Thermal Diffusivity and Quality Deterioration Index of Malaysian Pangasius Sutchi During Cold Storage

The knowledge on thermal properties of food material to be preserved is considered as one of the basic requirements for conducting heat transfer studies and hence to design proper heat transfer equipments such as refrigerators, freezers and cold storages. The local designers obtain those thermophysical properties data from Europe and America (Ansari et al., 2002). Experimental measurements have been carried out for the specific heat, mass density, water content, thermal conductivity and thermal diffusivity of Malaysian freshwater Pangasius Sutchi fish during precooling process. The mass density was determined by measuring mass and volume of the fish samples and the water content was measured gravimetrically through drying of fish samples in oven. The remaining properties were calculated by empirical formula, which correlated these properties with water content of fish. The most significant part in the experimental work was designing and fabrication of an air blast cooling plant of constant 1 O C air stream temperature. This plant has played the vital role in minimizing the error of the used techniques as well as thermal diffusivity determination. A non-dimensionalized mathematical model of temperature variation with time and spatial coordinates was made and solved by finite difference method. Factors affecting the solution have been investigated thoroughly to deliver the most accurate and reliable results with the shortest computational time. The r,alculation procedure has been developed and proposed for heat transfer and simultaneous heat and mass transfer model. The proposed scheme showed more superior results when compared with the results reported in the literature and yielded consistently good agreements with the measurements. Three approaches of estimating the surface film conductance (h) during air-blast cooling process were developed by the present author. Based on the above mathematical model, a comparison between the developed and five of the existing literature approaches was made to identify the best one. A thorough investigation was conducted to establish the most suitable and reliable method of measuring the thermal diffusivity of Pangasius Sutchi out of important methods reported in the literature. Due to its superiority, Ansari's method was adapted to calculate the thermal diffusivity, through the transient temperature measurements at five known locations in the fish flesh and at the surface. The estimated h was used in this method to deliver reliable values of a. Four lots of fish samples were preserved in 4 chillers set at 0, 3, 5 and 10°C for 28 days according to normal practice. During the course of cold preservation, the which comprises overall acceptance (consumer acceptability acc). Secondly, chemical tests, which included the pH and Thiobarbituric acid (TBA) tests. These tests play the main role in determining the development of rancidity evolution in the fish under present investigations. ?he last type of test was the thermal diffusivity determination through transient temperature measurements across the muscles orientation, as well as along the n~uscleso rientation. The above study has revealed that the consumer acceptability (acc), pH and TBA value were found to be strongly dependent upon temperature and time of cold preservation. The results of acc and PH led to yield a graphical solution by which the consumer acceptability and the shelf life of the fish, during cold storage, could be predicted. TBA was correlated with thermal diffusivity ratio (a/a) to develop a tool by which rancidity of fish could be predicted without going through the chemical test, hence, a new quality deterioration index was developed. When the value of a 1a ,+sh= 1.0 indicates absolutely fresh sample, and a/a pex>, 1 . O the lesser the freshness

An optimized method for thermal diffusivity measurement of peeled off fruits and vegetables.

The aim of the present work was to find out the most suitable method for thermal diffusivity measurement of peeled off fruits and vegetables. Three methods reported in the literature, have been examined. One of them is finite difference method, which needs temperature-time measurements at three equidistant locations in the food flesh. Another method is the well-known Riedel correlation, which determines thermal diffusivity of food item from its water content. The third method is based on the empirical correlation of the present author and his co-workers and reported earlier. Peeled off fresh potato, cucumber, apple and orange samples were exposed to chilled air blast cooling, and temperature-time records were made at five equidistant locations starting from center and at equal distances of 1/5th the distance between the center and the outer surface. Collected data was used to estimate thermal diffusivity values by the first and the third methods. The second method was also used to calculate thermal diffusivity from measured water content of the produce. After thorough investigations, it was concluded that the third method was most reliable when temperature records at the center were used

Fatty acids in fish and beef and their nutritional values: a review.

This review aims to summarize the latest developments and recent knowledge regarding the fatty acids in fish and beef, their profiles and nutritional values. The paper covered the types of different fatty acids such as unsaturated fatty acids (UFA), polyunsaturated fatty acids (PUFA), especially the omega-3 in different fish species. The study also summarized the nutritional values of the fatty acids as compared to those in other animal species. However, the strategies influencing the fatty acid composition of beef were also reflected. The study revealed that many fatty fishes were found as excellent sources of UFA and PUFA, especially the omega-3. On the other hand, beef was proposed major source of saturated fat in a diet. The quality attributes of beef meat such as tenderness, juiciness, and flavor intensity have been shown to be affected by the chemical properties and lipid content. Moreover, increasing dietary omega-3 fatty acid intakes for potential health benefits for protecting against cardiovascular diseases was recommended. This work may assist the researchers and scientists to have a clear picture about what have been achieved earlier and what critical work should be conducted in future

The significance of glass transition temperature in processing of selected fried food products : a review

This paper emphasized the significance of the glass transition temperature (Tg) by highliting its applications in drying (hot air and freeze drying) for various food systems such as skim milk powders, rice kernels, starch and sugar products and some freeze-dried products such as strawberries and surimi. The study revealed that the major components of the specified foods (which consist of mixture of ingredients), for example lactose in skim milk powder and sucrose in sugar mixtures, will influence the glass transition temperature of the food. Moreover, Tg is an important parameters for determining the optimum processing conditions of dried products. Thus, it is used in designing drying equipment to meet the purpose. In general, Tg affects the physical properties of food such as stickiness, caking and agglomeration. The effect of moisture content on Tg was covered by almost all studies focusing on Tg of foods. Meanwhile, the effect of pressure on Tg was not well covered due to its scarce availability in the existing literature. In term of test methods for determining the Tg of foods, it seems that not all test methods are suitable for certain type of foods, accordingly, more study on the recommended test methods should be carried out

