A Food Vehicle for Yeast Protein

A Food Vehicle for Yeast Protein Lynda P. Scott l and Mabel Sanderson

2

Depamnent of Consumer Studies and

Gordon O. Ashton3 Depamnent of Mathematics and Statistics University of Guelph Guelph, Ontario

Abstract In a preliminary study, five yeasts, Candida, Saccharomyces, Yeast Extract, Brewer's Yeast and Torula were organoleptically evaluated in cereal wafers as potential supplementary !protein sources. Each of the five was incorporated at various levels in the wafer doughs. Cereal wafers were chosen because they could serve as dietary staples. There was a reduction in general acceptability with all yeasts as the amount of yeast was increased; however, the rapidity with which the acceptability declined, varied with the kinds of yeast, and with the panelists for Torula, Brewer's Yeast and Saccharomyces. The maximum acceptable percentages of each yeast was determined by the average panel score. Brewer's Yeast or Torula could be incorporated to the greatest extent, which was 19% yeast, and this represents 8% yeast protein in the wafers.

Resume Au cours d'une etude preliminaire cinq levures (Candida, saccharomycetes, extrait de levure, levure de brasserie, torula) furent evaluees organoleptiquement en gaufrette comme source potentielle de proteine supplementaire. Chacune des cinq flit incorporee a differents niveaux dans la pate a gaufrette. On a choisi les gaufrettes parce qu'elles pouvaient servir de diete de base. L'acceptabilite generale des levures diminue avec l'augmentation de leur concentration dans la pate. Cependant le taux de decHn de l'acceptabilite est fonction de la sorte de levure et des individus formant le jury. Le pourcentage acceptable de levure fUt etabli en fonction de la moyenne de r opinion du jury. La levure de brasserie et la torula, obtinrent le plus haut degre d'acceptabilite soit au niveau de 19% de la levure. Ceci represente 8% de proteine de levure dans les gaufrettes.

Introduction The use of yeast as a valuable food supplement is not a new concept. Bunker (1963) reported that the idea of direct production of yeast for food is attributed to D'elbriick (1910) in Germany. Yeast was first used for a protein food during World War II in the diet of the German army. Yeast is also recognized as an excellent sonrce of the B vitamins and was added to INCAP Vegetable Mixture 8 to provide the B complex vitamins (United Nation, 1967). According to Swaminathan (1967) the most urgent nutritional deficiencies today could be corrected by an increased intake of protein rich foods. It has been estimated by Swaminathan (1967) that three million tons of dried yeast would meet the protein requirements of one thousand million needy children. Since the world population has been predicted to double within 30 years, and there is chronic undernourishment now in the developing countries, it is necessary to explore all possible protein sources. There are many advantages to the utilization of yeast as a protein supplement. It contains considerable lysine, which is deficient in many cereals, it is 1 Graduate student. 2 Professor, Department of Consumer StUdies. 3 Professor, Department of Mathematics and Statistics. Can. Inst. Food ScL TechnoI. J. VoI. 5, No. 2, 1972

a much more efficient producer of protein than conventional sources, and furthermore, arable land is not necessary as it is for plant and animal production. Yeasts could be cultivated on certain industrial waste products such as molasses and whey. Brewer's Yeast is a waste product itself and is available universally as a by-product of the brewing industry. The high nucleic acid content of yeasts is expected to present a problem in the use of yeast proteins f~r human food. Miller (1968) suggested that the nucleIc acids in veasts might give rise to high levels of urea and uric '~acid in blood and possibly to the formation of kidney stones. Research at the University of Guelph is currently being conducted on the reduction of nucleic acids in Yeast cells and on modifications of the processing of Brewer's Yeast to improve the flavour. The nutritive value of yeast protein has been assessed experimentally by several researchers. Bressani (1968) found rats could not be maintained on a diet in which yeast was the sole source of protei~. The reason for this was that yeast protein was defIcient in sulfur-containing amino-acids. Scrimshaw et al. (1962) fed rats on INCAP Vegetable Mixture 9 diluted with starch to a 10% protein level. They found that when 3% Candida yeast was added to the INCAP Mixture, growth and feed utilization were increased. Sure (1947) found that substituting 1, 3, and 5% of enriched wheat flour with equivalent amounts of yeast, "Strain G", resulted in marked increases in body weight of Albino rats . Contradictory results (von Loesecke, 1946) h~ve been reported with respect to the levels of yeast whIch humans can tolerate. It has been generally aclmowledged that small amounts of yeast are well tolerated by humans. Digestive disturbances have been caused by daily intakes of more than 15 g of yeast; however, others reported no side effects when humans consumed up to 85 g three times daily. Research has been done on the acceptability of yeast in a wide variety of foods. Sure (1946) reported that a satisfactory white bread could be baked containing 2.5% debittered yeast. Sure (1947) incorporated 1 - 3% yeast in a wide variety of foods in a university cafeteria and found these foods well accepted. Klapka et al. (1957) carried out a similar study using patients in a mental hospital. The maximum acceptable level of yeast was determined for only a few of the foods tested; however, the maximum levels tolerated never exceeded 2%. Researchers at Cornell (Durfee, 1943) added Brewer's Yeast to their favorite recipes and devel'oped therefrom 35 new recipes. She stated that in some of these recipes each person could get as much as one tablespoon of yeast per serving.

