Fourier Transform Infrared Spectroscopy (FTIR) Probing on Interactions of Proteins with Phenolic Compounds in the East African Highland Banana Pulp at Different Stages of Banana Juice Extraction

The ability of East African highland bananas to produce juice is hypothesized to be attributed to the interactions of proteins and phenolic compounds during mechanical kneading of the banana pulps. The mechanism on how this occurs is still unclear though the involvements of their chemical functional groups have been mentioned. To evaluate the influence of proteins and phenolic compounds on juice recovery, this study analyzed and compared functional groups present in the pulp of intact fruit and at different stages of juice extraction. Fourier transform infrared spectroscopy (FTIR) analysis was performed to provide novel information on the changes of the functional groups in the pulp structure in response to banana juice production by mechanical blending. Amide I, amide II regions in FTIR spectra were used to study the structural changes of proteins as the result of protein-polyphenol interactions. FTIR analysis displayed that the mechanical blending led to the decrease of phenolic compounds and shift of protein regions (Amide I and II). Result suggests that, the reduction of the intensity of OH spectra is attributed to interaction of these groups, while the shift in the wavenumber of OH from 3300 to 2250 cm -1, may be attributed to the formation of hydrogen bonding. Moreover, the observed reduced intensity at amide I region at 1655.14 cm -1 could explain the same phenomena. Reduced intensity in the carbohydrate region (995.65 cm -1) of the spent pulp after juice recovery could be ascribed to the reduction of these components in the pulp as most of them were released in the juice product during extraction. The involvements of proteins and pectin with phenolic compounds were validated by the addition of adsorbent and enzyme (bentonite and pectinase) during juice extraction, as the result no juice was recovered, suggesting the chemical structures in protein and pectin were partly broken, hence no observed interactions. The observations suggest interactions between polyphenol, protein and pectic polysaccharides and that all three compounds may have an impact on banana juice release. Understanding these mechanisms could inform improvements in juice production techniques and broader food science applications, particularly in optimizing extraction methods for plant-based beverages.