Abstract
The influence of ratio of feed and heat transfer surface area (RFHTSA) and heating medium temperature (HMT) on the rates of heat transfer during heat extraction of guava juice and tomato pulp and heating of ingredients for guava jelly and tomato ketchup in an agitated jacketed vessel as well as on the quality of the products was studied. Also, the effect of tamarind kernel powder (TKP) as gelling agent on the quality of guava jelly and as thickening agent on the consistency of tomato ketchup was studied. A pilot scale agitated jacketed vessel was fabricated where, mustard oil was used as heating medium in the jacket. Heat extraction of guava (Psidium guajava cv. Kazi Peyara) juice and tomato pulp was performed in the agitated jacketed vessel with variable RFHTSA and HMT. Considering the aspects of crude pectin and ascorbic acid content, the combination of RFHTSA and HMT of 40.71 and 135°C respectively was identified as the best heat extraction system for guava juice. Similarly, in case of heat extraction of tomato pulp, the best combination of RFHTSA and HMT was found as 32.32 and 152.5°C respectively. Crude pectin content gets decreased after a certain period of heat extraction in both the cases. Therefore, heat extraction should be continued up to a certain point, where the crude pectin will be maximum. The empirical dimensionless relationship of heat transfer characteristics during heat extraction of guava juice and tomato pulp was developed for the agitated vessel as, \(\text{Nu}_\text{m} = 0.37\text{Re}^{0.42}\text{Pr}^{0.33}(\mu_\text{b}/\mu_\text{w})^{0.14}\) ; at 3250 < Re < 20050 and anchor to wall clearance < 2.54 cm. Heat extracted guava juice and tomato pulp obtained through applying the best heat extraction conditions identified as above were used in preparation of guava jelly and tomato ketchup respectively while, heating of ingredients for the products was also conducted in the agitated vessel with variable RFHTSA and HMT. Considering the aspects of the ratio of invert sugar and sucrose, results on sensory evaluation, vessel capacity utilization and ascorbic acid, heating system using the combination of RFHTSA and HMT of 42.43 and 165°C respectively was identified as the best heating system for guava jelly making. Similarly, on the basis of the results on sensory evaluation, vessel capacity utilization, ascorbic acid and lycopene content, it was observed that, the best combination of RFHTSA and HMT was found to be 31.47 and 160°C respectively in preparation of tomato ketchup. Maintaining the above heating conditions, quality of the products may be ensured uniform in all the batches of production. The empirical dimensionless relationship of heat transfer characteristics found in cases of heating of ingredients for guava jelly and tomato ketchup as, \(\text{Nu}_\text{m} = 0.462\text{Re}^{0.44}\text{Pr}^{0.33}(\mu_\text{b}/\mu_\text{w})^{0.14}\); at 275 < Re < 625 and anchor to wall clearance < 2.54 cm. It was observed that with the increase of the RFHTSA, overall heat transfer co-efficient decreased in all the cases. In all the cases, the overall heat transfer co-efficient increases at a constant rate with the increase of HMT which, follows linear relationship between the two variables. The empirical co-relations found in this work will help in understanding the heat transfer phenomenon for preparation of the products. Applying the best combination of RFHTSA and HMT found as above in case of heat extraction of guava juice, guava juice was extracted followed by used in preparation of guava jelly with pectin, agar agar and different doses of TKP in different treatments using the agitated vessel. In respect to overall acceptability, use of 1.66% TKP on the basis of final product, the jelly formulation was highly acceptable and there was non-significant difference between the formulations of jelly prepared with this dose of TKP and pectin. Thus, the low-cost TKP could be a good substitute for costly pectin in making jelly. Similarly, using the best combination of RFHTSA and HMT found as above in case of heat extraction of tomato pulp, tomato pulp was extracted and then used in preparation of tomato ketchup with pectin, carboxymethyl cellulose (CMC) and TKP in different treatments using the agitated vessel. It was found that, tomato ketchup prepared using hot broken tomato pulp with 1.00% TKP on the basis of final product, was highly acceptable. Thus, the low-cost TKP also could be a good substitute for costly pectin and CMC in making tomato ketchup.