March | April 2011

Feature title: Effects of Corn Gluten Meal on Flesh Pigmentation of Rainbow Trout

The International magazine for the aquaculture feed industry

International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2009 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

Fish culture operations around the world are confronted to the significant challenges of managing their production

costs and ensuring that the quality of their products meets the high stand-ards that consumers demand.

In response to high price of fishmeal and other feed ingredients, feeds for salmon and trout have been progressively formulated to contain increasing levels of economical protein sources.

While the effect of various protein sources on growth performance and nutri-ent utilization of fish has been the focus of much research, relatively limited effort has been invested in assessing the effects of different feed ingredients on product quality.

Flesh pigmentation is a crucial quality criterion of farmed salmon and trout. The expensive pink or red carotenoid pigments (astaxanthin, cantaxanthin) included in the diet represents between 10 to 20 percent of the costs of salmon and trout feeds. Given the very high cost of these pigments

and the importance of pigmentation on final product quality, the impacts of feed ingredients on flesh pigmentation of salmon and trout is an issue that deserves more attention.

Corn gluten meal (CGM) is a by-product of the corn wet milling process with high protein and low phosphorus contents, high digestibility and consistent quality which makes it a valuable ingredient for fish feed formulations. Other corn products, such as corn distillers dry grains and soluble (DDGS), are also finding increase use in aquaculture feed formulations.

Anecdotal evidence from feed manufac-turers suggests that high dietary incorpora-tion levels of CGM or other corn products may negatively affect flesh pigmentation in fish.

CGM and other corn milling by-products contain relatively high levels (100-500 ppm) of yellow xanthophyll carotenoids, mainly lutein and zeaxanthin. Observations scat-tered in the scientific literature suggest that xanthophyll carotenoids may impair pigmentation on salmonid fish, either by

imparting an undesirable yellowish hue to the flesh and/or by reducing efficiency of utilization of the expensive carotenoid pigments incorporated in the diet. However, the results of most studies published so far have been equivocal.

Skonberg et al. (1998) observed that fil-lets from rainbow trout fed a diet contain-ing 22 percent CGM (and no supplemental synthetic pigments) had a higher ‘yellow’ colour value (measured by Tristimulus colorimeter) and received significantly lower preference scores than that fish fed a diet without CGM or a diet with 22 percent CGM supplemented with syn-thetic pigment (100 ppm canthaxanthin). Mundheim et al (2004) found a significant linear reduction in the colour (assessed using the Roche color fan) of fillets of Atlantic salmon fed diets (supplemented with 64ppm astaxanthin) with increasing replacement of fishmeal by a combination of CGM and soybean meal (2:1 ratio) in diets.

A linear reduction in growth and feed efficiency of the fish fed the diets with

Effects of Corn Gluten Meal on Flesh Pigmentation of Rainbow Troutby Patricio Saez1*, El-Sayed M. Abdel-Aal2 and Dominique P Bureau1

1UG/OMNR Fish Nutrition Research Laboratory, Dept. of Animal and Poultry Science, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.2Guelph Food Research Centre, Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, Canada.

*Corresponding author, email: psaez@uoguelph.ca

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increasing levels of CGM + soybean meal was observed.

Conversely, Olsen and Baker (2006) observed no effect of increasing dietary lutein levels (0, 11, 23ppm) on muscle astax-anthin concentration of Atlantic salmon fed a diet containing 55ppm astaxanthin.

Absorption of lutein was very low com-pared to that astaxanthin in these fish.

However, these authors identified a weak but non-significant tendency of lower flesh astaxanthin content in fish fed feed with 23ppm lutein.

Experimental designA 12-week growth trial was recently

conducted at the UG/OMNR Fish Nutrition Research Laboratory to assess the effect of CGM incorporation in the diet on

growth and feed efficiency, as well as flesh pigmentation and astaxanthin concentration of rainbow trout.

Two isoproteic and isoenergetic (on a digestible basis) practical diets were for-mulated to meet all the known nutrient requirements of rainbow trout (see Table 1). A control diet (Diet 1) was formulated to contain no corn gluten meal while a test diet (Diet 2) contained 19 percent corn gluten meal (see Table 1). The diets were supplemented with 50 ppm of astax-anthin (Carophyll® Pink, DMS Nutritional Products) and steam pelleted to appropri-ate size using a laboratory pellet mill.

