CHAPTER XVII 

 CHEMICAL COMPOSITION 



Page 



Proxiinate composition of oyster meat 381 



Seasonal and local variations.. 381 



Yield and quality of meat 382 



Inorganic constituents 383 



Iodine 383 



Heavy metals 383 



Observations on New England oysters 384 



Analytical procedures 384 



Variations in glycogen content 386 



Iron, copper, zinc, and manganese 387 



Variations in thecontentofproteins, amino acids, and vitamins 390 



Condition index 392 



Antibacterial agents 393 



Bibliography 393 



Regardless of the zoological group to whicli an 

 animal belongs the greatest mass of materials 

 which form the tissues and organs, exclusive of 

 skeleton or shells, consists of three major groups 

 of organic compounds: proteins, carbohydrates, 

 and lipids (fats). Many analyses reported in the 

 literature show that, in spite of great variability 

 in tlie composition of meat of several species of 

 Ostrea and Crassostrea, the order of magnitude of 

 the three components is common to all the species 

 studied. The proteins make up 50 percent or 

 more of tlie solids, carbohydrates are less than 25 

 percent, lipids constitute less than 20 percent. 



PROXIMATE COMPOSITION OF 

 OYSTER MEAT 



A general idea of the pro.ximate composition of 

 tiie meat of C. rirtjinica can be deduced from 

 tallies published by the U.S. Department of 

 Agriculture for dietitians, nutritionists, physicians, 

 and otiiers engaged in planning diets or in cal- 

 culating the nutritive value of foods^ (Watt and 

 Merrill, 1950, p. 36). The material used for such 

 analyses represents the average sample available 

 for purchase at the market or delicatessen store. 

 The figures do not refer, therefore, to oysters of 

 any particular locality or to time of the year. 

 For convenience in making a comparison all tlie 

 values originallv given for 1 cup (240 g.) of raw 

 oysters were recomputed for 100 g., which corre- 

 sponds to five to eight medium-size oysters. 

 The sample contained 9.8 g. of protein, 5.6 g. of 

 carboliydrates, 2.1 g. of fat, 94.1 mg. of calcium, 



FISHERY bulletin: VOLUME 64, CHAPTER XVII 

 733-851 O— 64 25 



143 mg. of phosphorus, and 5.6 mg. of iron, and 

 80.5 g. of water. 



When oysters are prepared for the market the 

 meats are shucked and washed, either in fresh 

 water or sea water. During this process the water 

 is stirred and air is blown through it to remove 

 grit, pieces of broken shell, and mud. The pro- 

 cedure affects the chemical composition because 

 some of the soluble salts present in the body are 

 lost, and the less soluble constituents, the proteins 

 and fats, then make up the greater proportion of 

 solids. Consequently the values for these two 

 components quoted above are somewhat higher 

 than for unwashed oysters. Correspondingly the 

 values of mineral salts in Watt and Merrill's data 

 are lower. 



SEASONAL AND LOCAL VARIATIONS 



Variations in the chemical composition of oys- 

 ters foUow distinct patterns related to environ- 

 ment and season of the year. The major environ- 

 mental factor affecting chemical composition is the 

 salinity of water. C. virginica is an estuarine 

 species which may be found in waters ranging 

 from almost 40°/oo, as in the sheltered bayous of 

 the Gulf Coast, to less than 3°/oo at the upper 

 reaches of bays after heavy rainfall (upper Chesa- 

 peake Bay, MobOe Bay, Apalachicola Bay, and 

 others). A change from wet to dry spells produces 

 a pattern of fluctuations in the contents of mineral 

 salts in oysters growing in waters of fluctuating 

 salinity. Such conditions prevail in the waters of 

 the south Atlantic and Gulf states where the 

 annual range of changes from maximum to mini- 

 mum ash content was reported to be 5.3 to 31.1 

 percent on a moistm-e-free basis. The solids, for 

 the same period of time, varied between 7.5 and 

 18.4 percent of the wet weight of oysters (Lee, 

 Kurtzman, and Pepper, 1960). Fluctuations in 

 the moisture content due to absorption of water 

 and loss of solids are the most significant features 

 of changes in the chemical composition of oyster 

 meat which affect their commercial quality. Good 

 oysters contain two and one-half times more solids 



381 



