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T P CHÍ KHOA H C VÀ CÔNG NGH T p 43, s 2, 2005 Tr. 6-12 SENSORY PROPERTIES AND CONSUMER’S PREFERENCE FOR FONDUE CHEESES IN HANOI’S MARKET CUNG THI TO QUYNH, HA DUYEN TU I. INTRODUCTION The word “cheese” is commonly used as a collective term for widely variable products such as matured and non-matured cheese made with rennet, acid curd cheese, fresh cheese, and even processed cheese. Fondue cheese is made by grinding and blending cheese, adding “emulsifying salts”, heating while stirring to the proper temperature, stirring the melted mass for several minutes at that temperature, putting it into suitable containers, and cooling. Additionally, water, butterfat, whey powder, and/or caseinate are often added. The flavor of fondue cheese distinctly differs from that of cheese, partly due to the heat treatment, partly to the melting materials (P.Walstra, 1999). In Vietnamese markets, the quantity and the variety of cheese are quite abundant. There are about 170 types of cheese sold in supermarkets and restaurants in Vietnam (Vu Te Xien, 2004). The quantity of cheese imported to Vietnam was 1,300 tons in 2003 and to Hanoi was about 365 tons with 125 types in the same year. Thirty percent of these cheeses was fondue cheese (mainly La vache qui rit – cheese made in France) and it makes up an essential part of the cheese market. Despite the fact that there are many types of cheese sold in Vietnamese markets, the application of sensory evaluation is limited in grading some food products. This kind of sensory practice is based on expert opinion. However, the quality of food products is a complex issue, not to be defined by experts who search for the default of products or for subtleties that are of little interest to the consumer. Furthermore, sensory profiling is a powerful tool to aid in quality assurance and is essential for new product development (Bride R. Mc., 2001). Advances in methodology and the development of integrated experimental design and analysis offer a practical tool for specific use in profiling the sensory character of cheese. Thus, this study was aimed at evaluating sensory properties, and consumer preference for some cheeses sold in Hanoi’s market, and helping cheese manufacturers to understand, control and optimize the sensory characteristics of cheese products. II. MATERIALS AND METHODS 1. Subjects Two groups of subjects participated in this study. The first group consisted of 8 students (5 males and 3 females ranging in age from 21 to 23 years old) from the Institute of Biological and Food Technology, Hanoi University of Technology. The panelists were enrolled in a training program from October, 1st 2005 to November, 15th 2005 (average 70h/panelist) to detect and identify sensory properties of Fondue cheeses and to evaluate the intensity of sensory characteristics of these cheese on a 10-point universal intensity scale. The second group consisted of 120 untrained subjects (55 males and 65 females, ranging in age from 18 to 65 years old). They were selected from staff and students at universities in Hanoi, according to the following criteria: they like fondue cheese. 6 2. Fondue cheeses The cheeses used in 2 experiments were selected from Hanoi cheese markets. There were 6 kinds from French (included Bridel, Kiri, La vache qui rit, Party cubes, Picon and President) and one from Vietnam (“Bo deo no” – made in Vinamilk company). All of cheeses were preserved at 4 - 6°C before tasting. The maximum time of preservation (at the same temperature) recorded in the packaging is 6 months. The cheese samples were served for each assessor for tasting at 1 x 1 x 1 cm sized in covered glass containers at 20°C.. 3. Methods Descriptive analysis This test aimed at pointing out the essential vocabulary needed for cheese product description, sensorial characteristics of each type of cheese and the relation between cheese samples and their attributes (Mc Bride R., Muir D., 2001). All cheeses were evaluated by a panel using descriptive sensory profiling as described in ISO 6564:1985. The sensory panel consisted of 8 panelists selected and trained according to guidelines in ISO 8586-1:1993 and the laboratory was designed according to guidelines in ISO 8589:1988. Three replicates were performed for each cheese variety. The samples were served in a randomized order and replicated with respect to each assessor. The assessors were asked to evaluate the cheese attributes on a non-structural linear scale and to rinse out their mouth with water and eat cucumber between samples. The tasting duration of each type of cheese was about 20 minutes and the break time was 5 minutes. The total duration of a session was 2,5h. The average