基于变异系数权重法评价三种干燥方法对牡蛎干品质的影响

以新鲜牡蛎为原料,通过鼓风干燥、真空干燥、真空冷冻干燥3种方法进行干燥,并对干制品的营养成分、色泽、复水率、质构、生产周期、能耗和感官评分进行测定,利用变异系数权重法得到3种牡蛎干制品的综合评分,以确定最佳干燥方法。结果表明:真空冷冻干燥可较好保留产品各种营养成分,其制得的牡蛎干色差最小,复水率与质构特性(硬度、咀嚼性和胶着性)显著优于鼓风干燥和真空干燥(p<0.05),但生产周期最长,能耗最高。真空干燥牡蛎干体型完整,有光泽,质地适中,鲜香味浓,感官评分最高。L*、硬度、咀嚼性、胶着性和干燥能耗在牡蛎干品质评价中占较大比重,权重值分别为0.105、0.112、0.121、0.109、0.120;综合评分结果为:真空冷冻干燥(0.780) > 真空干燥(-0.074) > 鼓风干燥(-0.707),真空冷冻干燥牡蛎干品质最佳。变异系数权重法可用于牡蛎干品质评价,为其在水产品加工技术优选中的应用提供理论参考。     

Effect of High Pressure and 4-Hexylresorcinol on Enzymatic Activity and Darkening in Oysters

ABSTRACT: Oysters treated with and without 4-hexylresorcinol were pressurized (400 MPa/7 °C/10 min) and stored chilled for 21 d, either vacuum-packed or packaged aerobically. The results of visual evaluation of darkening and polyphenoloxidase (PPO) activity levels suggest that during storage, non enzymatic browning occurred 1st, followed by blackening caused by PPO activity. PPO activity did not increase in the vacuum-packed oysters during storage, but pressurization was observed to activate the PPO. Autolytic activity in the oysters increased due to the high-pressure treatment, although higher autolysis levels were recorded in the unpressurized oysters at the end of storage. Inhibition of PPO activity by the 4-hexylresorcinol was observed chiefly in the vacuum-packed batches.     

广州秋季市售生蚝微生物污染状况调查

目的是了解广州秋季市售生蚝微生物污染状况。按照GB／T4789—2003《食品卫生微生物学检验》对样品进行微生物检测,结果发现秋季市售生蚝的微生物污染状况比较严重,菌落总数和大肠菌群指标均出现严重超标,超标率分别达到68％和78％,即使在温度偏低的11月份超标现象仍较严重。所检样品中,弧菌超标更为严重,3个月弧菌的检出率则高达90％。结论是广州市售生蚝的微生物污染状况严重,建议消费者不要生食或使用未煮熟的生蚝。     

Effect of heat pretreatment before isoelectric solubilisation/precipitation on the characteristics of Pacific oyster (Crassostrea hongkongensis) and Antarctic krill (Euphausia superba) protein isolates

Heat treatment is a convenient way to eliminate the effects of endogenous enzymes on the industrial production of stable products. This study describes the preparation of protein isolates from oysters (OPI and HOPI) and krill (KPI and HKPI) by isoelectric solubilisation/precipitation (ISP) with or without heat pretreatment and comparatively presents their characteristics. The results showed that the solubilities of HOPI (24.08 ± 1.94%) and HKPI (42.29 ± 0.78%) were higher than those of OPI (13.46 ± 0.78%) and KPI (21.71.46 ± 1.51%), and the free and total sulphhydryl (-SH) content and surface hydrophobicity of HOPI and HKPI were higher than those of OPI and KPI, which are related to higher fat content of HOPI (10.37 ± 0.55%) and HKPI (34.89 ± 1.19%). SDS–PAGE and gel chromatography pattern results showed that macromolecular proteins were degraded by endogenous enzymes in OPI and KPI, while they remained unaffected in HOPI and HKPI. The FT-IR spectra showed similar patterns between OPI and HOPI and between KPI and HKPI. While the essential amino acid content was similar for OPI and HOPI (47.06 ± 1.33% and 47.93 ± 1.02%), that of KPI and HKPI (50.89 ± 0.89% and 51.19 ± 1.11%, respectively) was not significantly different.     

