Biological Evaluation of Wheat Supplemented by a Whey Protein Concentrate or Whey Cheese on Growing Rats

ELISABET FORSUM Institute of Nutrition University of Uppsala

Box 551 S-751 22 UPPSALA 1, Sweden

ABSTRACT

Whey contains proteins of high nutri- tional value which are valuable as supple- ments to lower quality proteins, cereal proteins. Procedures for production of concentrates of whey protein have been developed but are generally expensive. Thus, nutritional properties of whey products which are less expensive need evaluation. Whey cheese is a traditional food in Scandinavia, but its protein is considered of low nutritional value. This paper describes determination of biological value and true digestibility on growing rats of mixtures of wheat and whey cheese as well as of wheat and whey protein concentrate. Additions of protein from whey protein concentrate or whey cheese to wheat resulted in mixtures with higher biological values although in most cases whey protein concentrate was as a wheat protein supplement superior to whey cheese. For example, a mixture containing 50% protein from wheat and 50% pro- tein from whey protein concentrate had a biological value of 92, while the corresponding figure for a mixture of 50% wheat protein and 50% whey cheese protein was 75. Nevertheless, the improvement in protein quality after addition of a relatively small pro- portion of protein from whey cheese to wheat is considerable and probably could be significant in human nutrition.

INTRODUCTION

Whey, a by-product of cheese manufacture, contains proteins of high nutritive value (6). Unfortunately, the high water, lactose, and

Received August 21, 1978.

mineral content of liquid whey complicate use of whey proteins which are in low con- centration. However, efforts have been made to develop processes, e.g. uitrafiltration, for the manufacture of whey protein concentrates (WPC). These products effectively have im- proved diets containing lower quality proteins (6). The cost of production of WPC is relatively high, and WPC is not used as a source of dietary protein for individuals whose protein supply is inadequate.

Forsum and Hambraeus (8) have reported that the protein qualities of several unsophisti- cated whey products prepared by conventional methods were high. This was unexpected since the high lactose content, together with high processing temperatures, could lower the availability of lysine in the protein and the protein quality of the products. The high protein quality for whey cheese was of special interest since this product represents a tradi- tional way of processing whey in parts of the world (10). Originally the process involved prolonged boiling of whey to a semi-solid product with brownish color and sticky consis- tency. This product traditionally is consumed together with bread. Its protein quality general- ly has been regarded as low due to its brownish color and the possibilities for MaiUard reactions in the product. Nowadays whey cheese is manufactured industrially, and this means more gentle treatment. The high biological value of whey cheese (8) shows that the limit- ing amino acids in whey cheese (methionine and cysteine) are available but gives no infor- mation on the availability of other important essential amino acids such as lysine and no information about the supplementary value of the product. The latter could be evaluated by study of the biological value of mixtures of whey cheese and a protein with a low lysine content such as wheat protein.

In this study the supplementary value of whey cheese protein on wheat protein was

1979 J Dairy Sci 62:1207-1210 1207

1208 FORSUM

compared to an ultrafiltered concentrate of whey protein. Nitrogen balance experiments on growing rats were on mixtures containing wheat and different proportions of supple- mentary protein from WPC or whey cheese, respectively. The experiment was designed to find a difference in supplementary value on wheat protein between WPC and whey cheese.

M A T E R I A L S A N D METHODS

Wheat flour, extraction ration 72%, con- taining 1.9% nitrogen in total solids was bought in a local Swedish shop.

Whey protein concentrate (WPC) prepared by uhrafihration was obtained from Mj61k- centralen, Arla, Stockholm, Sweden. The material contained 10.9% nitrogen and 22% lactose of total solids.

Whey cheese containing 2% nitrogen and about 80% lactose of total solids was bought in a local Swedish shop. The process of manu- facture is described by Samuelsson (12). Be- fore being incorporated into experimental diets, the material was dialyzed against dis- tilled water and lyophilized. This was to reduce the lactose content of the product to that ac- ceptable for nitrogen balance experiments on growing rats. The material obtained con- tained 5.7% nitrogen and 34% lactose of total solids.

Lactose was analyzed as described by Ekelund (3).

Total nitrogen was estimated according to Hambraeus et al. (9).

