DETERMINATION OF SOME PHYSICAL AND SENSORY PROPERTIES OF MILK, DARK AND WHITE CHOCOLATE AT DIFFERENT STORAGE TEMPERATURES

Ozlem Cağındı, Semih Otles
Food Engineering Department, Faculty of Engineering, Ege University, Izmir, Turkey

ABSTRACT

Chocolate and cocoa products are preferred by a large community and as well as being a pleasure to eat. Chocolate is a confection composed primarily of cocoa butter, cocoa mass, which are obtained from cocoa beans. The effects of 4, 20 and 30°C storage temperatures on color, texture, and sensory properties of dark, white and milk chocolates stored for 12 weeks were determined. Results showed that the storage temperatures significantly affected the physical and sensory properties of dark, white and milk chocolates. The storage at 4°C for 12 weeks was retarded changes in the samples. Surprisingly, sensory evaluation indicated that storage at 4°C is more suitable than 20 and 30°C.

Key words: Milk chocolate, dark chocolate, white chocolate, storage, chocolate quality.

INTRODUCTION

People from all age groups and the majority of cultural backgrounds consume chocolate. It has been known to humanity since 480-460 BC when it was considered a mystical and magical plant with medicinal properties [8]. Chocolate preparation, made from the fruit of the cacao tree, is one of the most popular foods in the world and also is used as a flavoring and an ingredient of beverages and various kinds of confectionery. Chocolate is made too many different recipes and contains extra ingredients in addition to cocoa products and can be defined as a mixture of cocoa butter, cocoa liquor, sugars and milk fats [12]. The cocoa beans removed from the cocoa tree (Theobroma cacao) and fermented. Dried and roasted beans contain about 300 chemicals including caffeine, theobromine, and phenethylamine. Chocolate liquor which is the basis for all chocolate products is prepared by finely grinding the nib of the cocoa beans. Cocoa powder is made by removing part of the cocoa butter from the liquor. Bittersweet chocolate, generally called as dark chocolate, contains at least 15% chocolate liquor but may contain as much as 60% with the remainder being cocoa butter, sugar, and other additives. All over the world, milk chocolate is the predominant form of chocolate consumed and typically contains10-12% chocolate liquor [4]. The nutritional value and the sorts vary with the ingredients. Chocolate has high nutritional content due to its high fat and carbohydrate contents and boosts energy levels. In the last 50 years, chocolate had been considered as a food with a nice aroma and texture, with calories and fats being its only contribution to diet. However, in recent years, numerous studies have shown that it can provide significant amounts of flavonoids, which contribute to reduce the risk of non-transmittable chronic illnesses such as cancer and heart disease [7]. Chocolate contains saturated, monosaturated, and a very small amount of polyunsaturated fatty acids. Human feeding studies it has been shown that the high proportion of stearic acid in the cocoa butter of chocolate does not adversely affect plasma lipids [10]. The latest studies indicated that chocolate included polyphenol flavanolic compounds, because cacao is its major constituent. Epicatechin, the major monomeric polyphenol antioxidant in chocolate [15] and an extract of chocolate liquor were both found to stimulate cellular immune response in vitro [16]. These health-promoting antioxidative compounds give chocolate its excellent shelf-life stability. These compounds are thought to inhibit the oxidation of plasma LDL-proteins indicating that cocoa and chocolate products may reduce the risk of atherosclerosis and coronary heart disease [9,19,20]. In addition, studies on cocoa flavonoids have indicated that they may be effective in the prevention of gastric ulcers, may inhibit nonspecific acute inflammation and may be anticarcinogenic and effective against certain cancers [14,19,20].

Dark chocolate has a high proportion of cocoa solids and therefore retain more of the nutritional value of cocoa than milk chocolate which has a lower proportion of cocoa solids. In milk chocolate the milk provides a rich source of proteins which the body can use and so its protein value is higher than that of dark chocolate. Chocolate is susceptible to temperature, external odors and flavorings, air and light, moisture, and time. The fat and sugar it contains will absorb surrounding odors. Chocolate should be stored in a cool, dry place away from light and air, odor-free place with good air circulation. Good storage practices help avoid decay, undesired features and help extend shelf life. Therefore, it is very important to protect the chocolate by storing it in closed packaging. Dark and milk chocolate naturally contain antioxidants, but white chocolate does not contain these substances [5].

