Effects of Temperature on the Decomposition of Pacific Coast Shrimp (Pandalus jordani)

Shrimp (Pandalus jordani) were allowed to decompose at five temperatures (0, 5.6, 11.1, 16.7 and 22.2°C). Mean aerobic plate counts on the shrimp as received at the laboratory were 1.6 × 10⁶/g. The most rapid growth was obtained at the higher temperatures but the highest maximum population was obtained at 0°C. A total of 638 bacteria were isolated and tested for identification. The heterogenous population at day 0 was composed of 38% Gram positives. The population changed becoming predominantly Gram negative by day 13. At the higher temperatures the indole producing Proteus emerged by day 7 and became an important component of the flora. Volatile base (N) and indole increased both with increasing time and temperature during storage.     

POSTMORTEM QUALITY CHANGES IN ICED PACIFIC SHRIMP (Pandalus jordani)

The postmortem biochemical changes in intact raw shrimp during iced storage were investigated and the relationship between these changes and the quality of the cooked product was evaluated. Changes in pH, microbial numbers, total and nonprotein nitrogen, tyro-sine and carotenoid pigment content, proteolytic and polyphenolase enzyme activities and levels of trimethylamine-oxide, trimethylamine, dimethylamine and formaldehyde were determined. Chemical changes were shown to be mediated by a combination of bacterial action and endogenous enzymatic activity. The washing action of melting ice could have played a major role. Organoleptic quality as shown by flavor panel evaluations progressively declined during an 8-day storage period. Dimethylamine and formaldehyde levels in intact shrimp progressively increased as flavor panel scores decreased and may offer additional sensitive indices of cooked meat quality     

大豆过氧化氢酶的分离纯化及性质研究

新鲜大豆芽经匀浆、磷酸缓冲液抽提、硫酸铵分级沉淀、DEAE-Sepharose离子交换层析、Superdex-200凝胶过滤层析,获得电泳纯的过氧化氢酶。该酶酶活回收率为30.92%,纯化倍数为293.09,酶比活力达到26 322.43 U/mg。该酶全分子质量为234.9 kD,亚基分子质量为57.42 kD;最适pH值为7.2,最适温度为30 ℃,在pH 4.0～10.6及25～35 ℃范围内有较好的稳定性;在30 ℃、pH 7.2条件下测得该酶对过氧化氢的Km值为31.82 mmol/L;十二烷基硫酸钠、草酸、Ag+、Cu2+对该酶有强烈的抑制作用,Pb2+对该酶有双重作用,低浓度时有激活作用而高浓度时抑制酶活性。     

Isolation and Partial Characterization of Okenia (Okenia hypogaea) Starch

Okenia hypogaea (Schlech. & Cham.) belongs to the family of the Nyctaginacea, which produces a seed that is composed mainly of starch, the probable origin of Okenia hypogaea is Mexico. The aim of this work was to isolate the starch from Okenia hypogaea and to evaluate its chemical composition, along with some physicochemical and functional properties. Okenia gave a starch yield of 36 %; this starch had an amylose content of 26.1 %, with a fat content similar to corn starch, but with a higher ash fraction. Okenia starch possessed a small granule size (1—3 μm), the same as amaranth starch, with similar characteristics of stability and clarity of pastes as corn starch. At 60 °C the water retention capacity of okenia starch was higher than that of corn starch, but at higher temperatures an inverse pattern was found. When the temperature in the experiments increased, solubility and swelling values increased; okenia starch had higher swelling values than corn starch over the range of temperatures assayed. Okenia starch also presented a lower freeze‐thaw stability than corn starch on the first two cycles. Overall, it was concluded that due to its physicochemical and functional properties, it is worthwhile to test the use of okenia starch in the cosmetic and food industry.     

Quality Changes of Shrimp (Pandalus borealis) Stored under Different Cooling Conditions

The influence of different cooling techniques and storage temperatures (‐1.5 °C or 1.5 °C) to prolong the shelf life of shrimp was evaluated by sensory analysis, physical methods, chemical analysis, and microbial analysis. Storage in liquid ice was more effective than flake ice or brine mixed with flake ice in delaying spoilage of the shrimp by slowing down microbial growth and formation of total volatile basic nitrogen (TVB‐N) and trimethylamine (TMA). Total viable counts (TVC) showed that bacteria grew most quickly in shrimp stored in flake ice and in brine mixed with flake ice, followed by those in liquid ice at 1.5 °C and ‐1.5 °C, respectively. Lowest counts were observed in shrimp stored in liquid ice at ‐1.5 °C where the lag phase of growth was apparently extended at the beginning of storage. Principal component analysis (PCA) showed a good correlation between quality indicators related to microbial growth, TVC, pH, TVB‐N, TMA, responses of an electronic nose and sensory evaluation.     

