Physicochemical and Organoleptic Properties of Yogurt with Cornelian Cherry Paste

Abstract

Stirred-type fruit-flavored yogurt was made by adding cornelian cherry paste and sugar at different ratios. The effects of the paste and sugar addition on the physicochemical and organoleptic properties of yogurt were examined. The titratable acidity, pH, viscosity, whey separation, and organoleptic properties of experimental yogurts were determined at weekly intervals for 21 days. Statistically significant differences were found between the control and fruit-flavored yogurts in terms of viscosity and whey separation. The addition of the fruit paste and sugar to yogurt resulted in an increase in the whey separation, and a decrease in the viscosity. During the storage, the values of the titratable acidity, viscosity and whey separations of experimental yogurts increased, while pH of the yogurts decreased significantly (P < 0.01). Yogurt with 10 kg/100 kg fruit paste and 10 kg/100 kg sugar was more acceptable and high scored with respect to overall acceptability value by panelists; however the result was not significant statistically.

Keywords:

• Fruit-flavored yogurt
• Cornelian cherry paste
• Whey separation
• Viscosity
• Organoleptic properties

INTRODUCTION

Cornelian cherry (Cornus mas L.) is a wild plant that grows in Asia and Europe, as well as being recently cultivated in Turkey, and its mature scarlet fruit has sour taste.[1] The fruit contains significant amounts of anthocyanins. It is known that anthocyanins have antioxidant and anti-inflammatory effects. Therefore, the use of anthocyanins-containing foods as part of a diet may also be beneficial for human health.[2] Also the fruit has been used for the medical treatment of gastrointestinal disorder and diarrhea among people in Turkey.[3]

In Turkey, approximately 12,800 tons of cornelian cherry fruit is produced per annum.[4] The fruit is either consumed directly or processed into various products such as jam, marmalade, pestil (a dried form of marmalade produced in the eastern part of Turkey), paste, and sherbet or is dried.[5,6] The composition of cornelian cherry paste was 14.8–15.5 kg/100 kg total solids, 10.8–11.8 kg/100 kg total sugar, 10.3–10.8 kg/100 kg invert sugars, 1.0–1.3 mg/100 g vitamin C, 2.0–3.0 ml/100 ml titratable acidity, and 2.7–2.9 pH.[6]

The improvement of aroma and flavor of yogurt can result in an increase in the consumption of final product. Fruit yogurt found to be more attractive organoleptically due to masking partially the excessive acetaldehyde flavor in plain yogurt.[7,8] Fruit-flavored yogurts are produced by adding fruit concentrates or flavored syrups to the cultured milk after or before the incubation process, and thus added flavor ingredients generally tend to decrease the product consistency.[9] At the same time, it leads to an increase in the nutritional value and causes product variability in the markets.

In Turkey, the production and consumption of fruit-flavored yogurt is rather low as compared to plain yogurt.[10] Also the consumption of milk is rather low and therefore, attention should be given to the production of fruit-flavored yogurt to increase the consumption of milk and milk products. The objective of this study is to develop new stirred type fruit-flavored yogurt by adding cornelian cherry paste and to determine the effect of the paste addition on the physicochemical and organoleptic properties of the final product.

MATERIALS AND METHODS

The cornelian cherry fruit was purchased from local sales-shop in Erzurum, and it was pasted in the laboratory. The total solids content of the paste was 16.13 kg/100 kg, and the pH was about 3.0. Commercial freeze-dried starter culture (YC-350, a blend of Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrucckii subsp. bulgaricus) was provided by Chr. Hansen Co. (A/S, Horsholm, Denmark) and used in the production of yogurt.

Production of Cornelian Cherry Paste

Cornelian cherry fruit was washed by following the separation of decayed and unripe cherries. The washed fruit was placed in a boiler and 100 ml water was added per kg of fruit. The fruit was preheated at 60 ± 2°C, and the pip and fruit skin were removed manually and then the paste was obtained after filtration of the crushed fruit. The paste was pasteurized at 90 ± 1°C for 5 minutes and hot filled into cleaned glass jars (1/2 kg).[6] The paste was stored at ambient temperature until being used in the yogurt production.

