Postharvest Microbiology of Farm-reared, Tropical Freshwater Prawn (Macrobrachium Rosenbergii)

ABSTRACT: The microbiological quality of farm-reared, tropical freshwater prawn ( Macrobrachium rosenbergii ) stored at 2 different temperatures was studied. The prawn muscle was found to have the initial bacterial load of 10⁴ cfu/g. The lactics and vibrios were in the range of 10² cfu/g, while the E. coli , aeromonads, staphylococci, anaerobes, and molds were in the level of 10¹ cfu/g. Salmonella and Vibrio cholerae were present in the prawn muscle. The prawn muscle held at room temperature (28 ± 2 °C) was organoleptically acceptable up to 8 h, when the bacterial load was more than 10⁶ cfu/g. However, the prawn muscle stored at freezer temperatures (−10 to −15 °C) was found to be in acceptable condition even after 30 d of storage and the bacterial load was fluctuating in the range of 10³ to 10⁴ cfu/g.     

Microbiological,physical and chemical characteristics of freshwater prawns (Macrobrachium rosenbergii) in modified‐atmosphere packaging

This study evaluated the influence of packaging atmosphere (air versus 50% N₂/50% CO₂) on microbiological (mesophiles, psychrotrophs), physical (gas measurement) and chemical (pH, total volatile basic nitrogen [TVB‐N], NH₃, H₂S and biogenic amines) parameters in freshwater prawns during storage at 0 ± 1 °C for 240 h. To select the most appropriate packaging, 21 batches of each treatment were analysed. Both the packaging permeability and the combination of gases affected the shelf life, but the modified‐atmosphere packaging (MAP) was more efficient than air packaging, increasing the shelf life by 40 h. The parameters of pH and TVB‐N showed no statistical difference between the two atmosphere conditions all along the storage period. The biogenic amine agmatine showed potential for use as a quality indicator due to the increased concentration during storage. In further studies, this amine can be applied as an indicator for public health issue.     

Structure of the olfactory receptor organs,their GABAergic neural pathways,and modulation of mating behavior,in the giant freshwater prawn,Macrobrachium rosenbergii

In the giant male prawn, Macrobrachium rosenbergii, the olfactory system is thought to be the main pathway for modulating sexual behavior through pheromone perception. In this report, we first used gross anatomical, histological, and SEM methods to describe the structures of the olfactory receptors (sensilla setae), their neural pathways, and possible role in modulating mating behavior. On the surfaces of antennule and antenna filaments there are four types of sensory receptors, viz single spike‐like setae, single flagellum‐like setae, multiple flagella‐like setae, and aesthetascs (ASs). The ASs, which had previously been proposed to be odor receptor setae, are found only on the short filament of lateral antennule (slAn). Each AS on the slAn connects with olfactory receptor neurons (ORNs), whose axons form an outer central antennule nerve (ocAnNv), which then connects with the olfactory neutrophil (ON) of the brain. Thus, the slAn is the major olfactory organ that conveys sensory inputs from each AS to the ON within the deutocerebrum. GABA immunoreactivity was present in ASs, neurons of ORNs, inner central antennular, lateral tegumentary nerve, ocAnNv and the ON, inferring that GABA is the likely neurotransmitter in modulating olfaction. Disruption of the slAn by ablation or covering with Vaseline, resulted in significant reduction of mating behavior, indicating that this organ is crucial for sex pheromone perception. Identification of the active pheromones and further bioassays are now being performed. Microsc. Res. Tech. 76:572–587, 2013. © 2013 Wiley Periodicals, Inc.     

Responses of freshwater prawn,Macrobrachium rosenbergii,to chemical attractants

Chemoreception in the adults of the freshwater prawnMacrobrachium rosenbergii was investigated under controlled laboratory conditions, using behavioral assays. Tests were carried out on groups, as well as on individuals, all at their intermolt stages of the molt cycle, and prestarved for three to four days. Of 28 different substances tested, the amino acids taurine, glycine, arginine, and betaine, as well as trimethylamine, elicited a positive behavioral response in at least 50% of the test animals when applied at a threshold concentration of 10^–5-10^–8 M. A positive response comprises enhanced antennular flicking and food search motion. Of the various nucleotides tested for chemoattraction, only adenosine monophosphate elicited a response similar to that of the above amino acids, although at a concentration of 10^–4 M, whereas adenosine diphosphate required a dosage of 10^–1 M.     

Isolation and Characterization of a Novel Dicistrovirus Associated with Moralities of the Great Freshwater Prawn,Macrobrachium rosenbergii

The giant freshwater prawn, Macrobrachium rosenbergii, is an economically important crustacean and is farmed in many countries. Since 2009, a larval mortality syndrome of M. rosenbergii has broken out and spread widely in the main breeding area, including Zhejiang, Jiangsu, Guangxi, and Guangdong Provinces in mainland China. A novel virus, named Macrobrachium rosenbergii Taihu virus (MrTV), was isolated from the moribund larvae and was determined to be the causative agent of the M. rosenbergii larval mortality syndrome by experimental infection. Further genomic sequencing suggested that the MrTV genome is monopartite, 10,303 nt in length, and dicistronic with two non-overlapping open reading frames (ORFs) separated by an intergenic region (IGR) and flanked by untranslated regions (UTRs). Phylogenetic analysis using the full-length genomic sequence and the putative amino acid sequences of the capsid protein revealed that MrTV was more closely related to the taura syndrome virus (TSV) than to any other viruses. According to these molecular features, we proposed that MrTV is a new species in the genus Aparavirus, family Dicistroviridae. These results may shed light on controlling larval mortality syndrome in M. rosenbergii.     

