The importance of pH control in the disinfection of cherries with ozonated water

When cherries are washed with ozonated water, the pH lowering increases the ORP (oxidation-reduction potential). A packing center was working with water at pH 4.5, but now they have lowered it to pH 2.5 with an increase in ORP to 750, providing greater cleaning power in less time. Is this consistent, or could there be side effects on the cherries? Apparently not, which makes sense given the short time the cherries remain in the water.

The decision to lower the pH of ozonated water from 4.5 to 2.5 in washing cherries, achieving an increase in ORP to 750 mV to improve disinfection in less time, is technically consistent, but requires careful analysis of possible side effects. Below we outline the key aspects:

1. Relationship between pH, ORP, and disinfection

ORP is a direct measure of the oxidizing capacity of the water. A higher value indicates a greater ability to destroy microorganisms like bacteria and fungi. Lowering the pH makes the ozone dissolved in the water more effective as an oxidizing agent because it is better stabilized in its active form. This increases ORP and improves the disinfectant's effectiveness.

ORP values above 650 mV are sufficient to eliminate pathogens like E. coli and Salmonella in a few seconds. An ORP of 750 mV ensures fast and effective disinfection.

2. Impact on cherries

• Short exposure time: if the cherries remain in ozonated water for a limited time, they will unlikely suffer significant damage. This is because the cherry skin acts as a protective barrier against surface oxidation.
• Low pH: although cherries have a natural pH between 3.7 and 4.2, such an acidic pH of water (2.5) could cause negative effects if the contact time is prolonged or if acid residues accumulate in the fruit of the cherries.
• Organoleptic quality: under these specific conditions, no perceptible changes in taste, color, or texture have been observed, which makes sense given the brief interaction with ozonated water.

3. Possible side effects

Although no immediate effects have been observed on the cherries:

• Corrosion of equipment: such a low pH can accelerate the corrosion of metal components in washing and transport systems.
• Workplace safety: handling water with acidic pH may generate irritating fumes or risks for workers if adequate precautions are not taken.
• Acid residues: it is important to ensure a good subsequent rinse to avoid residues that could alter the chemical properties of the fruit or compromise its preservation.

4. Recommendations

To optimize the process:

• Constantly monitor pH and ORP to avoid fluctuations that could compromise the safety or quality of the product.
• Conduct periodic checks on the organoleptic (taste, texture) and microbiological quality of the cherries.
• Implement measures to protect metal equipment from corrosion (coatings or resistant materials).
• Train staff on the risks associated with using low pH water and ensure adequate ventilation.

In conclusion, lowering the pH to 2.5 is technically valid for improving disinfection thanks to the increase in ORP. However, it is crucial to maintain strict controls to avoid secondary issues both in the cherries and in the equipment and work environment.

Side effects on cherries may occur if they are kept in water with such a low pH for an extended period. If cherries are stored for a long time in water with such a low pH (2.5), the following side effects could occur:

1. Damage to the cherry skin

• Dehydration or softening: prolonged exposure to acidic pH can degrade the protective cuticle of cherries, which is primarily composed of waxes and lipid compounds. This could increase water loss and cause dehydration or softening of the fruit, compromising its texture and quality.
• Chemical changes: a low pH can interact with natural pigments such as anthocyanins, responsible for the red color of cherries. This could cause color changes, especially if the stability of these compounds is altered.

2. Organoleptic changes

• Altered taste: although cherries have a naturally acidic pH (3.7-4.2), prolonged exposure to a more acidic environment could intensify this acidity, altering the original flavor of the fruit.
• Loss of sweetness: the acidic environment could accelerate the degradation of simple sugars such as glucose and fructose, reducing the perception of sweetness.

3. Increased susceptibility to diseases

• Post-harvest decay: if the water is not adequately refreshed or contains organic residues, the low pH combined with plant debris can promote the growth of pathogenic fungi such as Botrytis cinerea or Monilinia spp. after the initial exposure.

4. Impact on preservation

• Reduced shelf life: damage to the skin and chemical changes can accelerate processes such as respiration and dehydration, significantly reducing the fruit's storage and transport capabilities.

Recommendations to mitigate risks

• Limit the contact time to the minimum necessary to avoid cumulative effects.
• Continuously monitor pH and conduct periodic checks on the physical-chemical quality of the fruit.
• Ensure a good subsequent rinse with ozonated water at neutral pH to remove acid residues.

In summary, while a low pH temporarily improves the disinfecting power of the water, prolonged exposure could compromise both the visual and organoleptic quality of cherries, as well as reduce their shelf life. It is crucial to balance the contact time with preventive measures to minimize these side effects.

 How ORP affects the texture and flavor of cherries

ORP (oxidation-reduction potential) can affect the texture and flavor of cherries depending on processing conditions such as exposure time and the pH of the ozonated water. The possible effects are detailed below:

1. Effects on texture

Softening of the skin: a high ORP, especially when combined with a low pH, can cause oxidation of the protective cuticle of cherries. This could weaken the outer structure and, with prolonged exposure, lead to softening of the fruit.

Loss of consistency: although cherries naturally have a firm texture, a highly oxidative environment could degrade structural compounds like pectins and hemicelluloses in the epidermis and pulp, reducing their consistency. However, this effect would be more significant if the contact time were prolonged or the conditions were extreme.

