Post-haze and Protein Composition of Raw Sugarcane Juice
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Abstract:
Post-haze of raw sugarcane juice refers to the phenomenon that the clarified raw sugarcane juice undergoes changes in composition, increase of turbidity or precipitation during storage or commodity circulation. In this study, the basic composition as well as the molecular weight, type, amino acid composition and secondary structures of proteins of the sediment in sugarcane juice were studied by polyacrylamide gel electrophoresis, combined mass spectrometry, amino acid analysis and Fourier transform infrared spectroscopy. The experimental results showed that the main component in the sediment of the raw sugarcane juice was sugar (total sugar content 60.94%), followed by ash and protein (19.52% and 18.43%, respectively), and the content of total phenolics was only 0.62%. The molecular weight distribution of post-haze proteins was about 42 ku and lower than 20 ku, and 12 and 44 proteins were identified, respectively. Among them, the proteins with higher abundance are protein Z, PREDICTED: calmodulin-7 isoform X1, PREDICTED: calcium-dependent protein kinase 34 isoformX1, and hypothetical protein SORBIDRAFT_01g014740. The amino acid compositions of the post-haze proteins and the supernatant proteins were only marginally different, but their secondary structures differed significantly. Except that the content of random coil structure in the post-haze proteins was much higher than that of the supernatant protein, the α-helix and β-turn of post-haze proteins were lower than those of the supernatant protein by 33.43% and 22.42%, respectively, although the difference in the β-sheet was insignificant. In general, proteins with molecular weight slower than 42 ku, high hydrophobicity, low α-helix content and high random coil content more likely contributed to the post-haze of raw sugarcane juice.