Rainbow trout (Oncorhynchus mykiss), weighing 132g/fish, were reared at 15°C in four 500L plastic tanks (25 fish/tank) part of a freshwater recirculation aquatic system.

Each experiment diet was allocated to two tanks and the fish hand fed to near-satiety two times a day for 12 weeks.

Instrumental Colour Analysis

Fish were manually skinned and filleted right

after slaughter. Instrumental colorimetric analysis of fillets was performed with a tristimulus colorimeter.

Measurements were processed at three points over and tree point below the lateral line: close to the head; midway between the head and the tail; and close to the tail. All measurements were performed in the colori-metric space L* (lightness, L*=0 for black, L*=100 for white) with a* scale represents the intensity in red, and b* scale represents the intensity in yellow. The hue is an angular measurement where 0° (H°ab= 0) denotes the red hue and 90° (H°ab= 90) denotes the yellow hue. The C* is an expression of satura-tion or intensity and clarity of the colour.

Analysis of Carotenoids by HPLC

Carotenoids from the diets and muscle samples were extracted, separated and quantified by HPLC with short C30 column (YMC Carotenoid, Water, Mississauga, ON). The separated carotenoids were detected and measured at 450nm, and the identifica-tion of the carotenoids was based on the congruence of retention times and UV/vis spectra with those of pure authentic standards.

Table 1: Formulation, analyzed chemical composition and pigment content of experimental diets.

Diets

Ingredients (g/100 g diet) 1 2

Fish meal, herring, 68% CP 28 16

Corn gluten meal, 60% CP - 19

Poultry by-product meal, regular 15 11.5

Soybean meal, 48% CP 10 15

Feather meal, steam-hydrolyzed 6 4

Blood meal, whole, spray-dry 2 2

Brewer's dried yeast 6 6

Wheat middlings, 17% CP 12.4 8.9

Fish oil, herring 12 12

Vegetable oil 4 5

Vitamin premix 1 1

Biolys® (52% lysine) 1 1.5

DL-Methionine, feed-grade 0.5 0.5

Mineral premix 0.5 0.5

Ca(H2PO4)2 1.5 1.5

Carophyl pink (8% astaxanthin) 0.0625 0.0625

Analyzed composition (% dry matter)

Dry matter 94.0 93.9

Crude protein 50.9 50.6

Lipids 23.8 23.1

Digestible energy, MJ/kg (estimated) 20.1 20.6

Analyzed pigment concentration (mg·kg-1 dry matter)

Astaxanthin 48.2 56.7

Lutein ND 28

Zeaxanthin ND 15

�-cryptoxanthin ND ND

�-carotene ND ND

ND = not detected

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Although Top Ocean’s factory trawler worked the Southern Ocean grounds from 2000 to 2004—and even won an award at the Boston Seafood Show with its krill products—Top Ocean’s owners decided not to pursue it.

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The results of the present study support the anecdotal evidence that yellow xanthophyll pigment present in corn products may have the potential to negatively affect flesh pigmentation of salmonids.

The results from the present and other studies suggest a possible interac-tion between xanthophyll pigments and astaxanthin. The potential mechanisms (e.g competitive inhibition during intes-tinal absorption, transport in lymphatic lipoproteins, or deposition in muscle fibre cells) have not been studied (Olsen and Baker, 2006).

It is worth noting that the xanthophyll pigments concentration in CGM used in the present study was relatively low (142mg·kg-1). Much higher xanthophyll concentrations (224 to 550mg mg·kg-1) have been reported among different batches of CGM (Park et al., 1997). Discrepancies between studies may be related to differences in dietary xan-thophyll carotenoid concentrations and types (e.g. lutein vs. zeaxanthin).

The effects of yellow xanthophyll pigments on pigmentation of the flesh of salmonid fish remains very poorly characterized and more systematic work needs to be carried out on this issue.

References Bjerkeng, B., Følling, M., Lagocki, S., Storebakken, T., Olli, J.J., Alsted, N., 1997. Bioavailability of all-E-astaxanthin and Z-isomers of astaxanthin in rainbow trout (Oncorhynchus mykiss). Aquaculture 157, 63-82.

Choubert, G., Cravedi, J., Laurentie, M., 2009. Effect of alternate distribution of astaxanthin on rainbow trout (Oncorhynchus mykiss) muscle pigmentation. Aquaculture 286, 100-104.