Manufacture of Experimental Yogurts

Yogurt was prepared according to the method reported by Tamime and Robinson.[9] Non-fat milk powder (Pinar A.S., Dairy Product Company, Pinarbaşi, İzmir, Turkey) was reconstituted to 16 kg/100 litre-milk total solids and 1 kg/100 litre-milk starch was added to the milk. The reconstituted milk was pasteurized at 90°C for 5 minutes, divided into seven equal batches and cooled to 42 ± 1°C. After cooling, all batches of milk were inoculated with 2 litre/100 litre commercial yogurt starter culture, and incubated at 42 ± 1°C until the pH of the yogurts was 4.7. After 12 hours storage, one batch of yogurt was taken as control, and each of the remaining batches were mixed with one of the pasteurized mixture of A [5 kg/100 litre cornelian cherry paste and 10 kg/100 litre sugar], B [5 kg/100 litre cornelian cherry paste and 15 kg/100 litre sugar], C [10 kg/100 litre cornelian cherry paste and 10 kg/100 litre sugar), D [10 kg/100 litre cornelian cherry paste and 15 kg/100 litre sugar], E [15 kg/100 litre cornelian cherry paste and 10 kg/100 litre sugar] or F [15 kg/100 litre cornelian cherry paste and 15 kg/100 litre sugar], respectively. All experimental yogurts were stored into parts of approximately 200 g, which was at 4 ± 1°C for 21 days for further analyses. Experiments were replicated twice.

Analytical Methods

In the determination of whey separation, 5 ml of yogurt was centrifuged at 5000 rpm for 20 minutes at 4°C, and the separated whey was measured after 1 minute. Whey separation amount was expressed as volume of separated whey per 100 ml of yogurt.[11] The apparent viscosity was determined by using viscosimeter (RV-model, Selfe Elee Ltd. Wickford Essex SSII 8BJ, England) at 4°C. Samples were stirred for 40 seconds before measurement. The viscosity values were expressed as centipoises (cP) and measured at 20 rpm with spindle #4.[12] A combined glass electrode was used for the pH measurements (digital pH meter, WTW pH-340-A, Germany). In the determination of titratable acidity, the method given by Kurt et al. ref.[13] was employed, and the results were expressed as lactic acid. Yogurt samples were analyzed at weekly intervals for 21 days.

The experimental yogurt samples (coded with random numbers) were placed on white plates and presented together to the panel members in daylight, who were asked to evaluate each sample in turn covering a list of judged parameter attributes using a hedonic scale with 1 being the worst (1, very poor; 5, very good). The score given by panelists for each attribute of a sample was noted separately. The qualities judged were: exterior appearance (by looking to yogurt sample in daylight directly), consistency by spoon (by gentle mixing yogurt with a spoon) and by mouth, odor and taste intensity, perceived fruit, and sweetness. For consistency by mouth, odor and taste intensity, perceived fruit and sweetness, a spoon of yogurt is taken and spreaded out by tongue. The overall acceptability was calculated as sum of the scores of the parameters judged.[14] The yogurts were evaluated on 7, 14, and 21 days of storing by eight panelists familiar with yogurt. Water was provided for mouth washing between samples.

Statistical Analysis

The study was designed according to randomized complete block design by 3 (fruit paste) × 2 (sugar) factorial experiment.[15] Square root transformation was applied to the organoleptic data and the effects of cornelian cherry paste addition on each chemical, physical and organoleptic parameter of experimental yogurts were estimated by ANOVA using MINITAB^® statistical software. (MINITAB Inc., State College, PA). Duncan's Multiple Range Test was used for determination of statistically different groups.

RESULTS AND DISCUSSIONS

Physical and Chemical Properties of Experimental Yogurt

Titratable acidity of the control and fruit-flavored yogurts increased significantly during the storage period at 4 ± 1°C (P < 0.05). Some researchers reported that the titratable acidity of fruit-flavored yogurts increased along with storage.[10,16,17] In the fruit-flavored yogurts containing 10 kg/100 litre sugar, the rapid increase in titratable acidity continued up to the end of storage (Fig. 1). The titratable acidity of fruit-flavored yogurts contained 15 kg/100 litre sugar was found lower than the yogurt with 10 kg/100 litre sugar and control, while the acidity of the fruit yogurt with 10 kg/100 litre sugar was higher than the control (Table 1). Similarly, the pH of the control and fruit-flavored yogurts continued to decrease during the storage (Data not shown). Higher concentration of the paste in the yogurt resulted in a decrease in the pH, while higher sugar concentration caused to increase in the pH. This was probably due to the nature pH of the added ingredients to the yogurts.

