Comparative Analysis of Nutrient Composition of Different-Colored Yadong Trout Eggs

Abstract

Yadong trout (Salmo trutta fario) is an important and characteristic aquaculture fish species in Yadong, Xizang, China. Farmed Yadong trout has been produced on a large scale. Usually, two different-colored eggs (yellow and orange) are produced during Yadong trout farming and show differential reproductive performance. There has been very limited information on the nutrient composition of eggs with different colors, and relevant results have only been reported for rainbow trout. The present study aimed to analyze the nutrient compositions in different-colored Yadong trout eggs to elucidate the factors responsible for the different reproductive performances of the two egg types. The experimental samples were collected from Yadong Industry Park, where the broodstocks were reared with artificial compound feeds. Each egg type was analyzed in 3 replicates. Yellow eggs were produced by 2–3 year-old broodstocks, and orange eggs were produced from 3–5 year-old broodstocks. After spawning, the eggs were cryopreserved and transported to the laboratory by plane. The samples were lyophilized and used for the determination of proximate composition, fatty acids, amino acids, and other reproduction-related nutrients. The crude protein and crude lipid contents were analyzed using the Kjeldahl and Soxhlet extraction methods, respectively. The fatty acid composition (expressed as % total fatty acids) and amino acid composition (expressed as % dry matter) were assayed using gas chromatography and an automatic amino acid analyzer, respectively. The protein carbonyl and malondialdehyde concentration were assayed using commercial kits supplied by Nanjing Jiancheng Bioengineering Institute. The α-vitamin E and astaxanthin were assayed using national standard methods, and the α-vitamin E was measured from wet samples. The statistics of proximate composition, fatty acids, and amino acids data were determined using a t-test for independent samples. The results were expressed as mean ± standard error, and showed that yellow eggs had lower contents of crude protein and ash contents, but higher contents of crude lipid and moisture than orange eggs. There was no significant difference in carbohydrate and energy content between yellow and orange eggs. The saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (n-3 PUFA), and docosahexaenoic acid (DHA) contents of yellow eggs were significantly lower than those of orange eggs, while the n-6 polyunsaturated fatty acids (n-6 PUFA) and EPA contents did not differ significantly between the two egg types. The C16:0 and C20:0 contents of yellow eggs were significantly lower than those of orange eggs, while the contents of monounsaturated fatty acids (MUFA), including C16:1n-7, C18:1n-9, C20:1n-9, and C22:1n-9, of yellow eggs were significantly higher than those of orange eggs. The contents of essential amino acids, non-essential amino acids, and total amino acids were slightly lower in yellow eggs compared to orange eggs. Among the essential amino acids, the contents of valine, methionine, leucine, lysine, and histidine in yellow eggs were significantly lower than those in orange eggs. Among the non-essential amino acids, except for glycine and alanine which were significantly lower in yellow eggs than in orange eggs, the contents of other amino acids did not differ significantly between the two egg types. The contents of protein carbonyl and malondialdehyde in yellow eggs were higher than those in orange eggs, while the contents of α-vitamin E and astaxanthin in yellow eggs were lower than those in orange eggs. In conclusion, orange eggs had higher contents of protein, some essential amino acids, DHA, α-vitamin E, and astaxanthin, but lower contents of MUFA, crude lipid, and peroxidation products (protein carbonyl and malondialdehyde) than yellow eggs. These differences in nutrient composition may contribute to the superior reproductive performance of orange eggs over yellow eggs.

Keywords

• salmo trutta fario
• egg
• nutrient composition
• amino acid
• fatty acid