation time(s), pH and firmness during storage at 4°C. The product made with Y plus B. animalis subsp . lactis and L. rhamnosus had counts of viable cells at the end of shelf life that met the minimum required to achieve probiotic effect. However, L. acidophilus and L. delbrueckii subsp . bulgaricus were inhibited.     

Genotypic and phenotypic diversity of Lactobacillus delbrueckii subsp. lactis strains of dairy origin

Eighty-nine strains of Lactobacillus delbrueckii subsp. lactis isolated from Italian hard and semi-hard cheeses and artisan starter cultures were characterised by phenotypic and genotypic methods. Phenotypic diversity was evaluated by studying biochemical characteristics (i.e. acidifying and peptidase activities) of technological interest. Genotypic diversity was evidenced by RAPD-PCR and pulsed field gel electrophoresis (PFGE). Phenotypic characterisation indicated a wide variability of the acidifying activity within Lact. delbrueckii subsp. lactis. Although the data was variable, it allowed us to evidence groups of strains with different acidifying properties, especially in terms of acidification intensity. Concerning peptidase activity, Lact. delbrueckii subsp. lactis showed a homogeneously high x-prolil-dipeptidil-aminopeptidase activity and a considerable but more heterogeneous lysil-aminopeptidase activity. The increased resolution obtained by the use of two molecular typing techniques, i.e. RAPD-PCR and PFGE, allowed to widen the level of strain heterogeneity. Technological and ecological pressures are determinant in selecting Lact. delbrueckii subsp. lactis sub-populations which are more functional to the different cheese technologies.     

Effect of low-dose radiation on microbiological, chemical, and sensory characteristics of chicken meat stored aerobically at 4 degrees C

The effect of gamma-radiation (0.5, 1, and 2 kGy) on the shelf life of fresh skinless chicken breast fillets stored aerobically at 4 degrees C was evaluated. Microbiological, chemical, and sensorial changes occurring in chicken samples were monitored for 21 days. Irradiation reduced populations of bacteria, i.e., total viable bacteria, Brochothrix thermosphacta, lactic acid bacteria (LAB), and the effect was more pronounced at the highest dose (2 kGy). Pseudomonads, yeasts and molds, and Enterobacteriaceae were highly sensitive to gamma-radiation and were completely eliminated at all doses. Of the chemical indicators of spoilage, thiobarbituric values for nonirradiated and irradiated aerobically packaged chicken samples were in general low (<1 mg of malonaldehyde per kg of muscle) during refrigerated storage for 21 days. With regard to volatile amines, both trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) values for nonirradiated aerobically packaged chicken increased steeply, with final values of ca. 20.3 and 58.5 mg N/100 g of muscle, respectively. Irradiated aerobically packaged chicken samples had significantly lower TMA-N and TVB-N values (P < 0.05) of ca. 2.2 to 3.6 and 30.5 to 37.1 mg N/100 g of muscle, respectively, during refrigerated storage for 21 days. Of the biogenic amines monitored, only putrescine and cadaverine were detected in significant concentrations in both nonirradiated and irradiated chicken samples, whereas histamine formation was noted only in nonirradiated samples throughout storage. On the basis of sensorial evaluation, low-dose irradiation (0.5 and 1.0 kGy) in combination with aerobic packaging extended the shelf life of fresh chicken fillets by ca. 4 to 5 days, whereas irradiation at 2.0 kGy extended the shelf life by more than 15 days compared with that of nonirradiated chicken.     

Comparison of newly isolated strains of Lactobacillus delbrueckii subsp. lactis for hydrogen peroxide production at 5 degrees C

Isolates of Lactobacillus delbrueckii subsp. lactis obtained from raw milk samples were compared for the ability to produce hydrogen peroxide (H2O2) at 5 degrees C. Nineteen out of 101 lactobacilli isolated were identified as L. delbrueckii subsp. lactis. The isolates of L. delbrueckii subsp. lactis from most raw milk samples produced more H2O2 than did isolates of other species of lactobacilli from the same samples. Seven isolates of L. delbrueckii subsp. lactis, which produced the highest levels of H2O2 at 5 degrees C were selected for comparison with a laboratory strain, L. delbrueckii subsp. lactis I. In 24 h, isolate RM2-5 produced 7.0 microg/10(9) cfu in buffer containing 5 mM sodium lactate and 4.4 microg/10(9) cfu in buffer containing 5 mM glucose. Three other isolates also produced more H2O2 on sodium lactate than on glucose. However, three remaining new isolates produced more H2O2 on glucose than on sodium lactate. All seven of the most active new isolates of L. delbrueckii subsp. lactis produced significantly higher concentrations of H2O2 than did L. delbrueckii subsp. lactis I in both solutions. Strain RM2-5 produced more H2O2 than did the other six most active newly isolated strains of L. delbrueckii subsp. lactis in this comparison.     

