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.

Kinetic modeling of high-pressure induced inactivation of polyphenol oxidase in sugarcane juice (Saccharum officinarum)

BACKGROUND

Polyphenol oxidase (PPO) is the main enzyme in sugarcane juice associated with rapid browning and degradation of organoleptic properties. High-pressure processing (HPP) (300-600 MPa) of sugarcane juice in combination with moderate temperatures (30-60 °C) for different processing times (10-25 min) has shown promising results in minimizing PPO activity while preserving the juice's freshness.

RESULTS

A maximum PPO inactivation of 98% was achieved at 600 MPa/60 °C/25 min, while the corresponding value for thermal treatment at 0.1 MPa/60 °C was only 66%. The nonlinearity in the inactivation data was well described by the Weibull distribution model with a high adjusted R² and reduced χ² values at all levels of pressure and temperature. The PPO inactivation data were fitted at shape parameter, β = 1 (log linear) and β ≠ 1. A refitted Weibull model was used to predict kinetic parameters such as the inactivation rate constants (k), activation energy (E_a ) and activation volume (V_a ), which govern PPO inactivation in HPP-treated sugarcane juice. A secondary kinetic model was formulated to predict the k values as a function of pressure (P) and temperature (T), incorporating E_a and V_a .

CONCLUSIONS

Combined high-pressure and temperature processing has been considered a reliable alternative to conventional heat treatment for inhibiting PPO activity in sugarcane juice. While the isothermal inactivation of PPO followed first-order kinetics, inclusion of high pressure resulted in a strong deviation from log linear kinetics. Identification of suitable kinetic models describing these inactivation processes is expected to aid product development and process control of high-pressure processed sugarcane juice. © 2018 Society of Chemical Industry.

HPLC-UV-ESI-MS methods for flavonoid profiling of sugarcane juice extract

An efficient method combining liquid chromatography coupled to electrospray ionization mass spectrometry in tandem mode with negative ion detection was described for the qualitative analysis of flavonoids in sugarcane juice. The analyses were carried out on a Shim-pack C18 column (150mm×4.6mmI.D.,5µm), with a mobile phase composed by methanol: 5% aqueous acetic acid by linear gradient elution (0–20min, methanol 15–25%; 20–60min, methanol 25–33%; 60–90min, methanol 33–48%). Nine phenolic compounds were identified on the basis of their mass spectra in full scan mode and the pattern of their fragmentation. The diagnostic fragmentation patterns of the compounds during collision induced dissociation (CID) elucidated structural information of the compounds analysed. This is the first time that vitexin-rhamnosyl glucoside (8-glucopyranosyl-7-[6-O-(6-deoxy-mannopyranosyl)-glucopyranosyl]-5-hydroxy-2-(4-hydroxyphenyl)-4H-1-Benzopyran-4-one) has been detected or identified in sugarcane juice.