I n order to increase the availability of the cell bound protein in Scenedesmus algae, mechanical, enzymatic, and chemical methods of degrading the cell wall structure were investigated.The algae suspension together with glass beads was milled in a water-cooled chamber equipped with rotating disks. The enzyme tested was a cellulolytic enzyme (Meicelase) and the chemical employed was hydrogen peroxide.I n the ball-mill experiments a complete disintegration was achieved in a disintegrator, working with batches. Trials were also performed with a continuous disintegrator and the dependence of disintegration on bead size and flow rate was studied. The disintegration determined by microscopic cell count was compared to the increase of the pepsin digestibility.The Meicelase treatment caused a slight increase of the pepsin digestibility, as measured after 3 hr pepsin incubation. No increase of the pepsin digestibility could be detected with hydrogen peroxide treatment.After the ball-mill disintegration 95% of contaminating bacteria were killed and yields of extractable proteins were higher. The capacity of available continuous ball-mills is such that they could be used on a pilobplant scale and the energy cost of disintegration would be of the same magnitude as that of separation.Mechanical treatment involved the use of a ball-mill.
SummaryMethods for the production of protein concentrates, with a low content of nucleic acid, in kilogram quantities from yeast have been studied with the aid of equipment designed for operation on pilot-plant scale. The influence of drum drying and mechanical disintegration on the nutritive value of the yeast was also investigated. Drum drying and mechanical disintegration improved the nutritive value of the yeast but high extractability of protein and nucleic acid w&s only obtained after mechanical disintegration.Protein concentrates without and with cell walls were produced from mechanically disintegrated yeast. The different fractions which were obtained when separating cell walls and precipitating protein by heating a t alkaline pH, were analyzed. After protein precipitation, about 90% of the RNA could be precipitated from the supernatant by addition of acid, giving a product containing 50% RNA of the dry weight. The protein precipitate obtained after cell wall separation had an RNA content of less than 2y0 and contained 70-757, of the amino acids in the starting yeast material. Protein concentrates containing cell walls were produced by precipitating protein by heating a t alkaline pH directly after mechanical disintegration. The content of RNA was about 2% and the yield of amino acids was 70-80%. It was found that the nutritive value of the protein concentrate was higher than that of the starting yeast material. To produce such a protein concentrate on a large scale, the process described can probably be employed.
SummaryI n order to isolate proteins from microalgae, yeasts and bacteria, cell disintegration in a special ball-mill was performed. The degree of disintegration of the different microorganisms was compared. The dependence of disintegration on bead size and on the ratio between the volume of suspension and the volume of glans beads was also investigated. Sondisintegrated and disintegrated cells were extracted with sodium hydroxide and the amount of extractable nitrogen and the amount of nitrogen precipitable a t pH 4.0 were determined. The dependence of yield on the sodium hydroxide concentration, extraction time, and temperature waa studied. When extracting undisintegratd cells, very low yields were obtained and the nitrogen extracted waa mostly nonproteinous. For disintegrated cells high yields were obtained. An optimum was found after extraction with 0.3-0.5cT, sodium hydroxide at pH 11.0-11.5. The precipitate obtained represented W707, of the cell nitrogen. The nitrogen content of the precipitate was 12-14V0 of the dry weight.
SummaryMethods for reducing the content of nucleic acid in protein concentrates from disintegrated yeast and microalgae were investigated. Protein concentrates were prepared by acid precipitation of extracted protein after cell wall separation. The influence of alkaline protein extraction on the content of RNA in isoelectrically precipitated protein concentrates was studied. I t was found that when a strong decrease in the RNA content was obtained, this was followed by a decrease in the yield of protein concentrate. Protein concentrates were also prepared without cell wall separation by precipitation with different agents after cell disintegration. In the precipitates from microalgae, a RNA reduction was obtained. Precipitation of yeast protein gave no essential reduction with the precipitants used. Precipitation of yeast protein by heating at an alkaline pH gave a protein concentrate with a low content of RNA. A slightly lower RNA content was obtained when the precipitation was performed in the presence of NaC1. The yield of amino acid nitrogen was 70-80% and the RNA content was l-2yO. A process with precipitation a t alkaline pH for the production of microbial protein concentrates with a low content of nucleic acid is suggested.
Rats were fed for six consecutivedaysonadiet containingtheproteinsourcesunder test at a protein level of 20%. Protein synthesis by skeletal muscle ribosomes was measured in vitro. Synthetic activity was estimated per unit ribosomal RNA and per g of wet weight of muscle. In separate experiments the nitrogen efficiency ratio (n.e.r.) of the protein sources was determined after 21 days feeding at a 10% protein level.As measured by protein synthesis the nutritional quality of lyophilised baker's yeast Saccharomyces cerevisiae increased after mechanical disintegration. A further improvement was achieved by feeding yeast protein concentrates.Judged by these determinations the nutritional quality of the three yeast preparations was higher than that of the low-quality protein, wheat gluten but did not reach the level of the high-quality protein, casein supplemented with methionine.The metabolic utilisation of spray-dried microalga Scenedesmus obliquus increased after mechanical disintegration from a value similar to that of wheat gluten to the level of methionine-supplemented casein.Lyophilised Spirulina platensis had a nutritional quality between that of wheat gluten and casein supplemented with methionine. Addition of the limiting amino acid methionine to air-dried baker's yeast or drum-dried Scenedesmus obliquus and Spirulina platensis stimulated the metabolic utilisation of the micro-organisms.Supplementation of the diet with methionine increased the nitrogen efficiency ratio of air-dried yeast and of drum-dried Scenedesmus obliquus but had no effect on drum-dried Spirulina platensis. The ratios were significantly lower than those of casein supplemented with methionine.There was no difference in the nitrogen efficiency ratio between disintegrated yeast and yeast protein concentrate but the ratio of both was higher than that obtained with lyophilised yeast. The ratio was similar to that of casein without the addition of methionine.
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