| Dehydration process for the gel/gelatine aquatic food produces the products with special structure and texture as well as sensory quality while improving their storage stability. Currently, the starch-based products are the most main dehydrated gel food products. The popular technology used is air drying and/or frying expansion or extrusion expansion followed by air drying. The problems related to these products and technologies include long drying time, high-fat and low protein products as well as tedious process. Fish is rich in protein and fresh fish constitutes the most main fresh products, but the processing is the pooreast step in the utilization for the aquatic resources. For one thing, the deodorization inherent in the fresh fish limites its consumption and intensive processing. For anonther thing, both inappropriate processing properties arising from the raw material itselves and limited value added in the fish products restrict the new dehydration technology. Commonly dehydrated gelatine foods such as squid and kelp are produced using salting and natural drying, which are the lagging and extensive method; moreover the resulted products are the low quality and level. With the aim of improving the product quality and enhancing the process efficiency, the thesis studied and discuused the effect of dehydration conditions including (dehydration method, operating parameters and material ingredient) on the dehydration process and the quality of the typical gel (fish muscule and/or starch gel) as well as gelatine product (squid and kelp) using both instrument and sensory evaluation.In order to study the quality of the dehydrated fish muscule gel, the fish muscule gel slices from silver carp were dried using air drying (AD), freeze drying (FD), and vacuum drying (VD) and microwave-vacuum drying (MVD) and quality attributes of the dried products were evaluated in terms of shape, texture, rehydration property, sensory quality and volatile components. The results showed that AD, FD and VD resulted in the different levels of shrinkage while MVD caused some expansion in the4-,5-, and8-mm-thickness samples. MVD products rehydrated faster and had poor restored capacity, low hardness, springiness, cohesiveness aw well as chewiness. MVD products alone exhibited acceptable crispness and favorable odor. The rehydrated dried products were preferred in the order:FD, VD, AD, MVD. GC-MS revealed that drying significantly decreased the n-alkanals and1-octen-3-ol content and produced2-methylpropanal,3-methyl-butanal, and furfural in MVD products.To understand the role of thermal conditions and types of gels in the structure and quality development of MVD products, the property of the gels (tapioca starch gel and/or fish gel) produced under thermal conditions and the quality of MVD gel slices were studied. The results showed that after MVD the fish muscule gel and the mixed gel with good viscoelasticity devolope an expanded and/or porous structure similar to that created by frying in starch gel for which the interaction among proteins was resposible, the mixed gel slices with the higheast expansion showed a good sensory acceptability. The higher severity of thermal treatment favored greater expansion in the mixed gel chips due to developing a homogenous co-gel with a uniform structure and high moisture mobility.To understand the role of formulation in the structure and quality development of MVD products, the effect of salt, sugar, ratio offish meat and starch as well as types of starch on the quality of MVD gel slices were studied. The results showed that salt-soluble myofibrillar protein was the key factor of developed expansion structure in MVD product. Both high content in salt and high ratio in fish favored the expanded and crispy structure. The gel containing a high proportion of amylopectin, such as waxy corn, cassava, potato starch, displayed a more excellent expansion capacity than wheat and corn; the resulting products had a low hardness, high crispness and good sensory quality. Use of sugar inhibited the expansion of the gel slices and reduced their crispness; there was observed no significantly negative effect on sensory quality.Finally, the effect of infrared wavelength and air velocity on drying behavior and product quality of the shredded squid and kelp were studied base on their infrared absorption characteristics in a novel infrared heating forced convection system and compared with AD and MVD. By setting the dry medium temperature of50℃, the constant surface temperature reached is always higher than that of the dry medium and increases from52to63℃with the increase of the air velocity from0to2m/s. The heating and drying at the wavelength of2.5-3.0um is more effective than that at the infrared wavelength of5.0-6.0um. The total drying time significantly decreased while specific energy consumption linearly increased with the air velocity. Air velocity had no significant effect on the quality of the products of both, but the quality of the kelp strongly depended on the wavelength. Compared with AD, the infrared heating and drying took less time and consumption which produced the products similar to AD, but better than MVD ones. |
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