类蛋白反应修饰的牡蛎肽锌结合物的生物利用性

通过类蛋白反应(Plastein)修饰制备具有较高锌离子结合能力的牡蛎源肽(EVPPEEH),其锌结合能力为161 mg/g。以缺锌型SD大鼠为试验模型,以牡蛎酶解肽-锌结合物OPZ、类蛋白反应修饰的牡蛎酶解肽-锌结合物LPZ和ZnSO4(ZS)为对照,研究牡蛎源肽(EVPPEEH)与锌的结合物(MZ)在体内的生物利用率和生物利用途径。结果表明:MZ组大鼠血清锌水平,股骨锌储备量及肝脏锌含量和肾脏锌含量均显著高于各对照组。脾脏锌含量MZ组和LPZ组恢复程度相似,均显著高于OPZ组和ZS组。MZ组和各对照组大鼠体重和摄食量均显著增加,效果相似。大鼠小肠转锌蛋白(ZnT1)的表达量MZ组与无机锌组差异不是很明显,而小肽转运蛋白(PepT1)的表达量MZ组最高,相对于ZS组上调了20%,显著高于各对照组,说明大鼠小肠对MZ的吸收利用一部分是通过传统锌离子途径,另一部分是通过小肽途径。MZ有望成为一种新型高效的补锌制剂。     

中国部分沿海海域牡蛎体内多环芳烃和多氯联苯的空间分布及组分特征

对中国部分沿海海域牡蛎体内16种多环芳烃(PAHs)和16种和多氯联苯(PCBs)空间分布和组分特征进行分析,于2010年夏、秋季在辽宁、山东、浙江、福建及广东共设置175个采样点,分布采用气相色谱-质谱联和气相色谱方法进行检测分析。结果显示：所取175个采样点牡蛎体内16种PAHs总含量的平均值为3.79μg/kg,其中浙江省被测样品的PAHs总含量最低,辽宁相对略高;检测样品16种PCBs总含量在1.41～13.95μg/kg之间;PCBs含量总的空间变化趋势是由北向南先增加后减少;样品的PAHs优势组分为三环结构,五环和六环PAHs含量很低;PCBs被检出的仅有三氯代和五氯代两种。被测牡蛎样品总体PAHs和PCBs残留量符合中国和一些发达国家贝类卫生标准,不影响消费者食用安全。     

The efficacy of grape seed extract,citric acid and lactic acid on the inactivation of Vibrio parahaemolyticus in shucked oysters

The efficacy of grape seed extract (GE), citric acid (CA) or lactic acid (LA) on the inactivation of Vibrio parahaemolyticus in shucked oysters was studied. The minimum inhibitory concentration (MIC) of GE, CA or LA against V. parahaemolyticus in TSB-1% NaCl was also determined. The shucked oysters were artificially inoculated with V. parahaemolyticus, the inoculated shucked oysters (25 g) were then dipped in solution of GE (0.0, 10.0, 20.0, 50.0, 100, 200, 300 and 500 mg mL⁻¹), CA (0.0, 5.0, 10.0, 15.0, 20.0, 50.0, 100, 200 and 300 mg mL⁻¹) or LA (0.0, 1.0, 5.0, 10.0, 15.0, 20.0, 50.0, 100 and 150 mg mL⁻¹) for 10 min. The population of V. parahaemolyticus in shucked oysters was determined. The MICs of GE, CA or LA against V. parahaemolyticus were 10.0, 5.0 or 1.0 mg mL⁻¹, respectively. A 500, 300 or 150 mg mL⁻¹ GE, CA or LA solutions were needed to reduce the population of V. parahaemolyticus to below the detection level (1.0 log g⁻¹) in shucked oysters.     