不同品牌酸乳中德氏乳杆菌的分离鉴定及RAPD分析

从不同品牌的10 种酸乳中分离得到10 株德氏乳杆菌(Lactobacillus delbrueckii),经生理生化实验及特异性PCR 鉴定,L.d3、L.d4、L.d5、L.d6、L.d8、L.d10 为德氏乳杆菌保加利亚亚种(Lactobacillus delbrueckii subsp.bulgaricus),L.d1、L.d2、L.d7、L.d9 为德氏乳杆菌乳酸亚种(Lactobacillus delbrueckii subsp. lactis)。利用24 个随机引物对上述10 株德氏乳杆菌进行随机扩增DNA 多态性分析,并使用NTSYSpc-2.10e 软件对扩增图谱数据进行处理,得出10 个菌株之间的遗传相似系数矩阵及聚类分析图。结果表明,10 个菌株相互间的遗传相似系数在0.4167～0.8833 之间,不同菌株间存在一定的亲缘关系及遗传异质性。     

利用16S rDNA序列及tuf-RFLP鉴定蒙古国发酵乳中的乳酸菌

运用16S rDNA序列分析和tuf-RFLP技术对采于蒙古国扎布汗省的25份发酵乳样中分离出的110株乳酸菌进行鉴定。首先将分离的110株乳酸菌的16S rRNA基因进行扩增,测序并构建系统发育树,初步鉴定为41株嗜热链球菌,40株瑞士乳杆菌,11株德氏乳杆菌保加利亚亚种,2株发酵乳杆菌,1株乳明串珠菌,2株肠膜明串肠膜亚种,1株乳酸乳球乳酸亚种和12株属于干酪族的菌株。由于干酪乳杆菌族的16S rDNA序列差异很小,故采用tuf-RFLP技术对这12株进行了进一步的验证,通过分离菌株与模式菌株tuf-RFLP图谱的比较分析,结果表明这12株菌均为干酪乳杆菌。     

Postmortem biochemical behavior of giant squid (Dosidicus gigas) mantle muscle stored in ice and its relation with quality parameters

ABSTRACT:  Several freshness and spoilage indicators were monitored to characterize the postmortem biochemistry of giant squid ( Dosidicus gigas ) mantle muscle. Squid samples were obtained directly from the sea and kept at 0 °C during a 15-d storage period. Data at zero time were obtained from cryogenically frozen samples at time of capture. The adenosine 5'-triphosphate (ATP) degradation followed a different pattern as compared with that from fish species. ATP was almost completely depleted at 24-h postcatch from 6.54 to <1 μmol/g, while at the same time Hx was the predominant catabolite with a concentration of 4 μmol/g, reaching 6.85 μmol/g at day 15. K -value data followed a logarithmic pattern with time instead of a linear one, with no change after day 3, thus reducing its suitability as a freshness index. The coefficient Hx/AMP seems to be an adequate alternative for this purpose due to its constant increment with time. The high NH₄Cl content in mantle muscle (461.3 ± 24.5 mg of NH₄⁺/100 g) derived from its physiological importance for the species compromises the use of the distillation step of the TVB-N analysis commonly used as a spoilage index. This fact explains why the initially high value of TVB-N detected in mantle muscle (243.7 mg N/100 g) did not correlate with the initial low TMA-N content (1.5 ± 0.1 mg/100 g of muscle). The results suggested that under the experimental conditions the shelf life of squid exceeds 15 d.     