Recent advances, advantages and limitations of genetically modified foods

Despite the potential benefits of genetically modified foods (GMF), the technology has its limitations and is surrounded by controversy. This review focuses on the recent advances and applications of GM in food production, the present advantages of GMF as well as its limitations and challenges in safety assessment evolving from the recent developments. By summarizing the published information from scattered references in the literature, this paper attempts to contribute to the literature an overall understanding as well as the current status evolution of this field

Thermophysical properties of some species of Malaysian freshwater fish in unfrozen state

Five widely consumed species of freshwater fish in Malaysia were investigated to determine their thermophysical properties due to their handling need for food industry sector from the viewpoint of the heat transfer calculations. These properties encompassed thermal conductivity, specific heat and thermal diffusivity. The species under study were black tilapia, red tilapia, catfish, yellowtail catfish and red pomphret. The major components (moisture, fat, protein, carbohydrate and ash contents) of the fish muscle were determined for each species in a fresh state. Mathematical formulae, which correlate between the components’ values and the thermophysical properties were used to calculate these properties and their variation with temperature. The results were compared with the existing literature of other fish. Slight differences were noticed, however, the results were still within the common range of fish thermophysical values. The differences may be attributed to the different cultural and growing conditions. A logistic model correlated between the thermal diffusivity and temperature variation was developed in this work. It represents the basic requirement to the solution of heat transfer equation by which the thermal processing problems could be solved

The relationship between water activity and fish spoilage during cold storage : a review

This review paper presents clearer picture about the relationship between spoilage of cold stored fish and water activity. The paper was an attempt of presenting the recent existing information and the latest development in this regard. It covered the relationship between water activity and moisture content, water activity control, spoilage of fish and its different phases and the relationship between the spoilage and water activity. The paper revealed that during the initial period of storage some of the characteristics of the fish product reduce in intensity or are lost and in the later stage bacterial degradation of tissues became evident. The water activity (aw) played an important factor in fish spoilage and the growth of different microorganisms depends on its rate. If the aw reduced to 0.6, the growth of bacteria and moulds can be prevented. The detection of spoilage can be determined by controlling water activity and in the same time can be retarded by reducing the aw of the fish by either drying or freezing to keep the fish in good stage with high nutritional and organoleptic quality. The information presented in this study is very important and can assist in preventing spoilage of fishes and their products particularly when production and processing operations are applied

Thermal properties variation of Malaysian yellowtail catfish during precooling process and numerical verification

Malaysian yellowtail catfish, which is widely consumed in Malaysia, was investigated to determine the thermal properties and their variation during precooling process. These properties encompassed thermal conductivity, specific heat and thermal diffusivity. The moisture, fat, protein, carbohydrate and ash contents of the fish muscle were determined in a fresh fish. Mathematical formulae, which correlated between the constituent values and the thermal properties, were used to determine these properties and their variation with temperature. The results were compared with the existing literature of other fishes. Slight differences were noticed, however, the results were still within the common range of fish thermal properties values. The differences may be attributed to the different growing conditions. Models correlated between the thermal properties and temperature variations were developed which are the basic requirements of solving heat transfer problems related to precooling process. These models were used in conjunction with Ansari’s empirical equation to predict temperature history at the midpoint of preassumed slab subjected to precooling process. When a typical real slab was tested experimentally in the precooling process, similar experimental temperature history at the mid point was observed

The recent advances in the nanotechnology and its applications in food processing : a review.

The objectives of this paper was to discuss the latest development of nanotechnology, especially in food industries, to give clearer picture about the effect of nanotechnology in food industries and to highlight the latest applications of nanotechnology in food processing industry. However, the risk issues involving the use of nanotechnology in food were also explored. The outcome of this research revealed that the nanotechnology could be useful for controlling and manipulating the matter at the nanoscale level during processing. On the other hand, nanotechnology could also help the consumers to modify the food depending on their own nutritional needs and tastes. However, from health viewpoint, the potential risks of nanoscale materials and the possibility of the accumulation and translocation of nanoparticles in the body should be avoided

Novel Epstein-Barr virus immunoglobulin G–based approach for the specific detection of nasopharyngeal carcinoma.

Purpose This study was designed to find a reliable Epstein-Barr virus (EBV) immunoglobulin (Ig) G–based diagnostic/screening test for nasopharyngeal carcinoma (NPC) able to demarcate between the NPC-related seropositivity of EBV IgG antibodies and that of other head and neck cancer (HNCA) and control groups. The NPC-associated immunosuppression affects EBV IgA much more than IgG, leading to inconsistent detection of NPC using EBV IgA antibodies. Materials and methods One hundred twenty-two HNCA patients, 42 NPC, 66 laryngeal carcinoma, and 14 hypopharyngeal carcinoma and 3 groups of 100 control subjects were enrolled in this study. Enzyme-linked immunosorbent assay (ELISA) was used to find a specific cutoff value for the NPC-related seropositivity of EBV IgG antibodies. Results NPC group showed higher serum level of EBV IgG antibodies than control and other HNCA groups (P .05). The new cutoff value, mean + 2 SDs of the seropositives group of control subjects who had already been grouped by the traditional cutoff value, proved successful. It succeeded to demarcate between the NPC-related EBV IgG seropositivity and that issued from the persistent, latent, or reactivated EBV infection in the population (P < .05). The sensitivity/specificity of NPC detection by the new cutoff-based ELISA kit, 76.19% and 86%, was close or higher than that of EBV IgA antibodies. Conclusion EBV IgG-based ELISA could be used for the diagnosis of NPC using a new cutoff threshold that excludes the population baseline of EBV IgG seropositivity