Dual effectiveness of ascorbic acid and ethanol combined treatment to inhibit browning and inactivate pathogens on fresh-cut apples

Possible sources of Listeria monocytogenes contamination of fresh-cut apples and antimicrobial interventions during antibrowning treatments: a review

Fresh-cut apples, being rich in antioxidants and other nutrients, have emerged as popular snacks in restaurants, at home and in school lunch programs, partially due to freshness, convenience, and portion size availability. Two major challenges in processing fresh-cut apples are browning of cut surfaces and contamination with human pathogens. Regarding human pathogens, contamination by Listeria monocytogenes is a major concern, as evidenced by two recent outbreaks of whole apples and numerous recalls of fresh-cut apples. Antibrowning agents currently used by the industry have little to no antimicrobial properties. The present review discusses possible origins of L. monocytogenes in fresh-cut apples, including contaminated whole apples, and contamination via the processing environment and the equipment in fresh-cut facilities. Treatment with antibrowning solutions could be an opportunity for Listeria contamination and represents the last chance to inactivate pathogens. The discussion is focused on the antibrowning treatments where formulations and coatings with antibrowning and antimicrobial properties have been developed and evaluated against Listeria and other microorganisms. In addition, several research needs and considerations are discussed to further reduce the chance of pathogen contamination on fresh-cut apples.

Phytic Acid Treatment Inhibits Browning and Lignification to Promote the Quality of Fresh-Cut Apples during Storage

Browning and lignification often occur in fresh-cut apple processing, leading to quality deterioration and limiting the shelf life of products. In this study, 0.8% (v/v) phytic acid was used to improve the quality and shelf life of fresh-cut apples. From the results, the browning was inhibited by the phytic acid treatment and the browning index (BI) of the control fruit was 1.62 times that of phytic acid treatment at 2 d of storage. The lignin content in phytic acid-treated fruit significantly decreased at 2, 4, and 6 d of storage compared to the control. Phytic acid treatment also reduced H₂O₂ and malonaldehyde (MDA) contents, which may indicate lighter membrane damage to apples. Compared with the control, the polyphenol oxidase (PPO) and peroxidase (POD) activities decreased while superoxide dismutase (SOD) and catalase (CAT) activities increased in phytic acid-treated fruit. Consistent with the lignin content, the activities of phenylpropane metabolism-related enzymes phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate: CoA ligase (4CL) were inhibited by phytic acid treatment. In conclusion, phytic acid alleviated the browning and lignification of fresh-cut apples by reducing PPO and POD activities, maintaining cell membrane integrity, and inhibiting phenylpropane metabolism.

Tyrosinase inhibitory mechanism and the anti-browning properties of piceid and its ester

Different mechanisms for inhibiting tyrosinase can be exploited to avoid quality losses caused by the enzymatic browning of fruits and vegetables. Piceid (PI) and piceid 6″-O- azelaic acid ester (PIA) are oxidized by tyrosinase; however, their oxidation products may have inhibitory effects on tyrosinase. This notion is because l-DOPA oxidation was inhibited after the pre-incubation of PI/PIA with tyrosinase, however, l-DOPA oxidation was not affected if this pre-incubation was not performed. Circular dichroism analysis indicated a conformational change in the secondary structure of tyrosinase after pre-incubation. Further, molecular docking and enzyme reaction kinetics assays were employed to reveal the mechanism underlying the effects of PI/PIA on tyrosinase in the absence of pre-incubation with tyrosinase. PI/PIA had anti-browning effects in the potato models. The increased rate of A₄₂₀ in PI/PIA groups at 24 h were 281% and 279%, which were approximately 2.4- and 2.5-fold lower than that of control (668%).

Chemical inhibition of polyphenol oxidase and cut surface browning of fresh-cut apples

Fresh-cut apples, which offer consumers health benefits and convenience, have become popular in recent years. One of the main challenges for processing fresh-cut apples is rapid development of cut surface browning, immediately after fruits are cut. Browning, a physiological response that impacts organoleptic properties and deters consumer purchase of fresh-cut fresh produce, is mainly a result of enzymatic reaction of phenolic compounds with oxygen catalyzed by polyphenol oxidase (PPO), a decapper enzyme. Many antibrowning agents have been developed and evaluated to inhibit PPO activities by using reducing agents (antioxidants), chelating agents, acidulants, etc. The present manuscript reviews the diverse characteristics of PPO (such as optimum pH and temperature, and molecular weight) in apples reported in the literature and the enzyme's latency, multiplicity and copper states in the active site. It also summarizes the latest development in the investigation and formulations of antibrowning compounds, and discusses future research needs. This review should stimulate further research to discover more effective, low cost, and natural antibrowning compounds to meet the demand of consumers as well as the food industry for clean label and long shelf-life of fresh-cut apples.