Biological value (BV) and true digestibility (TD) were estimated according to Eggum (2) as modified by Forsum (7). The experiment was on male Sprague-Dawley rats, 28 days of age. The rats were divided into groups of 4 or 5 animals each and fed the experimental diets (Table 1) during a 4-days adjustment and 5-days balance period. Ten grams (total solids) were given each day, and during the balance period the uneaten food was collected and weighed. Endogenous nitrogen was deter- mined on a 4% egg protein diet. The experi- mental diets contained 8.2% lactose, 1% vita- mins, 5% minerals, 10% maize oil, 5% cellulose powder, and 1.36% nitrogen. Wheat starch was added to 100%.

Chemical score was calculated as described by FAO/WHO 1973 (4), and egg protein was

reference. Amino acid composition of wheat and

casein was taken from FAO/WHO (5) while figures for WPC and whey cheese were ob- tained as described in (8).

Significance of differences between means were by Student's t-test (1).

RESULTS

The protein qualities of the experimental diets are in Table 1. Wheat protein has a BV of only 51.3 while a mixture of 83% wheat protein and 17% protein from WPC has BV 68.0 (P<.001). Similarily, a mixture of 83% wheat protein and 17% protein from whey cheese has BV 70.1 which is higher than BV of wheat protein (.001<P<.01). Apparently WPC is a more effective supplement to wheat protein than whey cheese since the mixtures containing 33, 50, 67, and 83% supplementary protein had significantly higher BV values for WPC as the supplementary protein than for whey cheese. However, whey cheese is also an effective whey protein supplement. These findings are illustrated in Figure 1. The BV of whey cheese and WPC fed alone are not statistically different. Table 1 also shows that mixtures containing WPC generally have larger digestibilities than mixtures containing whey cheese. Values for mixtures containing WPC as compared to whey cheese were signifi- cantly higher for all mixutres containing 50% wheat protein or less.

Table 1 also includes results of chemical scores. Lysine is the limiting amino acid in the mixtures in which wheat is the main pro- tein source, and WPC improves the lysine score of the mixtures more effectively than does whey cheese. When mixtures contained less than 50% wheat protein, phenylalanine and tyrosine were the limiting amino acids in mix- tures in which WPC was the supplementary protein while meth ion ine and cystine were limiting in the mixtures containing whey cheese.

DISCUSSION

Egg protein was reference for chemical scores of the mixtures since this amino acid pattern gives closer agreement with rat experi- ments than the amino acid pattern suggested by FAO/WHO (4). Several of the mixtures

Journal of Dairy Science VoI. 62, No. 8, 1979

TABLE 1. Biological value (BV) and true digestibi l i ty (TD) of mixtures of wheat with whey protein concentrate (WPC) or whey cheese determined on growing rats.

Composi t ion of dietary Limit ing protein in percent of BV TD Chemical amino

Diet total d ie tary protein N 2 MV SD ~ MV SD ~ score acid

t~

WPC 100 5 93.8 1.1 97.0 1.6 b 70 phe + tyr Whey cheese 100 4 91.0 3.6 90.9 1.9 b 68 met + cys

Wheat + WPC 17:83 5 96.4 1.7 a 96.8 .6 c 71 phe + tyr Wheat-whey cheese 17:83 4 87.8 2.1 94.6 1.7 c 69 met + cys

Wheat-WPC 33:67 5 94.2 .8 a 95.8 .9 b 72 phe + tyr Wheat-whey cheese 33:67 4 82.8 .8 a 93.3 .3 b 69 met + cys

Wheat-WPC 50:50 5 91.9 2.5 a 95.2 .6 c 74 phe + tyr Wheat-whey cheese 50:50 4 74.5 2.0 a 92.6 1.9 c 66 lys

Wheat-WPC 67:33 5 81.4 2.0 c 93.5 2.0 67 lys Wheat-whey cheese 67 : 33 5 76.3 2.9 c 92.0 2.2 54 lys

Wheat-WPC 83:17 5 68.0 1.9 94.3 2.3 49 lys Wheat-whey cheese 83:17 5 70.1 6.9 92.1 1.5 42 lys

Wheat 100 4 51.3 3.2 92.4 3.8 30 lys Casein 100 5 71.5 6.8 97.4 1.8 58 met + cys

t~

Z ,d > -8

Z O

-q

-r t~

0

Z

<

ox to Z o o0

t Values within the same pair followed by a are different (P<.O01). Values within same pair followed by c are different ( .01<P<.05) .