responses over replicates and assessors were used in the multivariate analyses (PCA, PLSR). Consumer test A total of 120 regular cheese consumers, who were “naive” in that they had no training in sensory evaluation, expressed their preference for each of the seven fondue cheeses studied. The cheeses were evaluated for overall degree of preference of these cheeses on a 9-point hedonic scale anchored with “Like extremely” and “Dislike extremely” at either end. The cheeses were prepared at the standard described above. Spring water and cucumber were supplied for cleansing palates between samples. All the panels performed the tests in the sensory laboratory. No more information concerning the products or the experiment was given. All participants had answered a questionnaire about their age and gender. Additionally consumption data were also collected on all respondents. 4. Statistical analysis The results were analyzed by Analysis of variance – ANOVA - (using SAS 8.1 for Windows) in order to determine whether originality of cheeses had significant effects on cheese profile and cheese preference. The ANOVA model was S8*A3*B7*C25 (S: subject factor; A: replication factor; B: product factor; C: attribute factor). The t-student had been used to determine the difference of one attribute among the studied products. The means of the intensity of each attribute and each type of cheese were gathered a matrix T (m, n), where m is the number of product (m = 7) and n is the number of attribute (n = 25), was analyzed by Principal Components Analysis (PCA) and Hierachical Classification Analysis (HCA) in order to specify the correlation among sensory properties and the correlation among these products. The Partial Least Squares Regression (PLS) had been used to figure out the relation between the descriptive data and the preference scores of consumers. All analyses were performed by SAS® version 8.1 and SPAD® version 4.5. 7 III. RESULTS 1. Profile of Fondue cheeses a. Sensory vocabulary The 38 sensory terms (sensory attributes) were collected from various materials and from the panels. After reductions, the remaining list of sensory attributes contained 25 terms. These terms were divided in 5 categories as follows: Appearance (Color, brightness, flexibility), Odor (Cream, milk, cooked, rancid, butter, lactic, overall odor intensity), Taste (sweetness, sourness, bitterness, saltiness), Mouth-feel (Firmness, solubility, fineness, stickiness, elastic, variety of aroma, fatness), Aftertaste (sweet, sour, bitter, salty). b. Profile of fondue chesses The profile of 7 studied cheeses is expressed in Figure 1. The ANOVA results showed a significant difference among the 7 cheeses (F6,144 = 3.41; p < 0.01). The results also indicated a stability of the panels through 3 replicates (p < 0.001). Among the 7 cheeses studied, the overall odor intensity of Bridel was highest, Kiri was characterized by strong lactic and milk odor. La vache qui rit and Picon were the most salty and finest texture. The intensity of firmness, butter odor and sweetness of Party cubes was highest. President was characterized by fatness and “Bo deo no” by stickiness. Bitter aftertaste Color 10 Brightness Flexibility Sour aftertaste 8 Salty aftertaste Cream odor 6 Sweet aftertaste Milk odor 4 Cooked odor Fattiness Bridel 2 Kiri Rancid odor Variety of aroma 0 LVQR Party cubes Picon Butter odor Stickiness President Bo deo no Lactic odor Fineness Overall odor intensity Solubility Elastic Sweetness Firmness Sourness Saltiness Bitterness Figure 1. Conventional Profile scores of 7 fondue cheeses A map of the Attributes of the 7 cheeses on the first plan of PCA (variance explained 62%) was expressed in Figure 2. The results showed that sensory properties of the 7 cheeses were classified into 4 opposite groups: Group 1 (milk odor, lactic odor), Group 2 (sourness, sour aftertaste, solubility), Group 3 (firmness, stickiness and flexibility), and Group 4 (included the remaining attributes, mainly odor attributes). There were close correlations among sensory attributes, for example milk odor and lactic odor; brightness, cream odor, butter odor and variety of aromas. HCA analysis indicated that the 7 cheeses were principally classified into 4 groups (Figure 3). The numbers in Fig. 3 are expressed accumulated variances of classification of all products. The higher the number, the more significant the classification. The fist group was Kiri (coded 2), the second group contained Picon, Party cubes, La vache qui rit (coded 5, 4, 3), the third group was “Bo deo no” (coded 7); and the last group was President and Bridel (coded 6, 1). 