Development of Quality Index Method (QIM) scheme for fresh cod (Gadus morhua) Wllets and application in shelf life study

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1 Food Control 8 (7) Development of Quality Index Method (QIM) scheme for fresh cod (Gadus morhua) Wllets and application in shelf life study Alma Cardenas Bonilla a,c,, Kolbrun Sveinsdottir b, Emilia Martinsdottir b a Research Center of Foods and Development, CIAD-Guaymas Unit, A.C. P.O. Box 84, 854 Guaymas, Son, Mexico b Icelandic Fisheries Laboratories, Skulagata 4, Reykjavik, Iceland c The United Nations University, Fisheries Training Programme in Iceland, Skulagata 4, Reykjavik, Iceland Received 8 June 5; received in revised form 6 October 5; accepted 8 October 5 Abstract The aim was to develop and evaluate a Quality Index Method (QIM) scheme for fresh cod Wllets. Cod Wllets were stored at C on ice up to 4 days. Total viable counts (TVC) and counts of H S-producing bacteria were done. A QIM scheme for fresh cod Wllets to evaluate freshness was proposed. A high correlation between the Quality Index (QI) and storage time on ice was found. The remaining storage time could be estimated with accuracy of.3 days when the cod Wllets were evaluated with QIM. The maximum storage time was estimated 8 days based on Quantitative Descriptive Analysis and H S-producing bacteria counts. 5 Elsevier Ltd. All rights reserved. Keywords: QIM; Sensory evaluation; Fresh cod Wllets; Shelf life. Introduction In recent years, export of fresh Wsh from Iceland has increased. In 4 the Icelandic cod exports increased by % the Wrst nine months of the year compared to the same period in 3 (Lien, 4). Freshness makes a major contribution to the quality of seafood, which is a very perishable product. The principal method to evaluate the freshness of seafood is sensory evaluation. It is important to have an evective method to assess freshness of products in a fast, easy and reliable way. The Quality Index Method (QIM) is a scoring system for freshness and quality estimation of Wshery products originally developed by the Tasmanian Food Research Unit (Bremner, 985). QIM is based on signiwcant, well-dewned characteristic of appearance, odour and texture attributes changing through storage time. The descriptions of the * Corresponding author. Address: Research Center of Foods and Development, CIAD-Guaymas Unit, A.C. P.O. Box 84, 854 Guaymas, Son, Mexico. Tel./fax: address: almcarde@cascabel.ciad.mx (A. Cardenas Bonilla). individual grades are precise, objective, independent and primary rather than a cluster of terms (Hyldig & Green- Petersen, 4; Ólafsdóttir et al., 997; Sveinsdottir, Hyldig, Martinsdottir, Jorgensen, & Kristbergsson, 3). A score from to 3 demerit (index) points is given for each quality parameter according to the speciwc parameter descriptions. The scores are summarised to give an overall sensory score, the Quality Index (QI). The method has to be developed or adapted to each Wsh species. If the total length of shelf life of the species on ice is known, the total number of index points can also be used to estimate the past and remaining shelf life as the QI increases linearly with the storage time on ice (Luten & Martinsdóttir, 997; Martinsdóttir, Sveinsdóttir, Luten, Schelvis-Smit, & Hyldig, ). QIM schemes have been developed for several species and products including: fresh brill, shrimp, haddock, plaice, pollock, sole, turbot, dab (Luten, ), cod (Jonsdottir, 99; Larsen, Heldbo, Jespersen, & Nielsen, 99), Atlantic salmon (Sveinsdottir et al., 3), herring (Jonsdottir, 99), redwsh (Martinsdóttir & Arnason, 99), octopus (Barbosa & Vaz- Pires, 4), seabream (Huidobro, Pastor, & Tejada, ), European sardine, horse mackerel, Atlantic mackerel /$ - see front matter 5 Elsevier Ltd. All rights reserved. doi:.6/j.foodcont.5..9

2 A. Cardenas Bonilla et al. / Food Control 8 (7) (Andrade, Nunes, & Batista, 997), thawed whole cod, Wllets from thawed cod and cooked Wllets from thawed cod (Warm, Bøknæs, & Nielsen, 998). Quantitative Descriptive Analysis (QDA) method can be used on cooked Wsh samples to determine the maximum storage time in addition to giving a detailed description of the sensory prowle of the Wsh (Sveinsdottir, Martinsdottir, Hyldig, Jorgensen, & Kristbergsson, ). The method involves detection and description of the qualitative and quantitative sensory aspects of a product by a trained panel of people (Stone & Sidel, 985). Panellists detect and describe the attributes of a sample. They must be able to rate the quantitative or intensity aspects of a sample and to dewne the degree of each characteristic or qualitative note present in that sample (Meilgaard, Civille, & Carr, 999). The aim of this study was to develop a QIM scheme for raw cod Wllets and to evaluate the scheme in a shelf life study.. Methods.. Cod Wllets Raw Wllets of wild cod with skin were