Journal of Sensory Studies ISSN 0887-8250 FLAVOR OF COOKED CATFISH (PANGASIUS HYPOPHTHALMUS) FILLETS AS PREDICTION FROM RAW FRESH AND FROZEN-TO-THAWED joss_363 12 25 UYEN T.X PHAN and DZUNG H NGUYEN2,3 Institute of Biotechnology and Food Technology, Ho Chi Minh City University of Industry, Ho Chi Minh-City, Vietnam Faculty of Chemical Engineering, Ho Chi Minh City University of Technology, Ho Chi Minh-City HCM, Vietnam Corresponding author TEL: +84-908191277; FAX: +84-8-38636984; EMAIL: dzung@hcmut.edu.vn Accepted for Publication November 9, 2011 doi:10.1111/j.1745-459X.2011.00363.x ABSTRACT This study aimed to develop a lexicon of sensory descriptors for Vietnamese catfish (Pangasius hypophthalmus) fillet products, and to investigate the use of sensory characteristics of raw and frozen fillets to predict the flavor of cooked catfish fillets Descriptive Analysis (DA) was applied by a panel of 11 trained panelists to samples of raw fresh fillets and frozen fillets at three stages: frozen, thawing and thawed Samples were also cooked at 200C for 25 to evaluate their flavor A lexicon of sensory attributes was generated for three types of samples: raw fresh, frozen-to-thawed and cooked The validity of this lexicon has been discussed Raw fresh and frozen-tothawed samples were shown to be predictors for sensory characteristics of cooked samples Sensory quality of catfish fillets was indicated by textural properties and flavors more than appearances and colors PRACTICAL APPLICATIONS This study provides Pangasius processors with sensory lexicons of Pangasius fillets to support the development of their quality control plans The study also provides producers and purchasers with methodological guidelines for making prediction of flavor of Pangasius products at different phases of the processing: raw fresh, frozen, thawed and cooked INTRODUCTION According to the Pangasius Aquaculture Dialogue of World Wildlife Fund in 2010, pangasius farming is the world fastest growing type of aquaculture The production has increased dramatically from approximately 400,000 tons in 2005 to 825,000 tons in 2006 and reached million tons in 2007, according to the Vietnam Association of Seafood Exporters and Producers (World Wildlife Fund [WWF] 2010b) Pangasius is primarily farmed in Asia, mostly in Vietnam whose world market share was 89% in 2005 and whose exported value was $737 million in 2007 (WWF 2010a) Vietnam, however, is facing strong competition from many other catfish producing countries, such as Indonesia, China and the U.S.A According to the World Market and Trade report of USDA (2008), U.S fish and seafood exports topped $4 billion, and China remained the top fish and seafood exporter with the exported value of more than $8.5 billion in 2007 There12 fore, to be well competitive, Vietnamese pangasius products need (1) to meet international quality standards such as Codex Alimentarius, Association of Official Agricultural Chemists, American Society for Testing and Materials (ASTM) or EU standards; and (2) to possess outstanding typical properties These goals could be achieved through an appropriate sensory quality program Sensory evaluation has been often used in the fishing industry as a part of quality control management to ensure that the products will meet certain standards or consumers’ expectations (see Simeonidou et al 1997; Codex Alimentarius 2001; Pons-Sánchez-Cascado et al 2006) However, the most concern of a sensory program in fishery is always the quality of freshness Methods have been developed specifically for judging freshness by smell, color, appearance, taste and texture They include the EU scheme (Man and Jones 2000), Quality Index Method (QIM) (Martinsdóttir et al 2001) and Torry scheme (Man and Jones 2000) These Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc U.T.X PHAN AND D.H NGUYEN schemes have been proven to have many advantages in practice, especially in making purchase decision However, these systems are problematic in the sense that they give a single numerical value to a broad range of characteristics QIM, for instance, evaluates the freshness of fish using only one indicator, the quality index, which is the sum of the scores for all characteristics such as the eyes, skins and gills This system groups attributes with major changes into one grade, regardless their difference in nature QIM scheme for cod, for instance, groups “fresh, seaweedy, and metallic” with score of 0; “yeast, bread, beer, sour milk” with score of 2; “acetic acid, sulfuric, very sour” of score (Martinsdóttir et al 2001) Grading systems, therefore, are only useful to deal with quality standards but not appropriate for investigating sensory typical characteristics of fishery products Descriptive Analysis (ASTM International 1992; ISO 2003), on the other hand, is recommended as a good tool for quality control and product development According to Stone (1992), the method is based on the principle of a panelist’s ability to verbalize perceptions of a product in a reliable manner The best advantage of descriptive analysis is that it allows an integral understanding of the sensory characteristics of the product In fishery industry, many attempts have been made to apply descriptive analysis in quality programs of catfish