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Methods of Reducing Crop Deterioration in Agricultural Produce

Methods of Reducing Crop Deterioration in Agricultural Produce

Preservation procedures in agriculture aim at preventing microbial and biochemical deterioration, which are the main causes of crop spoilage.

Despite recent advances, no single preservation method alone can be fully effective microbiologically, physically, chemically, and organoleptically, even if the food value remains largely intact.

Various Methods Employed to Reduce Crop Deterioration

Several methods are used to reduce crop deterioration, including physical, chemical, and biochemical processes.

1. Technical Methods for Reducing Crop Deterioration

Physical MethodsChemical MethodsBiochemical MethodsHeatingSaltingLactic fermentation (natural acidification)CoolingSmokingAlcoholic fermentationLowering water content (drying, dehydration, concentration)Sugar additionSterilising filtrationArtificial acidificationIrradiationEthyl alcohol additionOther physical means (high pressure, vacuum, inert gases)Antiseptic substance action

Among these methods, some fruit and vegetable preservation procedures have been widely applied practically over the years.

2. Practical Procedures for Fruit and Vegetable Preservation

ProcedureApplication in AgricultureFresh storageFruits and vegetablesCold storageFruits and vegetablesFreezingFruits and vegetablesDrying/dehydrationFruits and vegetablesConcentrationFruit juicesChemical preservationSemi-processed fruitsPreservation with sugarFruit products and preservesPasteurizationFruit and vegetable juicesSterilizationFruits and vegetablesSterilizing filtrationFruit juicesIrradiationFruits and vegetables

These procedures have two main characteristics regarding their application to agricultural products:

1. Some methods are specific to certain food categories, while others, such as cold storage, freezing, drying, and sterilization, have wider agricultural application.

2. Some methods provide preservation independently, while others require combination with additional procedures (e.g., smoking usually follows salting).

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Combined Preservation Procedures in Agriculture

Methods of Reducing Crop Deterioration in Agricultural Produce

Preservation aims to prevent microbial and biochemical deterioration. No single method is fully satisfactory alone from microbiological, physicochemical, and sensory perspectives, even though the food’s nutritional value is largely maintained.

Heat sterilization can destroy microorganisms but may cause undesirable changes in the product. Dehydration ensures microbiological stability but may lead to vitamin loss and oxidation during storage.

a. Principles of Combined Preservation Methods

  1. Minimize secondary negative effects in microbiological preservation.
  2. Prevent quality degradation during storage of microbiologically preserved products.
  3. Enhance microbiological preservation efficiency through supplementary methods.
  4. Combine procedures to target different types of microorganisms.
  5. Use combined factors to act simultaneously on bacteria.

b. Examples of Combined Preservation Techniques

  1. Fresh storage combined with controlled atmosphere storage, adjusting carbon dioxide and oxygen levels for specific fruits (e.g., apples), requires airtight storage rooms.
  2. Fresh storage in environments with ethylene oxide to accelerate ripening for fruits such as tomatoes, bananas, and mangoes.
  3. Cold storage with added carbon dioxide or sulfur dioxide tailored to the product type.
  4. Drying combined with freezing (freeze-drying), reducing fruit and vegetable weight by 50% before freezing to preserve vitamins and sensory qualities.
  5. Cold storage of dried vegetables at -8°C with controlled humidity to maintain vitamin C.
  6. Vacuum or inert gas packaging to prevent oxidation, especially for beta-carotene-rich products.
  7. Chemical preservation combined with rehydration in potassium sorbate baths to reduce drying time and maintain quality.
  8. Packaging with desiccants to reduce moisture in powdered products.
  9. Concentration by evaporation combined with cold storage to inhibit microbial growth in products like tomato paste.
  10. Lactic fermentation combined with cold storage to extend shelf life of pickles.
  11. Sugar preservation combined with pasteurization for preserves with less than 65% sugar content.

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General Procedures for Fruit and Vegetable Preservation

Methods of Reducing Crop Deterioration in Agricultural Produce

a. Fresh Storage of Fruits and Vegetables

Once harvested, fruits lose natural resistance to spoilage microbes. Changes in enzymatic systems also accelerate spoilage.

Common measures to prevent spoilage include:

  1. Careful handling to avoid cutting or bruising.
  2. Refrigeration to reduce microbial growth and enzyme activity.
  3. Packaging or storage that controls respiration and ripening rates.
  4. Use of preservatives to eliminate microorganisms.

Major economic losses during transportation and storage result from degradation due to respiration. Methods to reduce this include:

  1. Refrigeration to slow respiration.
  2. Vacuum cooling.
  3. Reducing oxygen levels in storage to below 5% but above anaerobic thresholds, which minimizes deterioration.

b. Recent Advances in Post-Harvest Technology for Fresh Produce

  1. Harvest maturity assessment using resonant frequency measurement allows grading of under- and over-mature fruit, critical for export.
  2. Mechanical harvesting improvements aim to reduce crop damage using dwarfing rootstocks, pruning, and growth regulators.
  3. Field packing for export crops reduces handling costs and damage.
  4. High velocity, high humidity forced-air pre-cooling systems offer versatile, efficient cooling options.
  5. Growing restrictions on chemical use require alternative methods to control postharvest pests and diseases.
  6. Coatings that slow metabolism by modifying gas exchange are under commercial use.
  7. Controlled atmosphere transport with precise gas monitoring improves preservation during shipping.

