Investigation into the nutritive value of Adriatic oyster (Ostrea edulis Linné)
Abstract
Investigations into the values and variations of chemical composition and nutritive value of Adriatic oyster (Ostrea edulis L i n n é) provenient from Mali Ston Bay beds were conducted in monthly intervals over a period of twelve months (from April, 11th 1949 to March 24th 1950). This research involved the meat of the oysters only.
The total weight was taken for every sample consisting of about 50-60 oysters, aged from two to two and a half years. Then the meat was washed in fresh running water to clean in from intervalvular water, mud and food residue, and the excess moisture was absorbed in paper towels.
Net weight being taken, the oysters were finely minced in an amorphous, homogeneous mass and sampled one part for moisture and glycogen determination. The rest was dried and sampled for protein, fat and mineral determination. The energy content was calculated by the multiplication of the fat and protein values with R u b n e r's factors.
The average annual gross total weight was 89,1 grams, net weight 8,7 grams and the percentage of meat 9,7. The peak of meat percentage in oysters was reached in February, then in March, January and April. In these months oysters were in best market condition. In May, immediately after spring spawning which occurs with this species from the middle of April to the middle of May, and in November, after the second spawning which follows in September and October, the lowest net weight was observed.
The average annual composition of fresh oyster body was the following: moisture 79,94%, protein 11,34% fat 2,02%, glycogen 4,02% and ash 1,48%.
Considerable variations were found by comparing the results of the investigated samples with regard to the date of the catch and to the spawning season. In the composition of moisture the fluctuations were between 75,4 and 81,6 per cent; in proteins between 9,82 and 12,58%; in fat between 1,44 and 2,78%; in glycogen between 2,63 and 5,86% and in ash between 1,19 and 1,80 per cent.
The reciprocal varying of protein and glycogen values has been confirmed. After spawning an increase in protein values and a simultaneous decrease in glycogen values were noticed. The lowest percentages of the highest percentages of glycogen in dried substance were recorded in January, February, and March.
The maximum glycogen content occurred in February oysters; it is the period when the Adriatic oyster is though to be the best. In the winter and early spring this oyster is considered in the finest market condition being »the fattest« or »the thickest«. The oysters are then of an bulbous appearance and of white-yellowish colour. After spawning the oysters' flesh turns meager, languid, watery, and of dirty whitebrownish colour.
The highest percentage of fat was found during the months before the spring spawning; in the autumn months and early winter this percentage was the lowest.
The average energy content found 100 grams of the examined fresh oyster meat ammounted to 82 calories. Maximums were reached in March and April and the minimum value was found after spawning.
By comparing the average annual energy content of Mali Ston oyster with three non-European oysters species (Ostrea lurida, Ostrea gigas, Ostrea virginica) which were investigated by T u l l y (1935), Mali Ston oysters reveal somewhat higher values; the energy content was for ten calories lower when compared with the European species Ostrea edulis, investigated by R u s s e l l (H a v i n g a 1938).
