MAO Xiaocong, WU Fangbing, WANG Jiayan, SHI Feilong, TIAN Yuanyong, ZHAO Hui, LU Hang
To explore the effect of hemoglobin residue on the meat quality of frozen fat greenling(Hexagrammos otakii), two groups of fish were killed respectively using brainstem bloodletting or fish head tapping. The hemoglobin residues in frozen fish meat were compared between two groups. The change of hemoglobin, meat quality, and oxidation of lipids and proteins in frozen fish meat at 4 ℃ were analyzed and compared. The results showed that the hemoglobin content was reduced approximately 30% in the frozen fish killed by brainstem bleeding, and that it gradually decomposed and its content continued to decrease. During the 5-day refrigeration process, the hemoglobin content of fish meat in the bleeding and non-bleeding groups decreased from 12.86% to 4.65% and from 16.96% to 5.98%, respectively. The content of heme, a decomposition product of hemoglobin, gradually increased over time and then degraded. The content of oxygenated hemoglobin in the fish meat of the bleeding and non-bleeding groups decreased from 14.76% to 0.65% and from 16.86% to 1.08%, respectively, while the content of methemoglobin increased from 9.81% to 23.22% and from 14.88% to 25.22%, respectively. This pattern indicates that oxygenated hemoglobin was transformed into methemoglobin. Compared with the meat from the bleeding fish, the contents of hemoglobin, heme, free iron, Fe2+ and Fe3+ in the meat of the non-bleeding fish were significantly higher. During the 5-day refrigeration storage, the brightness(L*) and redness(a*) values showed an upward trend, while the yellowness(b*) value showed a downward trend. Over time, the peroxide values(POV) of the bleeding and non-bleeding groups increased by 0.83 μg/100 g and 1.11 μg/100 g, respectively, and the mass fraction of malondialdehyde increased by 0.22 μg/100 g and 0.31 μg/100 g. The carbonyl content of fish meat from the two groups increased by 3.16 nmol/mg and 6.21 nmol/mg, respectively, and the thiol content decreased by 4.04 nmol/mg and 7.32 nmol/mg. In summary, bleeding killing method delayed the decline in meat quality and reduced the oxidation degree of lipids and proteins in frozen fish meat. Correlation analysis indicated that the oxidative degradation of hemoglobin in fish meat during refrigeration intensified the occurrence of lipid oxidation and protein oxidation, which in turn significantly affected the rate of deterioration of the frozen fish meat.
total nitrogen (TN), and/or the permanganate index (CODMn) and negatively correlated with water transparency. The explanatory variables for density and biomass varied along different flow directions. Redundancy analysis results indicated that soluble phosphate 
water temperature (WT), TDS, TN, water depth (WD), CODMn, and pH were the key factors influencing the spatial and temporal distribution of benthic macroinvertebrate communities in Qiandao Lake (P<0.05). L. hoffmeisteri, Limnodrilus claparedeianus, and T. tubifex exhibited significant positive correlations with pH, CODMn, 
TN, and WT. In contrast, the insect Procladius choreus and oligochaetes Branchiura sowerbyi and Aulodrilus pluriseta showed significant negative correlations with WT, TSD, and WD. The results also showed that primary productivity was a key driver of spatial variations in macrobenthic abundance in Qiandao Lake and that most of the Lake was in a lightly polluted state, with good water quality in general.
