SUMMARY: A green pigment was produced when yellowfin (and other) tuna myoglobins, trimethylamine oxide (TMAO), and cysteine were heated together in 0.1 M phosphate buffer pH 5.7. The green product could not be produced with mammalian myoglobins, which contain no cysteine residues. The roles of myoglobin, cysteine, and TMAO in the production of off‐color (green) cooked tuna were investigated. Denaturation of myoglobin, apparently exposing a sulfhydryl group, was necessary for the greening reaction to occur. TMAO acted as a mild oxidizing agent to promote the formation of a disulfide bond between cysteine and the sulfhydryl group on the denatured myoglobin. TMAO could be replaced by oxygen (air), but cysteine appeared to be specific for the reaction. The green color could be reversed by sodium sulfite, but not by other reducing agents tested.
Shrimp, Penaeus stylirostris Stimpson, were tris and P. aztecus. Regression equations (mmol subjected to increasing and decreasing salinity, 100 g-l) for glycine, glycine plus proline, proline, ranging from 10 to 5 0 %~ Glycine, proline, and alaand total amino acids were 10.156 + 0.1512, 11.426 nine levels increased significantly with increasing + 0.2332, 2.016 + 0.0652, and 21.097 + 0.2492 (desalinity. Only glycine and proline levels decreased creasing salinity), respectively. The regression significantly when the salinity was reduced. Glyequation (mmol 100 g-l) for alanine was 0.685 + cine levels a t 36% were similar in both P. styliros-0.0702 (increasing salinity).Amino acids have been shown to be involved in osmoregulation in crustaceans by several investigators. These studies have been reviewed by Schoffeniels and Gilles (1970). Although total amino acid levels have been shown to participate in osmoregulation in different species of crustaceans, the role of specific amino acids has not been identified. In a recent study Cobb and Vanderzant (1974) indicated that glycine might be the osmoregulator in white shrimp, Penaeus setiferus.In addition to their role as osmoregulators, free amino acids have been implicated as being responsible for much of the flavor in shrimp. Glycine probably causes the sweet taste in freshly caught shrimp (Hashimoto, 1965;Rajendranathan Nair and Bose, 1965). If the levels of certain amino acids increase with increases in salinity, the production of more tasty, cultured shrimp might be possible by manipulating the salinity of the water.In this study the effect of salinity in the range of 10-50%0 on amino acid levels in the tails (abdomen) of Penaeus stylirostris was investigated. Amino acid levels in brown shrimp (Penaeus aztecus) from waters of constant salinity were measured to determine the possible applicability of the results to other species. EXPERIMENTAL SECTIONMaterials. Shrimp, Penaeus stylirostris Stimpson, used in the experiment were reared in ponds of the Texas Agricultural Extension Service's mariculture facilities in Corpus Christi, Tex. Twelve fiberglass tanks (89 X 52 X 55 cm) were equipped with substrate filters, each with two 1.27-cm PVX airlifts. The filters were covered by a 5-cm layer of sand and shell. Circulation and aeration were maintained by a Conde Dry-Air Blower. Each tank was covered by a lid with an internal black polyethylene lining to prevent water evaporation. Salinity was measured with an A.O. Goldberg refractometer. Water pH was measured with an Amstro pH meter.Water a t 46% was pumped directly from the Laguna Madre through 5-fi filters into each tank and maintained a t a depth of 30 cm. Shrimp were seined from the production ponds (-16%) and five shrimp, averaging 110 mm and 10 g, were placed in each tank. The salinity was adjusted to 50%0 with seasalts and the shrimp were allowed to acclimate for 7 days. Tanks containing shrimp were designated by random selection, with two replicates of each of the following: 5 0 L control (shrimp sampled a t e...
Freshly harvested white shrimp (Penaeus setiferus) were taken from 13 locations on the northwestern coastline of the Gulf of Mexico. Freshly harvested brown shrimp (Penaeus aztecus) were taken from 3 different water depths near Port Aransas, Tex. Brown shrimp taken from commercial fishing boats at time of landing also were examined. Samples were analyzed for amino nitrogen (AA-N), NH3, total volatile nitrogen (TVN), trimethylamine nitrogen (TMN), bacterial content, and pH. A portion of each sample was placed on sterile ice and allowed to spoil. Spoilage odors appeared in white sea-shrimp after storage for 11–50 days, for brown sea-shrimp in 20–30 days, and in brown boat-shrimp after 0–15 days. Both TVN and AA-N varied considerably from sample to sample and did not show a consistent pattern of change during iced storage. TVN/AA-N ratios increased as samples spoiled. TVN/AA-N ratios greater than 1.3 mg N/mm indicated a short shelf-life of boat shrimp. TMN production was evident in boat-shrimp samples (4 out of 9 samples) with high TVN levels. Bacterial counts of fresh shrimp did not exceed 104/g. Nine of the 10 boat-shrimp samples had counts in excess of 106/g. Counts of samples spoiled on sterile ice ranged from 2 × 106 to 1010/g. The estimated reduction of the maximum potential shelf-life of boat-shrimp by handling and storage was 0–15 days.
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