Fermentation Process of Aspergillus oryzae and Aspergillus niger of Kelp Paste Optimized by Response Surface Methodology

In order to study the optimal fermentation process of kelp paste, the effect of four single factors (the ratio of wet kelp to wet soybean, the ratio of Aspergillus oryzae to Aspergillus niger, the salt concentration and the amount of brine addition) on the amino nitrogen of kelp paste was investigated. Based on the single factor experiments, the fermentation process of kelp paste was optimized by response surface methodology. Results showed that, the optimal fermentation conditions for kelp paste were as follows: 3:1 of the ratio of wet kelp to wet soybean, 2:1 of the ratio of Aspergillus oryzae to Aspergillus niger, 14.5% of salt concentration, and 77% of the amount of brine addition. The amino nitrogen was up to 0.76%±0.04% under these conditions, which was basically consistent with the theoretical prediction value. This indicated that using these conditions to make kelp paste could increase the amino nitrogen content and enhance the umami taste. Meanwhile, the nutritional components of the kelp paste were as follows: 171.33±1.15 kJ/100 g of energy, 3.22±0.04 g/100 g of protein, 1.92±0.03 g/100 g of fat, 5.68±0.06 g/100 g of carbohydrate, 2633.00±1.00 mg/100 g of sodium. Among them, the amino nitrogen content conformed to the requirements of the standard of GB/T 24399-2009 "Soybean Paste". This study could provide a certain technical guidance for the development and utilization of fermented sauce products.