PURIFICATION AND CHARACTERIZATION OF HOMOGENEOUS ACID PHOSPHATASE FROM NONGERMINATED BUCKWHEAT (FAGOPYRUM ESCULENTUM) SEEDS

A buckwheat acid phosphatase (orthophosphoric‐monoester phosphohydrolase, EC 3.1.3.2) was purified about 250‐fold from nongerminated buckwheat seeds to apparent homogeneity with a recovery of 4% from the acid phosphatase activity in the crude extract. It is the major acid phosphatase among eight different acid phosphatases identified in the crude extract. The purified enzyme behaved as a monomeric protein of molecular mass about 45 kDa. The purified enzyme exhibited a single pH optimum at 5.25. Optimum temperature for the degradation of p‐nitrophenyl phosphate was 50C. The kinetic parameters for the hydrolysis of p‐nitrophenyl phosphate were determined to be K_M= 76 μmol L^?1 and k_cat= 924 s^?1 at pH 5.25 and 37C. While the enzyme failed to act on phytate as a substrate, the enzyme exhibited a broad substrate selectivity. The purified enzyme showed no measureable carboxylesterase activity and no divalent metal ion requirement.     

PURIFICATION AND CHARACTERIZATION OF PHENOLOXIDASE ISOFORMS FROM TAIWANESE BLACK TIGER SHRIMP (PENAEUS MONODON)1

Two phenoloxidase (PPO) isoforms were purified from Taiwanese black tiger shrimp (Penaeus monodon) purified via ammonium sulfate precipitation and high performance hydrophobic interaction chromatography on phenyl Sepharose CL-4B. Optimal DL-ã-3, 4-dihydroxyphenylalanine (D, L-DOPA) oxidation by these isoforms was observed to occur at pH 6.0, and at 45°C. The isoforms showed both mono- and di-PPO activities, and preferential medabolism of both monoand di-phenolic substrates lacking a carboxyl group either directly attached to the ring, or in the side chain moiety of the phenolic structure.     

PURIFICATION AND CHARACTERIZATION OF AN ALKALINE PROTEASE FROM THE VISCERA OF BOLTI FISH (TILAPIA NILOTICA)

An alkaline protease was extracted from acetone powder of the viscera of bolti fish (Tilapia nilotica) with distilled water, precipitated from the extract by 40–60% (NH₄)₂SO₄and then dialyzed. Enzyme homogeneity studies by polyacrylamide gel electrophoresis (PAGE) illustrated that the enzyme was homogenous. Sodium dodecyl sulfate–PAGE showed a molecular weight of 23.0 kDa. The optimal pH and optimal temperature were 8.0 and 45C, respectively, with casein as a substrate. A remarkable stability was observed under alkaline conditions (pH 6.0–10.0), where more than 90% of the enzyme activity was maintained. In the acidic region (pH 2.0–6.0), the enzyme retained more than 50% of its activity. Furthermore, the enzyme retained 85.4 and 41.8% of its activity after heating at 50 and 60C for 120 min, respectively, while the relative activity after heating at 70C for 120 min was 5.25%. The alkaline enzyme lost most of its activity when incubated at 80C for 30 min. A high percentage of total enzyme activity was inhibited when the enzyme was incubated with 50 mM of either soybean trypsin inhibitor or ethylenediaminetetraacetic acid. The presence of NaCl and CaCl₂at 10 mM concentration increased the enzyme activity by 6.9 and 10.6%, respectively.     