bought from a Wsh retailer (Fiskverslun HaXida Baldvinssonar ehf). The cod was caught with long line, stored whole in ice after catch and Wlleted after 3 up to 5 days. At the laboratory, the Wllets were stored at C on ice in plastic boxes. Low density polypropylene was used to cover the ice before the raw Wllets were placed in the boxes and also to cover the Wllets but without preventing access of air to the Wllets. Samples stored for, 3, 7, and 4 days were analyzed with QIM, QDA and microbial counts... Development of QIM scheme The methodology used to develop and evaluate the QIM scheme was based on the method earlier described by Martinsdóttir et al. (), Martinsdóttir (), Sveinsdottir et al. (3) and Hyldig and Green-Petersen (4). A preliminary QIM scheme for the sensory evaluation of fresh cod Wllets was designed during pre-observation of fresh cod Wllets. Two persons observed and registered the changes occurring in the Wllets from the day of Wlleting (day ) until spoiled. Each parameter evaluated received scores in which zero corresponded to very fresh Wllets. The scores increased according to spoilage up to 3 for each parameter. Eleven to twelve panellists of the Icelandic Fisheries Laboratories sensory panel, previously trained according to international standards (ISO, 993), participated in four training sessions. Raw cod Wllets of diverent storage time were placed on a white clean table at room temperature, under white Xuorescent light. The storage day was given with a note next to each Wllet at the Wrst two sessions. During the following sessions, the notes only showed three-digit numbers, but at the end of the session, the panel was informed about the storage time. The panel used the scheme developed during pre-observation of cod Wllets. The panel leader explained how to use the scheme and how to evaluate each quality parameter. Then, the panel evaluated cod Wllets by themselves. After each session, the panel leader and the panellists discussed the scheme. Some changes were made in the scheme during the training sessions, but before the last training session, the QIM scheme for fresh cod Wllets was completed..3. Shelf life study.3.. Sensory evaluation of raw cod Wllets with skin (QIM) The QIM scheme was used to evaluate raw cod Wllets with skin in two sessions. Eleven to twelve trained panellists of the Icelandic Fisheries Laboratories sensory panel evaluated 5 Wllets during the experiment; three Wllets per storage day (, 3, 7, and 4 days), coded with three-digit numbers without information about the storage time..3.. Sensory evaluation of cooked Wllets (QDA) Samples weighing 4 5 g were taken from the loin part of the Wllets and placed in aluminium boxes coded with three-digit random numbers. The samples were cooked at 95 C for 7 min in a pre-warmed oven (Convotherm Elektrogeräte GmbH, EglWng, Germany) with air circulation and steam. Eleven to twelve panellists of the Icelandic Fisheries Laboratories sensory panel familiar with the QDA method and experienced in sensory evaluation of cod were trained during three sessions to evaluate cooked cod Wllets with the QDA method (Stone & Sidel, 985). The panel observed diverences in appearance, odour, texture and Xavour of the Wllets. A list of sensory attributes to describe samples was made under the guidance of the panel leader and was trained in describing the intensity of each attribute for a given sample using an unstructured scale (from to %). All sample observations were conducted according to international standards (ISO, 988). The panel evaluated the cooked samples, coded with three-digit numbers without information about the storage time, using the list developed during training. Each sample was evaluated randomly in duplicate. A computerised system (FIZZ, Version., 994, Biosystémes) was used for data recording and for further processing. Average scores of the judges were calculated for each sample assessed and the reported value was the average of the duplicate samples Microbial counts Flesh samples for the microbial analysis were collected at each sampling point. Samples of minced Wllets, weighing 5 g each, were placed in a stomacher bag containing 5 g ButterWeld s BuVer solution to obtain a -fold dilution. Blending was done in the stomacher for min. The plates were incubated at C for 3 days. Total viable counts (TVC) and selective counts of H S-producing bacteria were