Multi-Analytical Approach to Study Fresh-Cut Apples Vacuum Impregnated with Different Solutions

The aim of this study was to evaluate the effect of different solutions for vacuum impregnation (VI) of fresh-cut (FC) apples through an innovative multi-analytical approach. In particular, the individual and synergistic effects of ascorbic acid and calcium lactate on the preservation of freshness of FC apples was assessed through color, texture, microscopy, isothermal calorimetry, and time-domain nuclear magnetic resonance (TD-NMR) evaluations. The analysis was performed immediately after VI and after 24 h of refrigerated storage. The obtained results showed a good preservation of color and higher firmness in the impregnated samples. Concerning the metabolic heat production, a decrease following the VI treatment was observed, especially when the combined solution was used for the impregnation. The TD-NMR studies showed higher changes in terms of signal intensity and transversal relaxation time T2 after 24 h of storage, evidencing the meta-stability of the plant material for its dynamic tissue nature, and the dewatering/impregnation processes evolution until the achievement of dynamic equilibrium.

The Effect of Lactiplantibacillus plantarum BX62 Alone or in Combination with Chitosan on the Qualitative Characteristics of Fresh-Cut Apples during Cold Storage

In order to explore whether beneficial lactic acid bacteria (LAB) could prolong the shelf life and improve the quality of fresh-cut apples, Lactiplantibacillus plantarum BX62, which was isolated from traditional fermented yak yogurt, and chitosan (CT), were applied to fresh-cut apples, subsequently stored at 4 °C. On days 0, 2, 4, 6, and 8, apple slices were taken for physicochemical, microbiological analysis, and sensory evaluation. The results showed that apple slices coated with L. plantarum BX62 (8 log CFU/mL) presented lower weight loss and browning rate, higher DPPH scavenging capacity, and achieved more effective inhibition of polyphenol oxidase (PPO) and peroxidase (POD) activities compared to the control samples. The application of CT alone or in combination with L. plantarum BX62 resulted in a significant reduction in aerobic mesophilic bacteria (AMB), aerobic psychrophilic bacterial (APB), yeast and molds (YAMs) counts (2.31 log CFU/g for AMB, 2.55 for APB, and 1.58 for YAMs). In addition, L. plantarum BX62 coated apples showed acceptable sensory properties in terms of color, flavor, taste, texture, and overall visual quality during 8 d of storage. On this basis, L. plantarum BX62 could be used as an excellent bio-preservative to extend the shelf life and improve the quality of fresh-cut apples.

Development of Strategies to Minimize the Risk of Listeria monocytogenes Contamination in Radish, Oriental Melon, and Carrots

Contamination by Listeria monocytogenes in packaged produce is a major concern. The purpose of this study was to find natural and affordable sanitizers to reduce L. monocytogenes contamination in agricultural products. Organic acids, ultraviolet-C (UV-C), and ethanol were analyzed either alone or in combination to assess their ability to reduce L. monocytogenes population in radish, oriental melon, and carrot samples. In radish samples, 3% malic acid combined with UV-C at a dosage of 144 mj/cm² significantly reduced (>4 log CFU/g) the population of L. monocytogenes (1.44 ± 0.5) compared to the control sample (5.14 ± 0.09). In the case of the melon samples, exposure to UV-C at a dosage of 144 mj/cm² combined with 3% lactic acid (2.73 ± 0.75) or 50% ethanol (2.30 ± 0.01) was effective against L. monocytogenes compared to the control sample (5.10 ± 0.19). In carrot samples, 3% lactic acid combined with 144 mj/cm² dosage UV-C reduced L. monocytogenes population (4.48 ± 0.25) more than in the control sample (5.85 ± 0.08). These results reveal that sanitizers that are effective for one crop are less effective for another crop indicating that effective prevention methods should be customized for each crop to prevent pathogen cross contamination during postharvest washing.

