大豆酱油电渗析脱盐工艺参数对其脱盐率及品质的影响

为了降低大豆酱油的含盐量，该文利用电渗析技术对大豆酱油进行脱盐处理，通过单因素试验探讨了电压、流速、pH值对电渗析脱盐效果的影响，确定了较佳电渗析工艺。结果表明在电压为9 V，流速为2.4 cm/s，pH值为4.2，电渗析50 min时脱盐效果较好，氨基酸态氮损失较小，氨基酸态氮损失19.4%，脱盐率达到81.6%。利用氨基酸自动分析仪和气相色谱-质谱联用仪（gas chromatography-mass spectrometry）分析了电渗析前后游离氨基酸及挥发性风味物质的变化规律，结果表明电渗析过程中氨基酸及风味物质均有损失。几种苦味氨基酸如组氨酸、精氨酸、赖氨酸损失较大，分别损失了23.79%、26.39%和28.5%；电渗析过程中，酱油风味物质中醇类、酚类损失较大，尤其是4-乙基愈创木酚损失最多，但因其气味阈值较低，因此对酱油风味影响较小。研究结果为减盐酱油系列产品的生产提供了参考和依据。

Effect of electrodialysis desalination technology parameters on ratio of desalinization and quality of soy sauce

Abstract: Soy sauce is a kind of nutritional condiment which contains various bioactive components. In the production of soy sauce, a lot of salt has been added in order to prevent the growth of pathogenic microorganisms. However, excessive intake of high salt food is harmful to our health, so the study of the desalination of soy sauce is very valuable. The technology of electrodialysis has applications in the areas of pollution controlling, resource recoverying and chemical processing. At present, no information is available about the effect of electrodialysis desalination (ED) on the changes of flavor compounds and amino acids of ED-treated soy sauce. In this paper, a traditional Chinese soy sauce containing 16 g/100 mL sodium chloride was desalted by laboratory-scale electrodialyser equipped with a stack composed of eight cation and seven anion-exchange membranes, and the impact of operating voltage, flow rate and pH value on desalination was evaluated. The optimal condition of electrodialysis was obtained through the single factor experiment. The result indicated that the salt content could be reduced by 81.6% at the voltage of 9 V, the flow rate of 2.4 cm/s, and the pH value of 4.2 with 19.4% amino acid nitrogen losing. The analysis of variance showed that pH value had a significant effect on the loss of amino acid nitrogen (P<0.05), while the desalination rate was not changed remarkably (P>0.05). After electrodialysis, the changes of free amino acids and volatile flavor compounds were analyzed with amino acid automatic analyzer and GC-MS (gas chromatography-mass spectrometer). The results showed that part of free amino acid and aroma of soy sauce lost. The influence of electrodialysis on the changes of free amino acids in soy sauce was determined under various pH value conditions (3.2, 3.7, 4.2, 4.7 and 5.2). Several kinds of bitter amino acids lost, and histidine, arginine and lysine lost by 23.79%, 26.39% and 28.5% respectively. As their isoelectric point was deviated from the solution pH value, they were positively charged in solution and susceptible to leave the material liquid chamber with the effect of electric field. Besides, some flavor compounds of soy sauce lost, including alcohols and phenols, especially the 4-ethyl-2-methoxy-phenol and 2-methoxy-phenol significantly decreased. However, due to its low odor threshold, it had little effect on the flavor of soy sauce. Since the ED unit was generally operated in the batch mode, it would be feasible to produce soy sauce with arbitrary salt concentration. The results prove that electrodialysis is a feasible method with a remarkable decrease of salt content.