Effects of hydroxyproline supplementation in low fish meal diets on collagen synthesis, myofiber development and muscular texture of juvenile Pacific white shrimp (Litopenaeus vannamei)

Abstract

This experiment aimed to evaluate the impact of dietary hydroxyproline (Hyp) supplementation on the muscle quality of juvenile Pacific white shrimp (Litopenaeus vannamei) fed a low fishmeal diet. Six formulated diets included one high fishmeal (HF; 25% fishmeal content) and five low fishmeal diets (10% fishmeal content) with 0%, 0.2%, 0.4%, 0.6% and 0.8% Hyp (LF0, LF2, LF4, LF6 and LF8, respectively). Each diet was assigned to four replicates, and 40 shrimp (0.32 ± 0.00 g) per replicate were fed four times a day for 8 weeks. Dietary Hyp supplementation had little effects on growth performance, but increased the contents of Hyp, prolyl 4-hydroxylases (P4Hs), and collagen. The meat yield, springiness, hardness, chewiness, and cohesiveness of muscle were the highest in the LF4 group among the low fishmeal groups (P < 0.05). Cooking loss and freezing loss of muscle were the lowest in the LF4 group (P < 0.05). Dietary supplementation with 0.4% Hyp increased the myofiber density and decreased the myofiber diameter of muscle (P < 0.05). Supplementation of Hyp in the diet up-regulated the mRNA expression of smyhc5, smyhc15, col1a1, col1a2, igf-1f, tgf-β and tor and down-regulated the mRNA expression of smyhc 1, smyhc 2, smyhc 6a (P < 0.05). Supplementation of Hyp in the diet up-regulated the protein expression of P-4E-BP1, P-AKT, AKT and P-AKT/AKT (P < 0.05). These results suggested that the addition of 0.4% Hyp to low fishmeal diets improved the muscle quality of L. vannamei.

Keywords: Collagen; Hydroxyproline; Litopenaeus vannamei; Muscle quality.

Fig. 1

Effect of hydroxyproline (Hyp) addition to low fishmeal diets on the content of prolyl 4-hydroxylases (P4Hs), Hyp and collagen in hemolymph, hepatopancreas and muscle of L. vannamei. (A to C) The P4Hs content in the hemolymph, hepatopancreas and muscle. (D to F) The Hyp content in the hemolymph, hepatopancreas and muscle. (G to I) The collagen content in the hemolymph, hepatopancreas and muscle. HF = high fishmeal; LF0 = low fishmeal; LF2 = LF0 + 0.2 g/kg Hyp; LF4 = LF0 + 0.4 g/kg Hyp; LF6 = LF0 + 0.6 g/kg Hyp; LF8 = LF0 + 0.8 g/kg Hyp. Bars with different superscripts are significantly different (P < 0.05).

Fig. 2

Effect of hydroxyproline (Hyp) addition to low fishmeal diets on the expression of muscle quality-related genes in the muscle and hepatopancreas of L. vannamei. (A to B) The expression of muscle quality-related genes in the muscle. (C to D) The expression of muscle quality-related genes in the hepatopancreas. tgf-β = transforming growth factor-beta receptor-associated protein 1-like; igf-1 = insulin-like growth factor-binding protein-related protein 1; tor = target of rapamycin complex 2 subunit mapkap1 -like; smych 1, smych 2, smych 6a, smych 5, smych 15 = myosin heavy chain gene family; col1a2 = collagen alpha-2(I) chain-like; col1a1 = collagen alpha-1(I) chain-like. HF = high fishmeal; LF0 = low fishmeal; LF2 = LF0 + 0.2 g/kg Hyp; LF4 = LF0 + 0.4 g/kg Hyp; LF6 = LF0 + 0.6 g/kg Hyp; LF8 = LF0 + 0.8 g/kg Hyp. Bars with different superscripts are significantly different (P < 0.05).

Fig. 3

Effect of hydroxyproline (Hyp) addition to low fishmeal diets on the morphology of muscle fibers of L. vannamei. (A) Myofiber microstructure of longitudinal sections. (B) Transmission electron microscope of longitudinal sections. (C) Myofibers diameter and sarcomere diameter. HF = high fishmeal; LF0 = low fishmeal; LF2 = LF0 + 0.2 g/kg Hyp; LF4 = LF0 + 0.4 g/kg Hyp; LF6 = LF0 + 0.6 g/kg Hyp; LF8 = LF0 + 0.8 g/kg Hyp. Bars with different superscripts are significantly different (P < 0.05).

Fig. 4

Effect of hydroxyproline (Hyp) addition to low fishmeal diets on the protein deposition of L. vannamei. (A) The Western blot analysis of P-4E-BP1,4E-BP1, P-AKT, AKT and α-Tubulin in muscle. (B to E) The relative quantification of protein levels of P-4E-BP1, 4E-BP1, P-AKT and AKT normalized to the α-Tubulin. (F to G) Phosphorylation levels of 4E-BP1 and AKT. P-4E-BP1 = phosphor-4E-binding protein; 4E-BP1 = 4E-binding protein; P-AKT = phosphor-protein kinase B; AKT = protein kinase B. HF = high fishmeal; LF0 = low fishmeal; LF2 = LF0 + 0.2 g/kg Hyp; LF4 = LF0 + 0.4 g/kg Hyp; LF6 = LF0 + 0.6 g/kg Hyp; LF8 = LF0 + 0.8 g/kg Hyp. Bars with different superscripts are significantly different (P < 0.05).