为了简便而准确地对水产品的新鲜等级进行判别，本文采用苦味酸比色法对样品中三甲胺和氧化三甲胺进行同时测定，本文提出通过三甲胺/氧化三甲胺（TMA/TMAO）摩尔比值对5、0、15 ℃贮藏过程中南美白对虾的新鲜程度进行测定,，并且同时对虾肉的挥发性盐基氮（TVB-N）、pH值、感官评分随贮藏时间的变化规律进行测定，利用最小二乘数法计算TMA/TMAO摩尔比值与挥发性盐基氮值（TVB-N）的相关性。结果表明：随着贮藏时间的增加，TMA和TMAO、pH变化趋势不稳定，很难对南美白对虾做出准确的鲜度评价。但是TMA/TMAO摩尔比值随贮藏时间的延长呈稳定的上升趋势，并且同一贮藏温度下TMA/TMAO摩尔比值与TVB-N值显著相关（P<0.01），相关系数r均大于0.936。说明TMA/TMAO摩尔比值作为判定南美白对虾的新鲜程度是可行的。

Picric acid colorimetric method was conducted to measure TMA and TMAO of Litopenaeus vannamei in this research. Variations as the mole ratio of TMA and TMAO, total volatile basic nitrogen (TVB-N), pH value and sensory evaluation were detected to determine the freshness of Litopenaeus vannamei at the store temperature of 0, 5 and 15 ℃. The result showed that TMA, TMAO and pH values grew unsteadily which were hardly to detect the freshness of sample whereas the mole ratio of TMA and TMAO and TVB-N increased steadily with the increasing storage time. Moreover, the mole ratio of TMA and TMAO and TVB-N were significantly correlation (p＜0.01), and all the correlation coefficients were greater than 0.936. Thus the mole ratio of TMA and TMAO was a feasible index for detection of the freshness of Litopenaeus vannamei simply and exactly.