Neelima Kaushik

High-Pressure Inactivation of Enzymes: A Review on Its Recent Applications on Fruit Purees and Juices

In the last 2 decades high-pressure processing (HPP) has established itself as one of the most suitable nonthermal technologies applied to fruit products for the extension of shelf-life. Several oxidative and pectic enzymes are responsible for deterioration in color, flavor, and texture in fruit purees and juices (FP&J). The effect of HPP on the activities of polyphenoloxidase, peroxidase, β-glucosidase, pectinmethylesterase, polygalacturonase, lipoxygenase, amylase, and hydroperoxide lyase specific to FP&J have been studied by several researchers. In most of the cases, partial inactivation of the target enzymes was possible under the experimental domain, although their pressure sensitivity largely depended on the origin and their microenvironmental condition. The variable sensitivity of different enzymes also reflects on their kinetics. Several empirical models have been established to describe the kinetics of an enzyme specific to a FP&J. The scientific literature in the last decade illustrating the effects of HPP on enzymes in FP&J, enzymatic action on those products, mechanism of enzyme inactivation during high pressure, their inactivation kinetics, and several intrinsic and extrinsic factors influencing the efficacy of HPP is critically reviewed in this article. In addition, process optimization of HPP targeting specific enzymes is of great interest from an industrial approach. This review will give a fair idea about the target enzymes specific to FP&J and the optimum conditions needed to achieve sufficient inactivation during HPP treatment.

Application of high pressure processing for shelf life extension of litchi fruits (Litchi chinensis cv. Bombai) during refrigerated storage

This study attempts to report the effect of high pressure processing (100, 200 and 300 MPa for 5, 10 and 15 min at 27 ± 2 ℃) on quality and shelf life extension of ‘Bombai’ variety peeled litchi fruits during refrigerated storage (5 ℃). High pressure processing significantly increased total colour difference, browning index, drip loss and total soluble solids, whereas pH decreased after processing. Also, ascorbic acid content significantly decreased after high pressure processing and retention of 83.5% was observed. Texture profile analysis showed that pressurization significantly affected firmness and increased cohesiveness, gumminess, springiness and chewiness of litchi fruits. Pressure-induced firming effect was observed at 100 and 200 MPa pressure. A maximum of 3.29, 3.24 and 3.77 log10 cycles reduction in aerobic mesophiles, yeast & mold and psychrotrophs count, respectively, was achieved after pressurization of 300 MPa for 10 and 15 min treatments. During storage, samples treated at 300 MPa for 10 and 15 min showed relatively minimal changes in physico-chemical attributes, textural parameters and maintained lower viable microbial counts. Treatments at 300 MPa for 10 min and 15 min were found to enhance the shelf life of litchi fruits up to 32 days as compared to 12 days of untreated during refrigerated storage (5 ℃).

Effect of High Pressure Processing on Rheological Properties, Pectinmethylesterase Activity and Microbiological Characteristics of Aloe Vera (Aloe barbadensis Miller) Juice

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.

Impact of pH and Total Soluble Solids on Enzyme Inactivation Kinetics during High Pressure Processing of Mango (Mangifera indica) Pulp.

UNLABELLED This study was undertaken with an aim to enhance the enzyme inactivation during high pressure processing (HPP) with pH and total soluble solids (TSS) as additional hurdles. Impact of mango pulp pH (3.5, 4.0, 4.5) and TSS (15, 20, 25 °Brix) variations on the inactivation of pectin methylesterase (PME), polyphenol oxidase (PPO), and peroxidase (POD) enzymes were studied during HPP at 400 to 600 MPa pressure (P), 40 to 70 °C temperature (T), and 6- to 20-min pressure-hold time (t). The enzyme inactivation (%) was modeled using second order polynomial equations with a good fit that revealed that all the enzymes were significantly affected by HPP. Response surface and contour models predicted the kinetic behavior of mango pulp enzymes adequately as indicated by the small error between predicted and experimental data. The predicted kinetics indicated that for a fixed P and T, higher pulse pressure effect and increased isobaric inactivation rates were possible at lower levels of pH and TSS. In contrast, at a fixed pH or TSS level, an increase in P or T led to enhanced inactivation rates, irrespective of the type of enzyme. PPO and POD were found to have similar barosensitivity, whereas PME was found to be most resistant to HPP. Furthermore, simultaneous variation in pH and TSS levels of mango pulp resulted in higher enzyme inactivation at lower pH and TSS during HPP, where the effect of pH was found to be predominant than TSS within the experimental domain. PRACTICAL APPLICATION Exploration of additional hurdles such as pH, TSS, and temperature for enzyme inactivation during high pressure processing of fruits is useful from industrial point of view, as these parameters play key role in preservation process design.