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Thaysen (1957) in discussing the utilization of food yeast stated that, f-ood yeast is best administered in bread or biscuits where bread forms a staple part of the diet. This report is concerned with the relationship between palatability and four levels of five yeasts, Candida Saccharomyces, Yeast Extract, Brewer's Yeast and 'Torula when each yeast was incorporated in a cereal wafer.

Experimental Preparation of wafers. Wafers were prepared using three levels of yeast plus a control, which constituted one replication. Increased levels of yeast in the wafers were obtained by substituting yeast for flour to maintain a constant weight of 226.5 g per sponge mix for yeast plus flour. (Table 1). The amount of water required varied with the kind of yeast and the quantity used; however, the weight of all other ingredients remained constant for all mixes. A sponge was prepared (Table 1) and allowed to stand -overnight, then the remaining ingredients (Table 1) were added to form a stiff dough. For the sponge, the yeast and most of the flour were ground together in a mortar with a pestle. The sugar and viable Baker's yeast were added in dry form. The shortening was cut in and water added. Approximately 26 hours later, the remaining ingredients (part 2) were added to stiffen the dough. Wafers were cut from the rolled dough and baked at 350°F until the edges of the wafers were browned. Baking times were the same for duplicate bakings of the same formula, but they varied according to the type and level of yeast. The wafers were evaluated, organoleptically, the day after baking. Yeasts. Five different yeasts were used: Saccharomyces Carlsbergensis a, Candida utilis a, Brewer's Yeast (Saccharomyces)b, Torula (Candida)b, and Yeast Extract (Saccharomyces)c. In the remainder of this report these yeasts will be referred to as Saccharomyces, Candida, Brewer's Yeast, Torula, and Yeast Extract. Table 1. Ingredients

:.!

112

The data were subjected to analyses of variances with associated regression analyses. Since there was a panelist by yeast-level interaction for Saccharomyces, Torula and Brewer's Yeasts, a regression analysis on yeast levels was done for each panelist separately. No such interaction was found for Candida and Yeast Extract and on yeast levels averaged over all panelists hence one regression was performed for each of these two yeasts. Estimated values of acceptability for plotting were determined from appropriate regression equations i.e. first, second or third degree polynomials. Evaluation of the significance of the treatment effects was made at the 5% probability level using the sequential F-test of Hartley (1955).

Results and Discussion From the graphs, Figure 1, 2,3 and 4, it is evident that the acceptability of all the wafers decreased as

Formulae for wafers

o

g Sponge 226.50 Flour Water1 135.00 Shortening 18.00 ?Yeast (Baker's) 0.55 Sugar 1.00 Yeast2 0.00 Ingredients added for final dough Flour 50.00 Flour (for rolling) 22.50 Shortening 18.00 Sugar 21.00 Salt 5.00 Soda 2.05 Diammonium phosphate 0.40 1

Organoleptic testing. Each wafer was coded and organoleptically tested under standardized lighting by a four or five member-panel, each member of which had exhibited the ability to discern low levels of yeast in the wafers. At one session four wafers, represent· ing the control and three levels of one yeast, were tested. The panelists evaluated wafers for relative palatability according to a Difference Test (Larmond, 1967) on a basis of scores that ranged from 1 to 6. Design of the experiments and analysis of the data. An experiment was conducted as a split plot design for each of the five yeasts. Four replications were made for each of the two yeasts supplied by the Microbiology Department (Saccharomyces and Candida) and three replications for each of the three commercial yeasts. The levels of yeast constituted the main plots and the panelists constituted the sub-plots. The mixing and baking order of the wafers for the different levels of veast followed a random and independent sequence for each replication. Each panelist evaluated the wafers for a complete set of yeast levels at one sitting. The order of yeast level evaluation also followed a random and independent sequence for each sitting.

