Lycopene is a major carotenoid in tomatoes and epidemiological studies suggest that consumption of food rich in carotenoids lowers the risk of developing certain types of cancer and chronic diseases. However, very little is known about its fate in tomato products subjected to a range of combined pressure-temperature (P-T) treatments. Likewise, little is known about the pressure-temperature uniformity during combined P-T processing. This study was conducted to investigate the effect of pressure-thermal treatments (0.1, 500, 600 & 700 MPa; 30-100 deg. C, different time intervals) on post processing extractability, isomerization, bioaccessibility and storage stability of lycopene in tomato juice. Finally, a study was conducted to evaluate the feasibility of using a chemical M-2 (4-Hydroxy-5-methyl-3(2H)-furanone) as a potential marker for understanding combined P-T process non-uniformity.
Combined pressure-thermal treatments (Pressure Assisted Thermal Processing (PATP), High Pressure Processing (HPP)) resulted in up to 12% increase in lycopene extractability over thermally processed (TP) and unprocessed control tomato juice. In addition, all-trans lycopene showed stability to isomerization in tomato juice samples subjected to HPP, PATP and TP. The post processing retention of β-carotene was a function of processing time, temperature, pressure, cultivar used and type of juice (raw vs. hot break).
During storage, lycopene degradation varied as a function of cultivar, processing method, storage temperature, and time. Increase in storage temperatures also increased degradation. Among the stored juices, HPP processed juice showed the least lycopene degradation. Also, HPP and PATP juice samples better retained lycopene cis isomers and color during storage. β-carotene showed good stability in the processed samples during storage. A two-step first order equation was used to predict the changes in lycopene concentration over the course of storage. The processed juice samples also showed microbial stability over the course of 52 week storage at 4, 25 and 37 deg. C.
The in-vitro bioaccessibility studies showed that regardless of the processing conditions, less than 0.5% of the lycopene originally present in the processed juice got micellarized. No significant difference was found between the amount micellarized between various treatments (p>0.05). All-trans β-carotene micellarization in the processed juice (HPP, PATP, TP) was significantly higher (p<0.05) as compared to the raw unprocessed juice (control). Interestingly, hot break juice subjected to P-T treatments showed 15-30% more all-trans β-carotene micellarization than the raw juice subjected to similar P-T treatments.
The formation and stability of chemical marker M-2 was influenced by heat (which favored the marker formation), pressure (which hindered marker formation) and pH (higher pH hindered marker formation). The initial concentrations of M-2 in the gels were 9.17 and 6.10 mg/100g at pH 6.10 and 8.25, respectively. The marker yield during thermal treatment (at 0.1 MPa, 105 deg. C) increased with increase in holding time (following a first order kinetics) and decreased with increasing pH. Pressure treatments from 350 to 700 MPa at 30 deg. C reduced the chemical marker formation for both pH values investigated. The net final concentration of the marker formed during PATP was higher than HPP, but lower than thermal treatments.
In summary, the present research shows that combined pressure-temperature treatments could be an attractive approach for preserving tomato juice quality.