FISHERY BL'LLETIN: VOL, 69, NO. 3 



between the natural and the artificial ripening- 

 process. These analyses included: assay of 

 total soluble nitrogen by the Kjeldahl method, 

 protein determination by the biuret method, and 

 determination of amino nitrogen (as a rough 

 measure for the amino acid content) . Assuming 

 that the soluble matter is evenly distributed be- 

 tween the fish and the brine formed, most of 

 the analyses were carried out in the latter. 



Some of our experiments are described below. 

 Other experiments gave similar results and are 

 omitted here for ease of survey. 



NATURAL RIPENING PROCESS 



Frozen maatjes herring that had been caught 

 in the North Sea at the end of May were used. 

 The protein content was 16.49;^ and the fat con- 

 tent IS.S^r . Herring in this stage is normally 

 used for the preparation of maatjes-cured her- 

 ring. 



The protein content was determined by the 

 Kjeldahl method; for the fat determination, the 

 Bligh and Dyer (19.59) method was used in a 

 modification according to Ederzeel and Ritskes 

 (1966). 



Part of the herring was gibbed and part was 

 gutted. One part of salt was added to 20 parts 

 of herring (light salting). The fish was kept 

 at 3° C for 1 week. 



In order to remove proteins which are assumed 

 to be of less importance in the study of the ripen- 

 ing process, the brines were heated for about 15 

 min at 80° C and then filtered warm over a 

 fluted filter paper. All analyses were carried out 

 with these clarified brines. In this experiment, 

 these analyses included a Kjeldahl nitrogen de- 

 termination, a measurement of the biuret value 

 according to Strickland, Freeman, and Gurule 



(1961) and a determination of the amino nitro- 

 gen content according to the method of the Dutch 

 Food Law (1963). This latter method is based 

 upon two alkalimetric titrations to different end 

 points. The salt content in the brines was de- 

 termined by the Volhard method. 



In order to elucidate the protein breakdown 

 process during ripening, gel chromatography 

 of the brine was applied; 0.8 ml of a clarified 

 brine was chromatographed on a Sephadex G-25 

 column- (length 44 cm, diameter 1.44 cm; frac- 

 tion volume 3.4 ml, elution rate 19.8 ml/h), dis- 

 ■tilled water being used as an eluant. In each 

 fraction the biuret value and the absorbence at 

 280 nm (nanometers or millimicrons) were 

 measured. The results of the organoleptic eval- 

 uations and the chemical analyses are shown in 

 Table 1. The results of gel chromatography are 

 plotted in Figures 1 and 2. As could be ex- 

 pected, the values found in the brine of the gibbed 

 herring were considerably higher than in that 

 of the gutted herring. 



TESTING OF TWO ENZYME 

 PREPARATIONS 



Frozen spawning herring, caught at the end 

 of August in the North Sea were used. The 

 ]irotein content was IT.Q'? and fat content 



18.2';r. 



Two enzyme preparations, Pr 8 and TG 21/63, 

 were tested. Their proteolytic activities were 

 determined according to Anson (1938), with 

 denatured hemoglobin as a substrate. Lipol>-tic 

 activity was determined on olive oil according 

 to Marchis-Mouren, Sarda, and Desnuelle 



- Reference to trade names in this publication does not 

 imply endorsement of commercial products by the Na- 

 tional Marine Fisheries Service. 



Table 1. — Results of organoleptic evaluation of naturally ripened maatjes-cured 

 herring and of analyses of brine in which herring ripened. 



' Solt conlent of brine was 10.5 ± 0.5% w/v. 



648 