40

Levels of Yeast 60

80

g 186.50

g 166.50

146.50

126.50

18.00 0.55 1.00 40.00

18.00 0.55 1.00 60.00

18.00 0.55 1.00 80.00

18.00 0.55 1.00 100.00

50.00 22.50 18.00 21.00 5.00 2.05 0.40

50.00 22.50 18.00 21.00 5.00 2.05 0.40

50.00 22.50 18.00 21.00 5.00 2.05 0.40

50.00 22.50 18.00 21.00 5.00 2.05 0.40

g

100 g

Total 365.00 365.00 365.00 365.00 365.00 The amount of water used in the sponge mixture for the wafers containing yeast varied with the kind of yeast used. The weights for water are not included in the total weights. Other than Baker's Yeast. J. Inst. Can. ScL Techno!. Aliment. Vo!. 5, No 2, 1972

'.0

'.0

Yeast Extract Candld.t

5.5

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5.0

'.5

'.5

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'.0

3.5

3.5

3.0

j

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oX

2.5

3.0

2.5

2.0

2.0

1.5

1.5

1.0

1.0

0.5

0.5

10

2'0 (5.48)

30

40

50

60

70

80

(10.96) (1'.«) (21.92) Gram Yeast (Percent by Dry Ingredient weight) .

90

100 (27.40)

10

20 (5.481

30

40 (10.")

50

60 (16.44)

70

80 (21.92)

90

100 (27.40)

Grams Yeast (Percent by Ory Ingredient Weight)

Fig.!.

Average Predicted Scores for Candida Yeast and Yeast Extract.

Wafers

Containing

the proportion of yeast increased. Panelists were similar in their evaluation of each of Candida and Yeast Extract; theref'ore, it was possible to generate one curve for each yeast which represented all panelists (Fig. 1). For each of the three yeasts (Saccharomyces, Brewer's Yeast and Torula) panelists lacked the uniformity in evaluation that they had for Candida and Yeast Extract. The lack of uniformity was confirmed statistically by the significant panelist x treatment interaction. Because all panel members were not uniform in their evaluation, individual curves were constructed for each panelist for each of Saccharomyces and Tontla yeasts and Brewer's Yeast (Figs. 2, 3 and 4). For any of the wafers to be considered organoleptically acceptable as a protein supplement, a score at least as great as 3 (fair) was considered necessary. The graph in Fig. 1 illustrates the average panelist responses to wafers containing various levels of Candida and Yeast Extract. The control wafers, which contained no yeast, received a. score of approximately 4.5. From Fig. 1 it can be estimated that at a level of 8.22%1 (30 g) Candida yeast in the wafers, a score of 3 would have been assigned by the taste panel. At this level of yeast the amount of yeast pl'otein would be estimated at about 3.27%, which was one-half as much as was contained in wafers made with 60 g Candida yeast. Comments made by the taste panel members indicated that wafers containing Candida yeast were strong flavoured, bitter, and had an unpleasant aftertaste. The acceptability of wafers containing Yeast Extract declined less rapidly than for Candida at the lower levels of yeast but declined more rapidly at the highel' levels of yeast, giving opposing curves of acceptability for the two yeasts (Fig. 1). This might be explained by the rather pleasant cheese flavour of the yeast extract at lower levels compared with the stronger flavour of the Candida yeast. As the amount of Yeast Extract was increased to the 21.9%1 level, the Can. Inst. Food SeL Teehnol. J. Vol. 5, No. 2, 1972

Fig. 2.

Average Predicted Scores for Wafers Containing Saccharomyces Yeast.

acceptability decreased more rapidly and panelists commented on the strong, sharp, bitter flavour of the wafers. The graph indicated a score of three would have been given the wafers at the 50 g level of Yeast Extract in the wafers. The estimated percentage of yeast protein would be approximately 5.59% based on the average of the per cent yeast protein in cooked wafers containing 40 and 60 g of Yeast Extract. An average score of three for wafers made from Saccharomyccs yeast was read from the graph (Fig. 2) at approximately the 35 g level of yeast in the

wafers. The scores decreased as the per cent yeast in the wafers increased. The estimated per cent yeast protein for wafers containing 35 g of yeast was approximately 3.83%. This estimate was based on the per cent yeast protein in wafers containing 60 g Saccharomyces yeast. Panelists commented that wafers containing all three levels of !Saccharomyces yeast (60, 80 and 100 g) were bitter, strong flavoured and unpleasant. The acceptability of the Brewer's Yeast wafers (Fig. 3) decreased as the proportion of yeast increased for all panelists except panelist four. Panelist no. 4 preferred wafers containing a small amount of yeast to the control which had no yeast. From Fig. 3 it can be estimated that at a level of 70 g Brewer's Yeast in the wafers, an average score of 3 would have been assigned by the taste panel. Panelists commented that wafers containing 80 g of Brewer's Yeast were strong flavoured and some mentioned a slight bitter after-taste; however, wafers containing 40 and 60 g of Brewer's Yeast were found acceptable by the taste panel. The acceptability of wafers containing Torula yeast (Fig. 4) decreased as the proportion of yeast increased for all panelists except no. 4. An average score of 3 would have been given to wafers containing approximately 70 g of yeast. The per cent yeast protein of wafers containing 70 g of Torula yeast is approximately 7.85% based on the average of the values for per cent yeast protein in wafers containing 60 and 80 g of yeast. 113

