Найдите в последнем абзаце текста подтверждение мнению, что биологическая промышленность не наносит вред окружающей среде. Согласны ли Вы с такой точкой зрения?

10. Перескажите текст по следующему плану:

1. Modern production of single cell protein.

2. The difference between microbiological industry and agriculture.

3. Their influence on the environment.

TEXT 16. SAFETY OFPROTEIN BIOMASS

What stands in the way of making such prospects a reality? Protein containing products of microbiological industry must be free from harmful nonprotein components. As it was shown in a number of experiments nucleic acids represent an undesirable component of unicellulars in case of their inordinate consumption in food. The high growth rate of unicellulars is accounted for by a higher, compared to meat and fish, content of nucleic acids (about 7% of dry wt, and may be considerably higher). The organism ofan animal turns the purine bases that are present in nucleic acids into uric acid, then into urea and ammonia prior to excretion. But in a human being the process of purine breakdown stops at the stage of uric acid production. An increase of the uric acid content in plasma may lead to an accumulation of uratesin the individuals predisposed to that. Therefore, according to nutritionists, daily consumption of nucleic acids with food by a human being must not exceed 2 g. Thus, it would be sage to add 10-20 g of yeast (dry wt) to food. Apparently, it would be advisable to make such additions to staple products, e.g. bread, groats.

A further increase of yeast content in dietwould be possible after a complete or partial removal of nucleic acids.

Some methods for nucleic acidsremoval (fermentative methods among them) have been worked out in the USA and some other countries. Nucleic acid content may be lowered to some extent by selection of proper conditions foryeast cultivation. For example, the nucleic acid level in the yeasts grown in methyl alcohol is markedly lower.

Finally, it is also possible to isolate proteins from the cells and then add them to food. Naturally, it would involve a further complication of production and thus, additional costs and a partial loss of protein. However, it would do away with the limitations connected with nucleic acids being in the product. Besides, digestibility of protein by digestive enzymes would increase. Isolated yeast protein may be used for production of new kind of food. The importance of attractiveness (taste, smell, colour, structure) of such unconventional foodstuffs would become extremely high. It would also be essential to overcome psychological unpreparedness of the consumer for the new kinds of food. Addition of yeast proteins to conventional foodstuffs represents another trend of research in adoption of yeast for nourishment.

We think that limited additions of dry yeast cells to conventional vegetable food should be the first step toward a wide adoption of unicellulars for human nourishment.

The nutritionists need lengthy investigations to establish the safety of adopting the biomass of various bacteria for food. It is only natural, because until now humanity has never used in food such bacteria, as Pseudomonas, E. coli, Bacilllus, Hydrogenomonas, etc. According to some authorities in the field of nutrition, it has not been proven yet that it is absolutely safe for people's health to add biomass of nonpathogenic bacteria even to the feed of livestock whose meat or dairy products will be used for food. Isolation of proteins from bacteria, seems to present a lesser problem, but even so, proof of its harmlessness would take years of research.

Bacteria contain much protein (up to 10%of dry wt), and their mass cultivation may prove to be extremely promising. But, undoubtedly, the mass cultivation of yeasts (their utilization for food has a history of many centuries) stays in the first place in the space of time.

The supposed carcinogenitу of hydrocarbon yeasts is not well-grounded. The 3,4-benzopirene content of the yeasts grown on gas oils or n-paraffins is the same or even lower than that of the conventional foodstuffs for nourishment. However, the yeasts grown on hydrocarbons contain residual hydrocarbons in variable quantity. In particular, the yeasts grown on gas oils contain gas oil fractions not metabolized by the animal organism. They can be removed by extraction but it will substantially complicate the process of production. The yeasts grown on n-alkanes contain residual n-alkanes. Small quantities of n-alkanes have been detected inthe cell of microorganisms grown on various non-hydrocarbon media. Synthesis of small quantities of n-alkanes, the yeast being grown on the medium with labelled glucose, has been proved at our Institute. Inconsiderable quantities of n-alkanes are contained in a great variety of products of vegetable and animal origin. Plants synthesize n-alkanes and cabbage leaves represent a classical object for revealing the metabolism of n-alkanes. That is why it is not true toconsider n-alkanes to be foreign to living nature. It has been shown by special investigations on animals that n-alkanes are metabolized by the animal organism. And yet their content in conventional foodstuffs is usually lower than that in “paraffin” yeast. Therefore technological processing has been worked out which makes it possible to decrease n-alkane content in yeast to efficiently low values (tenth parts of percent of dry wt).

Notes on the text:

1) inordinate consumption – чрезмерное потребление

2) prior to excretion – до выделения

3) daily consumption – ежедневное потребление

4) well – grounded – обоснованный

5) staple products – главные продукты

6) groat – крупа

7) to do away with – покончить

8) residual hydrocarbons – остаточные углеводороды

9) labelled glucose – меченая глюкоза

10) cabbage leaves – капустные листья

11) foreign – зд. инородный, чужой

Задания к тексту:

1) Найдите в тексте английские эквиваленты следующих слов и словосочетаний:

нежелательный компонент одноклеточных, высокий темп роста, по сравнению с мясом и рыбой, содержание мочевой кислоты в плазме, у людей, предрасположенных к этому, по мнению диетологов, дальнейшее увеличение, полное или частичное удаление нуклеиновых кислот, значительно ниже, привлекательность, принятие, до сих пор, в области питания, мясные или молочные продукты, предполагаемая канцерогенность углеводородных дрожжей, незначительные количества н-алканов.