A survey of oysters (Crassostrea gigas) in New Zealand for Vibrio parahaemolyticus and Vibrio vulnificus

A microbiological survey was conducted to determine the levels of total and pathogenic Vibrio parahaemolyticus (Vp) and Vibrio vulnificus (Vv) in Pacific oysters (Crassostrea gigas) collected from commercial growing areas in the North Island, New Zealand.The survey was intended to be geographically representative of commercial growing areas of Pacific oysters in New Zealand, while selecting the time frame most likely to coincide with the increased abundance of pathogenic vibrio species. Vp was detected in 94.8% of oyster samples examined (n = 58) with a geometric mean concentration of 99.3 MPN/g, while Vv was detected in 17.2% of oyster samples examined with a geometric mean concentration of 7.4 MPN/g. The frequency of Vp positive samples was 1.7 fold greater than reported in a study conducted three decades ago in New Zealand. Potentially virulent (tdh positive) Vp was detected in two samples (3.4%, n = 58) while no trh (another virulence marker) positive samples were detected. 16 S rRNA genotype could be assigned only to 58.8% of Vv isolates (8:1:1 A:B:AB ratio, n = 10). There was a good agreement [98.2% of Vp (n = 280) and 94.4% of Vv (n = 18) isolates] between molecular tests and cultivation based techniques used to identify Vibrio isolates and there was a significant (R² = 0.95, P < 0.001, n = 18) linear relationship between the MPN estimates by real-time PCR and cultivation. There was no significant correlation between any of the environmental parameters tested and Vp or Vv concentrations.     

Occurrence and distribution of Vibrio parahaemolyticus in retail oysters in Sao Paulo State, Brazil

Vibrio parahaemolyticus is a potentially pathogenic bacterium that occurs naturally in estuarine environments worldwide, and is often associated with gastroenteritis in humans following consumption of raw bivalve mollusks, especially raw oysters. The occurrence of total and pathogenic V. parahaemolyticus in 74 samples of raw oysters collected in restaurants, supermarkets, groceries and beach huts in Sao Paulo State, was monitored between February 2006 and January 2007. Enumeration of V. parahaemolyticus was performed according to the most probable number (MPN) procedure. Five to ten typical colonies were selected from thiosulfate-citrate-bile salts-sucrose (TCBS) agar plates for confirmation by the presence of the species-specific gene tlh and the virulence genes tdh and trh by multiplex PCR. V. parahaemolyticus was detected in 100% of samples. The densities of total V. parahaemolyticus varied from 1.78 to 6.04 log₁₀ (MPN/g), with higher densities being detected in fall and summer, and lower densities in winter (P < 0.05). There was no statistical difference among densities of V parahaemolyticus regarding the site of collection. None of the 1943 V. parahaemolyticus isolates contained tdh and/or trh. These data provide information for the assessment of exposure to V. parahaemolyticus in oysters consumed in Sao Paulo, State, Brazil.     

Fatty Acid Profile of Pacific Oyster,Crassostrea gigas,Fed Different Ratios of Dietary Seaweed and Microalgae during Broodstock Conditioning

The fatty acid (FA) profile of oysters generally reflects the dietary FA composition. Moreover, incorporation of FA into tissues is modulated by various metabolic factors, and final composition will depend upon the dietary sources, cumulative intake, and oysters' development stage. Thus, the aim of this study was to assess the impact of dietary incorporation of seaweed (SW) Ulva rigida, in replacement of traditional microalgae diet, on the FA composition of Pacific oysters Crassostrea gigas, during broodstock conditioning. The dietary conditioning consisted of direct replacement of microalgae (33% Tisochrysis lutea, 50.25% Skeletonema costatum, and 16.75% Chaetoceros calcitrans) by SW at four different substitution levels (0%, 25%, 50%, and 100% diet). The dietary docosahexaenoic acid (DHA) (22:6n-3) and eicosapentaenoic acid (EPA) (20:5n-3) contents showed a positive correlation with the dietary microalgae level. During the trial, oysters fed with higher percentages of microalgae revealed a depletion of DHA and accumulation of EPA. The 100% SW caused a significant reduction in oxygen consumption and, consequently, in the standard metabolic rate. Based on these results, a partial substitution of up to 25% of dietary microalgae seems to be a suitable alternative, because it elicited similar results to the commercial 100% microalgae diet.