EFFECT OF FEED DIET ON AMINOPEPTIDASE ACTIVITIES FROM THE HEPATOPANCREAS OF WHITE SHRIMP (PENAEUS VANNAMEI)

White shrimp (Penaeus vannamei) were fed one of seven diets for 30 days. Diets contained 85% of a reference ration and 15% of either anchovy, tuna waste meal, deboned fish meal, langostilla crab meal, soybean meal, menhaden meal A, or menhaden B as a protein replacer. At the end of the feeding trial, animals were sacrificed and 10 aminopeptidase activities of the hepatopancreas tissue were assayed. The hepatopancreas tissues contained Arg-, Leu-, His-, Ile-, Lys-, Met-, Thr- and Val-aminopeptidase activities but no activity was detected for Phe-aminopeptidase. Leu-aminopeptidase activity was inhibited by Zn⁺² and Mg⁺² salts and activity was also inhibited when more than 0.2 mg of hepatopancreas extract protein was included in the assay. Principal component analysis was used to determine whether diet had an influence on hepatopancreas
aminopeptidase activities. The aminopeptidase activities were greater for animals fed a diet containing menhaden fish meal B. This was principally the result of the higher levels of Met-, Val-, Pro-, Lys-, and Leu-aminopeptidase activities in animals fed menhaden fish meal. Menhaden fish meal B had a lower nutritional quality for shrimp than the other protein replacers. Seven of the 10 essential amino acids for shrimp were present at less than 100% of the recommended values. On the other hand, shrimp fed soybean meal replacer contained lower amounts of aminopeptidase activity, notably Gly- and Met-aminopeptidase activities, and the meal was of excellent quality having only one limiting amino acid. The results indicate that the shrimp diet can influence proteolytic activity of the hepatopancreas tissue. This is significant to the seafood technologist since previous studies showed that hepatopancreas proteases can leach into the meat postmortem and cause tissue softening.     

EFFECTS OF FEED DIETS ON DIGESTIVE PROTEASES FROM THE HEPATOPANCREAS OF WHITE SHRIMP (Penaeus vannamei)

Protease activities in the hepatopancreas extract (HP) from white shrimp (Penaeus vannamei) fed one of seven test diets for 30 days were evaluated by several methods. The test diet contained 85% of a reference ration for shrimp and 15% of either anchovy meal, tuna waste meal, deboned white fish meal, langostilla meal, soybean meal, and two menhaden meals as a protein replacer. One of the menhaden fish meals tested (B) had the lowest quality as a shrimp feed based on amino acid analysis. SDS-PAGE zymograms of HP from each of the seven diet groups showed similar proteins activity patterns with casein as substrate. The degree of hydrolysis of casein, measured by pH-stat, was also the same for HP from the seven diet groups (P > 0.05). However, total protease activity measured by azocasein hydrolysis (units/g HP) was higher for the diet group fed the test ration containing tuna waste as a replacer (P > 0.05). Trypsin and chymotrypsin activities measured with synthetic substrates (units/mg protein; units/g HP) from animals reared on the diet with menhaden meal B replacer were greater than in the other diet groups (P < 0.05). This study shows that a relatively small amount (15%) of a specific protein replacer in white shrimp rations can influence the protease activity of shrimp HP. Given that digestive proteases such as trypsin can leach into the muscle of postharvest shrimp and thereby cause softening of the meat, the impact of the rearing diet on postharvest shelf-life should be considered along with the standard measures of feed quality that are used by the fish farmer, i.e. animal growth and heatlh.     

Scavenging ability on ROS of alpha-lipoic acid (ALA)

The scavenging ability of alpha-lipoic acid (ALA) towards superoxide anions, hydroxyl radicals and hydrogen peroxide was evaluated by means of chemiluminescence (CL). In neutral or acid conditions, ALA could scavenge superoxide anions and its scavenging efficiency depended on its concentration. In neutral or alkaline conditions, the CL intensity of the reaction of ALA with hydroxyl radical (OH radicals) decreased after the first 10 min and then increased with time, suggesting that ALA could scavenge OH radicals at the beginning, but yielded unknown intermediate products that could lead to the increase of CL intensity at later stages. The increase of CL intensity in the reaction of hydrogen peroxide with ALA may also be due to these products.     

