Does Dietary Lipid Level Affect the Quality of Triploid Rainbow Trout and How Should It Be Assessed?

Abstract

Organoleptic properties and nutritional value are the most important characteristics of fish fillet quality, which can be determined by a series of quality evaluation indexes and closely related to fish nutrition. Systematic organoleptic and nutritional quality evaluation indexes consisting of 139 indexes for physical properties and chemical compositions of triploid rainbow trout were established. Besides, effects of dietary lipid levels (6.6%, 14.8%, 22.8% and 29.4%) on the quality of triploid rainbow trout were analyzed in the study. The main results showed that, for fillet appearance quality, fish fed diets with lipid levels above 22.8% had higher fillet thickness and redness but lower gutted yield and fillet yield (p < 0.05). For fillet texture, fish fed the diet with a 6.6% lipid level had the highest fillet hardness (5.59 N) and lowest adhesiveness (1.98 mJ) (p < 0.05), which could be related to lipid, glycogen, water soluble protein and collagen contents of the fish fillet. For fillet odor, the odor intensity of “green, fatty and fishy” significantly increased with the increase of the dietary lipid level (from 1400 to 2773 ng/g muscle; p < 0.05), which was related to the degradation of n-6 and n-9 fatty acids. For fillet taste, a high lipid diet (≥22.8%) could increase the umami taste compounds contents (from 114 to 261 mg/100 g muscle) but decrease the bitterness and sourness taste compounds contents (from 127 to 106 mg/100 g muscle and from 1468 to 1075 mg/100 g muscle, respectively) (p < 0.05). For nutritional value, a high lipid diet could increase the lipid nutrition level (such as the content of long chain polyunsaturated fatty acids increased from 3.47 to 4.41 g/kg muscle) but decease tryptophan and selenium content (from 2.48 to 1.60 g/kg muscle and from 0.17 to 0.11 g/kg muscle, respectively). In total, a high lipid diet could improve the quality of triploid rainbow trout. The minimum dietary lipid level for triploid rainbow trout should be 22.8% to keep the better organoleptic and nutritional quality.

Dietary Effects of Lipid and Protein Levels on Growth, Feed Utilization, Lipid Metabolism, and Antioxidant Capacity of Triploid Rainbow Trout (Oncorhynchus mykiss)

“…Excessive dietary lipid level may exacerbate the fat deposition in the body and produce fatty fish [8]. In addition, dietary lipid level also affects the muscle quality of fish including the lipid deposition in brown trout (Salmo trutta) [9] and flesh color and flavor in rainbow trout (Oncorhynchus mykiss) [10,11]. Different from lipid and carbohydrate, excess dietary protein level would be used for intermediate metabolism in the form of energy, or converted to glucose or lipid retention [12].…”

Replacing Fishmeal and Fish Oil with Complex Protein and Canola Oil: Effect on Organoleptic and Nutritional Quality of Triploid Rainbow Trout (Oncorhynchus mykiss)

“…Based on the sampled data, the condition factors, gutted yields and fillet yields were calculated by referring to Meng et al [ 12 ]. The specific growth rate was calculated with reference to Meng et al [ 13 ]. The calculation formulae are as follows: Condition factor (%) = [body weight (g)/body length (cm)] 3 × 100 Gutted yield (%) = [carcass gutted weight (g)/body weight (g)] × 100 Fillet yield (%) = [fillets weight (g)/body weight (g)] × 100 Specific growth rate (SGR, %/day) = 100 × ln [final body weight (g)/initial body weight (g)]/days of the experiment …”

“…We selected two points on the back and tail of the fillet for color measurement (CR-400, Konica Minolta, Tokyo, Japan), including lightness ( L *), redness ( a *) and yellowness ( b *). After measurement, the chroma ( C * ab ) and hue ( H ° ab ) values were calculated with reference to Meng et al [ 13 ]. The calculation methods are as follows: C * ab = [ a * 2 + b * 2 ] 1/2 H ° ab = arctan [ b */ a *] …”

Effects of Dietary Protein and Lipid Levels on Growth, Metabolism, Antioxidative Capacity, and Fillet Quality of Adult Triploid Rainbow Trout Farmed in Net Cage

“…Three biological replicates ( n = 3) were created for each diet group, and all samples were frozen in liquid nitrogen and subsequently kept at -80°C for further analysis. The fillet samples were prepared on the basis of the method described in our previous study [ 23 ].…”

“…The color card (SalmoFan™, DSM, Netherlands) was used to analyze the redness of the fillet visually. Fillet color described by lightness ( L ∗ ), redness ( a ∗ ), yellowness ( b ∗ ), chroma ( C ∗ ab ), and hue ( H ab °) was also assessed directly using a colorimeter (CR-400, Minolta, Japan) on the basis of our previous study [ 23 ].…”