Abstract:

To explore the effect of thermal treatment on quality of litchi juice, the changes in browning index (A420, absorbance at 420 nm), pH and the contents of soluble solid (SS), ascorbic acid, 5-hydroxy-ethylfurfural (5-HMF), sugar, total phenols and volatile aromatic compounds of litchi juice during thermal treatment at 60－100 ℃ were measured. Results showed that the A420 of litchi juice was followed by zero order reaction kinetics within 0－60 minutes of thermal treatment. During the thermal treatment, the contents of ascorbic acid and total phenols were sharply declined, while the change of sugar content was not obvious. These results suggest that degradation of ascorbic acid and condensation of phenols are the major factors affecting non-enzymatic browning of litchi juice. Meanwhile, thermal treatment exhibited a negative effect on flavor components of litchi juice. Detected by headspace solid phase micro extraction combined with gas chromatography-mass (HS-SPME-GC/MS), the contents of lower alcohols and esters exhibited a significant decrease, whereas some sulfur containing compounds and fatty alcohols were generated.

Key words: thermal treatment, litchi juice, browning, aroma