Effect of high-pressure thermal sterilization on quality of compound fermented wheat flour paste

Abstract: Compound fermented wheat flour paste is favored by Chinese consumers as a traditional condiment, which is made of fermented wheat flour by Aspergillus oryzae. During the fermentation process, sterilization plays a key role, because the compound fermented wheat flour paste is prone to getting polluted. Heat sterilization is a conventional and simple method to kill the microorganisms in the products. However, the method has undesirable influences on the qualities of the product such as texture and flavor due to uneven heating. Besides, the microorganisms cannot be killed thoroughly. The high-pressure thermal sterilization (HPTS) is a new type of sterilization technology which combines the methods of pressure and temperature. And this approach can extend the shelf life and maintain the safety of the products. The properties such as rheological characteristics, color, specific aroma compositions and fatty acid compositions in the compound fermented wheat flour paste before and after processed by the HPTS were analyzed, in order to study on the quality of the compound fermented wheat flour paste. Samples were subjected to different pressure treatments (300, 400 and 500 MPa) for 10 min at 45℃, and then the properties of rheological characteristics, color, specific aroma compositions of all the samples were analyzed by rheometer, automatic chromatic meter, and GC-MS, respectively. The results showed that under HPTS treatment the viscosity of the compound fermented wheat flour paste reduced, and with the increasing of the pressure, the viscosity decreased. However, the compound fermented wheat flour paste was still pseudoplastic fluid, and the type of the fluid was not changed after the processing. Besides, after dealed with the HPTS processing, the chromatic aberration of these samples reduced significantly, and the brown index (BI) declined. But there was no significant change in the level of the parameter of the properties of color (L* and a*), which present the brightness and the degree of the red and green, respectively. In addition, the volatile flavor substances in the compound fermented wheat flour paste mainly contained aldehydes and esters. 5-Methyl-2-phenyl-2-hexenal, Furfural and ethyl oleate were the main aroma components. After treated, various aldehydes content decreased significantly. In particular ethyl oleate cannot be detected in the processed samples. However, the contents of phenylacetaldehyde and limonene increased. Moreover, there were new compositions such as benzaldehyde and phenethyl alcohol found in the processed samples. Finally, the fatty acids contents of the samples were analyzed and the fatty acids composition didn't change significantly after the HPTS treatment at 400 MPa, 45℃, 10min , except the content of the oleic acid. To sum up, there was no significant change in the properties of color (L* and a*), specific aroma compositions and fatty acids compositions of the compound fermented wheat flour paste; the viscosity of the samples treated at 400 MPa was similar with the unprocessed samples than the samples treated at 500 MPa HPTS. Therefore, the treatment of HPTS at 400MPa, 45℃, 10min could maintain the quality of the compound fermented wheat flour paste such as texture, color, specific aroma compositions and fatty acids compositions.