3 354 A. Cardenas Bonilla et al. / Food Control 8 (7) done on iron agar (IA) by the pour plate technique with an overlay. 3. Data analysis The mean values of QI, QDA, TVC and selective counts of H S-producing bacteria were plotted separately against the storage time (using Microsoft Excel 97). Simple linear regression models were Wtted to the data. The uncertainty of prediction of days on ice from the QI was estimated using partial least-squares regression (PLS) with full cross validation. The analysis was carried out with the statistical program Unscrambler (version 8.; CAMO, Trondheim, Norway). Calibration models were calculated using the average QI of three samples evaluated per storage day. The root mean square error of prediction (RMSEP) was calculated providing a prediction error in original units (days). Bias was calculated and presented the averaged diverence between predicted and measured Y-values for all samples in the validation set. The standard error of performance (SEP) was used to estimate the precision of the results, corrected for bias (Sveinsdottir et al.,, 3). Analysis of variance (ANOVA) was carried out on QDA data in the statistical program NCSS (NCSS, Utah, USA). The program calculates multiple comparisons using Duncan s test. The signiwcance level was set at 5%, if not stated elsewhere. 4. Results 4.. Development of QIM scheme Parameters that describe changes in skin and Xesh were listed in a preliminary scheme during the pre-observation of raw cod Wllets. The maximum sum of points was 9. During training sessions, parameters related to skin scales, Xesh water, and skin Xesh dryness were removed. The descriptions of mucus on skin, Xesh colour, brightness, and gaping were modiwed to words that better described the parameters. After the last training session, the scheme was completed; the total sum of points was 8 (Table ). 4.. Shelf life study 4... Sensory evaluation of raw Wllets (QIM) The QI based on average of the whole panel ( panellists) was calculated for each trial day of storage. The QI was linearly related to storage time on ice (Fig. ) with a high correlation (R D.989) between the average QI and days of storage on ice. The standard error of prediction (SEP) was calculated for storage time (Table ). SEP was.95 days based on average QI scores of three samples per storage day. Since the QI is a sum of eight parameter values, the measurement error may be assumed to be normally distributed and the Table Quality Index Method scheme developed for fresh cod (Gadus morhua) Wllets with skin Quality parameter Description Skin Brightness Iridescent pigmentation Rather dull Dull Mucus Uniform, thin, transparent Little thicker, opaque Clotted, thick, yellowish Flesh Texture Firm Rather soft Very soft Blood Bright red, not present Dull red Shadowy, brown Odour Fresh, neutral Seaweedy, marine, grass Sour milk Acetic, ammonia 3 Colour White, greyish Some yellowish, a little pinkish Yellow, over all pink Bright Transparent, bluish Opaque Milky Gaping No gaping, one longitudinal gaping at the neck part of the Wllet Slight gaping less than 5% of the Wllet Slight gaping, 5 75% of the Wllet Deep gaping or slight gaping over 75% of the Wllet 3 Quality index ( 8)

4 A. Cardenas Bonilla et al. / Food Control 8 (7) QI score y =.7989x+.8 R = Fig.. QI of cod Wllets. Averages ( SD) over each day of storage analysed (N D 3) against days on ice. Table Partial least-squares regression model of QIM data from cod stored on ice Parameters Value Elements 5 Slope.95 OVset.34 Correlation.99 Root mean square error of prediction.85 Square error of prediction.95 Bias.3 Model based on the average QI scores of three Wsh evaluated per storage day. prediction can therefore be considered as t-distributed. The 95% conwdence interval (estimated by SEP t (df D 4) D D.64) may therefore be estimated as approximately.6 days. It can therefore be assumed that the QI based on average scores of three samples evaluated per storage day could predict the storage time with an accuracy of.3 days. The QI scores for all quality parameters increased with storage time on ice as shown in Fig.. The scores for all evaluated parameters were around zero at storage day zero. The scores for mucus on skin, Xesh colour and Xesh brightness showed a rather sharp increase between day 7 and. The Xesh gaping parameter increased less with time compared to other parameters QDA in shelf life study In the shelf life study the panellists evaluated the samples using the list of attributes that resulted from the training sessions (Table 3). The results on each attribute are presented as averages of the whole panel ( panellists). The attributes which were perceived at the beginning of storage may be considered to be positive. The attributes detected closer to the end of shelf life described spoilage were considered negative. The positive Xavour attributes such as sweet, metallic and meat decreased or showed a strong trend to decrease with storage time (Fig. 3A and Table 4). The scores of the negative Xavour attributes rotten, sour, TMA, and pungent increased during the storage time (Table 4), especially between 7 and days of storage on ice (Fig. 3B)..5.5 Skin brightness Flesh texture Flesh odour Flesh bright 5 5 Skin slime Fig.. Average scores for each quality attribute evaluated with QIM scheme for cod Wllets (N D 3) against days on ice. The scores of the positive odour attributes: sweet, boiled milk, boiled potatoes, vanilla and meat decreased or showed a trend to decrease with storage time (Fig. 4A and Table 4), but negative odour attributes: sulphur, rotten, table cloth, TMA, sour increased rapidly from 7 days of storage on ice (Fig. 4B and Table 4) Flesh blood 5 5 Flesh colour 5 5 Flesh gaping Table 3 Sensory attributes evaluated in cooked cod Wllets Appearance Odour Flavour Texture Light dark Sweet Sweet Softness Homogeneous/ heterogeneous Boiled milk Metallic Juiciness Boiled potatoes Sour Tenderness White precipitation Butter Butter Mushy Flakes Vanilla Meat Meaty Meat Pungent Cohesive Table cloth TMA Rubber TMA Sour Sulphur