6.0

6.0

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30 40 50 60 70 80 (10.961 (16.«1 (11.91) Grams Yeast (Percent by Dry Ingredient Weight)

Average Predicted Brewer's Yeast.

Scores

for

Wafers

90

._-._-~--:

---.:::: .~------=:~

10

100 (17.40)

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Fig. 4.

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30

40 50 60 10 80 (10.96) (16.") (11.911 Grams Yeast (Percent by Dry IngredIent Weight)

Average Predicted Torula Yeast.

Scores

for

Wafers

90

100 (17 .40)

Containing

Summary Two yeasts, Candida and Saccharomyces were incorporated into doug-hs at levels of 16.44, 21.92. and 27.40%. Three yeasts, Yeast Extract, Brewer's Yeast and Torula were incorporated into doup;hs at levels of 10.96, 16.44 and 21.92%. Wafers were made from each doup;h and scored org-anoleptically by a trained panel. The maximum acceptable percentages of yeast and yeast protein, respectively, in the wafers, based on a panel score of 3 was indicated as follows: Candida 8.22 and 3.27 Saccharomyces 9.59 and 3.83 Yeast Extract 13.70 and 5.59 Brewer's Yeast 19.18 and 7.66 Torula 19.18 and 7.85 Brewer's Yeast and Torula would seem to be of first and equal choice because they provided the maximum amount of protein in wafers that was organoleptically acceptable.

Acknowledgement This work was supported in part by the Ontario Department of Agriculture and Food. 'fhe assistance 'of Professor .r. D. Cunningham of the Microbiology Department, University of Guelph, in acting as consultant and in providing yeasts is gratefully acknowledged.

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References a Provided by Professor Cunningham, Microbiology Department, University of Guelph. b Purchased at a h""'Gh food store in Guelph. c Courtesy of Miles Laboratories. Lakeshore Foods Limited, Toronto. 1 All yeast levels refer to dry ingredient weight. Bressani, R. 1968. Single Cell Protein (Mateies and Tannenbaum, ed.). M.I.T. Press, Cambridge, Massachusetts, pp. 95-97. Bunker. H. J. 1963. Biochemistry of Industrial Organisms (Rainbow C. and A. H. Rose. ed.). Academic Press, London, p. 39. Durfee, Si!via T. 1943. The utilization of dried brewer's yeast in food products. Brewers Digest, 18:27. Hartley, H. O. 1955. The sequential F-test for multiple decisions on significance in an analysis of variance table. Communications on Pure and Applied Mathematics, 8(1): 47. Klapka, M. R., G. A. Duby and P. L. Paucek. 1957. Torula yeast as a dietary supplement. J. Am. Dietet. Assoc., 34:1317. Larmond, E. 1967. Methods [or-Sensory Evaluation of Food. Canada Department of Agriculture Publication 1284. Mlller, S. A. 1968. Single Cell Protein (Mateles and Tannenbaum, ed.). M.LT. Press, Cambridge, Massachusetts, p. 86. Scrimshaw, N. S. et a!. 1962. All vegetable protein mixtures for human feeding. Effect of Torula yeast on protein quality of INCAP Vegetable Mixture 9. Am. J. Clin. Nutr.. 11:537. Sure, B. 1946 Nutritional imorovement of cereal flour and grains. J. Am. Dietet. Assoc. 22:495. Sure, B. 1947. Further studies on the nutritional improvement of cereal flours and ceral grains with yeast. J. Am. Dietet. Assoc. 23:113. Swaminathan. M. 1967. Nutrition and the world food problem, Borden's Rev. of NutI'. Res., 28 (#1),26. Thayson, A. C. 1957. Ye""t~ (Roman, W., ed.). W. Junk, The Hague, Netherlands, pp. 204-206. United Nations, PAG, 1967. Present situation concerning vegetable protein mixtl1res in Colombia. October Meeting, New York, Document 19/9. von Loesecke, H W. 1946. Controversial Aspects: yeast in human nutrition. J. Am. Dietet. Assoc., 22:491. Received Sep. 3, 1971.

J. Inst. Can. ScL TechnoI. Aliment. Vo!. 5, No 2, 1972