Shahid Beheshti University of Medical Sciences, Iran
Tomato juice and paste are special type of dispersions, composed of suspended particles (pulp) dispersed in a colloidal liquid medium (serum), which can be separated by high speed centrifugation. The bright red appearance of soluble solid fraction separated by high speed centrifugation denoted the presence of lycopene in this fraction. Since lycopene is a hydrophobic compound it is not expected to appear in the water soluble fraction. HPLC analysis indicated presence of substantial amount of lycopene in soluble fraction and also confirmed by the appearance of lycopene crystals when observed under Transmission Electron Microscope (TEM). Considerable amount of pectin in the soluble fraction led to hypothesis that pectin facilitated the formation of hydrocolloidal system of suspended lycopene during processing. Enzyme treatment confirmed this hypothesis when pectinase effectively disrupted colloidal system and precipitated lycopene, while protease and cellulase treatment was ineffective. Necessity of the divalent ions to retain the suspension signified the electrostatic interactions in the matrix surrounding lycopene crystals. The presence of peptides in the soluble solids fraction further suggested that association between lycopene and hydrophilic compounds was facilitated by these amphiphilic peptides. Reconstitution of pectin-lycopene was not able to create associations as observed in the soluble solids fraction. Evidently, the hydrophobic lycopene molecules can interact with hydrophobic moieties on the peptide molecules to form complexes which can form a soluble complex in the presence of pectin, where the positively charged groups on the peptide could bind to the negatively charged pectin.