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Milk, curd, and yoghurt from glandless and degossypolized glanded cottonseed protein

N.S.Abu-Foul, Ayyat M. Youssef, and Y.G.Moharram

Abstract

The use of defatted glandless and defatted, degossypolized glanded cottonseed flour for the preparation of different types of dairy products was studied. It was found that acceptable products could be obtained by mixing cottonseed milk, particularly that from glandless flour, with a reconstituted commercial/ powdered fullcream cow's milk in proportions ranging from 1:3 to 1:1. These mixed milks were comparable in their physicochemical properties and sensory characteristics with the 100% reconstituted powdered cow's milk.

Introduction

Cottonseed contains gossypol, which is the main reason for not using it for food purposes. Gossypol can be inactivated, however, by cooking, chemical treatment, or liquid or air separation [1] It can also be bred out of the plant genetically. Two studies showed that the protein digestibility of glandless cottonseed flour was 91%; it also had a lighter colour and blander taste than the glanded flour [2, 3]. Abu-Foul has found that degossypolization of glanded cottonseed with organic solvents increased the content and availability of Iysine and improved the PER, digestibility, and chemical score to levels similar to those found in glandless cottonseed protein [4].

Although commercial production of glandless cottonseed is limited, research on it for food purposes has begun. The effect of adding defatted glandless cottonseed flour to cow's milk in preparing yoghurt (zabadi) has been studied [5]. It was found that the chemical and sensory properties of the product containing 5 g, 10 g, and 15 g of cottonseed flour per 100 g of milk were similar to those of the control. Increasing the cottonseed level to 25 g gave the product a salty flavour, weak consistency, yellow colour, and lower acidity. Tamucurd, a tofu-like product, has a bland flavour when prepared from glandless cottonseed kernels [6]. It has been suggested that this product might be used in the preparation of a linksausage-type meat-substitute product and as a substitute for cream cheese in cooking [6]. An acceptable processed cheese containing 5.4% of glandless cottonseed flour has been prepared [7]. It is also possible to replace non-fat milk solids with up to 10% of defatted glandless cottonseed flour in vanilla-flavoured ice cream and up to 15% in chocolate ice cream [8]

The purpose of this study was to prepare a vegetable milk from cottonseed. The physical and chemical properties and sensory characteristics of this milk - alone or mixed in various proportions with a common commercial dry milk powder (Nestle's Nido) - were evaluated and compared with those of a commercial liquid whole milk, 100% reconstituted powdered milk, and mixtures containing soybean milk. These milks were also used to prepare two dairy products commonly consumed in Egypt, curd (labnah) and yoghurt (zabadi).

Materials and methods

Materials

Cottonseed

Two varieties of cottonseed (Gossypium barbadenus) were used in the study - Giza 76, a glanded variety, and Alexandria IV, which is glandless. Both varieties were obtained from the Field Crops Research Farm of the University of Alexandria.

The seeds were decorticated using a common dehuller, then ground and passed through a 60-mesh sieve. Fat was extracted with hexane using a Soxhlet apparatus (40°-60° C) and the solvent was removed from the defatted flours in a vacuum oven at 40° C. The results of analysis of the flours are shown in table 1.

The defatted glanded flour was degossypolized by a successive extraction procedure with 70% acetone for two hours followed by 99.5% acetone for four to five hours using a Soxhlet apparatus. This process reduced the free gossypol from 0.8% to 0.2% and the total flavonoids from 0.2% to 0.05%, and increased the protein, crude fibre, and ash content.

Other ingredients

Instant Nido full-cream milk powder contains more than 20% fat, 26% protein, 37% lactose, 6% minerals, 0.2% lecithin, 3% moisture, and 1,500 IU vitamin A and 322 IU vitamin D₃ per 100 g.

Liquid whole cow's milk (Seklam), soybeans, sucrose, and sodium chloride were purchased from a local market. Butter and strawberry essences were obtained from the Bisco Misr Company in Alexandria.

Methods

Technological methods

The fat-free decorticated flours of glandless and degossypolized glanded cottonseed were used to prepare cottonseed milk, curd, and yoghurt according to the procedures digrammed in figure 1. Sucrose (2%) and sodium chloride (0.2%) were added to improve the taste. The milks were pasteurized by heating to 70° C for 10 minutes while stirring, then cooled rapidly in an ice bath. Butter or strawberry essence was added to the pasteurized milk, 0.05% of each. Powdered cow's milk was reconstituted and pasteurized following the same procedure.