Figure 1 The titratable acidity of the experimental yogurts during storage at 4°C for 21 days: (♦) control; ( ) 5 kg/100 litre fruit paste and 10 kg/100 litre sugar; (Δ) 5 kg/100 litre fruit paste and 15 kg/100 litre sugar; (×) 10 kg/100 litre fruit paste and 10 kg/100 litre sugar; (*) 10 kg/100 litre fruit paste and 15 kg/100 litre sugar; (•) 15 kg/100 litre fruit paste and 10 kg/100 litre sugar; (+) 15 kg/100 litre fruit paste and 15 kg/100 litre sugar.

Table 1 Mean values of the physical and chemical properties of the experimental yogurts.*

	Titratable acidity (La)	pH	Whey separation (ml/100 ml)	Viscosity (cP)
Yogurt types **
Control	1.15a	4.10a	41.52b	5215.0a
Fruit-flavored yogurt	1.15a	4.02a	46.61a	4314.6b
Note: *Significant differences were obtained between mean values marked with different letter in the same column. **mean of all (A, B, C, D, and E) fruit flavoured yogurts.
Levels of paste addition
5 kg/100 litre	1.16a	4.04a	45.61c	4465.6a
10 kg/100 litre	1.15a	4.02b	46.77b	4356.3b
15 kg/100 litre	1.15a	4.00c	47.47a	4121.9c
Levels of sugar addition
10 kg/100 litre	1.20 a	4.01b	45.14b	4587.5a
15 kg/100 litre	1.10 b	4.03a	48.09a	4041.7b

The viscosities of the control and fruit-flavored yogurt increased rapidly up to day 7, and continued to increase slowly up to day 14 of storage and afterwards decreased slowly. Similar viscosity pattern of yogurt during gelation process was reported by Juma et al.[18] On the other hand, the viscosities of the fruit-flavored yogurts were influenced by the rates of the paste addition (Fig. 2). The addition of the paste reduced the mean viscosity values of all yogurts, and it was also found to be concentration-dependent (P < 0.01). On the contrary, the pattern of the whey separation of the fruit-flavored yogurts was higher as compared to the control (Table 1). In general, whey separation of experimental yogurts increased during the 1-week of storage, and then the volume of the whey separation decreased slowly. Although during the last week of the storage, whey separation of fruit-flavored yogurts increased slowly. On the other hand, the whey separation profiles of fruit-flavored yogurts were similar to the control throughout the storage period with higher whey separation rates of fruit-flavored yogurt products (Fig. 3). Lower viscosity and higher whey separation were characteristics for fruit yogurt. The addition of concentrated fruit decreases water-holding capacity of protein (i.e., diluting the protein content in the milk base); thus decreases the viscosity and increases whey separation of fruit-flavored yogurt.[8,19] Similarly, it was reported that the viscosity of fruit-flavored yogurt containing concentrated grape[10] or mulberry[16] was lower, while the whey separation was higher than the control.

Figure 2 Whey separation of the experimental yogurts during storage at 4°C for 21 days: (♦) control; ( ) 5 kg/100 litre fruit paste and 10% sugar; (Δ) 5 kg/100 litre fruit paste and 15 kg/100 litre sugar; (×) 10 kg/100 litre fruit paste and 10 kg/100 litre sugar; (*) 10 kg/100 litre fruit paste and 15 kg/100 litre sugar; (•) 15 kg/100 litre fruit paste and 10 kg/100 litre sugar; (+) 15 kg/100 litre fruit paste and 15 kg/100 litre sugar.

Figure 3 Viscosity of the experimental yogurts during storage at 4°C for 21 days: (♦) control; (□) 5 kg/100 litre fruit paste and 10 kg/100 litre sugar; (Δ) 5 kg/100 litre fruit paste and 15 kg/100 litre sugar; (×) 10 kg/100 litre fruit paste and 10 kg/100 litre sugar; (*) 10 kg/100 litre fruit paste and 15 kg/100 litre sugar; (•) 15 kg/100 litre fruit paste and 10 kg/100 litre sugar; (+) 15 kg/100 litre fruit paste and 15 kg/100 litre sugar.

Organoleptic Properties of Experimental Yogurt

The organoleptic evaluation of the fruit-flavored yogurt was carried out at weekly intervals for 21 days and the mean scores obtained summarized in Table 2. Results of organoleptic evaluation showed that significant differences were observed among fruit-flavored yogurts (P < 0.05) except smell, taste intensity and perceived sweetness, while no differences were obtained statistically between the scores of all organoleptic properties of the yogurt made by adding 10 and 15 kg/100 litre sugar. By adding more fruit paste, the appearance of fruit-flavored yogurt was scored higher by panelists (P < 0.01). However, statistically significant differences were not found between the scores of samples with 10 kg/100 litre and 15 kg/100 litre fruit paste addition. In addition, the panelists preferred yogurt produced with 10 kg/100 litre sugar (Table 2).