products Yet, no standard application was done Suvanich and Marshall (1998), instead of a fully trained panel, used an experience panel with only h of training to examine the quality of catfish frames The authors also adapted the terminology from studies of Huss (1988) and of Pigott (1988), which focused more on detecting products’ spoilage Furthermore, fishery processors tended to use descriptive analysis and expert tasters to examine sensory acceptance/rejection as well as freshness/deterioration of their products (Harewood 1996; Bal’a et al 1996; Mai et al 2007) This approach, however, was inappropriate, as people like food flavors, not discrete sensory properties (Prescott and Murphy 2009) This inappropriateness has been long pointed out in literature, resulting in a wide application of acceptance testing with consumers (Sidel et al 1981; Lawless and Heymann 2010; Prescott et al 2011) One of the most common applications of descriptive analysis is to develop flavor lexicon for food products, due to the great benefit such lexicon can bring to the product development and quality control Drake and Civille (2002) stated that flavor lexicons can be used to record and define product flavor, compare products, and determine storage stability, as well as interface with consumer liking and acceptability and chemical flavor data These benefits of sensory lexicon were concluded in Lee and Chambers (2007) study of green tea A number of lexicons have been recently developed for a variety of food and nonfood products, Western European cheeses (Talavera-Bianchi and Chambers 2008), lip products (Dooley et al 2009), almond (Civille et al 2010), brewed coffee Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc FLAVOR PREDICTION OF PANGASIUS FILLETS (Hayakawa et al 2010a), French bread in Japan (Hayakawa et al 2010b), fresh leafy vegetables (Talavera-Bianchi et al 2010), beef (Adhikari et al 2011) to name but a few Therefore, a lexicon of pangasius sensory properties will definitely help processors, researchers and consumers to identify the common characteristics of pangasius products, acknowledge the on/off-flavors and identify the properties that are appealing to a specific market segment Another issue is that consumers often have to make purchase decision for raw catfish fillets (included fresh, frozen or thawed) but consume the cooked ones Some attempts have been made to investigate the possibility of making prediction for quality of cooked product from quality of raw product Rødbotten et al (2009) have productively applied descriptive analysis to demonstrate the quality of raw salmon fillet as a predictor of cooked salmon quality Prediction models for cooked sensory attributes of shrimps from raw sensory attributes were also made by Erickson et al (2007) These accomplishments encourage a similar prediction could be made for catfish fillet products, to assist purchasers in making purchase decision Given that, the present study aimed to develop a lexicon of sensory properties for catfish (Pangasius hypophthalmus) fillets, using QDA procedure This study also aimed to examine sensory characteristics of raw catfish fillets (fresh and frozen) as predictors of sensory properties of cooked catfish fillets The findings were expected to allow pangasius processors and purchasers to select pangasius fillet sources based on their products’ consistent sensory attributes and support the development of control plans before exportation, or create innovative products with specific organoleptic characteristics (Phan et al 2011) The lexicon, in addition, would be greatly helpful to product developers, researchers and technologists in understanding the sensory characteristics of pangasius fillets produced in Mekong Delta, the most important region for catfish farming in Vietnam (Nguyen et al 2007) MATERIALS AND METHODS Samples Samples used in this study were supplied by four different manufacturers in Mekong Delta and one manufacturer in Ho-Chi-Minh City in Vietnam These five factories were coded as Mekong1, Mekong2, Mekong3, Mekong4 and HCMC The samples included six raw fresh and 10 frozen products with different storage lengths of months, months and no storage Raw fresh fillets were evaluated in two sample types: raw and cooked (200C, 25 min, wrapped in aluminum foil) Frozen fillets were assessed in four sample types: frozen (evaluated right after taken from the freezer), thawing (45 after taken from the freezer), thawed (completely 13 FLAVOR PREDICTION OF PANGASIUS FILLETS U.T.X PHAN AND D.H NGUYEN TABLE DETAILED DESCRIPTION OF CATFISH FILLET SAMPLES USED IN THE STUDY Storage Sample name Type Sampling place Condition Storage time F-Mekong1 F-Mekong2 F-Mekong3 F-HCMC1 F-HCMC2 F-HCMC3 Fr-Mekong1-0T Fr-Mekong1-3T Fr-Mekong1-6T Fr-Mekong2-0T Fr-Mekong2-3T Fr-Mekong2-6T Fr-Mekong3-0T Fr-HCMC1-3T Fr-Mekong4-3T Fr-Mekong4-6T Fresh Fresh Fresh Fresh Fresh Fresh Frozen Frozen Frozen Frozen Frozen Frozen Frozen Frozen Frozen Frozen Cao Lanh – Mekong delta Sa Dec – Mekong delta Tien Giang – Mekong delta Ho Chi Minh city Ho Chi Minh city Ho Chi Minh city Cao Lanh – Mekong delta Cao Lanh – Mekong delta Cao Lanh – Mekong delta Sa Dec – Mekong delta Sa Dec – Mekong delta Sa Dec – Mekong delta Tien Giang – Mekong delta Ho Chi Minh city Can Tho – Mekong delta Can Tho – Mekong delta 0–4C 0–4C 0–4C 0–4C 0–4C 24 h 24 h 24 h 24 h 24 h No storage a No storage b months months No storage b months months No storage b months months months -18C -18C -18C -18C -18C -18C -18C -18C -18C -18C a Sample was evaluated right after filleting, at ambient temperature b Due to transportation to the sensory laboratory, samples were, in fact, stored at (-18)C in about 12 h before evaluation thawed at room temperature) and cooked (200C, 25 min, wrapped in aluminum foil) Information about each fillet product is shown in Table both surfaces have melted completely, facilitating the observation of color and fiber of the fillet Thawed Samples Sample Preparation and Serving (Codex Alimentarius 2001) Raw Fresh Samples Five fresh samples, preserved in ice, were delivered to the sensory laboratory in 10 h after filleting at the suppliers’ production plants These samples were then stored in a refrigerator (Toshiba GR-S22VPT/VT) at 0–4C overnight On the test day, these fillets were taken out of the fridge about h before the evaluation to let the sample temperature reach to the room temperature, which was 22–25C The sixth sample was purchased at a local market and was filleted at the sensory laboratory on the day of testing This sample was then served directly to the panel Frozen Samples These samples were received 24 h before evaluation and were stored in a freezer (Sanyo Freezer HF-S6L) at (-18) C overnight Frozen samples were evaluated immediately after taken from the freezer The panel had to evaluate all six the attributes of these samples within Thawing Samples The frozen samples were let to thaw at room temperature in 45 At the point of evaluation, the sample’s ice layers on 14 The frozen samples completely thawed at room temperature This process took about 1.5 h Raw fresh, frozen, thawing and thawed samples were served in disposable, odor-free, oval plastic plates (L340 ¥ W245 ¥ H25 mm, THH Co LTD, Vietnam) labeled with the appropriate three-digit code Cooked Samples This type of sample was prepared by cutting each fillet into three parts: head, middle and tail The middle part (about 50 mm length for big-size fillet) was wrapped in aluminum foil and cooked in an oven (Sanaky VH 50N, 1300 W) at 200C in 25 Cooked samples were served hot in disposable, odor-free, round plastic plates (d = 160 mm, THH Co LTD, Vietnam), coded by the random three-digit number Descriptive Panel (ISO 8586-1, 1993) A screening questionnaire has been distributed to the student, and faculties of two colleges The questionnaire asked about their food habit, any allergy they might have with fish and seafood products, if they smoke, health status and their availability for the project (they need to have commitment for at least months) Thirty-seven candidates (12 faculties and 25 students) were qualified to go to the next selection process Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc U.T.X PHAN AND D.H NGUYEN This process included two test sessions, each comprised of four tests The first session included basic taste detection test, ranking test on sweetness, two ranking tests on color and odor description The second session included ranking test on umami taste, texture description and taste matching All candidates were ranked from first to 37th based on their total scores in all eight tests Eleven panelists were chosen using following criteria: high total scores, not score zero in any test and high score in odor and texture description tests The panel had three h sessions for product orientation, each session dedicated to one of three types of samples: fresh, frozen (included three states: frozen, thawing and thawed) and cooked During the orientation, the panel manually generated as many as possible descriptors of odor, appearance and texture for raw fresh and frozen samples For cooked sample, the panelists opened the aluminum foil and sniffed the sample to develop odor/aroma descriptors Then they tasted the sample to develop descriptors for oral textural properties, taste and mouthfeel The product frame of reference included neither catfish beyond the samples in the study nor aged samples After completing the orientation sessions, the panel participated in a 55 h training course (about h per week), to improve their ability of detection and discrimination of sensory properties of fresh, frozen and cooked fillets, based on the descriptors generated above The panelists were trained to estimate the intensity of the sensory attributes using a line scale of 100 mm, anchored with “very weak” and “very strong” at two ends The panelists’ performances were monitored during the training phase and the testing phase The panel was required to reach the consensus in understanding and evaluating the attributes Panel agreement was evaluated by examining the interaction between panelists and the products in an ANOVA model Panel’s repeatability was also tested to assure that panelists could repeat their evaluation in different testing sessions Test Procedure A descriptive analysis procedure was adapted as the test method Evaluation took place at the Sensory Laboratory at Ho Chi Minh City University of Technology,Vietnam Testing environment was put under control for distracting factors such as temperature (22–25C), lighting (fluorescent only), odor (free of extraneous odor) and noise A total of six raw fresh, 10 raw frozen and 16 cooked samples (made from both raw and frozen fillets) were evaluated in three replicates, resulting in 96 sample trials The panel, on average, completed 12 sample trials per one h session In total, eight evaluation sessions have been conducted In each evaluation session, the panel was randomly served one sample at a time to estimate the intensity of all sensory attributes of the sample on a line scale of 100 mm, anchored by “very weak” and “very strong.” Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc FLAVOR PREDICTION OF PANGASIUS FILLETS References were also provided during testing The panelists tasted only the cooked sample to evaluate taste, mouthfeel and oral textural characteristics Data Analysis Multiple Factor Analysis (MFA) (Pagès 2004) was used to investigate the relationship between groups of properties of raw, frozen and cooked fillets Principal Component Analysis (PCA) was performed to the mean scores of sensory attributes of cooked samples to investigate the correlation between color attributes and flavor of cooked fillets These analyses were performed using R 2.10.0 (R Development Core Team 2007) and the SensoMineR (Lê and Husson 2008; Husson and Lê 2009) and FactoMineR packages (Husson et al 2007; Lê et al 2008) RESULTS AND DISCUSSIONS Sensory Lexicon of Catfish Fillets Produced in Mekong Delta of Vietnam Three sensory lexicons have been developed to describe catfish fillets corresponding to a sequential process from raw to frozen, thawing, thawed and cooked The descriptive procedures, basically, followed those for the quantitative descriptive method (Stone 1992) All descriptors were relevant to products, redundancy eliminated and discriminative Definition, references and evaluating procedure were also developed for each attribute by agreement The validation of these lexicons has been confirmed by referring to precedent studies and Codex guidelines for the sensory evaluation of fish and shellfish in laboratories (Codex 2001) However, while Codex only gives example of general attributes for a broad fishery product category, our study has gone further and more specific in describing all possible sensory aspects of catfish fillets, covered all phases of raw, frozen, thawing, thawed and cooked Raw Fresh Samples Raw fresh fillets were described by 22 descriptors, included five appearance properties, five colors, seven odors and five textural attributes (Table 2) The appearance attributes such as smoothness and fat leftover reflected the professional of the filleting process Fresh catfish fillet was mainly white and pink, but some samples exposed yellow and orange The brown-red color was only distributed at the flesh along the backbone of the fish This was also an indicator for the filleting professional since market fillet product should not contain any red meat Raw fresh catfish possessed aromatic notes associated with the growing (i.e., algae, sulfurous and ammonia) and processing (i.e., oxidized fat) conditions Raw 15 FLAVOR PREDICTION OF PANGASIUS FILLETS U.T.X PHAN AND D.H NGUYEN Category Attribute Description of attribute Reference Appearance Thickness Thickness of the fillet, especially the middle part Smoothness of the surface Fat quantity along the spine and edges of the fillet NA Smoothness Fat-leftover Color Odor Fiber-curvature Curvature of fiber on both faces of the fillet Fiber-sharpness Sharpness of fiber on both faces of the fillet White Pink Yellow Reddish brown Orange Fishy The whiteness of the flesh The pink color of the flesh The yellow color of the flesh The brownness with some red The orange color of the meat Odor associated with aged fish, as demonstrated by trimethylamine Odor associated with the blue-green algae growth in the pond water Odor associated with smell of raw clam Odor associated with sulfur smell in boiled aged egg Odor associated with ammoniac gas Odor associated with fish fat Odor associated with oxidized fish fat Easy to be deformed Mechanical textural attribute relating to the rapidity of recovery from a deforming force Textural attribute relating to the force required to achieve a given penetration of the fillet Textural attribute relating to the degree to which the fillet can be deformed before it breaks Water content in the fillet Algae Raw clam Sulfurous Ammonia Fat Oxidized fat Texture Soft Elastic Firm Cohesive Moist TABLE SENSORY ATTRIBUTES (n = 22) OF RAW FRESH CATFISH FILLETS THE SAMPLES WERE FILLETED AND KEPT IN ICE NO LONGER THAN 24 H BEFORE EVALUATION Soft tofu Picture of fillet extreme in this attribute, in agreement of the panel Picture of fillet extreme in this attribute, in agreement of the panel Picture of fillet extreme in this attribute, in agreement of the panel White paper Pink paint Yellow paint Color of beef Orange juice Fish liver oil Algae in pond Raw clam 10-day aged egg Ammonia Fat taken from catfish belly Fish belly fat kept for about h at room temperature Soft tofu Hard tofu Jelly candy Hard tofu Soft tofu NA, Non applicable catfish fillet was identified as soft, elastic, cohesive and moist in texture It was also characterized as firm This term, however, was not opposite to soft Instead, these