Flow characteristics of aloe vera juice concentrates (1.5-5.5°Brix) were determined over a range of temperatures (15-55C) by using coaxial cylinder geometry. Aloe vera juice exhibited non-Newtonian fluid behavior which was well described by power law model. Functional groups were characterized by Fourier-transform infrared (FTIR) spectroscopy indicating the presence of O-acetyl and shifting of -CH bonds. Effect of test temperatures at different shear rates on viscosity was evaluated using Arrhenius-type equation and the activation energy values were evaluated which ranged between 12.148 and 53.073 kJ/mol. Effect of concentration was evaluated using power type and exponential type equations. An expression for combined effect of temperature and concentration was developed. Small amplitude oscillation sweep measurement was also carried out and the frequency sweep test exhibited viscoelastic nature of juice.

The effect of high pressure processing (HPP) (600 MPa/15 min/56°C) and thermal processing (TP) (95°C/5 min) on the quality characteristics of aloe vera-litchi mixed beverage samples (ALMB) stored at 4, 15 and 25°C were studied. The total color difference and browning index of ALMB samples increased with the storage period for both HPP and TP treated samples under all storage conditions. HPP of ALMB resulted in inactivation of pectinmethylesterase (PME), polyphenoloxidase (PPO) and peroxidase (POD) to 34, 65 and 62 %, respectively after immediate processing, whereas, TP treatment lead to 83, 79 and 78 %, respectively. The residual activity of all the studied enzymes decreased with storage period. The ascorbic acid loss of up to 22 % was observed after HPP treatment and up to 31 % for thermally treated samples. Minimal changes were noted for phenolics content after HPP as well as thermal processing. The natural microbiota present in samples was below the detection limit (1 log CFU/mL) throughout the storage period. The shelf life of HPP and TP treated samples stored at 4°C was estimated to be 100 and 80 days, respectively, based on the sensory quality, ascorbic acid degradation and instrumental color difference.

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Effect of pressure level (60-740 MPa), process dwell time (3-40 min), and pH (2.32-5.68) on rheological properties, pectinmethylesterase (PME) enzyme activity and microbiological characteristics of aloe vera juice was studied. A quadratic model was developed for rheological parameters and it was found that pressure level had the most significant effect on all the responses (p < 0.05) followed by pH and dwell time. Pectinmethylesterase activity was evaluated and a maximum of up to 30% inactivation was obtained. Microbial analysis of high pressure treated samples revealed that samples treated at 400 MPa for 20 min at pH 4 reduced microbial counts to <10 cfu mL −1 achieving up to 5.66 log cycle reduction.

Effect of high pressure (HP) pre-treatments (300-500 MPa for 5-15 min) on dehydration characteristics of aloe vera cubes (AVC), dried at 50-70 °C and air velocity of 1-2 m/s were studied. Pre-treatments resulted in higher drying rates leading to a reduction in drying time compared to untreated ones. The drying rate and drying time were most significantly affected (p<0.05) by the drying temperature, followed by air velocity, pressure level and dwell time. HPP enhanced the firmness of AVC with a maximum of up to 21 % for the sample treated at 500 MPa for 15 min. Microstructural analysis using scanning electron microscopy (SEM) indicated non-uniform structures in the pre-treated and dried AVC samples. Semi quantitative elemental detection (EDS) confirmed the presence of the considerable amount (14.25 %) of calcium in aloe vera.

Supercritical fluid extraction of mint leaves was carried out at different process parameters using central composite rotatable design. The effects of temperature (35-55 8C), pressure (100-300 bar), dynamic time (20-90 min), and particle size (0.2-1.0 mm) were evaluated with respect to essential oil yield and carvone content in volatile oil. The particle size was found to have the most significant effect (p < 0.05) on essential oil yield followed by pressure, temperature, and dynamic time. Although in case of carvone content, pressure showed the most significant effect (p < 0.05) followed by particle size and dynamic time. The optimized SFE process parameter obtained though numerical optimization was 48 8C, 151 bar, 0.40 mm and 37.5 min, respectively having essential oil yield of 1.4%, carvone content of 998 mg/100 g and desirability value of 0.53. Quality of essential oil of mint obtained by SFE was compared with hydrodistilled oil. The essential oil obtained using SFE showed highest antimicrobial activity against E. coli and a moderate activity against S. typhi and S. aureus. Practical applicationsThe optimization of SFE process for mint oil extraction using response surface methodology approach is presented in the present study. The data obtained can be useful for scale up of batch scale SFE extraction of mint oil to a pilot or large scale system. A quadratic polynomial equation was developed, which can predict the oil yield as well as carvone content of mint leaves within the studied domain of the experimental SFE conditions. From the results obtained from this study, SFE can be used in industry for producing mint oil having high carvone content. The recommended operating condition for mint oil extraction is temperature 48 8C, pressure 151 bar, particle size of mint leaves 0.40 mm and dynamic extraction time of 37.5 min. K E Y W O R D Scarvone, essential oil, hydrodistillation, mint, supercritical fluid extraction

The present study focuses on the standardization of the supercritical fluid extraction of the Bhut Jolokia (Capsicum chinense) which is abundantly grown in the north eastern region of India. The effect of process parameters pressure (75–225 bar), temperature (40–60 °C) and time (30–90 min) of oleoresin extraction process was studied. The standardized condition to obtain maximum extraction of Bhut Jolokia oleoresin was found to be 207 bar, 60 °C and 73 min. The oleoresin extract was analyzed for its antimicrobial, antioxidant and total phenolics content. Four strains of bacteria namely Escherichia coli (ATCC -11,229), Bacillus subtilis (ATCC- 11,774), Salmonella typhimurium (ATCC- 14,028) and Staphylococcus aureus (12,600) were used for the antimicrobial assay. It was observed that the highest inhibition was seen against E. coli, moderate inhibition was seen against S.aureus and S. typhi and partial/no zone of inhibition was observed against B. subtilis. The extract of Bhut Jolokia oleoresin showed radical scavenging activity of 58.6 ± 3.86% and total phenolics content of 4250 ± 2.26 mg GAE/100 g sample indicating Bhut Jolokia oleoresin as a good antioxidant and is also a good source of phenolic compounds.

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