Table 2 Mean values of the organoleptic properties of fruit-flavored yogurts (n = 8).*

	AP	CS	CM	OD	TI	PF	PS	OA ^1
Levels of paste addition
5 kg/100 litre	3.03^b	2.82^b	2.62^b	4.08	3.13	3.06^b	3.35	22.09^b
10 kg/100 litre	4.00^a	3.76a	3.73a	4.16	3.39	4.04a	3.84	26.92a
15 kg/100 litre	4.08a	3.73a	2.92^ab	4.33	3.42	3.92a	3.65	26.05a
Note: *Significant differences were obtained between mean values marked with different letter in the same column, n: number of panelists, 1: sum of the scores of the parameters judged; AP: appearance; CS: consistency (by spoon); CM: consistency (by mouth); OD: odor; TI: taste intensity; PF: perceived fruit; PS: perceived sweetness; OA: overall acceptability.
Levels of sugar addition
10 kg/100 litre	3.96	3.61	2.89	4.29	3.35	3.73	3.47	25.30
15 kg/100 litre	3.46	3.24	3.28	4.08	3.28	3.61	3.73	24.68

The consistency (by spoon) value of fruit-flavored yogurt by adding 5 kg/100 litre paste was found to be lower than the yogurts produced with 10 kg/100 litre and 15 kg/100 litre fruit pastes. Significant differences were not obtained between the consistency values of experimental yogurts of 10 kg/100 litre and 15 kg/100 litre fruit pastes. With respect to consistency value, the fruit-flavored yogurt manufactured with 10 kg/100 litre sugar was more acceptable by panelists. On the other hand, it was observed that consistency values (by mouth) for all fruit-flavored yogurt types were found significantly different from each other, and the higher value was obtained for the yogurt with 10 kg/100 litre fruit paste (P < 0.01).

As a result of panelists’ evaluation, with respect to smell, taste, and perceived sweetness, significant differences were not observed between examined yogurts by adding different amounts of fruit paste and sugar. The perceived fruit value of 5 kg/100 litre fruit paste added yogurt was found to be the lowest, while the values of the yogurts made by adding 10 kg/100 litre and 15 kg/100 litre fruit pastes were similar (P < 0.01). In addition, panelists also stated that the fruit amount of the yogurt containing 15 kg/100 litre fruit paste was excessive. As shown in Table 2, there were significant differences between overall acceptability values of 5 kg/100 litre and 10 kg/100 litre or 15 kg/100 litre fruit added yogurts, however no significant differences indicated between yogurts with 10 kg/100 litre and 15 kg/100 litre fruits (P < 0.01). Yogurts produced with adding 10 kg/100 litre and 15 kg/100 litre fruit pastes were preferred by panelists with higher value of 10 kg/100 litre added fruit yogurt. Although, the result was not statistically significant, the overall acceptability value of fruit-flavored yogurt with 10 kg/100 litre sugar was slightly higher than the yogurt added 15 kg/100 litre sugar. Also it was reported that panelists gave higher scores to fruit-flavored set-type yogurt manufactured with adding 10 kg/100 litre cornelian cherry fruit and 7 kg/100 litre sugar with respect to overall acceptability.[20]

CONCLUSION

Various amounts of cornelian cherry paste and sugar were used in the production of fruit-flavored yogurt and the effects of these additives on physical, chemical and organoleptic properties of the products were examined. The whey separations were higher, while viscosities of fruit-flavored yogurts were found to be lower than the control, and they were found to be concentration-dependent. Panelists gave higher scores to the yogurt with 10 kg/100 litre fruit paste, although no significant differences were observed between the yogurts produced by adding 10 kg/100 litre and 15 kg/100 litre fruit paste. The overall acceptability values of the yogurts containing 10 kg/100 litre fruit paste and 10 kg/100 litre sugar was found to be higher than the other types of fruit-flavored yogurts. In the production of cornelian cherry paste yogurt, it can be concluded that the addition of 10 kg/100 litre fruit paste and 10 kg/100 litre sugar would be recommended.

Notes

1. Kalkışım, Ö. A study on the improvement by selection of cornelian cherry grown in Vezirköprü province of Samsun. M.Sc. Thesis, Samsun Ondokuz Mayıs University, Turkey, 1993.

4. Anonymous. Statistical Yearbook of Turkey; State Institute of Statistics, Prime Ministry Republic of Turkey: Ankara, 2000.