S adhan a Vol. 31, Part 5, October 2006, pp. 635643.
Printed in India
Shelf life assessment of Malaysian Pangasius sutchi during cold storage
K A ABBAS1 , S M SAPUAN2 and A S MOKHTAR2
1
Faculty of Food Science & Technology, and 2 Faculty of Engineering Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia e-mail: drsapuan@yahoo.com MS received 10 September 2005; revised 10 April 2006 Abstract. The ndings of the present work yield useful information about the Malaysian Pangasius sutchi concerning the marketing sector from the point of view of shelf life and storage temperature in the range of 0 to 10 C. A fresh batch of typical samples, were stored similarly in four chillers of different temperatures for a period of 28 days. During the course of storage, the samples were periodically subjected to pH and sensory tests performed by trained panelists. Experimental observations were analysed and regressed to develop three correlations. The rst one was between the sensory tests and the storage time and temperatures, while the second one related pH values to storage time and temperatures. Finally, a correlation between sensorial and pH values was developed as well. The rst correlation is presented in tabular form to yield a simple guide to sh retailers, by which quality and shelf life of the displayed sh commodity may be estimated. Keywords. Freshwater sh; cold storage; shelf life.
1. Introduction Patin (Pangasius sutchi) is a popular freshwater sh used as food in Malaysia (Mohsin & Ambak 1983; Fisheries Dept. 2000). This sh species is also abundantly available in the Amazon River, in parts of Russia and in other places of the world under different names. In Bangladesh, Indonesia (Borneo and Java), India and Thailand, it has the same name, i.e. Patin (Fisheries Dept. 2000). This species prefers the deep dark pools of large rivers and lives on a diet of vegetable matter, worms, various grubs, carrion, small sh and freshwater prawns (Aznir 1998). The environment in which they are grown inuences the properties of the sh. Due to this reason, differences in the composition of Patin sh are expected from country to country which eventually results in differences in shelf-life for sh from various countries. A data bank on the quality characteristics of the sh species of a particular location would be useful for marketing. Shelf life of a sh species is the time from when it is taken from the water until it is no longer t to eat. Shelf lives of fresh and frozen sh are very important criteria for marketing. The remaining shelf life allows a processor or a retailer to plan the length of time a product can be 635
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held, allowing control of the market. Adding one or two days to the shelf life allows the market to get good protability and assure repeat sales. Temperature and handling practices are the most important factors in determining the shelf life of all species of sh. If a sh product is handled carefully, the temperature at which it is held controls its useful life. Temperature controls the rate of bacterial spoilage and enzyme breakdown. An indisputable fact is that the higher the temperatures the faster sh get spoilt (Connell 1990) Fish consumption in Malaysia has increased dramatically in the past 10 years (Fisheries Dept. 2000). consumers have become more aware of the benets of eating sh and of consuming sh of high quality. While consumption has increased, the Malaysian sheries industry needs to meet this competition directly by improving quality and by marketing more fresh product. Freshwater sh was found to be a viable resource to meet the demand in the market. Karim (1990) reported that the Malaysian Fisheries Department is now encouraging and expanding freshwater sh-rearing industry among agriculturists and shermen to increase their income. Fish farming techniques are improving with the introduction of new techniques in order to have consistent supply of freshwater sh throughout the year. Recent marketing studies have indicated that consumers of seafood preferred fresh sh to frozen (Evans Kraft 1988). Accordingly, most sh-sellers prefer to display this commodity in chillers in the range of 0 to 10 C to attract customers. Further research is needed to enhance the consumption and utilization of Malaysian patin and also to analyse the quality characteristics of this species during cold storage. Due to the scarcity of such information (H A Hasimah personal communication; Ansari et al 2003, 2004; Sapuan et al 2003; Abbas et al 2005) and since a simple tool which delivers expected shelf life is still not available to sellers, this kind of research work is necessary and justied.
2. Materials and methods 2.1 Materials Pangasius sutchi, which is known locally as Patin species of local freshwater sh (Aznir 1998), is chosen as the sample. Pangasius sutchi sh were bought from a nearby farm. The sh were brought alive to the sh laboratory in batches, and were chosen according to their normal market sizes, their weight and length being recorded before lleting was done. Due to non-homogeneity in the esh of the sh over the entire body, the sampling area was selected from the upper portion with respect to the lateral line of the sh body as shown in gure 1. 2.2 Methods 2.2a Sample preparations: Prior to lleting, the sh were killed by stunning the head with a metal rod for fast death. The llets were taken from about 5 cm below the operculum up to about 10 cm from the tail end. This was followed by deskinning. Filleting and deskinning
Figure 1. The selected area for sampling.
