Reduction Of Acrylamide In Fried Potatoes By Biological Methods

The formation pathway of acrylamide was found to be linked with the Maillard reaction at more than 120℃, with reducing sugars and asparagine as crucial precursors. In order to reduce the amount of acrylamide, potato slices were subjected to yeast fermentation or asparaginase treatment prior to deep-frying to lower the level of precursors. Thermal stability of asparaginase during application was also studied.The paper studied the optimum conditions for yeast to metabolic reducing sugar in potato slices. Results showed that reducing rate of reducing sugar in experimental groups were higher than control groups. The optimum conditions for decreasing reducing sugar contents were a 1:4 solid-liquid ratio, a fermentation temperature of 37℃, and addition of 0.5% yeast. Reducing sugar reduced almost to zero in potato slices treated under optimum conditions for 110 min and the corresponding deep-fried potatoes had 70% less acrylamide than control groups detected by improved HPLC-MS/MS method. Sensory evaluation results showed that there were no significant difference between the quality of yeast pretreated fried potatoes and the samples without any pretreatment.Asparaginase hydrolyze asparagine to aspartic acid and ammonia specifically. Results showed that asparagine content in the potatoes treated by asparaginase were reduced by 31.11%, from the initial 2.25 mg/g to 1.55 mg/g in an asparaginase solution(1750 U/L) at 60℃ for 20 min. The acrylamide content in pretreated French fries were reduced by 52.91% and 78.55% compared to control groups and the samples without any pretreatment respectively. Chromatic meter was used to determine the color changes of fried potatoes. According to the results, the color of pretreated fried potatoes was more uniform and the oil content had no significant changes compared with the fresh samples.So as to improve recycle rate of asparaginase, stability of asparaginase in the application process was also studied. Results showed that potato extracts can improve thermal stability of the enzyme. Asparaginase can keep high activity in potato extracts after continuous use in 60℃ while the half-life of the enzyme in the pure water was 0.5 h. The paper concluded that the stability factors of asparaginase in potato extracts were small molecules by ethanol precipitation and dialysis methods. The paper also systematic studied the influence of metal ion, amino acid, sugar and alcohols on asparaginase thermal stability. Results showed that Fe2+, K+, [NH4]+ and amino acids can improve thermal stability without influencing asparaginase activity. The relative activity of enzyme were still higher than 40% in a 40 mmol/L [NH4]+ solution at 60℃ for 8 h, while asparaginase were completely inactivated in the water after 1 h. Some material such as glycerol, PEG 200, mannitol, trehalose were commonly used to reduce water activity can not significantly improve asparaginase thermal stability. The combination of different stabilizers were further studied and the best group to improve asparaginase thermal stability was 20 mmol/L [NH4]+ and 2%(m/v) glycine. The residual activity of asparaginase was more than 60% in the best complex stabilizers at 60℃ for 48 h. Thermal stability of the enzyme was greatly increased compared with the enzyme in any single stabilizers.Protein fluorescence spectroscopy and differential scanning calorimetry analysis methods(DSC) were used to investigate the change of protein structure and properties; thus reveal stabilizing mechanism of the stabilizers. Results showed that the surface hydrophobic strength of the enzyme were increased with the extension of time in the presence of complex stabilizers, rising to 302.38% and 384.76% at 60℃ for 8 h and 48 h, the corresponding residual enzyme activity reduced from 100% to 71.91% and 60.60% respectively. The increased protein surface hydrophobicity strength showed the constantly exposed hydrophobic groups inside the proteins. Enzyme activity decreased as the result of great changes of the structure. The fluorescence intensity of the enzyme can be quenched by complex stabilizer s. The mechanism is dynamic quenching because quenching constant increased with the rising temperature by fitting analysis of the Stern-Volmer equation. DSC results also showed complex stabilizers increased thermal denaturation temperature of asparaginase, thus improved thermal stability of the enzyme.