Effects of the Photovoltaic Fishery Breeding on Hepatopancreas and Gonad Odor of Chinese Mitten Crab (Eriocheir sinensis)

The photovoltaic fishery breeding is a new environmentally friendly breeding method that combines pond aquaculture and photovoltaic power generation. Combining Chinese mitten crab (Eriocheir sinensis) farming with photovoltaic power generation is a new attempt to utilize resources comprehensively. However, there is no research on the effect of photovoltaic fishery breeding on the odor formation of E. sinensis. In this study, we compared the differences in basic nutrition composition, sensory evaluation, and odor quality of E. sinensis cultured in photovoltaic fishery breeding (PM) and common pond breeding (CM) environments. Two kinds of female crabs under PM or CM had their hepatopancreas and gonads evaluated by sensory analysis, as well as their tissue indices determination, proximate composition, electronic nose, and content of volatile compounds were evaluated. The flavor-active substances (odor activity value, OAV > 0.1) generated by the two breeding methods were evaluated. The results of artificial sensory evaluation and volatile compounds determination were analyzed by partial least squares (PLS) to comprehensively evaluate the odor characteristics of the hepatopancreas and gonads of Chinese mitten crab. The results of tissue indices and proximate composition showed that the gonads index of female crab was increased by the photovoltaic fishery breeding mode (P < 0.05). The crude protein and crude fat contents in the PM group were significantly higher than those in the CM group (P < 0.05). The photovoltaic fishery breeding mode can promote the E. sinensis growth. The sensory evaluation showed that the hepatopancreas grassy and fatty taste scores in the PM group were higher than those in the CM group. The hepatopancreas' electronic nose response value in the PM group was the highest, and the gonads' grassy odor in the PM group was more noticeable. The principal component analysis (PCA) of the electronic nose showed that the two breeding methods had a significant effect on the hepatopancreas odor profile of female crabs. The determination of volatile compounds by GC-MS showed a total of 44 (PM group) and 33 (CM group) substances identified in the hepatopancreas, mainly including aldehydes (22.59% and 21.83%), alcohols (21.79% and 28.14%), and alkanes (37.03% and 38.00%). In the gonads, 31 (PM group) and 47 (CM group) substances were identified, mostly aldehydes (13.01% and 31.19%), aromatic (7.54% and 3.99%), alcohols (8.18% and 9.69%), and alkanes (67.49% and 44.20%). Twenty-two hexanal-related substances were detected simultaneously in the hepatopancreas and gonads of female crab, while fourteen 2-methyl-2-butenal-like substances were detected only in the hepatopancreas, and fourteen 2-pentenal-like substances were detected only in the gonads. In the hepatopancreas, the total volatiles content in the PM group [(70.53±2.91) ng/g] was significantly higher than that in the CM group [(16.63±0.73) ng/g] (P < 0.05), corresponding to 4.2 times more total volatiles in the PM group than in the CM group. Among these, the contents of fatty and grassy flavor substances such as 2-methyl-butenal, 2-methyl-2-butenal, 4-heptenal, 3, 5-3, 5-octadien-2-one, and 1-octen-3-ol in the PM group were higher than in the CM group (P < 0.05). In gonads, the total volatiles content in the PM and CM groups were (68.80±1.86) ng/g and (71.50±4.17) ng/g, respectively, showing no significant difference between the two groups (P > 0.05). Nonetheless, the PM group's 2-ethylfuran and D-limonene contents were significantly higher than those in the CM group (P < 0.05). The grassy odor in the PM group was stronger in relation to the CM group, and the trimethylamine content in the CM group was 17 times higher than that in the PM group. Sulfur-containing compounds (dimethyl disulfide and thiophene) were detected in the CM group, and the odorous substances in this group were more abundant than those of the PM group, reflecting the inferior odor quality of the CM group. Several different flavor active substances were detected in hepatopancreas (11) and gonads (10) of female crabs under the two breeding methods, respectively. In the hepatopancreas, the OAV of (E)-2-octenal, octenal, (E)-2-nonenal, nonanal, decanal, and 2-pentylpyridine of the PM group was greater than 1, while the CM group's OAV of only (E)-2-nonenal and nonanal was greater than 1. The OAV of (E)-2-nonenal and nonanal was greater than 1 in gonads of the PM group. In the CM gonads, the OAV of hexanal, nonanal, and decanal was greater than 1. Overall, the OAV content was higher than 1 in the hepatopancreas in the PM group, which was higher than that in the CM group. In the gonads, the OAV content was greater than 1 for the CM group, revealing a fishy and ammoniacal odor that resulted in an overall unpleasant odor. PLS analysis showed a strong correlation between the PM group and grassy and fishy odor. The volatiles associated with hepatopancreas in the PM group were octanal, (E)-2-octenal, 2-decanone, 1-octen-3-ol, 2-pentyl furan, among others, while few volatiles associated with hepatopancreas were found in the CM group. Compounds strongly correlated with the CM group gonads included nonanal, hexanal, and other fishy odor aldehydes, trimethylamine, and 2-ethylfuran. The gonads' odor in the CM group was higher than in the PM group. The photovoltaic fishery breeding method can improve the grassy and fatty odors in the hepatopancreas, reduce the content of odor substances in the gonads, and promote the odor quality of female E. sinensis. This study provides a theoretical basis for optimizing and popularizing the photovoltaic fishery breeding method.