Plant-based ingredients could alter the pigmentation of salmon fillets

The colour of salmonid fish fillets is one of the most important quality characteristics in the industry, and depends mainly on the accumulation and metabolism of the pigment astaxanthin.

It has been suggested that diets containing plant-based ingredients may decrease lipid digestibility due to the presence of antinutritional factors and/or the alteration of cholesterol and bile acid homeostasis in fish.

For this reason, scientists from the University of Chile, University of the Americas, University of La Frontera, and the Catholic University of Temuco conducted a new study with the objective of evaluating the effects of replacing fishmeal in the diet with a mixture of vegetable proteins on astaxanthin retention, pigmentation, lipid metabolism, and the composition of the intestinal microbiota of rainbow trout, reports Fish Farming Expert's Chilean sister site, Salmonexpert.cl.

To this end, a group of rainbow trout were fed three isoenergetic diets containing 60%, 36% or 12% fishmeal, each supplemented with equal amounts of natural astaxanthin from Haematococcus pluvialis, for 12 weeks.

Pigmentation alteration

In their results, the experts found that the diet high in plant protein (12% fishmeal) significantly reduced astaxanthin concentrations in the fillet and plasma, and also decreased dorsal and abdominal pigmentation scores.

Similarly, diets high in plant ingredients reduced plasma levels of cholesterol and bile acids by 18-30%, reduced astaxanthin digestibility by 15% and lipid absorption efficiency by 12%.

“Replacing up to 50% of the fishmeal (36% inclusion) preserved fillet pigmentation and astaxanthin concentrations, while a higher inclusion of plant protein (12% fishmeal) negatively affected both parameters. This decrease correlated with compromised lipid digestibility and lower astaxanthin retention efficiency, likely driven by lower dietary cholesterol availability and subsequent alterations in bile acid metabolism,” the authors explained.

Furthermore, the intestinal microbiota changed significantly, with a marked reduction in the Bacillaceae bacterial family, positively correlated with astaxanthin retention and pigmentation.

According to the researchers, these findings underscore the importance of balancing the inclusion of plant proteins with cholesterol and bile acid homeostasis to optimize astaxanthin assimilation in salmonids, as it is an antioxidant carotenoid of critical importance for fish health and fillet quality.

“Moderate inclusion of vegetable flour preserved pigmentation, which underlines the need to control dietary cholesterol and modulate the microbiota in plant-based aquaculture feeds,” the scientists concluded.

Read the full study titled “High Dietary Plant Protein Impairs Astaxanthin Pigmentation in Rainbow Trout by Disrupting Cholesterol–Bile Acid Metabolism and Gut Microbiota,” here.