Graduate Thesis Or Dissertation
 

Application of Ohmic Heating for Accelerating Fish Sauce Fermentation

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  • Fish sauce is a fermented condiment made primarily from anchovies and is popularly used in Asian countries as it provides unique salty and umami flavor. Its consumption is no longer limited to Southeast Asian countries, but extended to Europe, United States and Canada as a condiment in their food. Fish sauce fermentation is a time-consuming process at ambient temperatures and uses endogenous enzymes and microbes to completely degrade proteins to amino acids and/or di-peptides. Therefore, many trials and research efforts have been made to accelerate fermentation by adding exogenous protease or inoculating microbes. However, further research was suggested as there were issues such as undesired off-flavor and aroma, loss of color, and excessive energy consumption when the methods were applied. Therefore, ohmic heating and Pacific whiting were applied in this research to accelerate the fish sauce fermentation and suppress the negative outcomes. Ohmic heating is a heating system that can generate consistent and uniform heat in various heating rates through electrical resistance between two electrodes. Consistent and uniform heat was believed to accelerate the fermentation by increasing endogenous protease activity and microbial activity. Pacific whiting (Merluccius productus) is highly sustainable and abundant in the Pacific Northwest as a marine stewardship council (MSC)-certified species. Although Pacific whiting is cost effective and highly sustainable species, Pacific whiting was not fully utilized until surimi production started in 1991-1992 due to extreme softening of the fillet caused by three major proteases (cathepsin L, cathepsin B, and cathepsin H). However, intense protease activity was believed to accelerate fish sauce fermentation by rapidly degrading proteins during initial stage of fermentation. In addition, Pacific whiting is a gadoid fish which has low histidine, a precursor of histamine, content. Therefore, substituting anchovies, scombroid fish species which contains abundant histidine, with Pacific whiting was believed to lower the histamine content in fish sauce. In our research, Pacific whiting mince containing 25% salt was fermented in either water bath or ohmic heating at various temperatures sequentially for 8 weeks: 25oC for Week 1, 35oC for Week 2, and 55oC for Week 3 to 8. Different temperature conditions were applied for ohmic heating and water bath to provide optimum conditions for three major proteases in Pacific whiting (cathepsin L, B and H) and to mimic conventional heating method. Although identical temperature and incubation time were provided for both water bath sample and ohmic heating sample, a significant difference was found between the two samples. Brownness, taste value, and overall nitrogen content were significantly higher with ohmic heating than those with water bath (p < 0.05). The difference was hypothesized to be due to electroporation and uniform heat penetration by ohmic heating. Regardless of heating methods, Pacific whiting fish sauce demonstrated significantly lower histamine content when compared with commercial fish sauce made with anchovies (p < 0.05). This study discovered that ohmic heating can be utilized for fish sauce production as it significantly accelerates fermentation and add a value to the utilization of protease-laden Pacific whiting.
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