Storage quality of fresh-cut apples treated with yerba mate (Ilex paraguariensis)

Dipping fresh-cut fruits in antioxidant solutions is a useful method to avoid enzymatic browning. Yerba mate extracts have a high content of antioxidant compounds and could be a natural alternative to control browning and improve the bioactive properties of fresh-cut apples. Therefore, this study aimed to evaluate the performance of an antioxidant solution of yerba mate (1.2%), citric acid (0.9%) and ascorbic acid (1.0%) with water as control, on fresh-cut 'Granny Smith' apples during storage at 2 °C (18 days) and 10 °C (15 days) under MAP. Physicochemical characteristics, bioactive properties, sensory attributes, microbial quality as well as the gas composition within the packages were analyzed throughout storage. Samples from both treatments showed a slower quality loss at 2 °C than at 10 °C. The antioxidant solution increased the lag-phase of molds, mesophilic and psychrotrophic microorganisms stored at 2 °C. The phenolic compounds of yerba mate together with ascorbic acid, not only increased the antioxidant capacity of the fresh-cut apples but also reduced the enzymatic browning at both temperatures, increasing the storage time in 2-5 days with an acceptable appearance, when compared to control samples. The antioxidant solution containing yerba mate provided the fresh-cut apples with a higher content of healthy compounds throughout storage at both temperatures.

Effect of ethanol fumigation on pericarp browning associated with phenol metabolism, storage quality, and antioxidant systems of wampee fruit during cold storage

Wampee fruit is a popular fruit cultivar in South-East Asia due to its high levels of nutrients and antioxidants; however, pericarp browning leads to a short storage life with great economic loss during years. The purpose of this work was to determine whether postharvest ethanol fumigation affected pericarp browning development of wampee fruit during 12 days of storage at 8 ± 0.5°C, and if so, how it is related to phenol metabolism and how it affects quality attributes and antioxidant systems during storage. After fruits were fumigated with 100, 300, 500, and 800 μl/L for 5 hr at 22 ± 0.5°C, ethanol significantly reduced the development of pericarp browning by increasing total phenolics (TP) content and decreasing the activity of polyphenol oxidase (PPO), especially in 500 μl/L ethanol treatment. Additionally, ethanol delayed the losses in fruit firmness (FF), soluble solid content (SSC), and titratable acidity (TA), retarded weight loss and accumulation of malondialdehyde (MDA) content and maintained relatively high contents of ascorbic acid (AsA), total flavonoids (TF), and total antioxidant capacity (TAC) and activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In conclusion, results demonstrated that postharvest ethanol fumigation in wampee fruit has ability to reduce pericarp browning development by regulating phenol metabolism and enhancing antioxidant systems.

Effect of edible coatings based on alginate/pectin on quality preservation of minimally processed 'Espada' mangoes

The aims of the study were to develop and apply alginate and pectin-based edible coatings on minimally processed mango (Mangifera indica L.) variety 'Espada'. A full experimental design was performed using alginate, pectin and glycerol concentrations as independent variables and total soluble solids as response variable. Minimally processed mango was immersed in each film forming solution, calcium chloride and glycerol solutions pretreated with 1% (w/v) solution of ascorbic acid, dried at 25 ± 2 °C for 24 h and then refrigerated at 8 ± 1 °C for 14 d. Based on the results of the experimental design, the following formulations were evaluated: 2% (w/v) alginate/3% (w/v) pectin (with and without glycerol) and 3% (w/v) alginate/0.5% (w/v) pectin (with and without glycerol). Fruits coated with biopolymers had lower total soluble solids content and titratable acidity compared to the control group. The formulation containing 2% (w/v) alginate, 3% (w/v) pectin and 5.5% (w/v) glycerol showed the best performance for long-term refrigerated storage of minimally processed mango for a period of 16 d.

Effects of ethanol combined with ascorbic acid and packaging on the inhibition of browning and microbial growth in fresh-cut Chinese yam

The objective of this study was to investigate the effects of aqueous solutions of ethanol (25%, v/v) and ascorbic acid (AA, 1%, m/v) alone and in combination, along with modified atmosphere packaging (MAP) or vacuum packaging (VP), on the physicochemical properties and microbial quality of fresh-cut Chinese yam slices during 4°C storage. The data showed that ethanol (25%, v/v) combined with AA (1%, m/v) and MAP treatment resulted in the lowest changes for headspace gas composition, color, electrical conductivity, overall visual quality, aerobic plate count population, and mold and yeast population in fresh-cut Chinese yam over 21 days of 4°C cold storage, which was more effective at both inhibiting microbial growth and delaying browning than ethanol or AA alone or a commonly used sanitizer, sodium hypochlorite. The experiment on packaging demonstrated that samples treated with VP and 25% ethanol with 1% (m/v) AA dip can only preserve the sensory qualities of fresh-cut Chinese yam slices up to 7 days at 4°C, but 25% (v/v) ethanol in conjunction with 1% (m/v) AA packed with MAP had antibrowning potential and maintained the quality of fresh-cut Chinese yam slices up to 14 days when stored at 4°C.