8 Classification hierarchique directe 2 5 2.06 9.88 4 2.48 3 4.11 7 5.26 6 1.22 1 Figure 3. Cluster analysis of 7 fondue cheeses Figure 2. PCA-attribute map dimensions 1 and 2 Bo deo no President Picon Party cubes LVQR Kiri 8 7 6 5 4 3 2 1 0 Bridel Preference score Characteristic properties of each group of cheese are indicated in Figure 4. The characteristic property of Bridel was a sweet aftertaste and stickiness ; Kiri was milk odor and lactic odor; La vache qui rit and Picon were fineness, elasticity, color, saltiness, salty aftertaste; Party cubes was butter odor, sweetness, cream odor, brightness and rancid odor; President was fatness, firmness, stickiness; and “Bo deo no” was stickiness, flexibility. Product Group 1 Figure 4. PCA biplot of sensory properties and cheese products Group 2 Figure 5. Overall degree of preference of 2 groups 2. Consumer preference The Pearson correlations, among preference attributes, showed significant correlations (P < 0.01) between the overall degree of preference. Average preference of most cheeses was preferred at an above average level (from 5.70 to 6.51 points), and “Bo deo no” - cheese made in Vietnam - was preferred to La vache qui rit and graded at the same level with 3 types of cheese made in France. 9 Analysis clustering (HCA) and the result of the t-student analysis showed that the customers were principally classified into 2 groups with characters as follows: - Group 1: 48.31% males and 51.69% females; young people (< 25 ages) were 49.44%; the frequency of using cheese was high - Group 2: 32.26% males and 67.74% females; young people (< 25 ages) were 67.74%; the frequency of using cheese was lower than group 1. The overall degree of preference of the 7 cheeses of 2 consumer groups was performed in Figure 5. The overall degree of preference of group 1 (> 6 points) was higher than degree of group 2 (< 6 points). These results suggested that the cheese preference might be proportioned to the frequency of cheese consumption. Besides, “Bo deo no” - cheese made in Vietnam - was rated quite highly by both groups at an above average level (5.8 points). This reflects that this product is suitable for Vietnamese consumers, irrespective of age or gender. This is good news for Vietnamese cheese producers. PLS regression by overall degree of preference scores on data matrix showed that a linear model could explain the overall degree of preference from the answers of the study groups (120 people). The result was that the characteristics contributed positively to the preference of consumers in 2 groups were lactic odor, butter odor, and firmness. The attributes which reduced the consumer preference included bitterness and bitter aftertaste. Furthermore, the results also indicated that butter odor, lactic odor, the variety of aromas, firmness and fatness correlated positively to the preference of the consumer in Group 1. Color, brightness, bitterness, elasticity, salty aftertaste and bitter aftertaste were negative attributes for this consumer group. 0.6 Fatty 0.5 0.4 Variety of aroma 0.3 Butter odor 0.2 Flexibility Firmness Stickines Lactic odor 0.1 0 -0.1 -0.2 Color Brightness Milk odor Bitterness Elastic Overall odor A-saltiness A-bitterness -0.3 Group 1 Group 2 Figure 6. PLS regression of the descriptive profiling data and the preference scores for consumers For group 2, the positive attributes were flexibility, butter odor, lactic odor, firmness and stickiness. Otherwise, milk odor, overall odor intensity, bitterness and bitter aftertaste diminished the individual’s preference. This result initiated a new approach to the ideal model of fondue cheese, for further research concerned with quality and the processing of cheese. 10 IV. CONCLUSION In the summary, the study showed that 25 attributes are an essential part of the fondue cheese descriptions. Seven studied cheeses were classified in 4 groups with their corresponding characters: Group 1 (Kiri), Group 2 (Bridel and President), Group 3 (La vache qui rit, Party cubes, Picon) and Group 4 (Bo deo no). The overall degree of preference of 7 cheeses was rather clear, at an above average level (> 5.7/9 points) and was graded according to degree of preference as follows: Party cubes, President, Kiri, Picon, Bo deo no, Bridel and La vache qui rit. The “Bo deo no” - cheese made in Vietnam – was highly rated at 5.86 points. The regression analysis indicated that the most preferred attributes of the 7 above cheeses were lactic odor, butter odor, and firmness. Vietnamese consumers disliked bitterness, and a bitter aftertaste in all studied products. The results of this study initiated the new approach to the ideal model of fondue cheese for the other researches concerned with quality and the processing of cheese. Acknowledgment. Special thanks for Nguyen Thi Lan Anh, Nguyen Thi Minh Tu, Nguyen Ba Thanh and Cung To Nga for their precious help in consumer tests and thanks to all assessors for their participation. REFFERENCES 1. International Standard, ISO 6564:1985 - Sensory analysis – Methodology – Flavour profile methods. 