Alam, M. S.Afthab Saeed P.P2022-12-042022-12-042021Afthab Saeed P.P (2021). Development of vacuum assisted osmotic impregnation system and CAS freezing technique for safe storage of guava (Psidium guajava) (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.https://krishikosh.egranth.ac.in/handle/1/5810190345A vacuum impregnation (VI) system for the improvement of nutritional characteristics of fresh and fresh-cut porous products and a cell alive system (CAS) freezing setup was designed and developed. The vacuum impregnation system was evaluated for the mass transfer kinetics and specific energy consumption with sucrose impregnated minimally processed guava (Psidium guajava). The VI process was optimized for guava slices using Box-Behnken design under response surface methodology to study the effects of vacuum pressure (50-150 mbar), solution concentration (40-60 oBrix), and solution temperature (40-60 oC) on water loss, solute gain, ascorbic acid content, titratable acidity, color change and firmness. The results obtained suggested that the mass transfer followed second order kinetics and the ratio of water loss to solid gain (WL/SG) attained a mass transfer equilibrium after a vacuum time of 20 min (Relaxation time = 15 min). The optimum VI conditions were observed for a sucrose concentration of 60 oBrix at the solution temperature of 40 oC under the vacuum pressure of 103 mbar at which the WL, SG, ascorbic acid, titratable acidity, color change, and firmness attained a value of 13.0%, 7.73%, 97.85 mg/100g, 0.36%, 5.36 and 1.51 N respectively. The effects of alternating magnetic fields on the freezing kinetics and quality parameters of minimally processed guava in the developed CAS setup were also investigated. The freezing process parameters including magnetic field intensity (2.4 – 8.8 mT) and cube size (2 – 4 cm) were optimized for guava cubes using the Response Surface Methodology technique. A comparative evaluation of freezing kinetics obtained for guava cubes frozen under different magnetic field intensities (2.4, 5.6, and 8.8 mT) was drawn with respect to the control samples. The two-factor, three-level Box and Behnken design suggested that the samples of size 4 cm, treated with a magnetic field intensity of 7.02 mT yielded the optimum freezing characteristics for which the values of phase change time, drip loss, and firmness were 77 min 35 s, 4.97%, and 1.34 N respectively. Under freezing process, the reduction in the phase transition time, in comparison with control samples, was maximum (62.42%) for 4 cm guava cubes at 8.8 mT, followed by 44.71% (3 cm cubes, 5.6 mT) and 27.36% (2 cm cubes, 8.8 mT), indicating the significant effect of guava cube size and higher magnetic field intensities on their freezing quality. The developed passing cooling chamber was effective in reducing the energy cost by 91.36 % (ice-cooled system) and 77.78% (brine-cooled system) in comparison to the refrigerated system. The osmotically pretreated guava cubes developed under optimized conditions i.e. 4 cm cube size, 103 mbar vacuum pressure, 40 oC solution temperature & 60 oBrix solution concentration followed by magnetic field assisted freezing at 7.02 mT for 75 min can be stored safely up to 9 days under passive cooling chamber (<4 oC) with acceptable quality attributes. Overall, the developed system and the process were found to be effective in retaining the quality and enhancing the shelf life of frozen guava cubes.EnglishThesis