The main purpose of this study was therefore to determine the effect of different storage temperature on color, texture and sensory properties of milk, dark and white chocolate during the storage at refrigerator temperature 4 ± 1°C, at room temperature 20 ± 1°C and at high temperature 30 ± 1°C.

MATERIAL AND METHODS

Materials
The dark, white and milk chocolate samples were obtained from Nestle Turkey Food Industry, Karacabey, Bursa, Turkey.

Storage of chocolate samples

The chocolate samples were held for 12 weeks at 4±1, 20±1 and 30±1°C for further testing in aluminum packages and analyzed periodically in every two weeks.

Proximate analysis
Moisture and ash properties of chocolate samples were determined by using Chocolate Standard Methods [18]. Total nitrogen content was determined using the standard Kjeldahl method [13]. Crude protein was expressed as 6.25·N. Total fat content was obtained by the Soxhlet extraction method using n- hexane as described by IUPAC Method 1.122 [17]. Carbohydrate content was obtained by subtracting the sum of moisture, ash, protein and fat from 100.

Melting point
The melting point of chocolate samples was determined by using Büchi 510 Melting Point Determinator (Büchi Lab. Teck. AG, Flawil, Swiss).

Fatty acid composition
Methyl esters were prepared by transmethylation method [6]. The fatty acids methylesters (FAME) of chocolate samples were analyzed by using Hewlett Packard 5890 Series II gas chromatography with flame ionization detector; GLC column SP2560 (100 m·0.25 mm, 0.25 µm, cyanopropylpolysiloxane fused silica); flow rate: hydrogen 0.5 ml·min^-1, helium 35 ml·min^-1; injection temperature 220°C, starting temperature 100°C, final temperature 220°C, rate of temperature 4°C·min^-1; split ratio 1:100.

Determination of color
The color was measured by determining Hunter L (lightness), a (redness/greenness) and b (yellowness/blueness) values of chocolate samples. For measuring a Minolta Chroma-Meter CR-310 reflectance colorimeter (Minolta Co, Osaka, Japan) was used and all measurements were done at 20°C.

Determination of texture
Hardness or degree of softening was measured by determining the maximum penetration force of chocolate samples. For measuring the depth of penetration a Texture Analyzer Model TA-XT plus (Texture Technologies Corp, Scarsdale, NY) was used. The measurement parameters were; penetration depth 6 mm; probe needle PN2, pre-speed 1.0 mm·s^-1, test speed = 1.1mm·s^-1, post speed = 10.0 mm·s^-1 and all measurements were done at 20°C [3].

Sensory evaluation
Sensory properties; color, texture, flavor and overall acceptability of chocolate samples were evaluated by using a 7-point hedonic scale. The trained panelists were evaluated the samples like 1 for dislike extremely, 4 for moderate, 7 for like extremely [11].

Statistical analysis
The results were expressed as mean values ± SD. The statistical analyses for determining analysis of variance and degree of significance that compared with Fisher’s least significant difference (LSD) a multiply test of t tests were carried out using Tarist [1, 2].

RESULTS AND DISCUSSION

The results of the proximate chemical analysis and melting point of the dark, white and milk chocolate is presented in Table 1. The proximate chemical analysis results of white and milk chocolate were similar, and the results except carbohydrate of dark chocolate values were lower than white and milk chocolate samples. The melting point of samples was arranged in order white chocolate < milk chocolate < dark chocolate.

Table 2 shows the fatty acid composition of the samples. C 16:0 (palmitic acid), C 18:0 (stearic acid), C 18:1 (oleic acid) and C 18:2 (linoleic acid) were the common fatty acids in the chocolate samples.

The changes of color during 12 week of storage time were given in Table 3 by Hunter L, a and b values. It was seen that for dark chocolate, L values indicated no difference at 4 and 20°C storage temperatures at the end of the storage. a values varied at different storage temperature and time. The storage temperature had not a real effect on the L values of white chocolates but affected on b values 8 week period. The mainly differences on this value appears at the milk chocolate samples both L and a values. The temperature really affects the b values of dark, white and milk chocolate samples.