2. International Standard, ISO 8586-1:1993 - Sensory analysis – General guidance for the selection, training and monitoring of assessors. 3. International Standard, ISO 8589:1998 - Sensory analysis – General guidance for the design of test rooms. 4. B. A. Law - Technology of cheese making, CRC Press, Sheffield, England, 2002. 5. R. Mc Bride, D. D. Muir - The grading and sensory profiling of cheese, CRC Press, Sheffield, England, 2001. 6. J. M. Murray, C.M. Delahunty, and I. A. Baster - Descriptive sensory analysis: past, present and future, Food research International 34 (2001) 461-471. 7. H.D. Nguyen, Ha D.T., and D. Luu - The role of sensory evaluation in food quality management and development, Proceedings of the 8th Asian Food Conference, Hanoi, 2003, 862-866. 8. C. Salles, S. Dalmas, and C. Septier - Production of a cheese model for sensory evaluation of flavor compounds, Le Lait 75 (6) (1995). 9. P. Walstra, T. J. Geurts, A. Noomen, A. Jellema, and Van Boekel - M. A. J. S., Dairy Technology: Principles of Milk, Properties and Processes, USA, 1999, 539-708. 10. T. X. Vu - The habit of using cheese of customers in Ha Noi and Ho Chi Minh City, Industrial Journal 22 (2004) 37-39. SUMMARY The objective of this study was to analyze the sensory properties and to assess the preference of consumer in Hanoi for 7 types of fondue cheese (Bridel, Kiri, La vache qui rit, 11 Party cubes, Picon, President and “Bo deo no”). Two tests have been carried out: the descriptive test and the preference test. In the former, a trained panel of 8 members indicated that there were 25 profiled attributes of fondue cheese which have been used with high frequency and described exactly sensory quality of these types of cheese. The results of univariate and multivariate data analyses showed a significant difference among the cheese samples, and the 7 evaluated types of cheese could be separated into 3 groups with their characterized properties. In the preference test, a consumer panel of 120 assessors assessed the consumer preference of these 7 types of cheese on a 9-point scale (1-extremly dislike, 9-extremly like). The result was that these 7 types of cheese were preferred at an above average level. Hierarchical Classification Analysis (HCA) indicated that there were 2 consumer groups with different preferences and the overall preference of the consumer depended on the frequency of product use. Partial Least Squares Regression Analysis (PLS) showed the correlation between sensory properties and the consumer preference for a class of fondue cheese. An ideal model of fondue cheese for Vietnamese consumers had been initiated in order to aid in studies of consumer acceptability. Key words: descriptive analysis, fondue cheeses, consumer preference NGHIÊN C�U TÍNH CH�T C�M QUAN VÀ TH� HI�U NGƯ�I TIÊU DÙNG ��I V�I PHO MÁT NÓNG CH�Y T�I TH� TRƯ�NG HÀ N�I Nghiên c�u này t�p trung phân tích các tính ch�t c�m quan và th� hi�u c�a ngư�i tiêu dùng Hà N�i ��i v�i 7 lo�i pho mát nóng cháy (Bridel, Kiri, La vache qui rit, Party cubes, Picon, President và Bò �eo nơ). Hai phép th� c�m quan �ã �ư�c th�c hi�n là phép th� mô t� và phép th� th� hi�u. Thông qua s� phân tích c�a h�i ��ng g�m 8 thành viên �ã qua hu�n luy�n, chúng tôi �ã tìm �ư�c 25 thu�c tính c�m quan c�a pho mát nóng ch�y �ư�c s� d�ng v�i t�n su�t cao nh�t và mô t� chính xác tính ch�t c�m quan c�a nhóm pho mát này. K�t qu� phân tích s� li�u �ơn và �a bi�n �ã ch� ra r�ng các m�u pho mát khác nhau có ngh�a, và 7 m�u này có th� �ư�c phân chia thành 3 nhóm v�i các tính ch�t c�m quan ��c trưng. Trong phép th� th� hi�u, chúng tôi m�i 120 ngư�i th�, tham gia �ánh giá m�c �� ưa thích ��i v�i 7 s�n ph�m trên thang th� hi�u 9 �i�m (v�i 1 là c�c kì không thích và 9 là c�c kì thích). K�t qu� phân tích cho th�y c� 7 s�n ph�m ��u �ư�c �ánh giá trên m�c �� trung bình (5 �i�m). Phép phân tích phân nhóm theo th� b�c (HCA) ch� ra r�ng có 2 nhóm ngư�i tiêu dùng có m�c �� ưa thích khác nhau và m�c �� ưa thích chung ��i v�i s�n ph�m c�a h� ph� thu�c vào t�n su�t s� d�ng s�n ph�m. K�t qu� c�a phân tích h�i quy bán ph�n nh� nh�t (PLS) ch� ra m�i tương quan gi�a tính ch�t c�m quan và m�c �� ưa thích c�a ngư�i tiêu dùng ��i v�i các s�n ph�m pho mát nóng ch�y. Mô hình lí tư�ng c�a pho mát nóng ch�y c�a ngư�i tiêu dùng Vi�t Nam �ã bư�c ��u �ư�c hình thành, k�t qu� này s� góp ph�n h� tr� nh�ng nghiên c�u v� m�c �� ch�p nh�n c�a ngư�i tiêu dùng ��i v�i s�n ph�m. 45a ch6: ��i h�c Bách khoa Hà N�i. 12 Nh8n bài ngày 12 tháng 4 n;m 2004