Objective tests which are useful for assessing the number of days elapsed in ice storage and/ or which reflect the early changes occurring prawns

before the onset of spoilage are essential for quality control in the prawn processing industry

Govindan, T K

Velankar, N K

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Reprinted from <<Curr. Sci.", NOV.' 1958, 27, 451 -452 -- - - - - - -- THE FREE AMINO NITROGEN CONTENT ASAN INDEX OF QUALITY OF ICE-STORED PRAWNS OBJECTIVE tests which are useful for assessing 200 mg. N/lOO g. charaderise the first two days, the number of days elapsed in ice storage and/ values between 100 and 200 mg. the next three or which reflect the early changes occurring in or four days and values below 100 longer dura- prawns before the onset of spoilage are essen- tions. According to Bailey et al. (loc. St.) the tial for quality control in the prawn processing prime quality phase of ice-stored prawns lasts industry. Our earlier findings1 that the free for about six days. The rapid d m a s e  in amino amino nitrogen content of the crustacean mus- N is seen to be arrested about the sixth or cle is over 300 mg. N/100 g. of muscle whereas seventh day (Fig. 1).  It appears therefore that it is only about l/lOth of this value in the the amino N is also. useful as the other tests fishes suggested that the determination of mentioned by Bailey et al. The determinatio~ amino nitrogen might be of use in studies on of amino N by the method employed3 is sim- crustacean spoilage. Hence this determination was included among other chemical and bac- teriologial tests in investigations on the quality of ice-stored prawns which are in progress at this Station. The results of one series of obser- vations on prawns obtained at Mandapam and also on prawns landed at Cochin on the West Coast are shown in Figs. 1 and 2. FIG. 1. Decrease in amino N during ice storage. It is seen that the decrease in arkno nitro- gen is more regular than the decrease in the orthophosphate which shows some scattering. Also there is close agreement in the amino nitrogen values of the Mandapam prawns and Cochin prawns after equal periods of storage in ice. Bailey et al.2 did not include amino N among the tests which show definite changes in the prime quality of ice-stored prawns but con- sidered it among other tests for judging the relative quality. Our observations on prawns comprising of different species* and taken from different environs indicate that definite ranges of amino N values are associated with the num- ber of days in ice storage. Values of over ple, accurate and needs m special equipmat or instruments. Campbell and Williams4 had reported an in- crease in the amino N in Gulf coast shrimps during ice storage ; but Fieger and Friloux6 observed a decrease in the amino N. Our ob- servations are in agreement with those of the latter workers ; however, the fall in amino N is more rapid and much lower values are reach- ed after two weeks' storage in ice in our ex- periments. The reason for this is not clear at present. The initial amino N values for Gulf coast shrimps reported by Fieger and Friloux are of the same level as in Indian prawns, crabs and lobsters reported by us (loc. cit.). Bailey et al. attributed the differences in their observations and those of Campbell and I FIG. 2. Decrease in orthophosphate during ice storage. Williams to possible differences in the bacte- rial flora. The mechanism of the decrease in the amino N during ice storage is not clearly elucidated yet ; but experiments carried out by us have shown that leaching by contact with melting ice is the most significant factor. Bac- terial action is not probably involved since the bacterial population is low especially during the early days of storage when the decrease in 

Free amino nitrogen content as an index of quality of ice-stored prawns

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Free amino nitrogen content as an index of quality of ice-stored prawns

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