Effect of freshness and salt on quality of white shrimp

Abstract

The concentration of salt (NaCl) in white shrimp, which is one of the main export products of Thailand, is very important in quality control. In this research study, Na and Cl distribution in white shrimp was investigated using the X-ray fluorescence (XRF) technique to examine salt absorption and distribution within samples at two freshness levels, freshness levels 3 and 4. White shrimp of both freshness levels were soaked in a salt solution at 9 % (w/v) for 90 min and boiled for 110-130 sec, in accordance with work instructions from a factory. Additional samples were cooked after soaking, and still other samples of raw shrimp (not soaked, not cooked) were examined by the XRF technique and the results obtained were compared with quantitative salt analysis by the titration method. The concentration of Na and Cl can be matched to a color scale to represent the level of Na and Cl absorption. The results show that white shrimp with freshness level 3 absorbed a higher concentration of salt solution (2.49±0.11 %) than the samples with freshness level 4 (2.20±0.14 %). The results were similar to those resulting from the titration method, although the samples at freshness level 3 indicated higher salt concentration. However, white shrimp with freshness level 4 also indicated a higher TVB-N value than that of freshness level 3, but still meets the Thai standard for frozen shrimps and prawns.