Shelf life assessment of Malaysian Pangasius sutchi during cold storage
Table 1. Sensory evaluation score by panelists. Score 1 2 3 4 5 6 7 Overall acceptance Liked very much Liked moderately Liked slightly Neither liked or disliked Disliked slightly Disliked moderately Disliked very much
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were both done manually. Fillets were kept in styrofoam boxes containing crushed ice while waiting for all sh in the batch to be lleted and deskinned. The llets were then washed under running tap water to remove blood, dirt and slime, weighed and divided into four lots. The rst lot was used for storage study at 0 C and the second, third and fourth lots at 3 , 5 , and 10 C respectively. 2.2b pH measurement: Fish muscle was blended in a Waring blender with 1 part of muscle to 5 parts of distilled water. The pH was read directly from a laboratory pH meter (Hanna Instrument, 471, Italy-made). Determination was done as 3 replicates. 2.2c Sensory evaluation: Sensory evaluation was performed by a trained panel of 10 members drawn from the Faculty of Food Science and Technology, Universiti Putra Malaysia (Woyeda et al 1986). Panelists were asked to evaluate the overall acceptance of the thawed llets cut in to about 4 cm length and 1 cm thick pieces. The evaluation used was based on a scale of 7 points. Table 1 lists sensory evaluation scores for the overall acceptability according to each panelists judgment. It is notable that shelf life cannot be assessed without sensory evaluation. Based on the above table scores, shelf life could be dened as the time needed for the stored sample to reach the score value of 7. 3. Results and discussion 3.1 Changes in pH values The initial pH values of the fresh samples were measured to be 603. A signicant increase in pH of the four batches during storage course has been noted. All the batches exhibit similar increasing behaviour. However, each batch yielded different pH value in the end of the storage period according to the storage temperature of that chiller. Figure 2 revealed that 68, 696, 712, and 76 are the end pH values of the storage temperatures 0 , 3 , 5 and 10 C respectively. Observations of pH values along with those of time and temperature of preservation were regressed to obtain a correlation by which an estimate of pH value at any prescribed storage (chilling) temperature and storage time could be predicted without using the pH meter. The MMF model was found to deliver satisfactory tting as follows: pH = (ab + cD d )/(b + D d ). (1)
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Figure 2. Evolution of pH value during storage period.
Constants a, b, c, and d are functions of storage temperature, therefore for the purpose of precise estimation the following equations may be used along with the storage temperature. a = 1/(0166 000031T + 189633E 5T 2 ), b = 15149489 exp[(47 T )2 /0529], c = [12544 567T ]/[1 01357T 00127T 2 ], d = [1645 + 945E 9T ]/[1 + 1011E 10 1587E 8T 2 ]. (2) (3) (4) (5)
Earlier, Gould & Peters (1971) associated the increase in pH during storage of sh muscle with depletion of tissues. They also reported measurement of the pH of surface esh as a rapid test for detection of spoilage at sea. However, they neither mentioned the exact cause of spoilage nor the acceptable range of pH. Jamilah & Mohd (1993) also reported the increase in pH during their study of bighead carp kept at ambient temperature. Love (1983) and Rhee et al (1984) reported that enzyme-catalysed oxidation in sh muscle tissue reached the optimum rate at pH 65. This implies that enzyme-catalysed oxidation is at its peak at pH 65. The activity still goes on thereafter, though at a lower rate. 3.2 Sensory evaluation Spoilage and quality deterioration can be assessed by chemical and physical methods and sensory evaluation (Connell 1990). Not all chemical assessments give good correlation to quality changes, hence sensory evaluation is a necessity (Hardy 1979). Ismail (2000) reported that the necessity of conducting sensory evaluation. Sensory testing plays an important role in food quality evaluation since the ultimate test of food quality is consumer response. Instrumental methods to determine some physical, chemical or biological properties of food have been developed and are being used to assess avour, colour and texture. However, sensory
Shelf life assessment of Malaysian Pangasius sutchi during cold storage
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Figure 3. Relationship between acceptability and pH ratio.
evaluation panels must be used to ensure that instrumental methods are properly correlated with sensory data. In general, sensory evaluations were carried out for all samples kept at different temperatures. The results were then evaluated using the hedonic scale. These sensory evaluations have been correlated with the pH/pH0 variation to yield the following relationship, as shown in gure 3 (acc = acceptability) acc = 48331307 + 50431848(pH/pH0 ). (6) For samples kept at 0 C, in order to correlate the storage time with the pH/pH0 , the following fourth-degree polynomial with standard error 00092364 and correlation coefcient 09791578 has been suggested satisfactorily as shown in gure 4. (pH/pH0 ) = 000 + 000139D + 000152D 2 0000187D 3 + 6355 106 D 4 . (7)
Equations (6) and (7) make it possible to predict the sensory evaluation of the samples kept at 0 C.
