FISHERY BULLETIN: VOL. 76, NO. 1 



tubes in the heat exchanger were made of 

 titanium to avoid corrosion. Carbon dioxide was 

 metered into the suction side of the pump for 

 maximum diffusion; at a rate of 0.2 1/min (0.2 

 ft^/h), thepH was lowered from 7 to 4 in 5 h. In this 

 14-day experiment, 8.8 kg (4 lb) of carbon dioxide 

 were used. 



A chest-type home freezer was used as an insu- 

 lated box to hold shrimp in ice. One day before its 

 use the refrigeration was disconnected and the 

 door raised to allow the ice to begin to melt in order 

 to simulate conditions in a boat's hold. 



SAMPLING 



Sampling Procedure 



In this comparative holding experiment, a sam- 

 ple was taken daily from each holding system and 

 allowed to drain for 30 min before weighing (iced 

 shrimp were first rinsed briefly in cold water to 

 remove ice). Four subsamples were prepared from 

 each sample — three to represent commercial 

 practices and the fourth for laboratory analyses to 

 determine chemical changes in the shrimp. The 

 subsamples, stored at -34°C (-30°F) for later 

 analyses, are as follows. 



Subsampling Procedure 



1. Whole shrimp: The total weight of whole 

 shrimp was determined at each period of hold- 

 ing to simulate the weight of shrimp landed at 

 the dock and to determine yield of products. 

 Water uptake was determined by a solids 

 analysis in a blended sample. 



2. Hand-peeled, raw shrimp meats: This 

 laboratory sample was used to determine basic 

 chemical changes, mainly spoilage. 



3. Hand-peeled, raw, washed shrimp meats: 

 This sample simulated a machine peeled raw 

 frozen product. Washing was required to ap- 

 proximate the leaching action of commercial 

 machine peelers. The hand-peeled meats were 

 washed gently in cold water for 2 min, drained 

 on hardware cloth for 10 min, then weighed, 

 and frozen for later analyses. 



4. Hand-peeled, washed, cooked shrimp meats: 

 This sample simulated a cooked frozen product. 

 A portion of the washed meats after frozen 

 storage, as in 3 above, was thawed and cooked 

 in boiling water for 2 min at a 12:1 ratio, 



drained 1 min, cooled 5 min, and blended for 

 analyses. 



To prepare subsamples 2 and 3 for analyses, 

 they were removed from the freezer left at room 

 temperature for 2 h, stored in a refrigerator over- 

 night to thaw, and then blended. 



Analytical Techniques 



After the frozen samples were thawed and 

 blended, the following analyses were performed: 

 total nitrogen, solids, total chloride (Horwitz 

 1975), total volatile base (TVB; Stansby et al. 

 1944), total volatile acid (TVA; Friedemann and 

 Brook 1938), trimethylamine (TMA; Dyer 1945), 

 and carotenoids (Kelley and Harmon 1972). 

 Sodium and potassium were determined by using 

 a Beckman Model B hydrogen-oxygen flame 

 photometer on appropriate dilutions of a 20-g 

 sample digested with nitric and perchloric acids. 

 The pH of the brine was determined daily. 



RESULTS AND DISCUSSION 



Whole Shrimp 



The change in weight of whole shrimp held in 

 these systems has commercial importance. The 

 yield of product obtained in a processing plant is 

 calculated from the weight of whole shrimp landed 

 at the dock. The time of holding and the holding 

 system affect the weight of landed shrimp (Table 

 1) and, therefore, the yield of the final product. 

 Whole shrimp held in MRSW gained 5% in gross 

 weight during the first 1.5 days and slowly gained 

 an additional 2% during the next 7 days. A much 



Table l. — Change in gross weight and percentage solids with 

 time of holding 2,100 g of whole pink shrimp in modified refrig- 

 erated seawater (MRSW) and ice and pH of the brine. 



74 