Soybean milk was prepared as described by El-Deeb and Hassan [9], and was also pasteurized and mixed with reconstituted powdered milk.

Curd was prepared from the cottonseed and soybean milk mixtures, powdered milk, and regular whole milk as described by Kosikowski [10]. Lactic acid (10%) was used to precipitate the curd at pH 4.5. The precipitate was put into cloth bags and kept at room temperature (22°±3°C) overnight to drain. The curd was mixed thoroughly until of proper consistency, then put into plastic cups, covered, and refrigerated at 4° C.

Yoghurt was prepared from the various milks according to the methods used by El-Deeb and Hassan [9]. The milks were heated to 85° C for 30 minutes, cooled to 43° C, mixed with a 2% yoghurt starter, and incubated for three to four hours at 40° C. After coagulating, the yoghurt samples were refrigerated at 4° C overnight.

Physicochemical properties and sensory evaluation

The acidity and total solids of the prepared milks were determined [11]. Viscosity was determined using an Ostwald viscometer [12].

The products were judged organoleptically by ten panelists from the department staff, using a composite scoring test in which points were assigned separately for appearance and colour, consistency, flavour (odour and taste), and absence of defects, with a total possible composite score of 100 points [13]. The overall acceptability of each product was rated according to its total score as excellent (90-100 points), good (80-90), fair (7()-80), or poor (60-70).

TABLE 1. Analysis of defatted cottonseed flours (percentages)

FIG. 1. Flow chart for the production of cottonseed dairy products

TABLE 2. Physicochemical properties of blends of cottonseed or soybean milk and reconstituted powdered full-cream cow's milk, compared with liquid whole milk and 100% reconstituted powdered milk

a. Ratios represent the proportion of vegetable-protein milk to reconstituted powdered cow's milk.
b. Degossypolized.

Results and discussion

Drinking milks

The milks prepared from either 100% glandless or 100% degossypolized glanded cottonseed flour were rejected by the panelists during sensory evaluation. Therefore, for the trials the cottonseed milks were mixed with reconstituted powdered milk in the proportions 1:3, 1: 1.5, and 1:1. Mixtures of soybean milk with powdered milk in the same proportions were also prepared.

The physicochemical properties of these products are shown in table 2 and compared with two control milks - 100% reconstituted powdered milk and regular whole milk. The total solid content in the products containing vegetable milks ranged from 11.8% to 13%, acidity from 0.17% to 0.19%, pH from 6.5 to 7.1, and viscosity from 2.8 to 3.4 cP. These properties agree generally with the specifications for drinking milk.

Total solids and acidity were higher, while pH was lower, in the products with vegetable milks, particularly cottonseed milk, than in the regular whole milk; and they had higher viscosity than either of the control milks. The cottonseed-milk products had a higher acidity than the reconstituted powdered milk.

With the increase in the proportion of the vegetable milks to reconstituted powdered milk from 1:3 to 1 :1, the total solids and viscosity increased and pH values decreased. The protein of vegetable milk may be responsible for some of these changes, particularly for the increase in viscosity, since most of the solids of cottonseed milk are not completely soluble. It may also contain some acid salts.

Generally, the products containing cottonseed milk had higher total solids and lower pH values than those containing soybean milk. Viscosity was similar in both. Slight differences in the physicochemical properties of the cottonseed-milk products were noted depending on whether they contained glandless or degossypolized glanded cottonseed milk.

TABLE 3. Evaluation of sensory charctetistics of flavoured cottonseed- or soybean-milk blends, compared with liquid whole milk and reconstituted powdered milk

Figures in parentheses indicate maximum possible scores
B = with butter essence; S = with strawberry essence

Table 3 summarizes the evaluation of the sensory characteristics of these milks after flavouring with butter and strawberry essences.

When butter flavouring was added, no significant overall differences were detected in sensory quality between the products containing cottonseed milk and the controls except for the 1:1 blend of degossypolized glanded cottonseed milk, which was rated fair, with a total score of 78 points, while the others were rated good. The products containing soybean milk were rated poor except for the 1:3 blend, which was rated fair, with a score of 70.