two terms characterized two different textural dimensions Soft referred to the ease of deformation, and firm related to force resistance 16 Frozen Samples Frozen ones were characterized by seven descriptors for frozen phase (mostly appearance and color) (Table 3), six descriptors for thawing phase (only appearance and color) (Table 4) and nine descriptors for thawed phase (only texture Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc U.T.X PHAN AND D.H NGUYEN TABLE SENSORY ATTRIBUTES (n = 7) OF FROZEN CATFISH FILLETS FLAVOR PREDICTION OF PANGASIUS FILLETS Category Attribute Definition Reference Appearance Equality of glaze The equality of ice on both sides of the fillet Quantity of ice Quantity of ice flakes on both sides of the fillet Fiber-sharpness Sharpness of the fiber on both sides of the fillet White Pink Yellow Fishy White Pink Yellow Odor associated with aged fish, as demonstrated by trimethylamine Picture of fillet extreme in this attribute, in agreement of the panel Picture of fillet extreme in this attribute, in agreement of the panel Picture of fillet extreme in this attribute, in agreement of the panel White paper Pink Yellow Fish liver oil Color Odor was described) (Table 5) At frozen phase, the fillets did not expose any aromatic notes but fishy Since fillet was covered by ice, colors were barely exposed At thawing phase, the ice surface of the fillet has melted completely, facilitating color and fiber evaluation However, the fillet was still very firm and cold, which suppressed any noticeable odor Color and appearance attributes of thawing phase were also found in thawed phase Frozen catfish fillet, after thawed, possessed similar aromatics and textural properties to raw fresh fillets However, aged-frozen fillets were perceived stronger in odors such as fishy, ammonia, sulfur and softer and less elastic than raw fresh fillets Cooked Samples Cooked samples were profiled by 18 descriptors, included four colors, five odors, five oral textural properties and three tastes/mouthfeel (Table 6) Some of the attributes were found in both odor/aroma and flavor in the mouth, i.e., fishy, fat and boiled chicken The panel has come to agree to list those attributes in the odor/aroma category, since those attributes were more intense when perceived orthonasally than retronasally Boiled shellfish, boiled chicken, boiled egg, fat aromatic and ammonia were perceived strongest when the aluminum foil was just opened About 10 later, only fishy remained In general, cooked fillets were mild in flavor and aromatic They were slightly salty but more “savory” (umami taste) and TABLE SENSORY ATTRIBUTES (n = 6) OF THAWING CATFISH FILLETS fatty Boiled chicken was the most intense note in terms of intensity comparing to other aromatics Catfish were also found to be soft, moist, flaky and slightly cohesive but less chewy in texture Chambers and Robel (1993) have developed an extensive flavor and texture lexicon for freshwater fish including pond-raised and raceway-raised channel catfish from Kansas and Mississippi The authors reported that catfish has a full base flavor in which earthy is one of the keynotes This attribute, however, was not present in our lexicon for cooked fillet Instead, boiled-egg note was reported This note associated with the sulfurous smell in boiled-aged egg It was reminiscent of decaying vegetation note in the “muddy” flavor group reported in Chambers and Robel (1993) Other similarity was also found, such as boiled-chicken note in our lexicon could be related to corn-like, nutty/buttery, white meat and sweet aromatic; fat aromatic related to oily aromatic; fishy to fresh fish in Chambers and Robel’s lexicon Besides, similar textural terms, such as flaky, juicy, cohesive, chewy (chew count) were reported in both studies Our lexicon was also consistent with the lexicon of pond-raised catfish documented in Johnsen et al (1987), which comprised similar descriptors such as boiled chicken, cardboard (oxidized fats and oils),and salty The fish in our study possessed sensory properties similar to southern flounder, reported in Drake et al (2006) Both catfish and flounder possessed aromatics associated with chicken broth, fresh fish, earthy, fat and slightly salty The only common in odor Category Attribute Definition Reference Appearance Fiber density Fiber curvature Red Pink Yellow Orange Density of fiber on the fillet Curvature of fiber Redness of the flesh along the spine Pink Yellow Orange Catfish fillet Catfish fillet Red Pink Yellow Orange juice Color Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc 17 FLAVOR PREDICTION OF PANGASIUS FILLETS U.T.X PHAN AND D.H NGUYEN Category Attribute Definition Reference Odor Fishy Odor associated with aged fish, as demonstrated by trimethylamine Odor associated with sulfur smell in boiled-aged egg Odor associated with ammonia Odor associated with fish fat Easy to be deformed Mechanical textural attribute relating to the rapidity of recovery from a deforming force Textural attribute relating to the force required to achieve a given penetration of the fillet Textural attribute relating to the degree to which the fillet can be deformed before it’s broken Water-content in the fillet Smoothness of the fillet surfaces Fish liver oil Sulfurous