脱毒海星微波真空干燥工艺优化

为了提高脱毒海星干燥效率、品质及降低能耗,选择微波真空干燥方法进行试验研究。通过单因素试验研究了微波功率密度、脉冲时间及真空度对干燥特性、能耗及蛋白质保留率的影响。结果表明,在3~7 W/g、20~60 s和-0.070~-0.090 MPa范围内,较高的微波功率密度、较长的脉冲时间和较高的负压会缩短干燥时间、提高干燥平均速率、降低能耗;提高微波功率密度不利于蛋白质的保留,缩短脉冲时间和提高负压可提高脱毒海星的蛋白质保留率。利用响应面法探讨了微波功率密度、脉冲时间及真空度对脱毒海星微波真空干燥工艺的综合影响,建立了二次多项式回归模型,并对干燥工艺参数进行了优化。通过分析得出各因素影响的显著性依次为微波功率密度脉冲时间真空度,微波功率密度、脉冲时间对脱毒海星微波真空干燥有极显著性影响(P0.01),且微波功率密度与脉冲时间的交互作用比较明显(P0.05);脱毒海星的最佳微波真空干燥条件为微波功率密度为4 W/g,脉冲时间为60 s和真空度为-0.090 MPa,在此条件下脱毒海星微波真空干燥的综合评分最高,为0.751。研究结果可为脱毒海星干燥的工业化生产和有效利用提供参考。

Optimization of microwave-vacuum drying for detoxified starfish

Starfish is widely distributed in inshore aquaculture zones in China and it is the predator for many aquaculture animals such as oyster, scallop and abalone. Since starfish has strong fecundity and regenerative capacity, the number of starfish has been growing in recent years with the development of inshore aquaculture. The annual yield of starfish has reached 50 000 tons in Dalian, which seriously imperils the development of aquaculture industry. Starfish is rich in nutrients such as protein and polysaccharide, but it contains some toxic substances (such as saponin) as well. It is accordingly a potential resource for feed processing industries after being detoxified. The drying of detoxified starfish has been paid more attention because the traditional drying methods are inefficient and hardly for product quality controlling. In this paper, microwave-vacuum drying of detoxified starfish was carried out and the drying rate, product quality and energy consumption were evaluated. The influences of microwave power density (3-7 W/g), pulse time (20-60 s) and relative vacuum degree (between -0.070 and -0.090 MPa) on the drying characteristics, energy consumption and protein retention rate were firstly studied by single-variable experiments. Results showed that when the microwave power density increased from 4 to 7 W/g, the drying time reduced from 18 to 11 min, the average drying rate increased from 2.95%/min to 4.87%/min, and the energy consumption decreased from 0.0130 to 0.0054 kW·h/g, but the protein retention rate dropped to 83.06% from 92.77%; meanwhile, when drying under the pulse time of 60 s, the average drying rate, energy consumption and protein retention rate would be respectively 1.17 times, 75.16% and 97.47% of that when drying under 20 s pulse time. Similarly, drying under -0.090 MPa relative vacuum degree, the average drying rate, energy consumption and protein retention rate were 1.19 times, 68.41% and 1.09 times of that drying under -0.070 MPa, respectively. It would be more favorite by controlling the microwave power density, pulse time and relative vacuum degree respectively within 4-7 W/g, 30-60 s and -0.080--0.090 MPa. In addition, the response surface methodology (RSM) was employed for the multi-variable experiments, and the regression model was accordingly established. Results of RSM experiments demonstrated that the drying process of detoxified starfish was significantly influenced by microwave power density, followed by pulse time and relative vacuum degree. The microwave power density and the pulse time had significant effect on the comprehensive score (P<0.01). An interaction worked between the microwave power density and the pulse time on comprehensive score (P<0.05). The average drying rate of starfish, energy consumption, protein retention rate and comprehensive score would be 2.95%/min, 0.0118 kW·h/g, 93.80% and 0.751, respectively, under the drying conditions of 4 W/g microwave power density, 60 s pulse time and -0.090 MPa relative vacuum degree. Under this condition, the energy consumption of 1 kg detoxified starfish dried with microwave vacuum drying method could be saved by 8 kW·h compared to hot air drying and the drying cost of starfish could reduce by 4 RMB. Meanwhile, a higher protein retention rate and good quality of the dried detoxified starfish could be obtained by microwave vacuum drying. Microwave-vacuum drying is an effective method for detoxified starfish processing and it is a promising approach for the industrial utilization of starfish.