| Umami taste was accepted as one of the five ‘official’ taste modalities later than the other four(sweet, bitter, sour and salty), which could generate pleasant feeling to some extent. Umami materials include amino acid, peptide, nucleotide, organic acid, multiple flavor agent and so on. It turns out that peptides generally do have a complex taste, causing the unique and full-bodied flavor of food. Despite of its nutrition value, peptide have better absorption and low antigenicity when compared to free amino acid. A large number of peptides with specific amino acid sequences are released during protein hydrolysis. But the process is too complex to figure out completely, leading to the obstruction of umami peptide industrial production. Therefore, it is of great importance to clear the interaction mechanism of taste materials and to enhance the umami taste.Defatted peanut meal hydrolysate with the best umami taste was obtained by a combination of fermentation and hydrolysis. After the blending of hydrolysate and ethanol with various concentrations, different fractions with distinct taste and physico-chemical property were produced. Then an ethanol-treated fraction with the best umami taste was selected for Maillard reaction to create an umami-enhancing hydrolysate(UEH). Seveal techniques were used to further investigate the mechanism of enhancing effect.The defatted peanut meal was hydrolysated efficiently by protease, diastase and cellulase prepared from Aspergillus oryzae. The study on enzymatic processing revealed that the hydrolysate with good umami was obtained after an optimum design. The best ratio of solid to liquid was 1:8. The adjustment of p H value was forbade during the whole 18 hours of hydrolysis with temperature of 55°C. During the hydrolysis, large molecules like proteins are catalyzed into small molecules as peptides or amino acids, causing the reduction of p H value. It was proved that the changing of p H value from 7-5.2 when hydrolysis was beneficial to getting a better umami taste, indicating that umami peptides were released more easily by a combined action of acid protease and neutral protease.The umami hydrolysate was preliminarily separated by different concentrations of ethanol(20%, 40%, 60%, 80%, 100%). The data showed that 60%-fraction occupied the highest total nitrogen percentage of hydrolysate(34.71%) and 100%-fraction ranked the second of 28.70%. Significant difference of taste was determined by panelists. 60%- and 80%-fractions exhibited strong and clear umami taste like sodium glutamate while 20%-and 40%-fractions were tasteless. Supernate-fraction elaborated intensely bitter taste. Being consistent with taste, every fraction had its own specific amino acid composition and peptide distribution. 60%-fraction possessed the highest percentage of umami amino acids(Asp and Glu), reaching to 42%, as well as the highest percentage of 1-3 k Da peptides. And 100%-fraction contained 46.76% of hydrophobic amino acids which mostly showed bitterness and over 91% of the peptide in this fraction were smaller than 1 k Da.60%-fraction was selected for Maillard reaction to get enhanced umami hydrolysate(EUH). The optimal parameters were obtained by single factor experiment and response surface methodology. The best formμLa was solid contents of hydrolysate 10%, p H value 6.5, xylose contents 0.57%, reaction time and temperature 70 min and 94°C. The umami taste of EUH was averagely 28% higher than that of 60%-fraction. It was added xylose that mainly reacted with amine compounds, demonstrating tracking the transformation of xylose could reveal the mechanism of enhancing procedure. After comparing the difference of non/heating or Maillard reaction, some results were concluded as follows: There were less difference of peptide molecular weight distribution and middle reacting products in non/heating and Maillard reaction. As for advanced reacting products(aldehyde/ alcohol/ ketone/ ester/ pyrazine/ furan/ furfural/ ketone and fluorescence material) and final reacting products, Maillard reaction caused the highest production followed by heating reaction. Thus it could be suggested that xylose involved Maillard reaction was able to generate the substance which may possess intense umami and those substances mainly formed in middle and advanced reacting phase. |
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