2 Number of rats in the de terminat ion of BV and TD.

the same pair followed by b are different (.O01<P<.O1). Values within the

0 xO

1210 FORSUM

BV --o-- whey cheese --wheat 100 - - ~ - - WPC- whe=d

60

50 100 %Wheat protein

Figure 1. Biological value determined on growing rats of mixtures containing different fractions of pro- teins from WPC (whey protein concentrate) and wheat as well as from whey cheese and wheat.

ments for children whose diets are inadequate in protein, should be at least 60 (11). Thus, a relatively small addi t ion o f supplementary whey cheese prote in is sufficient to improve the prote in qual i ty of whea t -whey cheese mixtures to an ex ten t which is of practical significance in human nutr i t ion.

A C K N O W L E D G M E N T S

This study was suppor ted by grants f rom the Swedish Internat ional Deve lopment Author - i ty (SIDA), the Swedish Nutr i t ion Foundat ion , and the Swedish Board for Technical Develop- ment . The technical assistance o f E. Bj0rk, J. Lewin, and Britt Marie Johansson is ac- knowledged gratefully.

containing WPC were l imited by phenytalanine and tyrosine. However, the concept o f l imit ing amino acids has not been subjected to suff icient testing except for those containing sulfur and lysine so some caut ion is warranted (4). The inf lect ion poin t in the curve of BV when wheat and whey cheese were fed occurred near the change in l imiting amino acids (Figure 1).

Whey proteins are effect ive supplements for improving the nutr i t ional qual i ty o f a cereal protein as wheat . Moreover, they show that a t radi t ional p roduct such as whey cheese has this valuable qual i ty al though to less ex ten t than a sophist icated p roduc t as a WPC pro- duced by ul trafi l t rat ion. As discussed in (8), wheat protein is inadequate for a growing in- fant. Calculat ions o f chemical score af ter addi t ion of whey cheese to wheat showed that a mix ture of 30 g wheat and 15 g whey cheese would have an acceptable prote in qual i ty for a growing child. This mix ture con- tains ca. 70% prote in f rom wheat and 30% prote in f rom whey cheese. In this s tudy biologi- cal evaluat ion o f a mix tu re o f 17% prote in f rom whey cheese and 83% f rom wheat showed a significant improvement in prote in qual i ty as compared to wheat protein, the NPU 1 value of this mix ture being 64. According to the r ecommenda t ions of the prote in advisory group (PAG) the NPU value is so called pro- tein-rich weaning foods, in tended as supple-

~NPU (net protein utilization) = (BV X TD) 100.

R E F E R E N C E S

1 Armitage, P. 1973. Page l18 in Statistical methods in medical research. Halsted Press, John Wiley and Sons Inc., New York.

2 Eggum, B. O. 1973. The influence of lactose on protein utilization. Page 120 in a study of certain factors influencing protein utilization in rats and pigs. Landhusholdningssellskabeds forlag. Kepen- havn.

3 Ekelund, S. 1966. Page 67 in Statens Lantbru- kskemiska kontrollanstalt. Meddelande nr 28, bilaga 12.

4 Food and Agricultural Organization/World Health Organization Expert Committee. 1973. In Energy and protein requirements. World Health Organiza- tion, Tech. Repr. Ser. No. 552. Geneva.

5 Food and Agricultural Organization. 1970. Amino acid contents of foods and biological data on proteins. Nutr. Stud. No. 24. Food and Agricul- tural Organization, Rome.

6 Forsum, E. 1975. Whey proteins for food and feed supplement. Page 433 in protein nutritional quality of foods and feeds. Part 2. M. Friedman, ed. Marcel Dekker, Inc., New York.

7 Forsum, E. 1975. Effect of dietary lactose on nitrogen utilization of a whey protein concentrate and its corresponding amino acid mixture. Nutr. Rep. Int. 11:419.

8 Forsum, E., and L. Hambraeus. 1977. Nutritional and biochemical studies of whey products. J. Dairy Sci. 60: 370.

9 Hambraeus, L., E. Forsum, L. Abrahamsson, and B. Lrnnerdal. 1976. Automatic total nitrogen analysis in nutritional evaluations using a block digestor. Anal. Biochem. 72: 78.

10 Mann, E. J. 1974. Digest of world literature. Whey utilization-part 1. Dairy Ind. 39:303.

11 Protein Advisory Group Guideline No. 8. 1975. Protein-rich mixtures for use as supplementary foods. PAG Compendium, Vol. F 1:631.

12 Samuelsson, E. G. 1975. Sm]ltost Mesvaror. Page 77 in part 7 of Mejeril~ra. Sveflska Mejeriernas Riksft~rening. Stockholm.

Journal of Dairy Science Vol. 62, No. 8, 1979