[Biological value of the unicellular protein of Kluyveromyces marxianus var. lactis]. / Estudio del valor biológico de la proteína unicelular de. Kluyveromyces marxianus var. lactis.

The ever increasing problem of environmental pollution and protein scarcity led us to begin producing protein biomass from cheese whey, having selected for this aim, Kluyveromyces marxianus va. lactis strain, which represents the right relationship between its protein content (53.3% d.w.) and that of the RNA (4.63% d.w.). On the other hand, the distribution of its essential amino acids is balanced, although it shows a deficiency in methionine, its value being 1.5 g/16 gN. The purpose of this work was to assess the biological quality of this protein concentrate, so as to use it in animal feeding. Protein quality was determined by the NPU method (net protein utilization), according to Miller and Bender's technique. Three balanced diets were prepared (10% protein), the test sample with casein, and the rest with protein biomass, one of then supplemented with methionine (0.5 g/100 g food). Based on the results it can be concluded that the biomass analyzed has an adequate biological value (55.37%) for use in animal feeding, especially when methionine as added (60.23%).

[Chemical composition of the cellular biomass of yeasts]. / Estudio de la composición química de biomasas celulares de levaduras.

This work is aimed at analyzing yeast strains, possibly used in animal feeding, obtained by batch cultivation from cheese whey as main carbohydrated substrate. For that purpose 10 yeast strains selected for its biomass production capacity were chemically analyzed. From the results, it can be observed that the chemical composition of the strains is quiet variable, showing in all cases high protein content, good solubility and enzymatic digestibility. In all of them, the RNA content is low, being this important if the biomass is utilized in human feeding. On the other hand, they have an adequate content of essential amino acids, although the sulphur amino acids content is deficient. Among the tested yeasts, Kluyveromyces marxianus var. lactis (No. 10) stands out for the good relationship it has between protein and RNA content, as well as for the detection of methionine among its essential amino acids.