2. Effects on flavor

Alteration of sweet-acid balance: a high ORP can interact with organic compounds present in cherries, such as sugars and organic acids (e.g., malic acid). This could modify the flavor perception by slightly reducing sweetness or intensifying acidity.

Changes in volatile compounds: volatile compounds responsible for aroma and flavor (such as esters and aldehydes) could oxidize under high ORP conditions, negatively affecting the sensory profile of the fruit. This could reduce the aromatic complexity that characterizes fresh cherries.

3. Mitigating factors

• Short exposure time: if the contact time with ozonated water is brief (seconds or a few minutes), the negative effects on texture and flavor will be minimal.
• Post-rinse: washing with neutral pH water after treatment can help eliminate oxidative residues and minimize chemical alterations.
• Although a high ORP improves disinfection, it may have slight side effects on the texture and flavor of cherries if treatment conditions are not adequately controlled.
• It is crucial to optimize exposure times and perform periodic sensory tests to ensure the maintenance of the fruit's organoleptic qualities.
• It is necessary to adjust the immersion time in low-pH ozonated water to avoid damage to the cherries.
• It is necessary to adjust the immersion time in low-pH ozonated water to avoid damage to the cherries.

Although using ozonated water in acidic conditions (low pH) increases the disinfectant's effectiveness due to the increased ORP and the stability of molecular ozone, prolonged exposure can lead to undesirable side effects.

The key factors are explained below:

1. Effects of prolonged immersion time

• Damage to the structure: prolonged exposure can weaken the protective cuticle of cherries, causing softening or loss of firmness due to the oxidation of structural compounds like pectins and natural waxes.
• Chemical alterations: prolonged contact with acidic and oxidative water can alter natural pigments (anthocyanins), changing the color of cherries. Additionally, it could alter the sweet-acid balance, intensifying acidity and reducing the perception of sweetness.
• Loss of shelf life: damage to the skin can increase the fruit's susceptibility to post-harvest microorganisms and accelerate decomposition processes. This would reduce the effectiveness of the disinfection process, which is intended to extend the product's shelf life in perfect organoleptic conditions, and reduce losses.

2. Benefits of controlled contact time

Studies indicate that short times (between 1 and 5 minutes) are sufficient to achieve effective disinfection without compromising the organoleptic quality of the fruit. For example, Botrytis sp and Penicillium sp can be eliminated by more than 90% with just 1-5 minutes of exposure to ozonated water.

Times longer than 8 minutes are not required to eliminate common germs from the fruit, even at low ozone concentrations.

3. Recommendations to avoid damage

• Limit immersion time: keep the contact between cherries and ozonated water to the minimum necessary (ideally 1-2 minutes).
• Monitor pH and ORP: ensure that the values remain consistent during treatment to avoid fluctuations that may affect quality.
• Subsequent rinse: wash the cherries with neutral pH water after treatment to eliminate oxidative residues.
• Periodic testing: conduct sensory and microbiological assessments to ensure there are no cumulative negative effects.

We can conclude that regulating immersion time is crucial to maximize the disinfectant benefits of ozonated water without compromising the physical and sensory quality of the cherries. A brief yet effective treatment ensures their freshness and shelf life.

Using ozonated water with a low pH could impact the lifespan of washing equipment. The use of ozonated water with a low pH can negatively affect the longevity of washing equipment, primarily due to the accelerated corrosion these conditions generate.

The mechanisms and factors involved are detailed below:

1. Effects of low pH on materials

• Accelerated corrosion: acidic solutions (pH < 7) are highly corrosive to metals and other materials. This is due to the high concentration of hydrogen ions (H+), which promote electrochemical reactions on metal surfaces, weakening them over time.
• Ozone-enhanced oxidation: ozone is a very powerful oxidizer (redox potential of 2.07 V), and in combination with low pH, it increases its oxidative capacity, which can accelerate the degradation of metal components, especially those not protected by corrosion-resistant coatings.

2. Affected materials

• Common metals: carbon steel or untreated materials are particularly vulnerable to corrosion in these conditions.
• Sensitive components: parts, seals, and gaskets made of synthetic rubber may degrade more rapidly due to prolonged exposure to ozone and the acidic environment.
• Unprotected equipment: pumps, pipes, tanks, and other metal components can suffer significant damage if they are not made from durable materials such as 304 or 316 stainless steel.

3. Factors that exacerbate the impact

• Prolonged exposure time: the longer the equipment remains in contact with ozonated acidic water, the greater the risk of corrosion.
• Ozone concentration: high ozone concentrations (>1.5 mg/L) increase the aggressiveness of the medium towards materials.
• Temperature: high temperatures can accelerate the chemical reactions responsible for corrosion.

4. Recommendations to minimize damage

• Use of resistant materials: use 304 or 316 stainless steel or protective coatings on parts exposed to ozonated water.
• pH control: maintain the pH as close as possible to moderate values (between 6 and 7) to reduce the aggressiveness of the medium without compromising disinfectant efficacy.
• Preventive maintenance: regularly inspect the equipment to identify early signs of corrosion or wear.
• Design optimization: incorporate systems that minimize the contact time between ozonated water and metal components.

In conclusion, using low pH ozonated water can be very effective for disinfection, but it also presents a significant challenge to equipment longevity. Implementing preventive measures and using appropriate materials can help mitigate these negative effects.

Roberto Garcia Gracia
Consultant in Environmental Engineering and Foreign Trade

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