Preservation by Reducing Water Content in Crops

a. Water and Water Activity in Agricultural Products

Microorganisms require water for growth, typically over 80%. Removing water from food also removes water from microbial cells, stopping their growth.

Partial drying may be sufficient for some microbes, but bacteria and yeasts usually need more moisture than molds, which can grow on semi-dry foods such as partially dried fruits.

Small changes in relative humidity around stored products can significantly affect microbial growth rates. Microorganisms live in microenvironments within food, where moisture can vary even over millimeters.

Water activity (aw) measures the free, unbound water available for microbial and chemical reactions, and it is a better indicator than total moisture content.

Water activity is the ratio of vapor pressure of the food solution to that of pure water at the same temperature, calculated as:

aw = RH / 100

Most bacteria require water activity between 0.90 and 1.00 for growth. Some yeasts and molds grow at water activity as low as 0.65.

Water activity influences biological and chemical reactions in food and affects bacterial growth, enzyme function, and chemical stability at the microenvironmental level.

Preservation by Drying/Dehydration

Drying is one of the oldest and most effective methods of preserving food. Removing moisture from fruits and vegetables prevents the growth of micro-organisms that cause spoilage and reduces moisture-related chemical changes.

This method also lowers weight and volume, cutting down on packaging, storage, and transportation costs, which is crucial for farmers and traders, especially in developing countries.

1. Osmotic Dehydration

Osmotic dehydration involves soaking fresh produce in a concentrated sugar or salt solution before sun or solar drying.

This process removes some moisture while protecting the product’s color, flavor, and texture. Because it uses little sulfur dioxide, it produces dried products of high quality suitable for market.

2. Heat and Mass Transfer in Drying

Drying requires heat to vaporize water and a way to remove water vapor from the food. Hot air is the most common heat source, transferring heat through convection. Water moves from inside the food to its surface, then evaporates into the air. Rapid drying is necessary to maintain quality and reduce costs.

Four main factors affect drying rate and time

1. Product properties: Size and shape of the pieces.

2. Arrangement: How the food is placed relative to the heat source.

3. Drying medium: Temperature, humidity, and air velocity of drying air.

4. Equipment: Design and efficiency of the dryer.

Drying typically has a constant rate period, where moisture evaporates steadily, followed by a falling rate period, where drying slows as moisture becomes harder to remove.

Factors Influencing the Drying Process

Methods of Reducing Crop Deterioration in Agricultural Produce

1. Surface area: Cutting fruits or vegetables into small pieces or thin layers speeds drying by increasing contact with hot air and shortening moisture travel distance.

2. Temperature: Higher air temperatures increase drying rate by providing more heat and carrying away moisture faster.

3. Air velocity: Moving air removes moisture quickly from the product’s surface, preventing saturation and speeding drying.

4. Dryness of air: Dry air absorbs more moisture, making drying faster and allowing food to reach lower moisture content.

5. Atmospheric pressure and vacuum: Using vacuum dryers lowers the boiling point of water, allowing drying at lower temperatures and preserving heat-sensitive foods better.

6. Evaporation cooling: Water evaporation cools the food surface by absorbing heat, so drying requires continuous heat supply.

7. Time and temperature balance: Fast drying at high temperatures preserves quality better than slow drying at lower temperatures because it reduces the time food is exposed to heat.

Drying Techniques

Various drying methods suit different types of fruits and vegetables:

1. Sun and solar drying: Uses natural heat, cheap and simple, best in hot, dry climates. Suitable for many traditional crops.

2. Atmospheric drying: Includes batch dryers like kilns and continuous dryers like tunnels and belts, used mainly for vegetables and some fruits.

3. Spray drying: Ideal for fruit juice concentrates.

4. Vacuum drying: Good for heat-sensitive, low moisture or high sugar fruits such as peaches and apricots.

Dryers can be grouped as:

1. Air convection dryers: Kiln, cabinet, tunnel, belt, fluidized bed.

2. Drum or roller dryers: Atmospheric and vacuum types for purees and liquids.

3. Vacuum dryers: Vacuum shelf, belt, and freeze dryers for delicate products.

Fruit and Vegetable Natural Drying

1. Sun and Solar Drying

Surplus fruit and vegetables can be naturally dried and stored for later use or transported to areas with shortages. This low-cost method depends on good-quality, ripe produce and dry weather during harvest and drying periods.

2. Preparation Before Drying

i. Sorting: Remove damaged, insect-infested, or discolored parts.

ii. Washing: Clean the produce before slicing.

iii. Cutting: Slice into uniform thickness (3-7 mm) to ensure even drying.

iv. Prevent browning: Some produce like bananas and apples brown quickly due to enzyme activity and should be soaked in salt or sulphite solutions before drying.

3. Drying Setup

Drying trays should be above ground to avoid contamination by dust, insects, and animals. Trays made with wooden frames and nylon mosquito netting allow air circulation. Drying sites must be dust-free and sheltered from rain.

Blanching as a Pre-Treatment

Blanching fruits and vegetables in hot water before drying offers several benefits:

  1. Cleans the produce and reduces surface microbes.
  2. Preserves natural color by protecting pigments from oxidation.
  3. Shortens rehydration time during cooking.

Some nutrients and flavors may be lost during blanching, but this can improve quality by reducing unwanted browning and spoilage.

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