5 356 A. Cardenas Bonilla et al. / Food Control 8 (7) A 5 5 Sweet Metallic Meat B 5 5 Sour TMA Pungent Fig. 3. Positive (A) and negative (B) Xavour attributes (average scores, N D ) of cooked cod Wllets against days on ice. Table 4 Mean sensory scores of Xavour and odour attributes of cooked cod Wllets Storage time (days on ice) p Attributes Flavour Sweet Metallic 3 a 3 a 3 8 b b. Meat Sour 3 a 9 a 6 a 44 b 47 b. Pungent 9 a 8 a 3 b 36 b.3 TMA 9 a a a 43 b 54 b. 6 a a 8 a 4 b 56 c. Odour Sweet 35 a b 5 b.5 Boiled milk 36 a b 8 b.5 Boiled potatoes Vanilla Meat 8 a 5 3 b 4 b. Table cloth a 7 a 3 a 35 b 59 c. TMA 7 a a a 49 b 5 b. Sour 9 a a 3 a 9 b 37 b. Sulphur 3 a 3 a 6 a 8 b 37 c. 3 a 3 a 8 a 3 b 59 c. DiVerent letters indicate signiwcant diverent values between samples within a line Microbial counts The microbial counts increased with storage time (Fig. 5). At the beginning of storage, the TVC was around 5 cfu/g and H S-producing bacteria were 3 cfu/g, but increased to approximately 9 cfu/g for TVC and 8 cfu/g for H S-producing bacteria at the end of storage time. 5. Discussion 5.. Development of QIM scheme The deteriorative changes occurring in cod Wllets were observed during the pre-observation. Some attributes that were included in the preliminary scheme, were omitted from the QIM scheme during the training sessions because they were not detected during training. Those changes were dry surface, single scales lost and Xesh dryness. This incongruity between the pre-observation and the training session could be due to the repeated handling of samples during the pre-observation, as during training sessions each sample was evaluated only once. Previous work using a QIM scheme for whole cod showed that the parameters dealing with scales could not be evaluated, as described by Larsen et al. (99). 7 6 A 7 6 B Sweet Boiled potatoes Meat Boiled milk Vanilla Table cloth TMA Sour Sulphur Fig. 4. Positive (A) and negative (B) odour attributes (average scores, N D ) of cooked cod Wllets against days on ice.

6 A. Cardenas Bonilla et al. / Food Control 8 (7) Log cfu/g Storage time (days) Total Viable Count H S-producing bacteria Fig. 5. Total viable counts and counts of H S-producing bacteria in Xesh of cod Wllets (N D ) against days on ice. The description of gaping in the preliminary scheme was modiwed during the training sessions to describe more clearly the number and deepness of gaping present in the Wllet. In the process of gaping, as described by Botta (995), the Xakes that are originally connected to each other by connective tissue in a fresh Wllet, separate and the Wllet loses the appearance of a continuous muscle. Although this is a natural process and was observed during the pre-observation, it is likely that the repeated handling of Wsh accelerated the process. The Wllets evaluated during training sessions did not show much change in gaping and scores for gaping did not change much after 7 days of storage. The Xesh texture was found to be rather diycult to evaluate during training. It varied and depended on where in the Wllet it was evaluated. At the loin near to the neck it was always Wrm, but soft at the tail. Therefore, it is important to always evaluate the texture at the same spot in the Wllet and give detailed guidelines to panellist. Such guidelines exist (Martinsdóttir et al., ) and include recommendations to evaluate the texture in the middle of the spine muscle by pressing a Wnger and observing if and how fast the Xesh recovers. The number of parameters included in the QIM scheme developed in this study for fresh cod Wllets was higher than that for thawed cod Wllets developed by Warm et al. (998) and used by Jensen and Jørgensen (997). Both authors did not considered evaluation of skin and they considered the presence of parasites as a parameter in the QIM scheme. However, changes on skin were observed during the preobservation and were subsequently conwrmed during the training sessions, and were therefore included in the QIM scheme developed in this study. Martinsdóttir and Stefánsson (984) developed a freshness quality grading scheme for cod Wllets including evaluation of smell, gaping, blood veins and colour. They