Dietary supplementation with glutamate improves the flesh quality of gibel carp (Carassius gibelio) by altering muscle texture characteristics and increasing the deposition of flavour substances

Abstract

Nutrition intervention is an effective way to improve flesh qualities of fish. The effect of feed supplementation with glutamate (Glu) on flesh quality of gibel carp (Carassius gibelio) was investigated. In trial 1, the fish (initial weight: 37.49 ± 0.08 g) were fed two practical diets with 0 and 2% Glu supplementation. In trial 2, the fish (37.26 ± 0.04 g) were fed two purified diets with 0 and 3% Glu supplementation. The results after feeding trials showed that dietary Glu supplementation increased the hardness and springiness of muscle, whether using practical or purified diets. Glu-supplemented diets increased the thickness and density of myofibres and collagen content between myofibres. Furthermore, Glu promoted muscle protein deposition by regulating the IGF-1-AKT-mTOR signalling pathway, and enhanced the myofibre hypertrophy by upregulating genes related to myofibre growth and development (mef2a, mef2d, myod, myf5, mlc, tpi and pax7α). The protein deposition and myofibre hypertrophy in turn improved the flesh texture. In addition, IMP content in flesh increased when supplementing Glu whether to practical or to purified diet. Metabolomics confirmed that Glu promoted the deposition of muscle-flavoured substances and purine metabolic pathway most functioned, echoed by the upregulation of key genes (ampd, ppat and adsl) in purine metabolism. The sensory test also clarified that dietary Glu improved the flesh quality by enhancing the muscle texture and flavour. Conclusively, dietary Glu supplementation can improve the flesh quality in this fish, which can further support evidence from other studies more generally that improve flesh quality of cultured fish.

Keywords: 4e-bp2, eukaryotic translation factor 4E-binding protein 2; AKT, protein kinase B; AMP, adenosine monophosphate; CWL, centrifugal weight loss; FAA, flavour amino acids; FBW, final body weight; FE, feed efficiency; FR, feeding rate; Flavour; Flesh quality; GMP, guanosine monophosphate; Glu, glutamate; Glutamate; HSI, hepatosomatic index; IGF-1, insulin-like growth factor-1; IMP, inosine monophosphate; MRFs, myogenic regulatory factors; Myf, myogenic factor; MyoD, myoblast determination protein; Myofibre; Myog, myogenin; PI3K, phosphoinositide 3-kinase; S6, ribosomal protein s6; SGR, specific growth rate; SR, survival rate; TOR, target of rapamycin; Texture; adsl, adenylosuccinate lyase; adss, adenylosuccinate synthetase; ampd, AMP deaminase 2; atic, bifunctional purine biosynthesis protein; cast, calpastatin; eif4e, eukaryotic translation initiation factor 4E; gcn2, general control nonderepressible 2; gmps, GMP synthase.; impdh1, inosine5’-monophosphate dehydrogenase 1; mef, myocyte-specific enhancer factor; mlc, myosin light chain; mstn, myostatin; nt5c3, 5’-nucleotidase III; pax, paired box; pfas, phosphoribosylformylglycinamidine synthase; pnp, purine nucleoside phosphorylase; ppat, phosphoribosyl pyrophosphate amidotransferase; s6k1, ribosomal protein S6 kinase 1; samd, SMAD family member; tpi, troponin I; tpt, troponin T.

Graphical abstract

Fig. 1.

Effects of Glu supplementation in the practical diets on texture and microstructure of dorsal muscle of gibel carp. (a–h) Muscle textural properties (n = 9). (i) Histological observations of the dorsal muscle after Hematoxylin-Eosin and Masson staining (magnification 400×). Black arrows represent myofibre diameter. Green arrows point to myofibres. (j) The quantitative graph of myofibre diameter. (k) The quantitative graph of frequency of myofibres with different diameters. For each index, ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 2.

Effects of Glu supplementation in the purified diets on texture, microstructure and collagen content of dorsal muscle of gibel carp. (a–h) Muscle textural properties (n = 9). (i) Centrifugal weight loss. (j) Histological observations of the dorsal muscle after Hematoxylin-Eosin and Masson staining. Black arrows represent collagen. (k) The quantitative graph of myofibre density. (l) The quantitative graph of collagen content. For each index, ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 3.

Effects of Glu supplementation in the practical diets on protein and mRNA expression related to protein synthesis in dorsal muscle of gibel carp. (a) AKT and S6 protein phosphorylation in dorsal muscle were measured by western blot. GAPDH was used as a loading control (n = 3). (b) The relative protein expression of p-AKT/AKT. (c) The relative protein expression of p-S6/S6. (d) The relative mRNA expression of protein synthesis in dorsal muscle. ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 4.

Effects of Glu supplementation in the practical diets on muscle growth and development of gibel carp. (a) The relative mRNA expression of myocyte enhancer factors in dorsal muscle. (b) The relative mRNA expression of myofibre growth in dorsal muscle. (c) The relative mRNA expression of myogenic regulatory factors in dorsal muscle. (d) The relative mRNA expression of myofibre development in dorsal muscle (n = 3). ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 5.

Effects of Glu supplementation in the practical diets on flavour nucleotide, flavour amino acids and IMP metabolism in dorsal muscle of gibel carp. (a–b) Flavour nucleotides (IMP and AMP) content and flavour amino acids (Umami: aspartic acid and glutamic acid: sweet: aspartic acid, glycine, alanine, methionine, leucine, arginine, and proline; bitter: valine, isoleucine, leucine, tyrosine, phenylalanine, histidine, and lysine) content in muscle (n = 3). (c) The relative mRNA expression of IMP synthesis in muscle (n = 6). (d) The relative mRNA expression of IMP catabolism in muscle (n = 6). For each index, ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 6.

Effects of Glu supplementation in the purified diets on flavour nucleotide, flavour amino acids and IMP metabolism in dorsal muscle of gibel carp. (a–b) Flavour nucleotides (IMP, AMP and GMP) content and flavour amino acids (Umami: aspartic acid and glutamic acid: sweet: aspartic acid, glycine, alanine, methionine, leucine, arginine, and proline; bitter: valine, isoleucine, leucine, tyrosine, phenylalanine, histidine, and lysine) content in muscle (n = 3). (c) The relative mRNA expression of IMP synthesis in muscle (n = 3). (d) The relative mRNA expression of IMP catabolism in muscle (n = 3). For each index, ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 7.

Effects of Glu supplementation in the purified diets on the metabolomic features in flesh. (a) The PCA score plots for metabolomic profiles of muscle. Con2 group in red, 3%Glu group in green. (b) Heatmap visualisation of differential and overlapping metabolites in Con2 group VS 3%Glu group. Red indicates high abundance, whereas the relatively low-abundance metabolites are shown in blue. (c) Summary of pathway analyses of the effects of dietary 3%Glu supplementation for flesh with MetaboAnalyst 5.0, as visualised by bubble plots. The colour and size of each circle is based on the P value and the pathways impact value, respectively. (d) Metabolic pathways affected induced by Glu supplementation in muscle; Red indicated increase; green indicated decrease.

Fig. 8.

Effects of Glu supplementation in the purified diets on the levels of purine metabolites in dorsal muscle of gibel carp. Data are shown as mean ± SEM (n = 3). For each index, ‘*’ showed significantly differences between groups (P < 0.05).

Fig. 9.

Effects of Glu supplementation in the practical diets on the appearance, smell and taste of flesh in gibel carp.

Fig. 10.

A schematic diagram showing the effects of Glu supplementation on the flesh quality in gibel carp.