Ammonia Texture Fat Soft Elastic Firm Cohesive Moist Smooth TABLE SENSORY ATTRIBUTES (n = 10) OF THAWED CATFISH FILLETS (THAWED AT ROOM TEMPERATURE) Boiled-aged egg Ammonia Fat in the belly of catfish Soft tofu Hard tofu Jelly candy Boiled chicken meat Soft tofu Soft tofu TABLE SENSORY ATTRIBUTES (n = 18) OF COOKED CATFISH FILLETS SAMPLES WERE WRAPPED IN ALUMINUM FOIL AND COOKED IN OVEN AT 200C IN 25 MIN Category Attribute Definition Reference Color White Pink Yellow Gray Boiled shellfish Boiled chicken Boiled egg Fat Fishy White Pink Yellow Gray Odor associated with boiled shellfish Odor associated with boiled chicken Odor associated with boiled-aged egg Odor associated with cooked fish fat, evoke greasy perception Odor associated with aged fish, as demonstrated by trimethylamine Odor associated with ammonia Easy to be deformed Capacity of easily forming flake of the fiber Numbers of times required to chew a piece of sample to the state ready to swallow Textural attribute relating to the degree to which the fillet can be deformed before it breaks Water content in the fillet The taste on the tongue associated with glutamate ions The taste on the tongue associated with sodium ions The mouthfeel described as greasy and associated with fat White paper Pink Yellow Gray Boiled shellfish Chicken stock Boiled-aged egg Cooked fish fat Fish liver oil Odor/aroma Oral textural properties Ammonia Soft Flaky Chewy Cohesive Taste Mouthfeel Moist Umami Salty Fatty Chinese steamed bun (baozi) Soft tofu NA Boiled chicken, ¥ cm cube Boiled chicken NA Monosodium glutamate (MSG) Monosodium chloride Boiled catfish fat NA, non applicable 18 Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc U.T.X PHAN AND D.H NGUYEN between catfish in our study and farmed cod reported in Sveinsdóttir et al (2010) was the aroma associated with trimethylamine and sulfur However, these two fish were similar in many of textural characteristics In addition, sensory properties of catfish were fundamentally different from those of salmon (Green-Petersen et al 2006) and ocean fish due to its white meat character (Chambers and Robel 1993) In aquaculture quality control, it’s very important to detect off-flavors of a fishery product, since this defect jeopardizes consumer satisfaction and future purchase Therefore, projects in aquaculture often focus on testing and managing off-flavors in fishery products Van der Ploeg (1991), from the perspective of flavor quality control, has developed a flavor wheel for channel catfish, consisting of six categories of flavor descriptors, i.e., acceptable (such as corn, nut-like, buttery/ fat, chicken), blue green algae (woody, musty, etc.), chemical (metallic, diesel, etc.), decay (egg-sulfuric, rotten, etc.), vegetable (grassy, mushroom, etc.) and fishy (fish oil, rancid, stale, etc.) The author reported that blue green algae, chemical and decay were three objectionable categories for channel catfish Depending on intensity, flavor descriptors in fishy and vegetable categories could be acceptable or objectionable to the consumers Another study of Tucker and van der Ploeg (1999) on pond-raised catfish also reported common offflavors in catfish consisting of blue-green algae, decay/rotten and petroleum Adopt the classification of van de Ploeg, in this study, we considered algae, boiled egg, sulfurous, oxidized lipid, ammonia and fishy as objectionable flavors Boiled chicken, boiled shellfish, boiled fat, clam and lipid smell were on-flavors of the catfish fillets Other attributes, depending on their intensity, were acceptable or objectionable Due to its validity and completion of describing catfish fillets, this lexicon could be a reference for Vietnamese fish producers and purchasers to establish a quality control program for catfish fillets Common Structure between Catfish Fillets in Two Phases: Raw Fresh and Cooked As one of our main objectives was to identify raw fresh fillets sensory descriptors that could be used to predict cooked fillets sensory descriptors, we performed an MFA on both types of descriptors The first MFA maps of individuals and variables for fresh samples are shown in Figs and The first factor was highly correlated with the variables belong to the two groups This axis opposed samples F-HCM2, F-HCMC3 to F-Mekong1, F-Mekong2, F-HCMC1 and F-Mekong3 This first MFA factor opposes also the descriptors boiled fat, greasy mouthfeel, umami, elastic, cohesive to the descriptors boiledaged egg, oxidized lipid, ammonia, sulfur In the literature, the higher (resp lower) the value of the descriptors of the first (resp second) group, the better (resp the poorer) the quality of the catfish product This first axis can be interpreted as a Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc FLAVOR PREDICTION OF PANGASIUS FILLETS FIG FIRST FACTORIAL MAP FROM MFA FOR FRESH SAMPLES gradient of quality The two products F-HCMC2 and F-HCMC3 were firm, cohesive, chewy and flavored-boiled fat and chicken; whereas the others possessed the smell of oxidized lipid, sulfur and ammonia in raw phase; soft and smelled of boiled-aged egg in cooked phase It was noticed that colors such as pink, yellow and orange were found to have correlation with off-flavors (Fig 2) Pink highly correlated with oxidized lipid, sulfurous and ammonia; while yellow and orange well correlated with algae smell However, white did not show any relationship with the on-flavors of both raw-fresh and cooked samples This result was consistent with the finding of Rødbotten et al (2009) that color had less impact on the quality of cooked salmon sample These findings casted doubt on the rule of thumb of using color to judge the quality of catfish fillet, which has been very common in catfish quality assurance and trading Factors from separate PCA of two groups are presented in Fig The figure showed a strong correlation between the first factor of MFA and the first factor of each separate analysis These factors of separate analyses were also highly correlated to one another The same observation can be made for the second factor This shows that the first map of MFA was similar to the one of each separate analysis In other words, this suggested a possibility to obtain one map from the other by slight rotation This finding supported our assumption of a feasible prediction of sensory properties of catfish fillets at cooked phase from fresh phase and vice versa Representation of groups was performed to give a better demonstration of the common structure between the two groups of variables (Fig 4) The two groups of raw fresh and cooked were almost identical on the map They were strongly related to MFA factor 1, which meant that many of variables of these two groups were related to this factor This result, once again, 19 1.0 FLAVOR PREDICTION OF PANGASIUS FILLETS RawFresh (f) CookedFresh (c) salty_c flaky_c fishy_f lipid_f smoothness_f moist_c ammonia_c 0.0 0.5 moist_f ammonia_f soft_c cleamess.of.fiber_f sulfur_f pink_f oxidized.lipid_f pink_c boiled.egg_c boiled.shellfish_c soft_f thickness_f firm_f umami_c reddish.brown_f grey_c elastic_f cohesive_f fishy_c fat.leftover_f yellow_c orange_f yellow_f boiled fat_c algae_f cohesive_c chewy_c clam_f curve.of.fiber_f fatty.mouthfeel_c –0.5 Dim (21.49%) U.T.X PHAN AND D.H NGUYEN white_c white_f –1.0 boiled.chicken_c –1.0 –0.5 0.0 0.5 FIG FIRST FACTORIAL MAP FROM MFA FOR FRESH SAMPLES: VARIABLES AT TWO PHASES: RAW FRESH (f) AND COOKED (c) 1.0 Dim2.CookedFresh Dim2.RawFresh RawFresh CookedFresh Dim3.RawFresh 0.0 Dim4.CookedFresh Dim5.CookedFresh Dim3.CookedFresh Dim4.RawFresh Dim1.RawFresh Dim1.CookedFresh Dim5.RawFresh –1.0 –0.5 Dim (21.49%) 0.5 1.0 Dim (47.32%) –1.0 –0.5 0.0 Dim (47.32%) 20 0.5 1.0 FIG REPRESENTATION OF THE FACTORS FROM SEPARATE ANALYSES (PCA) OF TWO GROUPS: FRESH AND COOKED Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc U.T.X PHAN AND D.H NGUYEN FIG GROUPS REPRESENTATION FOR FRESH CATFISH FILLET SAMPLES stabilized the possibility of making prediction of sensory properties of cooked fillet from sensory properties of raw fresh fillets Common Structure between Sensory Characteristics of Catfish Fillets in Four Phases: Frozen, Thawing, Thawed and Cooked The relationship among the sensory properties of catfish fillets at four different phases, i.e., frozen, thawing, thawed and cooked was another main focus of this study In other words, the feasibility of making mutual prediction among the four was investigated An MFA was also performed on those four types of properties Figures and showed the representation of individuals (products) and variables (attributes) from MFA for frozen samples The first axis was highly correlated with the variables of two groups of thawed and cooked Those variables were attributes of odors and textures According to these two figures, the catfish fillets coded Mekong1, and Mekong3 were “firm,” “elastic” and “cohesive” at the thawed state; have smells of “boiled chicken,” “boiled shellfish,” “boiled fat” as well as cohesive texture and umami taste when cooked These properties were considered on-flavors Fillets from Mekong2 and Mekong4 were “smooth,” “soft” and “ammoniac” at thawed phase; possessed “boiled aged egg,” “ammonia” smells and “salty” once cooked These were regarded as off-flavors This axis can also be interpreted as a gradient of quality The second axis was contributed by the variables of frozen and thawing groups, with the dominant contribution of color attributes This axis opposed the sample “Mekong1-6T” to the rest This product Mekong1-6T was Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc FLAVOR PREDICTION OF PANGASIUS FILLETS perceived to have bright colors of “orange,” “pink,” while the others were “white” and “yellow.” Length of storage, statistically, did not have any influence on the sensory quality of the samples, especially at thawed and cooked phases However, from observation, the appearances of the fillets with months of storage were not as good as the ones with shorter length of storage Furthermore, there was no clear evidence of origin-resulting differences among the samples Factors from separate analyses, which were performed on four types of catfish descriptors, were presented in Fig As observed from the plot, the first factor of MFA was highly correlated with the first factors of separate analysis of thawed, cooked and frozen groups These factors of separate analyses were highly correlated with each other The second MFA factor was only correlated with the second factor of frozen group However, there were strong correlations