suggested that.5 was added to the average grade if worms were present in the Wllet. In the QIM scheme developed in this study, the presence of parasites was not considered to be related to freshness of Wllets. However, parasites are present in the cod Xesh and they contribute to an unpleasant appearance. This avects the total quality of the Wsh, but does not contribute to the freshness changes through the storage time. 5.. Shelf life study 5... Sensory evaluation of raw Wllets (QIM) A high correlation was found between the total QI score (sum of all attributes) and the storage time, which shows that the attributes gradually deteriorated with time. The individual attributes were independent of each other, but all changed and received higher scores through the storage time. The QI may be used to predict the remaining storage time with an accuracy of.3 days if three Wllets from the same lot were assessed by a trained panel. Due to individual variation present in the samples (even from the same storage day), a minimum of three samples should be used. According to the guidelines for freshness assessment of whole Wsh given by Martinsdóttir et al. (), a minimum of three (large Wsh) to (small Wsh) random samples should be taken to cover the biological diverences in spoilage rate of Wsh. Sveinsdottir et al. () reported that when more than three whole Wsh per batch of storage time were assessed, it could increase the precision of the prediction of storage time QDA in shelf life study Cod Wllets reached the limits of acceptance between 7 and days of storage according to the sensory evaluation of cooked cod. End of shelf life is usually determined when spoilage related sensory attributes such as TMA, rotten odour and Xavour become evident (average score above ). Those odours and Xavours had mainly microbial origin (Huss, 995). The end of shelf life was determined when the average sensory score was above and the counts of H S- producing bacteria were around 7 cfu/g. Based on this, the maximum storage time of the Wllets was 8 days on ice. This is a shorter shelf life compared to what has earlier been reported for cod Wllets. Vacuum packed cod Wllets passed the limit of acceptability after 9 days of storage (Gram, Trolle, & Huss, 987) and Huss (995) reported 4 days for packed cod at C. A shelf life study of fresh cod Wllets Wlleted day after catch showed that the Wllets have a shelf life of around days on ice according to Magnússon and Martinsdóttir (995). The shorter storage life obtained in this study may therefore be due to the storage time of the whole Wsh from catch until Wlleting, which was from 3 up to 5 days Microbial counts Growth curves for TVC and counts of H S-producing bacteria had very similar shape, though the proportion of H S-producing bacteria of the TVC increased with storage time. The bacteria counts were between 7 and 8 cfu/g for TVC and 6 and 8 for counts for H S-producing bacteria between 7 and days. The microbial counts were

7 358 A. Cardenas Bonilla et al. / Food Control 8 (7) higher than in a previous experiment done by Magnússon and Martinsdóttir (995), in which they reported TVC of 6 and 7 cfu/g between days 6 and 9 for cod Wllets stored in ice at C. 6. Conclusions The use of the QIM scheme developed for fresh cod Wllets in this study showed a clear linear relationship to storage time on ice. The QIM scheme consisted of eight parameters which gave a total of 8 demerit points. The maximum storage time was estimated 8 days on ice based on counts of H S-producing bacteria and sensory evaluation with QDA. At the beginning of the storage time, small changes of the positive attributes of odour and Xavour were observed. After the seventh day of storage they were hardly detectable, due to the increase of negative attributes. The QI could be used to estimate the remaining storage time on ice with an accuracy of.3 days if three Wllets per lot were evaluated. This information may be used in quality management of cod Wllets stored on ice (assuming optimum storage conditions) to estimate the remaining storage time. Acknowledgements This work was carried out at the Icelandic Fisheries Laboratories (IFL) as a part of the Fisheries Training Programme at the United Nations University. The work was performed within the Integrated Project SEAFOODplus, contract no. Food-CT The partial Wnancing of the work by the European Union is gratefully acknowledged. The authors would like to thank Asa Thorkelsdottir and the sensory panel at IFL, stav at the service department for microbial analysis and Dr. Tumi Tomasson, programme director and Mr. Thor Asgeirsson, deputy programme director of the UNU-FTP for valuable guidance, discussions and support. References Andrade, A., Nunes, M. L., & Batista, I. (997). Freshness quality grading of small pelagic species by sensory analysis. 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