Mundheim, H., Aksnes, A., Hope, B., 2004. Growth, feed efficiency and digestibility in salmon (Salmo salar L.) fed different dietary proportions of vegetable protein sources in combination with two fish meal qualities. Aquaculture 237, 315-331.

Olsen, R.E., Baker, R.T.M., 2006. Lutein does not influence flesh astaxanthin pigmentation in the atlantic salmon (Salmo salar L.). Aquaculture 258, 558-564.

Park, H., Flores, R.A., Johnson, L.A., 1997. Preparation of fish feed ingredients: Reduction of carotenoids in corn gluten meal. J. Agric. Food Chem. 45, 2088-2092.

Skonberg, D.I., Hardy, R.W., Barrows, F.T., Dong, F.M., 1998. Color and flavor analyses of fillets from farm-raised rainbow trout (Oncorhynchus mykiss) fed low-phosphorus feeds containing corn or wheat gluten. Aquaculture 166, 269-277.

to that of the fish fed the control diet. This suggests an adverse effect of CGM inclusion on flesh astaxanthin deposition. No lutein and zeaxanthin were detected in the flesh of the fish fed the two diets (see Table 3).

The absence of significant differences for any of the colour attributes measured by colorimetric analysis between muscles from fish fed Diet 1 and Diet 2, even though the former contained a significantly (p<0.05) lower astaxanthin concentration is perplexing.

However, this phenomenon has been reported in the past for rainbow trout (Choubert et al, 2009). Numerous fac-tors, such as muscle light scattering and absorption, can affect salmon flesh colour. Colour and pigment concentra-tion are not always perfectly and linearly related.

ResultsCGM inclusion in the diet had no signifi-

cant effect on growth and feed efficiency of the fish (see Table 2). On average, rainbow trout grew from 132g to 535g during the 12 weeks trial, representing an average thermal-unit growth coefficient (TGC) of 0.240, with a feed efficiency (gain:feed) of 0.89.

Tristimulus colorimetric analysis did not show significant (P>0.05) differences for any of the colour attributes meas-ured for the flesh of fish fed Diet 1 and Diet 2, suggesting that the incorporation of CGM had not effect on flesh pigmen-tation (see Table 3).

However, analysis of carotenoid pig-ments by HPLC revealed significantly (p<0.05) lower astaxanthin concentration of the flesh of fish fed the diet containing 19 percent CGM (Diet 2) compared

Table 2: Growth performance and fed efficiency of rainbow trout (IBW=132 g/fish) fed experimental diets for 12 weeks.

ParameterDiet 1 Diet 2

Final body weight 540 ± 29 531 ± 5

Gain (g/fish) 402 ± 27 400 ± 4

Feed efficiency (gain:feed)1 0.91 ± 0.05 0.88 ± 0.05

TGC2 0.239 ± 0.01 0.243 ± 0.01

Data are mean ± Standard deviation, n=2 tanks.

1Feed efficiency (live weight gain:dry feed intake), 2TGC=thermal unit growth coefficient.

No significant differences observed.

Table 3: Fillet carotenoid concentration and retention, and colour of rainbow trout fed experimental diets for 12 weeks.

Initial Final

Fillet colour attributes Diet 1 Diet 2

L* 45.9 ± 1.8a 40.5 ± 0.6b 40.4 ± 1.4b

a* 1.3 ± 1.1b 9.9 ± 1.3a 9.6 ± 0.7a

b* 4.8 ± 1.4b 13.4 ± 0.5a 12.8 ± 1.0a

H°ab 76.1 ± 11.5a 53.6 ± 2.6b 53.2 ± 0.1b

C* 5.0 ± 1.6b 16.6 ± 1.2a 16.0 ± 1.2a

Fillet carotenoid concentration (mg·kg-1)

Astaxanthin NDc 5.6 ± 0.5a 3.2 ± 0.5b

Lutein ND ND ND

Zeaxanthin ND ND ND

β-cryptoxanthin ND ND ND

β-carotene ND ND ND

Data are mean ± standard deviation, n=2 tanks, means of 5 individuals per tank.

ND = Not detected.

34 | InternatIonal AquAFeed | March-april 2011

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Volume 14 I s sue 2 2 011

the international magazine for the aquaculture feed industry

Aquaculture: Producing aquafeed pellets

Krill:Feed makers need to look at krill

Feed Management:An assessment of aquaculture production with

special reference to Asia and Europe

Pigmentation Effects of Corn Gluten Meal on Flesh

Pigmentation of Rainbow Trout

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