2) Переведите следующие предложения на английский язык:

1. Было бы желательно добавить 10-20 грамм (сухого веса) в основные продукты.

2. Дальнейшее увеличение содержания дрожжей в диете было бы возможно после полного или частичного удаления нуклеиновых кислот.

3. Выделение белков из клеток и добавление их в пищу повлекло бы дальнейшее усложнение производства, дополнительные затраты и частичную потерю белка.

4. Было бы важно преодолеть психологическую неподготовленность потребителя к новому виду жизни.

5. Это покончило бы с ограничениями, связанными с присутствием нуклеиновых кислот в продукте.

3) В последнем абзаце найдите предложения с глаголом-сказуемым в Present Perfect Passive и переведите их на русский язык.

4) Найдите в тексте ответы на следующие вопросы:

1. What stands in the way of making protein biomass safe?

2. At what stage does the process of purine breakdown stop in a human being?

3. When would a further increase of yeast content in diet be possible?

4. What methods have been worked out in some countries?

5. How may nucleic acid content be lowered?

6. What would involve a further complication of production?

7. Would digestibility of protein by digestive enzymes increase?

8. What is meant by “attractiveness” of foodstuff?

9. What would it be essential to overcome?

10. What do you think of adding biomass of some nonpathogenic bacteria to the feed of livestock? Is it absolutely safe for people’s health or not?

11. What do you know of the yeasts grown on n-alkanes?

5) Напишите аннотацию к этой статье, используя следующие выражения:

1) The article is devoted to the problem of …

2) It deals with …

3) It is of great interest for …

4) The author stresses …

5) He draws the reader’s attention to…

TEXT 17.

Oxidation of n-alkane molecule by yeasts leads to the formation of the fatty acids containing as much carbon atoms as initial alkane. When growing on the mixture of n-alkanes with odd and even numbers of carbon atoms the yeasts synthesize the mixture of odd and even fatty acids. It is well known that odd fatty acids are present in very different products of the vegetable and animal origin. It has been shown that they are rather intensively metabolized. The harmfulness of the small quantities of the mentioned lipid fractions has not been established by the very careful experiments on animals. However, this is not an absolute proof of the harmlessness of such products when utilizing them systematically directly for human nourishment. Because of this, in Russia, "paraffin" yeasts are allowed to be utilized in animal feed only. "Paraffin" yeast usage recommendations have been devised which guarantee absolute harmlessness of cattle-breeding products for human consumption.

The marked increase in attention to the utilizing of the products of hydrocarbon oxidation, but not hydrocarbons themselves, as the raw material for the yeast growing, is a tendency of the research work in the field of the single cell protein production in the last few years. Methyl and ethyl alcohols, lower acids and other oxy-hydrocarbon derivatives are investigated from the view point of their practical utilization as the raw material for the microbiological production of yeasts. Investigations carried out at our Institute discovered that yeasts grown on acetic acid and ethyl alcohol contain much less "odd" fatty acids in synthesized hydrocarbons than the yeasts grown on glucose. On the contrary, tri-carbon compounds, propionic acid especially, stimulate the increased synthesis of fatty acids with an odd number of carbon atoms. The lipid composition of the yeasts grown on methyl alcohol is similar to that of the yeasts grown on glucose.

The state of our knowledge shows that yeasts grown on some oxy-hydrocarbon derivatives possess rather favourable chemical composition and meet the requirements of food quality.

Practice confronts the investigators with some questions connected with the laws of product cost formation.

What substrate is better for the yeast growing? Hydrocarbon with a large store of chemical energy or its oxidated derivative with a smaller store of chemical energy? The special investigations demonstrated that the process of growth requires the least expenditure when the larger part of the chemical energy of the utilized substrate transforms to the chemical energy enclosed in the biomass. In other words, the expenditure in the fermentation decreases with increasing energy efficiency of the fermentation process.

It is known that the prices of one and the same raw material are different in different countries. The energetic yields of microorganisms growing on one and the same substrate also differ according to the strains used and the cultivation conditions.

Investigations carried out in different countries show that methyl alcohol is rather promising as a substrate for biosynthesis. Ethyl alcohol, acetic acid and some other products of hydrocarbon oxidation turn out to be of great economic utility in the food yeast production under some conditions.

Notes on the text:

1. initial alkane – исходный алкан

2. odd and even numbers – нечетные и четные числа

3. the marked increase – заметное увеличение

4. oxy-hydrocarbon derivatives – производные окисленных углеводородов

5. acetic acid – уксусная кислота

6. on the contrary – наоборот

7. view point – точка зрения

8. store – запас

Задания к тексту: