Peroxidase (POD) and polyphenol oxidase (PPO) photo-inactivation in a coconut water model solution using ultraviolet (UV)

Impact of pulsed light treatment on enzyme inactivation and quality attributes of whole white button mushroom (Agaricus bisporus) and its storage study

Whole white button mushrooms (WWBM) exhibit a limited shelf-life owing to the oxidative enzymatic browning. Inactivation of polyphenol oxidase-PPO and peroxidase-POD in WWBM and its kinetic behavior were studied using pulsed light(PL) treatment (0.13-1.11 J/cm2). The first-order kinetics explained PL-induced enzyme inactivation. Rate constants(k) for PPO and POD were 3.84 and 2.55 cm2/J. FTIR-analysis revealed secondary-structural changes in partially-purified enzyme. PL-treatment retarded browning, retained phenolics and enhanced vitamin D2. PL-treatment at 1.11 J/cm2 rendered WWBM both microbially and enzymatically stable. The PL-treated WWBM's shelf-life at 4, 20, and 37 °C were 5, 3, and 1 day. At 4 °C, browning increased by 6.1 %; firmness decreased by 55.2 %, while PL-treated mushrooms retained 90.6 % phenolics, 78.9 % antioxidant capacity, and 64.2 % D2 after 5 days. Higher activation energy value confirmed phenolics were most sensitive during storage. PL-technology supports UN Sustainable Development Goals by reducing chemical use, lowering carbon-footprints, minimizing pollution, and enhancing shelf-life, promoting sustainable global trade.

An investigation on the effect of ultrasonication and microfiltration processing on the quality of king coconut (Cocos nucifera var. aurantiaca) water compared to minimal and thermal processing

The study aimed to investigate the effect of thermal and non-thermal processing on the physicochemical, microbial, and sensory characteristics of king coconut water. King coconut water samples were subjected to ultrasonication (50 kHz, 30 min at 35 °C), microfiltration (0.5 µm), and thermal treatments (at 90 °C for 10 min) with sodium metabisulfite (0.1 g/L) except the fresh sample (control). Samples were tested for physiochemical, microbial, and sensory parameters. Storage studies were conducted at 4 °C for 28 days. pH, titratable acidity, and total sugar of all treated samples were within the Sri Lankan Standard (SLS) limit (4.6-5.5, 0.07-0.1%, 4.1-6.5%, respectively) during the 28 days of storage. Sodium metabisulfite addition was significant in lowering the browning index. Antioxidant and phenolic contents of microfiltered and ultrasonicated samples varied between 49%-65% and 2.5-2.8 GAE mg/100 mL, respectively, during 4 weeks of storage, which was significantly higher compared to the heat-treated samples. Sensory evaluation scored the lowest attribute values for thermally treated samples. Microbial analyses indicated that microfiltered and ultrasonicated king coconut water remained safe for consumption for up to 4 weeks. Ultrasound and microfiltration, with the integration of sodium metabisulfite, were identified as effective methods for processing king coconut water while preserving its wholesome properties.

Effects of variety and maturity stage of coconut on physicochemical and sensory characteristics of powdered coconut drink

Introduction. Coconut water is rich in nutrients and biologically-active compounds. However, it has a short shelf life that can be prolonged by freeze drying. The purpose of this study was to analyze the physicochemical and sensory characteristics of fresh and powdered coconut drinks. Study objects and methods. The experiments included eight samples, namely fresh and powdered coconut drinks obtained from coconuts of different varieties (tall and hybrid) and maturity stages (4 and 6 m.o.). The samples were analyzed for nutrient content (ash, protein, fat, total carbohydrate, and fibre), physicochemical properties (titratable acidity, pH, viscosity, total soluble solids, turbidity, water activity, and browning index), and sensory characteristics (color, aroma, taste, texture, and overall acceptance). Results and discussion. The results obtained showed that there were significant differences among the coconut drinks of different varieties and maturity stages. They differed in nutrient content, pH value, titratable acidity, viscosity, and water activity. Meanwhile, the aroma, taste, and overall acceptance scores of all the samples were not significantly different. The powdered drink from 6 m.o. hybrid coconut was selected as the optimal sample due to its good sensory and physicochemical attributes. These attributes were similar to those of the fresh coconut drink. Conclusion. The powdered drink from 6 m.o. hybrid coconut obtained by freeze drying could be considered as an alternative healthy drink with good quality characteristics.

