Effects of handling and preservation methods on qualities of giant freshwater prawns | |
| Author | Punchira Vongsawasdi |
| Call Number | AIT Diss. no.AE-96-02 |
| Subject(s) | Shrimps Food handling |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AE-96-02 |
| Abstract | During ice storage, giant freshwater prawn (macrobrachium rosenbergii) are susceptible to textural problem called mushiness. It is believed that the cause of this phenomena is mainly due to the activities of enzymes released from hepatopancreas after the death of the prawns. In this study, the qualities of prawns subjected to efferent preparation procedures, postharvest handling techniques, and preservation methods were evaluated using various instrumental, chemical and sensory methods. The relationship between the resulting quality parameters obtained from the different evaluation methods was studied by correlating the parameters with each other. Textural quality was determined instrumentally using three types of test cells (compression anvil, Kramer shear cell and Warner-Bratzler apparatus) based on maximum load (Load) and energy up to breaking point (Energy). All test cells yielded good linear relation with storage time but the compression anvil test provided the highest R-square values from regression of Load and Energy on time (0.93 and 0.96, respectively) while requiring the least quantity of sample and yielding average values from the whole body of the prawn, The compression anvil was subsequently used for all instrumental tests in the succeeding experiments. The instrumental and chemical quality parameters used to evaluate the feasts of cooking time were Load, Energy, percent cooking loss (% Loss) proteolysis index (PI) and percent expressible juice (% Juice). All parameters increased with cooking time except PI and % Juice which showed the opposite trend. Regression of the chemical and instrumental parameters on the results of sensory evaluation yielded good correlation among the three methods with the resulting R-square values ranging from 0.93 to 0.99. Prawns cooked for 5 min. were moderately firm and very juicy thus obtaining the highest acceptability in sensory evaluation. Subsequently, the cooking time used for all succeeding experiments was 5 min. Effects of handling on quality attributes were also investigated by subjecting prawns to conditions which simulated handling practices in the domestic and export markets. Prawns mixed with crushed ice were stored at room temperature (25+2'c) for 48 hrs for domestic handling trial, while for export handling, the samples were kept in a cold room at0+1'c for 72 hrs. Both resulted to similar trends in quality changes evaluated through sensory, chemical and instrumental means but the magnitude of the change in domestic handling was greater than in the export trial. Load, Energy and % Loss increased as storage time increased up to 12 hrs., after which prolonged storage resulted to a decrease in these parameters. On the other hand, % Juice decreased during the first 12 hrs, then gradually increased afterwards. Other chemical parameters such and soluble-insouluble collagen ratio (Collagen ratio), PI and total volatile nitrogen (TVN) increased with storage time. All events can be attributed to post-mortem change theory and autolysis due to enzyme activities. Good correlations among instrumental, chemical and sensory evaluation results were obtained for texture and taste-odor attributes of samples from both handling trials. Blanching and deheading prawns were found to maintain prawn qualities very well due to reduced enzyme activity while samples which underwent proper handling procedures exhibited some quality changes after 48 hrs. blanched prawns had less expressible juice but and more shrimp-like flavor than deeded prawns. The effects of three common commercially-practiced preservation methods, individual quick freezing (IQF), freeze drying and canning, were studied. IQF increased the moisture content of prawns due to the glazing process. However, in atramental and chemical quality parameters of the prawns changed slightly after storage at -25=3'c for 6 months. Goo correlations between instrumental, chemical and sensory quality results and storage time were obtained with R-square values ranging from 0.93 to 0.99. Treatment with citric acid to optimize the color of the prawns prior to freeze-drying was also studied and highest acceptability was attained with prawns dipped for 25 min. in 0.25% citric acid solution. Freeze-dried prawns showed no significant instrumental, chemical and sensory quality changes after 6 months of storage due to inactivation of enzymes during processing. Prior to canning, soaking the prawns in 7% sodium tripolyphosphate (STPP) for 15 min was found to counteract the effects of heat treatment (done at 115'c for 24 min) on color and texture of the product. STPP treatment had significant effects on Load, % Loss and texture, Juiciness and acceptability scores. Due to exposure to high heat which deactivated autolytic enzymes, canned prawn samples exhibited no significant quality changes (instrumental, chemical or sensory) after 6 months of storage. Product cost/unit of IQF prawns were the cheapest compared to Freeze dried and canned prawns mainly due to the minimal weight loss during process. |
| Year | 1996 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AE-96-2 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Athapol Noomhorm |
| Examination Committee(s) | Lin, Chang Kwei;Yakupitiyage, Amararatne;Nip, W.K. |
| Scholarship Donor(s) | Royal Thai Government(RTG) |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1996 |