Chilled Storage of High Pressure Processed Black Tiger Shrimp (Penaeus monodon)

The effect of high pressure (HP) treatment (at 100, 270, and 435 MPa for 5 min at 25°C) on microbiological (total viable count and total psychrotrophic count), physical (color, texture, and drip loss), and microstructural characteristics of black tiger shrimp (Penaeus monodon) during storage at 2°C for 35 days was investigated. Pressure treatment increased drip loss, maintained low microorganisms level, imparted cooked appearance to the muscle, and resulted in improved texture. Results of scanning electron microscopy revealed more compact structure in treated samples, confirming the results of texture profile analysis. Pressure treatment of 435 MPa was most effective in preserving the quality of shrimp.

Comparative analysis of thermal-assisted high pressure and thermally processed mango pulp: Influence of processing, packaging, and storage

Storage stability and shelf-life of mango pulp packed in three different packaging films and processed using an optimized thermal-assisted high pressure processing treatment ‘HPP’ (600 MPa/52 ℃/10 min) was analyzed during refrigerated (5 ℃) and accelerated (37 ℃) storage and compared with the conventional thermal treatment ‘TT’ (0.1 MPa/95 ℃/15 min). After processing, HPP resulted in relatively lower total color difference (3.5), retained higher ascorbic acid (95%), total phenolics (106%), total flavonoids content (118%) in mango pulp compared to TT, with values of 5.0, 62, 83, 73%, respectively. However, HPP led to ∼50% enzymes inactivation (pectin methylesterase, polyphenol oxidase, peroxidase) in comparison to >90% obtained during TT. Both HPP and TT resulted in > 5 log10 units reduction of the studied microorganisms to give a safe product. In contrast to the refrigerated storage, quality changes under accelerated conditions were found to be considerably rapid and dependent on packaging material irrespective of the method of processing. Shelf-life under refrigeration was limited by microbial growth and sensory quality; whereas, browning restricted the shelf-life during accelerated storage. HPP in aluminum-based retort pouch was adjudged superior processing -packaging combination for maximizing the shelf-life of mango pulp to 120 and 58 days during refrigerated and accelerated storage, respectively. In comparison, TT led to higher quality changes upon processing than HPP and resulted in shelf-life of 110 and 58 days under the same packaging and storage conditions, respectively.

Effect of High Hydrostatic Pressure on Natural Microflora of Mango Pulp (Mangifera indica cv. Amrapali)

High pressure processing (HPP) is a novel non thermal technology involving the application of hydrostatic pressure in the range of 100-900 MPa on packaged or non packaged food product which renders the food shelf stable due to inactivation of enzymes and destruction of microorganisms. In addition to increasing the product shelf life, this technology enhances food quality in terms of better nutrition retention, minimal changes in appearance and desirable texture modifications than conventional processing methods. Mango pulp (Mangifera indica cv. Amrapali) having TSS 16-17.5 °brix and pH adjusted to 4 was pressurized at 100 to 600 MPa pressure for different hold times between 0 to 20 min at pressurization ramp rate of 300 MPa/min (process temperature: 28±2 °C). The treated samples were analyzed for viable microbial counts viz. total plate count (TPC), total yeast and mold count (YMC), lactic acid bacteria count (LAB), total coliforms (TC) and total psychrotophic count (PC).