Studies On Drying Technology Of Dongting Whitebait And The Quality Changes Of Dried Product In Storage Period

The nutritional characteristic of whitebait of high protein, low fat, conforms to modern people advocate the scientific concept of health food. Whitebait is divided into Chaohu lake whitebait, Taihu lake whitebait, Dongting lake whitebait and so on in our country according to different producing area, but Chinese scholars’ studies of whitebait much more concentrated in the Chaohu lake whitebait and Caihu whitebait. Dongting lake whitebait possesses its unique regional characteristics, in order to providing technical support and developing whitebait industry of Dongting lake whitebait’s development and utilization, this paper take Dongting lake whitebait as raw materials to research in the aspects of nutrient content, hot-air drying technology, quality changes in storage period in detail. The most research contents and results of the whole paper as following:1. Nutritional analysis of Dongting whitebait.In the experiment, the main nutritional contents had been tested, and do the analysis and evaluation of fatty acids, amino acids. From the results we know, the average contents of each essential nutrient are followings:moisture content87.27%; ash content (dry basis)1.02/100g; mineral elements (dry basis), sodium (240.59mg/100g), potassium (228.251mg/100g), magnesium (73.128mg/100g), calcium (935.263mg/100g), zinc (3.260mg/100g), iron (3.321mg/100g), manganese (1.328mg/100g), copper(0.117mg/100g); crude fat1.23g/100g (dry basis); crude protein84.56g/100g (dry basis). Dongting whitebait contains21kinds of fatty acids, including eight kinds of saturated fatty acids (37.37%),7kinds of monounsaturated fatty acids (36.57%) and eight kinds of polyunsaturated fatty acids (26.06%); the relative content of unsaturated fatty acid was62.63%. Dongting whitebait contains8kinds of essential amino acids and10kinds of non-essential amino acids, and the ratio of essential amino acid and non-essential amino acids (EAA/NEAA) is83.9%; the ratio of essential amino acid and total amino acids (EAA/TAA) is45.6%, accord with the advantage mode of protein amino acids composition put forwarded by the FAO/WHO. 2. Optimization of hot-air drying technologyThis experiment uses response surface analysis to optimize the hot-air drying technology of Dongting whitebait, which taking hot air temperature, hot air strength and loading capacity for test factors, taking the average energy consumption, the average drying rate, rehydration ratio and sensory evaluation for response value, finally we conclude the optimal process parameters combination of Dongting whitebait under hot-air drying through single factor test and quadratic rotational regression test.(1). In the process of hot-air drying of Dongting whitebait, moisture decrease mainly in the constant speed drying stage, which reduced about65%water content. From the single experiment we can find the higher drying temperature, the higher hot-air intensity and the less load capacity, then the drying rate of Dongting whitebait will be faster, but at the same time, the average energy consumption is much more higher and the overall sensory quality will decline.(2). From the results of quadratic rotation regression orthogonal experiment, we established the quadratic regression equation of average energy consumption (Y1), average drying rate (Y2), rehydration ratio (Y3) and sensory evaluation (Y4) which built on the factors of hot-air temperature (x1), hot-air strength (X2) and loading capacity (X3): Y1=9.6+2.31x1+0.71x2-1.14x3-0.74x1x3-1.45x2x3+1.95x12+1.33x22+1.52x32Y2=0.57+0.081x10.022x2-0.023x3-0.031x1x2+0.031x1x3-0.023x2x3+5.99*10-3x12+4.935*10-3x22-0.044x32Y3=2.92+0.31x1-0.019x2-0.041x3-0.02x1x2-0.02x1x3-0.015x2x3-0.4x12-0.098x22-0.099x32; Y4=8.71-0.89x1-0.35x2-0.27x3-0.37x1x2-0.17x1x3+0.15x2x3-0.69x12-0.33x22-0.53x32. After using the optimization method of nonlinear multi-objective function and expected function, we got the optimal drying technological parameters combination is temperature48℃,hot-air strength0.9m/s, loading capacity0.520kg/m2, and under the technology combination, the results of average energy consumption, average drying rate, rehydration ratio and sensory evaluation are9.34kW-h-kg-1、0.55%·min-1、2.91、8.88.(3). Taking the qualities into compared between the two dried product which dried by optimized hot-air drying technology and natural drying, the result is that the qualities of the former are better than the latter at the aspects of color and luster, organizational structure and freshness, what’s more is hot-air drying can improve40RMB/kg economic income, so this studies’ results has broad application prospects in actual production.3. Effect of storage temperatures and packaging on the quality of the dried Dongting whitebait.Taking the dried Dongting whitebait of optimized technology for raw material to study the effect of storage temperatures(-10、0、10、20、30℃) and packaging types (no packaging, ordinary packaging and vacuum packaging) on the quality, in the experiment, the color and luster, sensory score, TBA value (Thiobrabituric acid), mold content were selected as a quality indicator(1). The change of color:the change of the total chromatic aberration of dried whitebait shows the tendency of increasing at first and then stabilizing during the period of storage. Under the temperature of-10、0、10、20、30℃and30days later, the changes of color are3.38、3.21、3.47、7.75、14.11, the three changes under color of-10、0、10℃are acceptable, changes of color under20,30℃show moderate and severe degradation of color and luster. When studying the effects of packaging to color changes, the results shows, the change value of color under package of no packaging, ordinary packaging and vacuum packaging are4.12,7.75,13.43, that’s to say it is good to control the color by no packaging under storage temperature20℃。(2). The sensory score:the sensory quality of dried whitebait will be declined with time extension. Under the temperature of-10、0、10、20、30℃and30days later, sensory score decreased to10.5、10、9.3、7、4from original14points; it’s obvious to find quality declined under temperature30℃. When studying the effects of packaging to sensory score, the decreased score are12、7、4, so the results infer vacuum packaging is much better than no packaging and ordinary packaging in keeping sensory quality of dried whitebait.(3). TBA value changes: Results showing, storage temperature has obvious significance on TBA value, under temperature of-10、0、10、20、30℃and30days later, the TBA value change to0.021、0.027、0.051、0.23、0.270mg/kg. When studying the effects of packaging to TBA value, result/shows that, in vacuum packaging and15days later, TBA value changes from0.005mg/k to0.021mg/kg, but in no packaging and ordinary packaging condition the time will be shorted by9days, and the difference become much more significant, that’s to say vacuum packaging can prevent dried whitebait fat oxidation effectively. (4). Mould content: in the aspect of studying storage temperature effect on mould content, we known, at temperature of-10、0℃, the mould content are similar at50cfu/g, and under temperature of10、20、30℃, the mould content up to92、128、160cfu/g, it infers that low temperature could prevent mould effectively. When studying the effects of packaging to mould content, the increased range are30、107、150cfu/g respectively under vacuum packaging, ordinary packaging and no packaging. That’s to tell, there is a significant difference at packaging types in controlling mould content.