When strawberry flavouring was added, the evaluations were similar except that all the soybean-milk products were rated poor. The reconstituted powdered milk was only rated fair, with a score of 77. This indicates that the butter flavouring improved the sensory quality of the various types of drinking milk more than the strawberry.

Curd and yoghurt

Curd and yoghurt prepared from the various milks that have been described were subjected to sensory evaluation (table 4).

No significant overall variations in sensory quality were observed among the curds made from the blends containing glandless cottonseed milk and the controls; the total scores varied from 81 points for that made from regular whole milk to 87 points for both that from 100% powdered milk and from the 1:3 blend, indicating good sensory characteristics. The sensory characteristics of the curds made from the 1:3 and 1:1.5 blends of degossypolized glanded cottonseed milk as well as that from the 1:3 soybean-milk blend were rated as fair, with scores ranging from 71 to 78 points. The other curds had scores of 70 points or less and were considered poor in quality. An increase in the level of vegetable protein milk gave the products a light green colour and a bitter taste, which may be attributed to the water-soluble pigments and short chain polypeptides in vegetable milk.

The panel preferred the yoghurts made from the 1:3 and 1:1.5 blends of glandless cottonseed milk and from 100% powdered milk, rating their sensory characteristics as good. The yoghurts made from regular whole milk and from the l:1.5 soybean-milk blend were acceptable, while the others were rated poor because of their thin consistency, light green colour, and bitter taste.

TABLE 4. Evaluation of sensory characteristics of curd and yoghurt prepared from cottonseed- or soybean-milk blends, compared with those from liquid whole milk and reconstituted powdered milk

C = curd; Y = yoghurt

Conclusions

Low-cost drinking milks with a quality equal to that of commercial animal milks can be prepared by blending either glandless or degossypolized glanded cottonseed milk with reconstituted Nido powdered milk at a ratio of 1: 1, 1: 1.5, or 1:3. These products were equal to 100% reconstituted powdered milk and to regular liquid whole milk in physicochemical properties and sensory characteristics. Dry blends of both milks can be prepared commercially.

Milks prepared by blending glandless cottonseed milk with reconstituted Nido powdered milk at a ratio of 1 :3 or 1: 1.5 can be used for the preparation of acceptable curd and yoghurt.

These products not only can help in the treatment and prevention of malnutrition but also can help to lower the cost of animal milk. They would be useful especially in developing countries that suffer from shortages of animal protein sources.

References

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2. El-Sayed KA. Utilization of cottonseed flour in human food: 11, Effect of cotton protein fractions on the physical properties of wheat flour dough. Alexandria J Agric Res 1978;26:609ff.

3. Wan PJ, Green J, Cater CM, Mattil KF. Factors influencing the colour of cottonseed protein products. J Food Sci 1979;44:475ff.

4. Abu-Foul NS. Physico-chemical, nutritional and technological studies on food uses of glanded and glandless cottonseed protein. PhD thesis. Food Science and Technology Department, Alexandria University. Alexandria. Egypt 1990.

5. El-Soda M, El-Sayed KA, El-Bary AA, Abou-Donia S, Mashaly Rl. The utilization of cottonseed flour in zabadi manufacture. J Dairy Sci 1979;62:161ff.

6. Kajs TM, Lawhon JT, Rhee KS. Tamucurd: a high protein ingredient. Food Tech 1974;33:82ff.

7. Abou-Donia SA, Salem AK, El-Sayed KA. Enrichment of processed cheese with cottonseed flour. Indian Dairy Sci 1983;36: 119ff.

8. El-Deeb SA, Salam AK. The use of flour vegetable proteins in ice cream manufacture. Alexandria Sci Exch 1984;5:87ff.

9. El-Deeb SA, Hassan HN. Effect of partial substitution of non fat milk solids with defatted soy flour on the qualities of zabadi. Alexandria Sci Exch 1987;8:87ff.

10. Kosikowski FV. Cheese and fermented milk foods. 4th printing. New York: F. V. Kosikowski, 1978.

11. Ling ER. A text book of dairy chemistry. Vol 2. 3rd ed. London: Chapman and Hall, 1963.

12. Rahma EH, Narasinga Rao MS. Removal of polyphenols from sunflower meal by various solvents: effect on functional properties. J Food Sci 1981.46: 1521ff.

13. Ranganna S. Manual of analysis of fruits and vegetable products. New Delhi: Tata McGraw-Hill, 1979.

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