| Soy protein isolate(SPI) is a kind of high valuable plant origin protein without cholesterol, which could be easily digested and has good processing functionalities, thus has widely application prospect. However, the flavor could be destroyed when added with SPI due to the raw materials and processing procedures, off-flavor residual and absorption of SPI to the flavor ingredients, especially for certain flavor systems such as strawberry, lemon, mango and yogurt. As a result, the system had an unsatisfactory sensory characteristic and its application was also be limited. In this study, we identified the main flavor ingredients of lemon; prepared L-SPI with lower levels of flavor compounds compared to N-SPI with common preparation procedures; head space solid phase microextraction gas chromatography mass spectrometry was employed to analyze the absorption ability of C-SPI, N-SPI and L-SPI to flavor components in lemon; the absorption parameters of protein to flavor components were calculated with the help of equilibrium adsorption theory; effects among different flavor components when bound to soy protein were explored; the flavor of model systems was adjusted and compensated, so as to provide reference for processing procedures. The main contents are as follows:1. The main flavor compounds in lemon were identified by GC-MS, and 8 kinds of flavor compounds from three categories including aldehyde(citral, furfural), alcohols(linalool, α-terpineol, terpinen-4-ol, geraniol) and alkene(cinene, pinene) were selected and employed for the research of their interactions with SPI.2. The effects of different proteins, categories of flavor compounds, protein concentrations and p H values on flavor compounds-protein interaction were investigated, and the results have demonstrated that C-SPI has the best absorption ability to flavor compounds, and significantly higher than N-SPI and L-SPI; aldehydes and alcohols could be absorbed by proteins, while the release of alkene in solution could be promoted; for aldehydes and alcohols, the absorption ability increased with the increasing of protein concentration; the influence of p H showed the weakest binding affinity of aldehydes and alcohols when p H closes to the isoelectric point, while the highest to the alkene. Calculated the parameters of different compounds, in turn of the absorption abilities from strong to week was citral(n=0.92), geranyl acetate(n=0.55), linalool(n=0.43), geraniol(n=0.35), furfural(n=0.32), terpenol(n=0.26). The binding affinity of compounds with hydrocarbon side chain structure is better than that with the aromatic structure, which was the same to the number of binding site. Four ingredients with long hydrophobic chain and different functional groups including citral, geranyl acetate, geraniol and methyl heptenone were selected and verified the competition between each other. When geraniol was added with citral, geranyl acetate and methyl heptenone, the percentage of adsorption of geraniol was decreased with 6.78%, 5.94% and 8.02%, respectively, which implied that the binding ability of geraniol declined when added with others. For methyl heptenone and geranyl acetate together, the binding ability will be enhanced by each other, 13.52% and 11.64%, respectively. These general conclusions were appropriate for the system with more compounds existing.3. The changes of lemon flavor profiles when added with SPI and its compensation were evaluated. The flavor profile changed significantly, citral and sweetness flavor decreased dramatically, the beany flavor dominated and the wood/leaves flavor was enhanced. According to the absorption proportion, we developed a special formula to adjust the flavor of model system, which was 1.28 : 0.17 : 0.19 : 0.24 : 35.25 : 0.56. The flavor of the mixed system was compensated, and the flavor profile was similar to lemon flavor profile with more citral and sweetness flavor. |
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