Figure 4. Variation of pH ratio during storage.
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Figure 5. Effect of storage temperature on spoilage.
Knowledge of the relative rates of spoilage at different storage temperatures are often useful when estimating the quality of sh of known temperature history, although, as indicated earlier, this applies only to sh kept above 0 C. Since ice melts at 0 C under normal conditions, a reference temperature of 0 C is normally used when comparing storage times for fresh sh and shellsh. An extrapolation from the Arrhenius reaction rate equation allows the calculation of relative spoilage rates of sh and shellsh for temperatures above 0 C Gorga & Rousivalli 1988. The relative spoilage rate (R ) is given by R = (1 + 01Tchilling )2 . (8)
This gives an indication of the quality of the sh by assuming that the sh is in prime condition when caught, and that handling is of a sufciently high standard to avoid problems such as bruising. Poor handling would result in much more rapid spoilage than the calculated equivalent length of time on ice would indicate. Figure 5 depicts the relationship between the relative rate of spoilage and storage temperatures used in this study. Equation (1) was utilized to calculate pH/pH0 every day during the course of storage, and the sensory evaluation score were deduced via (6). Since (8) has been explained already to predict the relative rate of spoilage for storage temperature other than 0 C. According to this it may be inferred that it is possible to predict the sensory evaluation score for other storage temperatures as shown in table 2. In this table, the relationship between the hedonic score with time and temperature of storage is described numerically. The time corresponds to the sensory score of 7 which is the shelf life. Therefore, such marginal values are highlighted to remind the reader of the shelf life under that storage temperature. Samples kept at higher temperature exhibit a shorter shelf life as compared to samples kept at 0 C. The results of table 2 were regressed to represent the relationship between the shelf life and the storage temperature (gure 6). With a standard error of 06970091 and a correlation coefcient of 09957484 the Harris model was found to be the most suitable one to represent that relationship mathematically in the following equation: S = 1(0056 + 00006T 327 ). (9)
4. Conclusion The work presented above reveals that all cold-stored samples under various temperatures are subject to increasing in pH and sensory score values. The higher the storage temperature
Table 2. Predicted quality and shelf life with temperature and time of storage. 2 2750002 3265714 3491012 3788723 4129234 4485042 4829415 5128008 536311 5532849 5630982 5692173 5746221 5839985 603991 6433087 7166972 3227433 3832678 409709 4446488 4846115 5263695 5667855 6018287 6294206 6493413 6608583 6680397 6743829 6853871 7088506 7549943 3743059 4444999 4751655 5156873 5620346 610464 6573371 6979789 7299789 7530822 4296879 5102678 5454706 591988 6451928 7007877 7545961 4888893 5805713 6206243 6735508 7340861 5519102 6554106 7006267 7603757 6187505 7347856 7854777 3 Storage temperature ( C) 4 5 6 7 8 9 6894103 8186963 10 7638896
Day
Shelf life assessment of Malaysian Pangasius sutchi during cold storage
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1909724 2267857 2424314 2631058 2867524 3114612 335376 3561117 3724382 3842256 3910404 3952898 3990431 4055545 4194382 4467422 4977064 585511 7402022
2310766 2744107 293342 318358 3469704 3768681 405805 4308951 4506503 464913 4731589 4783006 4828422 490721 5075202 540558 6022247 7084683
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Figure 6. Relationship of shelf life with storage temperature.
the faster is the increase in these values. Two correlations describing the variation of pH and sensory score during storage have been developed. Since each correlation is a function of time and temperature of storage, this had lead the authors to develop another relationship between sensory score and pH/pH0 via (7) and (8). This relationship is presented in tabular form in table 2. The table represents a simple tool by which quality deterioration and shelf life of the stored sh may be predicted in the sh marketing sector.
List of symbols a, b, c, d acc D pH S T Subscript 0 polynomial coefcients; Hedonic score; the storage time (day); acidity index; shelf life (day); storage temperature ( C); fresh
References
Abbas K A, Sapuan S M, Ahmad M M H M, Mokhtar A S, Jamilah B 2005 Determination of thermal conductivity of Malaysian patin sh. J. Food. Agric. Environ. 3: 4448 Ansari F A, Abbas M, Hamdan M, Ashraf O A, Mahdi E, Bakar J, Sapuan S M, Wan M A 2003 Thermal diffusivity investigation of fresh water patin sh during cold preservation. Proc. 2nd Int. Conf. on Heat Transfer, Fluid Mechanics and Thermodynamics (Victoria Falls, Zambia: Univ. of Zambia) Paper number:AF1-5 Ansari F A, Abbas K A, Ahmad M M H 2004 A correlation between thermal diffusivity variation and quality of cold preserved sh. ASEAN J. Sci. Technol. Dev. 21: 110
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