ผลของกล้าเชื้อจุลินทรีย์ โปรตีเอส และโคจิถั่วเหลืองต่อคุณภาพของน้าปลาปลาสร้อย

Abstract

The study aimed to investigate the effects of microbial seed culture, proteases and soybean koji on quality of Siamese Mud Carp fish sauce. Totally 45 isolates of halophillic bacteria were isolated from 38 samples of fermented freshwater fish. Screening for protease producing capability by plate screening found that only 8 isolates demonstrated the protease production and formed clear zone and the isolate VK31 and VK20 were selected as the protease producer for further study. According to the morphological characteristics and the comparison data of 16S rDNA nucleotide sequence analysis, isolate VK20 and VK314 were identified to be Virgibacillus halodenitrificans and Kushneria avicenniae, respectively. Fermentation of Siamese Mud Carp fish sauce were conducted at 25-35oC for studying the effects of additional ingredients on qualities of fish sauce. The experimental were divided into 5 formulas including control (CTR1), addition of VK31 and VK20 seed culture (PCU2), soybean koji addition (SBK3), addition of crude enzyme from VK31 and VK20 (CEZ4) and commercial protease (CMZ5), respectively. Fish sauce samples were sampling with 1 or 2 months intervals during the fermentation and analyzed for microbiological and chemical properties. For the microbiological quality, the number of total bacteria was the lowest in the control formula (CTR1) and none of yeast, fungi and lactic acid bacteria was detected, while yeast and fungi were found in the largest number in the formula of SBK3. The chemical quality analysis found that the pH values of all Siamese Mud Carp fish sauce formulas were gradually decreased to acidic condition after 10 months fermentation. The pH values were ranged from 5.75 to 6.55. In addition, SBK3 formula contained the highest quantities of total protein up to 17 gram per 100 gram fish sauce. Moreover, the total amino acid was found 7.57 gram per 100 gram fish sauce which is 44% of total protein by weight and passed the industrial standard of local fish sauce. Whereas, the commercial Siamese Mud Carp fish sauce was found only 6.73 gram per 100 gram fish sauce. SBK3 formula showed the amino acid glutamic acid and lysine as high as 1.17 and 0.94 gram per 100 grams of fish sauce. Additionally, the profiles volatile compounds of SBK3 fish sauce were different from others particularly a peak at retention time of 54.63 minute. The physical quality by color determination found that the range of L* values were 24.79 - 27.78, a* values were -0.22 - 1.77, and b* values were 6.05 - 8.55. The sensory test of all Siamese Mud Carp fish sauce formulas found that all are not different from commercial Siamese Mud Carp fish sauce. The scores of odor and overall of SBK3 formula were the highest and almost similar to the commercial Siamese Mud Carp fish sauce. This was suggested to be affected by the specificity of enzymes either from Aspergillus oryzae in soybean koji or commercial enzyme with Siamese Mud Carp protein. The results from this experiment indicated that addition of 3% by weight of soybean koji and commercial pepsin improved the Siamese Mud Carp fish sauce properties particularly the amino acid content, color and odor.