Effects of soybean protein diets supplemented with different levels of sodium alginate or carrageenan in rats

Abstract

Manufacturing low-fat food products based on plant protein sources calls for the use of texturizing agents. The interaction between these agents and plant proteins during food processing could produce foodstuffs which provoke changes in early development of rats (1). Furthermore, the ingestion of soluble fibers, such as guar gum or pectin, reduces cholesterol levels (2). This work aimed at studying the effect of ingesting different levels of alginates or carrageenans, mixed and heated with soybean protein, on growth and lipid levels in rats. The study covered three consecutive experimental periods. During the first period of four weeks, twenty-one-day-old male Wistar strain rats followed a diet made up of 10% protein from defatted soybean meal, supplemented or not with 0.5, 1,2 or 3% sodium alginate or carrageenan and heated before feeding and then, the protein efficiency ratio (PER) has been determined. In the second 16week period, all the rats were given a standard 17% protein diet. Finally, in the third period of 6 weeks, the rats used in the earlier PER study were again given their original diet, whose protein content was increased to 20%. Body weights were measured throughout the study. At the end of the study, the rats were killed by decapitation and blood was collected on a mixture of EDTA and Iniprol. Lipid assays were made enzymatically using commercial kits (Boehringer Mannheim). Results were compared by one-way ANOVA test and Fisher's test using a MacIntosh computer and Statview program. Values of P <0.05 were considered to be significant. During the first period, soybean meal supplemented with alginate, whatever its proportion, had no effect on the amount of protein ingested or on daily weight gain. A significant increase in protein intake was observed in rats fed meal containing 3% carrageenan (0.62% of the diet). There was a significant decrease in the PER in animals who had eaten carrageenans. Throughout each period of the study, growth in rats fed soybean meal supplemented with alginate was the same as that of rats fed only soybean meal. Compared to rats fed only soybean meal, the rats fed on 3% carrageenan showed a significantly slower rate of growth from the end of the first period, and for rats fed 1 or 2% of carrageenan slower rate of growth became significant from the 9th week of the standard diet. Body weights were 8 to 10% below those of rats fed only soybean meal and were not compensated for later. The results relative to the effect of thickeners used on the different lipid levels are given in Tables I and II.