日本沼虾中氨基脲含量检测方法的优化

目的以农业部783号公告-1–2006方法为基础,优化高效液相色谱-串联质谱法及样品前处理方法,使其更适用于日本沼虾中不同组织中氨基脲含量的检测。方法样品经过HCl水解,2-硝基甲苯衍生,乙酸乙酯萃取后,采用高效液相色谱-串联质谱法检测氨基脲含量,内标法定量。为考察优化后方法在日本沼虾不同组织测定结果的准确性和稳定性,对不同基质样品进行标准添加实验。结果氨基脲的添加水平为1.0~120.0μg/kg时平均回收率为74.3%~113.5%,精密度小于6.3%,方法检出限为0.25μg/kg(S/N≥3),定量限为0.5μg/kg(S/N≥10)。结论虾壳中氨基脲含量最高,肌肉中含量最低;肌肉中氨基脲主要以结合态形式存在,壳中氨基脲主要以游离态形式存在。     

Ultrastructure of differentiating oocytes and vitellogenesis in the giant freshwater prawn, Macrobrachium rosenbergii (de man)

The ultrastructure of oogenesis in Macrobrachium rosenbergii, with reference to vitellogenesis, has not been reported. We used light and electron microscopy, as well as vitellin (Vn) purification and antibody production, to study the temporal and spatial production of Vn in the ovary by immunofluorescence. Histologically, the ovary is subdivided into cone‐shaped ovarian pouches with a central core containing layers of oogonia. These divide to produce oocytes that migrate outwardly and differentiate into mature oocytes. During the course of differentiation, oocytes undergo modifications, including the rearrangement of nuclear chromatin, the accumulation of ribosomes, rough endoplasmic reticulum (RER), and lipid, and the formation of secretory and yolk granules, resulting in four stages. Ultrastructurally, early previtellogenic oocytes (Oc₁) are characterized by the accumulation of new ribosomal aggregates, translocated from the nucleus. Late previtellogenic oocytes (Oc₂) show nuclear heterochromatin with a “clock face” pattern, the presence of RER, and three types of secretory granules. Follicular cells occupy the intercellular spaces and surround the Oc₂. Early vitellogenic oocytes (Oc₃) are larger, with nuclei containing predominantly decondensed euchromatin, and cytoplasm with yolk and secretory granules, and few lipid droplets. Late vitellogenic oocytes (Oc₄) are characterized by completely euchromatic nuclei, an indistinct plasma membrane, yolk platelets and secretory granules, and abundant lipid. Vitellogenin (Vg) in ovaries of M. rosenbergii consist of two main bands at MW 90 and 102 kDa. Our data indicates that Vn is present, and probably synthesized in Oc₃ and Oc₄, but there may be some undetected exogenous Vg production. Microsc. Res. Tech. 2012. © 2012 Wiley Periodicals, Inc.     

Quality of giant freshwater prawn (Macrobrachium rosenbergii) during the storage at −18°C as affected by different methods of freezing

This study investigated the effects of liquid nitrogen quick-freezing, ?35°C air-blast freezing, and ?18°C refrigerator direct-freezing on quality retention of frozen giant freshwater prawns using various indicators: microscopic structure, physicochemical, texture, and color properties. The results showed that the shelf lives of prawns treated with liquid nitrogen quick-freezing, ?35°C air-blast freezing, and ?18°C refrigerator direct-freezing were about 20, 12, and 8 weeks, respectively, in terms of total volatile basic nitrogen content and K-value. Meanwhile, liquid nitrogen quick-freezing could effectively improve texture property of frozen giant freshwater prawn. These findings confirm that liquid nitrogen quick-freezing is a promising method to extend the shelf life of frozen prawns.     

冻藏温度对罗氏沼虾冻藏品质的影响

以解冻汁液流失、蒸煮损失、TVB-N、K值、硬度、剪切力和色差为指标,研究不同冻藏温度对速冻罗氏沼虾冻藏品质的影响。试验结果表明:经液氮速冻后的罗氏沼虾,在-50,-18℃2种条件下冻藏,随着冻藏时间的延长,罗氏沼虾的持水能力和质构特性均变差,冻藏20周后,硬度分别下降了55.79%和59.45%。2种冻藏条件下的罗氏沼虾TVB-N和K值均随时间的延长而增加,而-50℃下冻藏的罗氏沼虾TVB-N和K值增加缓慢,说明较低的冻藏温度,有利于罗氏沼虾冻藏品质的保持。