SOFTENING OF PUMPKIN SEEDS (CUCURBITA MOSCHATA) BY ALKALINE MACERATION

The nutritional value of pumpkin seeds is widely recognized. This article shows that alkaline maceration of pumpkin seed makes them soft and improves their market acceptability as an important source of fiber, unsaturated lipids, minerals and proteins. Microscopic characterization of pumpkin seeds was realized. The results indicate elimination of minerals from the seeds through the delignification process due to the nature of the phenolic compounds eliminated in the maceration liquid. The alkaline maceration process of pumpkin seeds may contribute to a larger consumption of fibers and other nutritive elements from them.

PRACTICAL APPLICATIONS

This work shows that the pumpkin seeds softened by chemical maceration improve sensory preferences, compared to nonmacerated products. Solid waste from pumpkin process can be converted to a new product as a snack rich in fiber and other important compounds, normally discarded as an industrial solid waste.     

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     

EXTRACTION OF CAROTENOPROTEIN FROM BLACK TIGER SHRIMP SHELLS WITH THE AID OF BLUEFISH TRYPSIN

The effect of bluefish (Pomatomus saltatrix) trypsin on the recovery and characteristics of carotenoprotein from black tiger shrimp (Penaeus monodon) shells was investigated. Trypsin concentration and reaction time both affected the hydrolysis and the recovery of carotenoproteins ( P <  0.05). The recovery of carotenoproteins from shrimp shells was maximized by the hydrolysis of shrimp shells using 1.2 trypsin units/g shrimp shells for 1 h at 25C. Freeze-dried carotenoprotein recovered contained 70.20% protein, 19.76% lipid, 6.57% ash, 1.50% chitin, and 87.91 µg total astaxanthin/g sample, indicating a substantial reduction in the levels of antinutrients associated with shrimp waste, while enriching the product in carotenoid pigments and valuable essential nutrients (proteins and lipids). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the recovered carotenoprotein revealed that protein with molecular weight of 45 kDa was the major constituent. When hydrolytic activities of bluefish and bovine trypsins toward carotenoproteins in black tiger shrimp shells were compared, the recovery efficacy of protein and pigment by bluefish trypsin was similar to that achieved by trypsin from bovine pancreas. Therefore, bluefish trypsin could be used as an alternative cheap proteinase for extraction of carotenoproteins from black tiger shrimp shells.

PRACTICAL APPLICATIONS

Carotenoproteins from black tiger shells, the byproduct of shrimp processing, can be recovered with the aid of fish trypsin. This product can be used for both food and feed applications. Additionally, the fish trypsin can be used instead of bovine trypsin. As a whole, the utilization of fish and shellfish processing wastes can be maximized.     

EFFECT OF ROSEMARY ON THE QUALITY CHARACTERISTICS OF WHITE SHRIMP (LITOPENAEUS VANNAMEI)

ABSTRACT

We assessed the influence of rosemary on some of the quality characteristics of Litopenaeus vannamei shrimp stored under freezing temperature for 180 days. Whole shrimp (WS), peeled shrimp (PS) and PS with dehydrated rosemary (RS) were stored at −28.3 ± 3.8C. Physicochemical and sensorial analysis was carried out. After 180 days, RS had lower pH (P = 0.001) and thiobarbituric acid‐reactive substances (TBARS; P = 0.001) values and higher carotenoids (P = 0.003). WS samples were firmer at 180 days (P = 0.001), although rancid taste and smell were perceived with greater intensity (P = 0.001). The color was more intense in RS and PS than in WS (P = 0.030). Rancid taste was detected in RS only at 120 days at significantly lower intensity (P = 0.001) than WS and PS. Our study suggests that dehydrated rosemary can improve the quality of frozen L. vannamei peeled shrimp.

PRACTICAL APPLICATIONS

Farmed shrimp has gained importance in the global market, and the study of their physicochemical and sensory characteristics is therefore essential. Commercially, shrimp is mainly available in the frozen form, and alternatives to extend its quality during storage are of great interest for consumers and suppliers in the food industry. Dehydrated rosemary can be added to frozen shrimp to improve its quality and maintain the nutritional characteristics during storage.