The Queensland production of aquacultured black tiger prawns (P. monodon) was 1104.3t in 1995/96. The product is mainly bulk packaged fresh and frozen, and is sold onto the domestic market. Only 2% of Australia’s black tiger prawn production was exported in 95/96. The ex farm gate value of black tiger prawns rose only slightly during the 95/96 season to record an average price of $13.41/Kg. Production of this species is expected to rise in subsequent seasons (Lobegieger 1997). The value of black tiger prawns can be improved through assisting the development of a retail and wholesale frozen product.
The foodservice industry is rapidly growing in Australia, and seafood is a popular choice for consumers when dining out. The National Seafood Consumption Study (1992) found that this was more than likely due to the mess and waste involved with home preparation of seafood products such as prawns but also found that customers were willing to pay premium prices for convenience and top quality. An opportunity exists to target the catering and restaurant trade with high quality and convenient prawn products especially frozen ones due to the capacity to store them. Increased competition has forced producers world wide to look at the downstream activities and increasingly ask the question - "What does the customer want and how can I best satisfy these wants?". The industry recognises that aquaculture shrimp producers from Asia are now providing stiff competition in price and quality (National Seafood Consumption Study 1992).
This project needs to be performed because of a series of extremely valid reasons:
1) Spiral blast freezers, although producing individual products frozen to -35°C through the use of conveyor belts, are expensive to purchase and run. Small room type blast freezers offer a cheaper alternative but unfortunately because the product needs to be packaged before freezing the resultant form is block or bulk frozen. Consideration must be given to the economic status of small to medium domestic and export businesses (SME's & SMD's). These business are unable to expend the capital required to install units such as spiral blast freezers. The growth of small to medium export and domestic businesses needs to be fostered to allow improvement in Australia’s economic status. SME’s and SMD's greatly outnumber the larger companies in the aquaculture and seafood processing industries
2) Brine freezing offers a rapid reduction in temperature for the product to approximately -15°C, but during the steps of glazing and packaging the temperature will rise. During commercial production we have logged temperature rises to between -4 to -9°C (refer to attachment 1). This places the product into the critical freezing zone and causes damage to the texture and water holding capacity as well as magnifying the risk of oxidation. Because the temperature is not low enough the glaze does not instantly freeze onto the prawn so that during storage some degree of fusing together occurs. The standard industry solution to this problem is to simply drop the package onto a hard surface such as the floor to loosen the attachments. Unfortunately, this also results in breakage to the feelers, legs and tails of the prawns detracting from the visual appeal of the product.
3) The product temperature after packing causes a heat load on the storage freezers increasing production costs for manufactures. It also damages products from previous harvests already stored in the freezers compounding the problem. The only alternative economically viable course of action is for the producer to place the product into a standard room type blast freezer to reduce the temperature and industry recognises this as potentially damaging to the product and inefficient due to the slow rate of heat transfer of the combination of packaged product and these freezers.
4) Temperature fluctuations damage the glaze allowing parts of the prawns to be subjected to freezer burn and desiccation. This makes the prawns unattractive to consumers and lowers the value.
5) The producers need to pack the prawns quickly so they are transferred to the storage freezer as soon as possible. This limits the producer to packing in bulk packages, a very unfriendly method for consumers and lessening the likelihood of retail products being produced.
6)Freezing to a lower frozen temperature and more stable storage conditions combined with the protection of an ice glaze will markedly increase the storage stability and shelf life. This makes it easier for producers to plan their years harvest and sales. It also makes retailers and wholesalers/caterers more confident in continuity of supply.
7) Woolworths is currently importing 5 Kg bulk packs of brine immersion frozen Black Tiger prawns from Thailand. Examples of this product were recently viewed / evaluated by the co-investigator of this project and found to be vastly inferior to Australian product in both appearence and taste. This product could easily be produced in Australia and be of a much higher quality. There is also the added benefit of producing a future export commodity for the growing Asian seafood markets.
8) The current solution used in brine immersion freezers is a 26.4% salt solution. With the increasing health awareness of today’s society, there is greater demand for low or reduced salt and fat products. Our proposal would reduce the amount of salt required by the brine immersion system because the freezing point of the refrigerant would be lowered by means other than brine. In fact we would call our system the immersion freezing technique as brine is usually associated with saturated salt solutions.
9) The only change to the refrigeration units envisaged to enable lower temperatures is the replacement of the expansion (TX) valves and refrigerant gas. The current environmental move is to replace Chloro-Fluro-carbons (CFC’s) with non ozone depleting substances as quickly as possible. It is therefore likely that the operator will be required to cover the cost of replacing the gas in his refrigeration system with a newer less damaging gas in the future as services and repairs occur.
10) The challenge associated with the brine immersion system is simply to achieve a lower immersant temperature. A new solution can be used as a substitute for salt brine. One which has a lower freezing point and results in lower product temperature, when removed from the immersion freezer. By doing this the temperature rises during glazing and packing would result in minimum damage to the product. For example, temperature fluctuations between -35 and -25 °C do not damage the product as do fluctuations between -5 and -15 °C. This procedure would involve the minimum financial outlay by small to medium businesses. It also opens up opportunities for producers to increase the amount of value adding they perform and enhances the likelihood of new retail products being developed.