Isolation and Partial Characterization of a Polysaccharide Gum from Cryptocarya wightiana Bark

The present investigation describes the isolation and partial characterization of a gummy polysaccharide derived from the bark powder of Cryptocarya wightiana tree. The isolated polysaccharide is highly viscous, exhibits ‘pituity’ characteristics, and is composed of arabinose and xylose in 6:1 ratio, respectively. Preliminary fractionation by precipitation with alcohol gave four fractions of varying compositional and viscosity characteristics. The major fraction (58%) was composed of arabinose and xylose in 5:1 ratio, respectively, together with an unidentified peak (∼21%) coeluting at the ascending part of the arabinose peak. The gum has potential applications both in food and non-food industries.     

Isolation and Partial Characterization of Black Gram (Phaseolus mungo L) Starch

Black gram (Phaseolus mungo L.) starch was isolated. The starch yield was 45% on flour weight basis. Starch granule size ranged from 7.5–28.5 μm (length) to 7.5–27.0 μm (width). Hylum length ranged from 25–100% of the starch granule length. Amylose content of starch was 26.65% (starch basis). Gelatinization temperature range for the starch was 71.5–74.0°C. Unlike several legume starches, black gram starch had a peak viscosity as indicated by Brabender Viscoamylograph. The starch viscosity was dependent on pH and ionic strength. The raw as well as cooked starch was resistant to hog pancreatic α-amylase hydrolysis in vitro.     

韭菜过氧化氢酶的分离纯化及其部分酶学特性

为获得韭菜过氧化氢酶纯品并对其性质进行研究,将新鲜韭菜通过匀浆、抽提、硫酸铵分级沉淀、DEAE-Sepharose 离子交换层析、Superdex-200凝胶过滤层析等步骤,获得了电泳纯的韭菜过氧化氢酶(CAT),纯化倍数为70.36,回收率为18.33%,酶比活力达到22064.57U/mg。其全酶分子质量和亚基分子质量分别为241.76、62.43kD。该酶反应的最适温度为37℃,最适pH值为7.2。该酶在25～40℃以及pH5～9有较好的稳定性,同时在最适条件下测得其Km值为46.93mmol/L。甲醇、乙醇、异丙醇、SDS以及Cu2+、Ag+、Fe2+等金属离子对该酶有较强的抑制作用。     

牛肾溶菌酶的分离纯化及部分酶学性质

将新鲜牛肾匀浆后,经由缓冲液提取,正丁醇除脂,硫酸铵分级沉淀,CM-Sepharose阳离子交换层析,Superdex-200凝胶过滤层析后得到电泳纯的牛肾溶菌酶。结果表明：该酶比活力为15 145.63 U/mg,回收率为29.13%,纯化倍数为231.05;分子质量约12.66 kD,为单亚基酶。最适反应温度为65 ℃,在65 ℃以下较稳定;最适pH 9.0,pH值在3.0～9.0范围内稳定性较好;测得最适条件下牛肾溶菌酶对溶壁微球菌的Km值为0.399 μg/mL;甲醇、乙醇、异丙醇和硫氰化钾（KSCN）对该酶有激活作用;十二烷基硫酸钠、Pb2＋、Ag＋对该酶有明显抑制作用。     

以绞股蓝为活性成分的天然抗氧化剂的制备

采用不同的溶剂提取绞股蓝的茎、叶中的抗氧化活性成分,研究不同提取物对二苯代苦味酰自由基(DPPH)的清除作用。试验结果表明:绞股蓝叶的95%乙醇提取物对DPPH自由基的清除作用强于其它提取物。具体工艺为:95%乙醇于80℃回流提取2次,每次2h。初步鉴定表明:绞股蓝中含有酚类、甾醇、甾体皂甙和三萜类化合物以及黄酮、异黄酮、查耳酮、双氢黄酮等抗氧化活性物质。     

Amaranth Starch - Isolation and Partial Characterization

Starch was isolated from a new amaranth variety (Amaranthus hypochondriacus Mercado type) with outstanding agronomic traits. Some of its physicochemical and functional properties were comparable to a maize starch sample. After annealing, both starches exhibited little change in gelatinization peak temperature as assessed by differential scanning calorimetry. It is suggested that this behaviour might be due to the high amylopectin content of the amaranth starch and to a previous annealing effect undergone by the commercial sample during the isolation procedure. Amaranth starch granules showed by scanning electron microscopy a polygonal shape.     

Preparation and Molecular Characterization of Chitosans Obtained from Shrimp (Litopenaeus vannamei) Shells

Four chitosan samples were prepared from shrimp shells without deproteination and decoloration steps, by a deacetylation process at 2 reaction times (2 and 4 h) and with/without using a reducing agent (R.A.). Variations in the physicochemical properties of the final products were analyzed. Viscosity average molecular weight (Mw) determinations demonstrated the protective action of the R.A. on the molecular oxidative degradation. Oppositely, an increase on the reaction time produced samples with low Mw. Deacetylation degrees (DDs) were chemically evaluated by the nitrogen content and by spectroscopic techniques as infrared and nuclear magnetic resonance. The existing differences in crystallinity were studied by X‐ray diffraction. Differential scanning calorimetry and thermogravimetry were used to demonstrate the dehydration and thermal degradation processes of the different chitosans. A novel method from calorimetric profiles is presenting for DD determinations of chitosan, which achieved highly satisfactory results (linear fit and Pearson's correlation coefficient) and is proposed to be generally extended to complex curves application.     

