Kinetic and Thermodynamic of Thermal Inactivation of the Peroxidase, Polyphenoloxidase and Inulinase Activities during Blanching of Yacon (Smallanthus sonchifolius) Juice

Application of non-thermal pretreatment techniques on agricultural products prior to drying: a review

BACKGROUND

Most agricultural crops contain high moisture content (80-95% wet basis (wb)) which makes them very susceptible to microbial damage leading to shorter shelf-life and high postharvest losses. The high perishability of these agricultural products requires preservation techniques to prolong their shelf-lives. Drying remains an important component of processing in this regard. Therefore, any pretreatment methods for drying agricultural product that decreases the moisture content and minimizes drying time by conserving the quality of the crop product is of prime significance. This article is a comprehensive review of recent developments of non-thermal pretreatment (NTP) methods. A summary of their significance, emerging and innovative methods of this technology together with its applications and limitations are discussed. This article further examines the environmental impact of NTP techniques.

RESULTS

NTP techniques, such as high pressure, ultrasound, pulsed electric field and osmotic dehydration methods are essential operations for pre-dehydration of agricultural products prior to drying. These techniques can avoid the deleterious effects of heat on nutritive value, colour and flavour of agricultural products compared to thermal pretreatments. They also enhance the inactivation of the enzymes, improve energy efficiency and mass transfer, reduce processing time, preserve bioactive compounds, improve drying kinetics and drying rate, minimize enzymatic browning, and enhance product quality.

CONCLUSION

These findings will provide a better understanding of different NTP methods and also make available more information for selecting pretreatment techniques for drying of agricultural products. © 2020 Society of Chemical Industry.

Inhibitory effects of organic acids on polyphenol oxidase: From model systems to food systems

Organic acids are widely utilized in the food industry for inhibiting the activity of polyphenol oxidase (PPO) and enzymatic browning. This review discusses the mechanisms of inhibition of PPO and enzymatic browning by various organic acids based on studies in model systems, critically evaluates the relevance of such studies to real food systems and assesses the implication of the synergistic inhibitory effects of organic acids with other physicochemical processing techniques on product quality and safety. Organic acids inhibit the activity of PPO and enzymatic browning via different mechanisms and therefore the suitability of a particular organic acid depends on the structure and the catalytic properties of PPO and the physicochemical properties of the food matrix. Studies in model systems provide an invaluable insight into the inhibitory mechanisms of various organics acids. However, the difference in the effectiveness of PPO inhibitors between model systems and food systems and the lack of correlation between the degree of PPO inhibition based on in vitro assays and enzymatic browning imply that the effectiveness of organic acids can be accurately evaluated only via direct assessment of browning inhibition in a particular food system. Combination of organic acids with physical processing techniques is one of the most viable approaches for PPO inhibition since the observed synergistic effect helps to reduce the undesirable organoleptic quality changes from the use of excessive concentration of organic acids or intense physical processing.

Thermodynamic and kinetics study of phenolics degradation and color of yacon (Smallanthus sonchifolius) microparticles under accelerated storage conditions

This study aimed to investigate the kinetics and thermodynamic of the phenolics degradation and the kinetics of degradation of the total color difference of yacon juice microcapsules produced by spray drying using Gum Arabic and polydextrose as wall materials. The degradation of the microcapsule was evaluated by accelerated tests under controlled conditions at 35 and 45 °C, and relative humidity of 75 and 90%, for 35 days. Degradation of phenolics followed the first order model and the degradation constant was in the range of 0.0124-0.0209 days^-1. The microparticles with gum Arabic were more stable than those with polydextrose for all conditions studied, with longer half-lives. Both wall materials showed similar thermodynamic characteristics, indicating similar mechanism of degradation of phenolics. With respect to the color parameters, the first order model adjusted to data of the total color difference, and no significant differences were observed for the conditions studied.

A Novel Color Parametric Technique for Kinetic Evaluation of Thermal Degradation and Stability of Fresh-Cut Yacon Slices

Fresh-cut yacon slices were first heat treated (60–80 °C, 5–25 min) and then exposed to air at room temperature for up to 10 min. Color parameters of internal surface were measured and two kinetic models were evaluated: 1) Color degradation during thermal treatment, and 2) Color stability during subsequent air exposure. More severe treatments led to lower color quality but higher stability. The relative white index was the best color parameter and the color changes followed a zero-order kinetics. The temperature dependence of rate constants were evaluated using the Arrhenius model. The activation energy for color degradation was 14.7 kJ/mol, and for color stability it was 47.9 kJ/mol indicating color stability parameters to be more sensitive to temperatures than color degradation. The color parameter models developed were comparable to polyphenoloxidase inactivation model and provided a rapid physical method for evaluating color degradation and subsequent color stability of yacon slices.