The effect of different storage temperatures were concerned the hardness or degree of softening especially dark and white chocolate samples during 12 week storage time. The hardness is shown in Table 4.

As shown in Table 5, there were significant differences in sensory attributes. The flavor, color, texture and overall acceptability of dark, white and milk chocolates stored at 30°C were significantly (p < 0.05) least preferred then 20°C. In all sensory attributes and in samples the chocolates stored at 4°C were generally good accepted. In spite of the 12 weeks storage period at 4°C, sensory attributes of dark chocolate given better results than the other storage temperatures.

CONCLUSIONS

The experimental data presented in this paper on the physical properties like color and texture, and sensory properties of dark, milk and white chocolates have pointed out significant differences between the various temperature and storage time of chocolate samples. Storage at 4°C gives the better sensory results than storage at 20°C and 30°C. It is very surprisingly result in the respect of common chocolate storage temperature, 20°C.

REFERENCES

1. Acikgoz N., Akbas M.E., Moghaddam A., Ozcan K., 1994. Turkish data based statistics programmer for PC. 3rd Turkey Field Crops Cong. Ege University Press, Izmir, Turkey, 264-267.

2. Acikgoz N., Akkas E., 1997. Tarist: Veri tabanına dayalı bir bioistatistik paketi. Araştirma Sempozyumu ‘97, DİE – 24-26 Kasım, Ankara.

3. Ali A., Selamat J., Che Mana Y.B., Suria A.M., 2001. Effect of storage temperature on texture, polymorphic structure, bloom formation and sensory attributes of filled dark chocolate. Food Chem. 72, 491-497.

4. Apgar J.L., Tarka S.M., 1988. Methylxanthine composition and consumption patterns of cocoa and chocolate products. In: Caffeine. G.A. Spiller [ed} CRC Press, Boca Raton.

5. Beckett S.T., 2000. The science of chocolate. RSC, London.

6. International Organization for Standardization animal and vegetable fats and oils, preparation of methyl esters of fatty acids. Method ISO 5509. 1978. Geneva.

7. Jaramillo M.P., Salinas V.P., Ochoa G.M.A. Food antioxidants and their relation to chronic disease: Chocolate and its antioxidants content. 2006 www.chocolates.com.co/ingles/nut_cho_antiox.htm.

8. Keen C.L., 2001. Chocolate: Food as medicine/medicine as food. J. Am. Coll. Nutr. 20, 436-439.

9. Kondo K., Hirano R., Matsumoto A., Igarashi O., Itakura H., 1996. Inhibition of LDL oxidation by cocoa. Lancet 348, 1514.

10. Kris-Etherton P.M., Mustad V., 1994. Chocolate feeding studies: a novel approach for evaluating the plasma lipid effects of stearic acid. Am. J. Clin. Nutr. 60, 1029-1036.

11. Larmond E., 1997. Laboratory method for sensory evaluation of food. Food Research Institute, Ottawa. Canada.

12. Lee F.A., 1983.Cocoa and chocolate in basic food chemistry. Westport, Awi. 1983.

13. Offical methods of analysis, 1980. AOAC, Washington DC. USA.

14. Richelle M., Tavazzi I., Enslen M., Offord E.A., 1999. Plasma kinetics in man of epicatechin from black chocolate. Eur. J. Clin. Nutr. 53, 22-26.

15. Sanbongi C., Osakabe N., Natsume M.., Takizawa T., Gomi S., Osawa T., 1998. Antioxidative polyphenols isolated from theobroma cacao. J. Agric. Food Chem. 48: 454-457.

16. Sanbongi C., Suzuki N., Sakane T., 1997. Polyphenols in chocolate, which have antioxidant activity, modulate immune functions in humans in vitro. Cell. Immunol. 177: 129-136.

17. Standard methods for the analysis of oils. Fats and derivates. 1979. IUPAC. Pergamon Press., Oxford.

18. TS 7800 Chocolate Standard 1990. The Institute of Turkish Standards. Ankara, Turkey.

19. Waterhouse A.L., Sirley J.R., Donovan J.L., 1996. Antioxidants in chocolate. Lancet 348, 834.

20. Zumbé A., 1998. Polyphenols in cocoa: are there health benefits? BNF Nutr. Bull., 23, 94-102.

Accepted for print: 20.09.2007

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.