平贝母多糖的分离纯化及抗氧化活性研究

采用乙醇沉淀、DEAE-纤维素离子交换层析和Sepharose CL-6B凝胶过滤层析法,从平贝母(Fritillaria ussuriensis Maxim)水提取液中分离纯化得到水溶性多糖,命名为FUP-1。通过红外光谱和高效液相色谱对其结构和单糖组成进行初步分析,分子筛层析法测定其分子质量。结果表明,FUP-1为均一组分的杂多糖,主要由木糖、葡萄糖和半乳糖组成,其物质的量比为5:1:1,平均分子质量为4.1×104D。体外抗氧化活性分析表明,FUP-1具有较强的清除羟自由基、超氧阴离子自由基和DPPH自由基的能力。     

牛肝谷氨酸脱氢酶的分离纯化及部分酶学性质

取新鲜牛肝,经匀浆、缓冲液抽提、正丁醇脱脂、硫酸铵分级沉淀、DEAE-Sepharose离子交换层析、Superdex-200凝胶过滤层析等方法纯化,获得了电泳纯的牛肝谷氨酸脱氢酶（glutamate dehydrogenase,GDH）。经过纯化后的结果：GDH的酶比活力为306.06 U/mg,纯化倍数为93.60 倍,酶活回收率为23.12%。GDH的分子质量为380.2 kD,亚基分子质量约为61.7 kD。酶学性质研究结果表明：GDH的最适反应温度为50 ℃,在温度为30 ℃以下时较稳定;最适反应pH值为8.2,该酶对烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide,NADH）的Km值为0.696 mmol/L。甲醇、乙醇、异丙醇、Cd2+、Co2+、Ca2+、Ag+、Pb2+、Zn2+、Cu2+对该酶具有抑制作用,低浓度Ba2+、Mg2+、K+、Li+与乙二胺四乙酸（ethylenediamine tetraacetic acid,EDTA）对其具有一定的激活作用。     

鸭肝乳酸脱氢酶的分离纯化及部分性质研究

新鲜鸭肝经匀浆、磷酸盐缓冲液抽提,乙醇和硫酸铵分级沉淀,DEAE-Sepharose离子交换层析及Superdex-200凝胶过滤层析,获得电泳纯的乳酸脱氢酶。该酶经纯化后酶比活力达到668.82 U/mg,酶活回收率为25.79%,纯化倍数为185.78。该酶的全分子质量约为170.93 kD,亚基分子质量为44.72 kD;最适反应温度为45 ℃,最适pH值为7.4,在25～45 ℃及pH 5～10的范围内稳定性较好;在45 ℃、pH 7.4条件下,测得该酶对底物还原型烟酰胺腺嘌呤二核苷酸（reduced form of nicotinamide-adenine dinucleotid,NADH）的Km值为3.407 μmol/L,对丙酮酸钠的Km值为8.431 μmol/L;草酸、十二烷基硫酸钠（sodium dodecyl sulfate,SDS）、Cu2＋、Ag＋对该酶的抑制作用最强,Co2＋、K＋对该酶有双重作用,低浓度时有激活作用,而高浓度时具有抑制酶活性的作用。     

猪肝乙醇脱氢酶的分离纯化及部分性质

新鲜猪肝经匀浆、缓冲液抽提、硫酸铵分级沉淀、DEAE-Sepharose离子交换层析及Superdex-200凝胶过滤层析,获得电泳纯的乙醇脱氢酶（alcohol dehydrogenase,ADH）。纯化结果显示：该酶比活力为1 622.33 U/mg,回收率为29.05%,纯化倍数为34.58;该酶分子质量约为171.79 kD,亚基分子质量约为43.68 kD。ADH酶学性质研究显示：最适反应温度和pH值分别为45 ℃和10.0;在25～45 ℃及pH 7.5～9.0范围内稳定性较好;最适条件下测得该酶对乙醇的Km值为19 mmol/L;正丁醇、氯仿、异丙醇、十二烷基硫酸钠、草酸、Zn2＋、Cu2＋、Ag＋对该酶的抑制作用最强,Mg2＋对该酶有激活作用,EDTA对该酶有双重作用。     

Purification and Characterization of Proteases from Digestive Tract of Grass Shrimp (Penaeus monodon)

Proteases in grass shrimp (Penaeus monodon) digestive tract were extracted. Four fractions, A, B, C and D, demonstrated caseinolytic activity and were purified to electrophoretic homogeneity. A, C and D were trypsin-like, while B was a chymotrypsin-like protease. Optimal temperature for proteases A, B and C were 65°C, and that for D was 55°C for hydrolysis of casein. Optimal pH of proteases A and C was 8.0, and that of D was 7.0 for hydrolysis of p-toluenesulfonyl-L-arginine methyl ester. Optimal pH of protease B for hydrolysis of N-benzoyl-L-tyrosine ethyl ester was 8.0. Inactivation of 50 % enzyme activity in 5 min occurred at 67°C for protease B and 50°C for proteases A, C and D.