between the first factor of MFA with the second factor of thawing group; and between the second factor of MFA with the first factor of thawing group This suggested that the first MFA map was roughly similar to the one of frozen group with a slight rotation The first MFA map could also be derived from the PCA map of thawing group by counterclockwise rotation and flip First factor was the only common between MFA map and the separate maps of thawed and cooked groups This factor, however, was the only factor significantly distinguishing the individuals (products) Thus, it could be said that the MFA map was also similar to separate ones of thawed and cooked in the sense of discrimination of the products Valid predictions can be made for cooked from thawed due to the strong relationship one another (Fig 6) Thawed fillets, which were elastic, firm and cohesive, tended to possess on-flavors such as chicken, shellfish, fat smells and umami FIG FIRST FACTORIAL MAP FROM MFA: MEAN INDIVIDUALS (FROZEN PRODUCTS) 21 1.0 FLAVOR PREDICTION OF PANGASIUS FILLETS Frozen Thawing Thawed Cooked U.T.X PHAN AND D.H NGUYEN white_fr yellow_tw curve_fiber_tw elastic_t 0.0 yellow_fr smooth_t ice_flake_fr ammonia_t cohesive_t fishy_fr fatty_mouthfeel_c sulfur_t glaze_equality_fr boiled.chicken_c boiled.egg_c flaky_c firm_t fishy_f cohesive_c fishy_c soft_c salty_c ammonia_c umami_c moist_c chewy_c red_tw soft_t boiled.shellfish_c cleamess_of_fibre_fr fiber_density_tw moist_t pink_c boiled.fat_c fat_t –0.5 Dim (20.51%) 0.5 white_c yellow_c orange_tw grey_c –1.0 pink_fr pink_tw –1.0 –0.5 0.0 0.5 FIG FIRST FACTORIAL MAP FROM MFA: VARIABLES OF FROZEN CATFISH FILLETS AT FOUR PHASES: FROZEN (fr), THAWING (tw), THAWED (t) AND COOKED (c) 1.0 0.0 Frozen Thawing Thawed Cooked Dim2.Frozen Dim5.Thawed Dim2.Cooked Dim4.Thawed Dim5.Frozen Dim5.Thawing Dim3.Thawing Dim4.Frozen Dim1.Frozen Dim3.Frozen Dim1.Cooked Dim5.Cooked Dim4.Thawing Dim1.Thawed Dim2.Thawed Dim2.Thawing Dim3.ThawedDim4.Cooked –0.5 Dim (20.51%) 0.5 1.0 Dim (32.23%) –1.0 Dim3.Cooked Dim1.Thawing –1.0 –0.5 0.0 Dim (32.23%) 22 0.5 1.0 FIG CORRELATION BETWEEN PARTIAL AXES WITH THE FACTORS OF MFA Journal of Sensory Studies 27 (2012) 12–25 © 2011 Wiley Periodicals, Inc U.T.X PHAN AND D.H NGUYEN FLAVOR PREDICTION OF PANGASIUS FILLETS revealed that good textural properties such as firmness, elasticity and cohesiveness tended to go with on-flavors such as boiled chicken, boiled shellfish, boiled fat and umami taste Appearance and color contribute very little in verifying sensory quality of catfish fillets The gradient of quality much correlates to textural properties and flavor By this study, quantitative descriptive method has proven its value as the most powerful method to explore every sensory dimension of the products, which was what has been in short of in other quality programs such as QIM or Torry scheme Catfish fillet producers could employ the results of this study (the lexicon and prediction model) to establish any sensory quality program for their products This was the most important practical value of this study Further studies will investigate consumer preferences of catfish products, focusing on making prediction for preferences among raw fresh, frozento-thawed and cooked FIG REPRESENTATION OF GROUPS OF VARIABLES FROZEN: VARIABLES, THAWING: VARIABLES; THAWED: 10 VARIABLES; COOKED: 18 VARIABLES taste In the meanwhile, fillets, which were smooth, soft and ammonia at thawed phase tended to have off-flavors such as boiled-aged egg, ammonia when cooked The groups’ representation showed strong relation between thawed and cooked groups (Fig 8) This meant that these two phases had similar characteristics This affirmed again a possible prediction could be made for one group from the other The frozen group was closer to thawed and cooked than thawing This could be due to the fact that all properties at frozen and thawing phases were appearance and color, and there was no color evaluation at thawed phase This is why thawing and thawed were very different in the factor All MFA analyses performed on properties of catfish at four phases have confirmed our hypothesis of practically making prediction of sensory characteristics of catfish fillets at one phase from the other phases CONCLUSIONS The lexicon of sensory descriptors developed in this study for all types of Vietnamese catfish fillet products (raw fresh, frozen-to-thawed and cooked) has been demonstrated to be valid and reliable There existed strong correlations between sensory properties of frozen catfish fillets at four different phases of frozen, thawing, thawed and cooked Properties of thawed 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MAP FROM MFA FOR FRESH SAMPLES: VARIABLES AT TWO PHASES: RAW FRESH (f) AND COOKED (c) 1.0 Dim2.CookedFresh Dim2.RawFresh RawFresh CookedFresh Dim3.RawFresh 0.0 Dim4.CookedFresh Dim5.CookedFresh... Boiled-aged egg Ammonia Fat in the belly of catfish Soft tofu Hard tofu Jelly candy Boiled chicken meat Soft tofu Soft tofu TABLE SENSORY ATTRIBUTES (n = 18) OF COOKED CATFISH FILLETS SAMPLES WERE... a feasible prediction of sensory properties of catfish fillets at cooked phase from fresh phase and vice versa Representation of groups was performed to give a better demonstration of the common