Technological characterization and survival of the exopolysaccharide-producing strain Lactobacillus delbrueckii subsp. lactis 193 and its bile-resistant derivative 193+ in simulated gastric and intestinal juices

The capacity of lactic acid bacteria to produce exopolysaccharides (EPS) conferring microorganisms a ropy phenotype could be an interesting feature from a technological point of view. Progressive adaptation to bile salts might render some lactobacilli able to overcome physiological gut barriers but could also modify functional properties of the strain, including the production of EPS. In this work some technological properties and the survival ability in simulated gastrointestinal conditions of Lactobacillus delbrueckii subsp. lactis 193, and Lb. delbrueckii subsp. lactis 193+, a strain with stable bile-resistant phenotype derived thereof, were characterized in milk in order to know whether the acquisition of resistance to bile could modify some characteristics of the microorganism. Both strains were able to grow and acidify milk similarly; however the production of ethanol increased at the expense of the aroma compound acetaldehyde in milk fermented by the strain 193+, with respect to milk fermented by the strain 193. Both microorganisms produced a heteropolysaccharide composed of glucose and galactose, and were able to increase the viscosity of fermented milks. In spite of the higher production yield of EPS by the bile-resistant strain 193+, it displayed a lower ability to increase viscosity than Lb. delbrueckii subsp. lactis 193. Milk increased survival in simulated gastric juice; the presence of bile improved adhesion to the intestinal cell line HT29-MTX in both strains. However, the acquisition of a stable resistance phenotype did not improve survival in simulated gastric and intestinal conditions or the adhesion to the intestinal cell line HT29-MTX. Thus, Lb. delbrueckii subsp. lactis 193 presents suitable technological properties for the manufacture of fermented dairy products; the acquisition of a stable bile-resistant phenotype modified some properties of the microorganism. This suggests that the possible use of bile-resistant derivative strains should be carefully evaluated in each specific application considering the influence that the acquisition of a stable bile-resistant phenotype could have in survival ability in gastric and intestinal conditions and in technological properties.     

Preservation of iced refrigerated sea bream (Sparus aurata) by irradiation: microbiological, chemical and sensory attributes

Quality and shelf life of non-irradiated and irradiated (2.5 and 5 kGy) sea bream in ice conditions and stored at +4 °C were investigated by measurement of microbiological, chemical and sensory analysis. Microbial counts for non-irradiated sea bream samples were higher than respective irradiated fish. Total volatile base nitrogen (TVB-N) values increased value of 38.64 mg/100 g for non-irradiated, sea bream during iced storage whereas for irradiated fish lower values of 13.48 and 12.06 mg/100 g were recorded at 2.5 and 5 kGy, respectively (day 19). Trimethylamine (TMA-N) values and thiobarbituric acid (TBA) values for irradiated samples were lower than non-irradiated samples. Acceptability scores for odour, taste and texture of cooked decreased with storage time. The sensory scores of sea bream stored in control and 2.5–5 kGy at +4 °C were 13 and 15 days, respectively. The results obtained from this study showed that the shelf life of sea bream stored in ice, as determined by overall acceptability all data, is 13 days for non-irradiated sea bream and 15 days for 2.5 kGy irradiated and 17 days for 5 kGy irradiated sea bream.     

Chilled bulk storage of gutted hake (Merluccius merluccius L.) in CO2 and O2 enriched controlled atmospheres

This work compares hake gutted whole and placed in boxes in ice under controlled atmospheres (CA) with four different gas mixtures: M1 CO₂/O₂/N₂(%) (60/15/25), M3 (40/40/20), M4 (60/40/0) and M5 (40/60/0) and hake in air for 33 days of storage. The storage chamber temperature was 0±1°C. Biochemical analyses [pH, total volatile basic nitrogen (TVB-N), trimethylamine nitrogen (TMA-N) and thiobarbituric acid (TBA index) and sensory analyses (inspection and tasting)] were carried out to study the quality of the hake. The hake, kept under controlled atmospheres, did not exceed the limits for acceptability of 35 mg/100 g and 12 mg/100 g of TVB-N and TMA-N, respectively, throughout the storage period, and the TBA values remained lower than the recommended limits of 14 mg of malonaldehyde/100 g. Chemical results accorded with the tasters who did not detect any off-odour in the samples, and the M4C lots stored under 60/40/0 (CO₂/O₂/N₂%) was rated the best. However, this result did not accord with the inspection or pH by which all the lots were rejected at day 25 of storage. Despite this, the atmosphere system for preservation of chilled hake could be used safely and effectively on fishing boats to extend the shelf life of this species, and was better than conventional storage in ice.     

开菲尔粒中乳酸菌的分离与鉴定

从4个不同来源的开菲尔粒中分离得到40株乳酸菌，并对这40株乳酸菌进行了鉴定．结果为德氏乳杆菌8株，德氏乳杆菌保加力亚种6株，高加索奶乳杆菌2株，嗜酸乳杆菌1株，粪肠球菌7株，屎肠球菌2株，嗜热链球菌1株，乳脂链球菌3株。