Effect of UV-C irradiation on the inactivation kinetics of oxidative enzymes, essential amino acids and sensory properties of coconut water

The impact of ultraviolet light (UV-C) irradiation on oxidative enzymes [Polyphenol oxidase (PPO) and Peroxidase (POD)], free essential amino acids and sensory profile of coconut water were investigated. PPO and POD activities were lost to 94 and 93%, respectively of its original value at fluence level of 400 mJ/cm2. Inactivation kinetics of both enzymes were fitted to nonlinear Weibull model with an increase in UV dosage with a high coefficient of determination (R2 > 0.97) and low root mean square error (RMSE < 0.06). No significant change was observed in all essential amino acids (p > 0.05) after UV-C treatment up to maximum delivered fluence of 400 mJ/cm2. Sensory attributes of coconut water up to a treated UV-C fluence level of 200 mJ/cm2 were well retained in terms of chosen descriptors (p > 0.05). This study allow to further investigate the development of UV-C light technology for inhibition of spoilage enzymes and prolonged shelf-life of low acid beverages.

Microwave heating effect on total phenolics and antioxidant activity of green and mature coconut water

Coconut water (Cocos nucifera L.) from fruits of two ripening stages (green and mature) was used to perform microwave heat treatments. Three different heating conditions with maximum temperatures of 70, 80 and 90 °C were tested in three holding times (0, 2 and 4 min). The Total Phenolic Content (TPC) using the Folin-Ciocalteu method and ABTS radical scavenging capacity were evaluated for each combination of coconut fruit age, heating temperature and holding time. It was observed that green coconut water exhibited significant differences (p < 0.05) compared to mature coconuts in terms of TPC (46.03 and 69.16 mg GAE/L, respectively) and ABTS radical scavenging capacity (422.31 and 549.1 μmol TE/L, respectively). An increase in TPC (up to 23%) and antioxidant activity (up to 19%) was also observed with increasing temperature in the range of 70–90 °C. Green coconut water showed the largest increase in both TPC and antioxidant activity.

Ozone and plasma processing effect on green coconut water

In this study, the effect of plasma and ozone processing on the quality of coconut water was evaluated. For ozone processing, the samples were submitted to different ozone loads and temperatures. For atmospheric cold plasma processing (ACP), samples were exposed to plasma under different frequencies and voltages. The coconut water pH, soluble solids, titratable acidity, color, total phenolic content, and enzymatic activity were determined before and after treatments. The main compounds were also determined by NMR spectroscopy and chemometric analysis. Both processes did not change the pH values, total soluble solids, titratable acidity, and color. Chemometrics analysis of 1H NMR dataset showed no relevant changes after the processing. All ozone treatments promoted complete inactivation of POD activity and did not affect the content of phenolic compounds. After ACP, the smallest POD residual activity was observed when higher frequencies were applied, and slight changes in phenolic compounds content were observed.

Ultraviolet inactivation of bacteria and model viruses in coconut water using a collimated beam system

This study investigated the effect of ultraviolet-C irradiation on the inactivation of microorganisms in coconut water, a highly opaque liquid food (1.01 ± 0.018 absorption coefficient). Ultraviolet-C inactivation kinetics of two bacteriophages (MS2, T1UV) and three surrogate bacteria (Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes) in 0.1% (w/v) peptone and coconut water were investigated. Ultraviolet-C irradiation at 254 nm was applied to stirred samples, using a collimated beam device. A series of known ultraviolet-C doses (0-40 mJ cm^-2) were applied for ultraviolet-C treatment except for MS2 where higher doses were delivered (100 mJ cm^-2). Inactivation levels of all organisms were proportional to ultraviolet-C dose. At the highest dose of 40 mJ cm^-2, three surrogates of pathogenic bacteria were inactivated by more than 5-log₁₀ (p < 0.05) in 0.1% (w/v) peptone and coconut water. Results showed that ultraviolet-C irradiation effectively inactivated bacteriophage and surrogate bacteria in highly opaque coconut water. The log reduction kinetics of microorganisms followed log-linear and exponential models with higher R² (>0.95) and low root mean square error values. The D₁₀ values of 3, 5.48, and 4.58 mJ cm^-2 were obtained from the inactivation of E. coli, S. Typhimurium, and L. monocytogenes, respectively. Models for predicting log reduction as a function of ultraviolet-C irradiation dose were found to be significant (p < 0.05). Fluid optics were the key controlling parameters for efficient microbial inactivation. Therefore, the ultraviolet-C dose must be calculated not only from the incident ultraviolet-C intensity but must also consider the attenuation in the samples. The results from this study imply that adequate log reduction of vegetative cells and model viruses is achievable in coconut water and suggested significant potential for ultraviolet-C treatment of other liquid foods.

Thermal inactivation kinetics and effects of drying methods on the phenolic profile and antioxidant activities of chicory (Cichorium intybus L.) leaves

The thermal inactivation kinetics of enzymes, including polyphenol oxidase (PPO) and peroxidase (POD), in chicory (Cichorium intybus L.) leaves were evaluated. In addition, the influences of different drying techniques (shade drying, hot air drying and freeze drying) on the phenolic profiles and antioxidant activities of chicory leaves were determined. The antioxidant activities of chicory leaves were evaluated on the basis of their 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, reducing power, and 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity. The results showed that the activation energy for PPO and POD inactivation were 123.00 kJ/mol and 78.99 kJ/mol, respectively. Preliminary treatment with hot water for 3 min at 90 °C was beneficial for preserving the phenolics present in fresh leaves. Hot air drying was better for the phenolics preservation. The hot air-dried and freeze-dried leaves possessed good antioxidant activities. The leaves with higher phenolics contents had better antioxidant activities, which indicated that the preservation of the phenolics was important for maintaining the antioxidant activity of chicory leaves.

Using ultrasound technology for the inactivation and thermal sensitization of peroxidase in green coconut water

Green coconut water has unique nutritional and sensorial qualities. Despite the different technologies already studied, its enzymatic stability is still challenging. This study evaluated the use of ultrasound technology (US) for inactivating/sensitizing coconut water peroxidase (POD). The effect of both US application alone and as a pre-treatment to thermal processing was evaluated. The enzyme activity during US processing was reduced 27% after 30min (286W/L, 20kHz), demonstrating its high resistance. The thermal inactivation was described by the Weibull model under non-isothermal conditions. The enzyme became sensitized to heat after US pre-treatment. Further, the use of US resulted in more uniform heat resistance. The results suggest that US is a good technology for sensitizing enzymes before thermal processing (even for an enzyme with high thermal resistance). Therefore, the use of this technology could decrease the undesirable effects of long times and/or the high temperatures of the conventional thermal processing.

Effects of Ultraviolet Light and High-Pressure Processing on Quality and Health-Related Constituents of Fresh Juice Products

Fresh juices are highly popular beverages in the global food market. They are perceived as wholesome, nutritious, all-day beverages. For a fast growing category of premium juice products such as cold-pressed juices, minimal-processing nonthermal techniques such as ultraviolet (UV) light and high-pressure processing (HPP) are expected to be used to extend shelf-life while retaining physicochemical, nutritional, and sensory characteristics with reduced microbial loads. Also, UV light and HPP are approved by regulatory agencies and recognized as one of the simplest and very environmentally friendly ways to destroy pathogenic organisms. One of the limitations to their more extensive commercial application lies in the lack of comparative effects on nutritional and quality-related compounds in juice products. This review provides a comparative analysis using 92 studies (UV light: 42, HPP: 50) mostly published between 2004 and 2015 to evaluate the effects of reported UV light and HPP processing conditions on the residual content or activity of bioactive compounds such as vitamins, polyphenols, antioxidants, and oxidative enzymes in 45 different fresh fruit and vegetable juices (low-acid, acid, and high-acid categories). Also, the effects of UV light and HPP on color and sensory characteristics of juices are summarized and discussed.