Unit 2 - Pre-harvest factors affecting postharvest quality | Post-harvest Management and Value Addition of Fruits and Vegetables

Table of contents
Pre-harvest factors affecting postharvest quality, maturity, ripening and changes occurring during ripening;

Pre-harvest factors affecting post-harvest quality

Several pre-harvest factors significantly impact the quality, maturity, and ripening of the produce. Understanding these factors is essential for ensuring optimal post-harvest outcomes. These factors are:

1. Harvest Maturity: Harvest maturity refers to the stage of development at which fruits and vegetables are harvested. It directly affects their quality and taste. Harvesting too early may result in immature produce with less flavour and reduced nutritional content. Conversely, harvesting too late can lead to overripeness, causing the produce to become soft, less palatable, and more susceptible to decay.

2. Climatic Conditions: Weather and environmental conditions during the growing season play a vital role in determining the maturity and quality of fruits and vegetables. Adequate sunlight, temperature, and water availability promote proper growth and development, leading to better-quality produce. Extreme climatic conditions, such as excessive heat or cold, can affect the ripening process and cause irregularities in the produce.

3. Cultural Practices: Farming practices, including irrigation, fertilization, and pest control, have a direct impact on postharvest quality. Providing adequate water and nutrients helps plants grow optimally and produce high-quality fruits and vegetables. Effective pest management ensures that the produce is free from damage caused by pests and diseases.

4. Handling Practices: Gentle and careful handling during pre-harvest operations, such as harvesting, sorting, and packing, is crucial for preserving postharvest quality. Rough handling can cause physical damage, bruises, and cuts, which may lead to spoilage and decay during storage and transportation.

5. Varietal Differences: Different crop varieties or cultivars exhibit varying rates of maturity and ripening. Some varieties ripen quickly after harvest, while others have a slower ripening process. Choosing appropriate varieties based on the desired postharvest characteristics is essential for optimizing quality and shelf life.

6. Ethylene Production: Ethylene is a natural gas produced by certain fruits and vegetables, which acts as a ripening hormone. It plays a key role in the ripening process. Some fruits, like bananas and tomatoes, are known as ethylene producers and can influence the ripening of nearby ethylene-sensitive fruits. Proper storage and separation of ethylene-producing and ethylene-sensitive items are essential to control ripening and avoid premature spoilage.

7. Pathogen and Disease Management: Effective pre-harvest disease management is crucial for post-harvest quality. Fungal and bacterial infections during the growing season can lead to post-harvest decay and spoilage. Proper disease management practices help reduce post-harvest losses and maintain product quality.

Ripening of Fruits:

Ripening is a natural process that transforms raw, immature fruits into mature, flavorful, and edible ones. It involves a series of biochemical and physiological changes that alter the texture, color, aroma, taste, and nutritional composition of the fruit. Proper ripening is crucial for enhancing the quality, taste, and consumer acceptance of fruits.

Terminal period of maturity during which fruit attain maximum aesthetic value and edible quality is called as ripening.

Ripening is associated with change in compound i.e. conversion of starch to sugar.

Natural Ripening Process:

The natural ripening process is primarily regulated by plant hormones, with ethylene being the most important one. Ethylene is a gaseous hormone produced by fruits themselves as well as other plant parts. It acts as a signaling molecule that triggers various changes in the fruit.

Biochemical Changes During Ripening:

1. Starch to Sugar Conversion: Starches stored in fruits are broken down into sugars, making the fruit sweeter as it ripens.
2. Pectin Breakdown: Pectin, a complex carbohydrate responsible for the firmness of unripe fruit, breaks down, leading to softening of the fruit's texture.
3. Acid Degradation: The acidity of the fruit decreases during ripening, leading to a milder and less sour taste.
4. Aroma and Flavor Development: Compounds responsible for aroma and flavor develop, enhancing the sensory appeal of the fruit.
5. Color Change: Green chlorophyll pigments break down, revealing other pigments like carotenoids (orange, yellow) and anthocyanins (red, purple).

Controlled Ripening:

Controlled ripening is a post-harvest technique used to manage and optimize the ripening process. It involves regulating environmental conditions to ensure uniform and timely ripening. This is particularly important for fruits that are harvested before they are fully ripe.

Methods of Controlled Ripening:

1. Ethylene Gas: Ethylene is used to initiate and accelerate the ripening process. Fruits can be exposed to ethylene gas in controlled environments.
2. Temperature Control: Temperature significantly influences the rate of ripening. Warm temperatures accelerate ripening, while cooler temperatures slow it down.
3. Humidity Management: Proper humidity levels prevent moisture loss and maintain the texture of fruits.
4. Ventilation: Adequate ventilation ensures even distribution of ethylene gas and other gases produced during the ripening process.
5. Ripening Chambers: Specialized ripening chambers or rooms provide controlled conditions for ripening, including temperature, humidity, and ethylene concentration.

Benefits of Controlled Ripening:

1. Quality Assurance: Controlled ripening ensures uniform ripening, consistent quality, and desirable flavor in fruits.
2. Extended Shelf Life: Managed ripening helps extend the shelf life of fruits, reducing wastage.
3. Market Timing: Ripening can be timed to match market demand, optimizing sales and reducing post-harvest losses.
4. Less Transit Damage: Controlled ripening allows fruits to be harvested slightly unripe and then ripened later, reducing damage during transportation.

Proper ripening and controlled ripening techniques are vital for maintaining fruit quality, reducing losses, and ensuring that consumers enjoy fruits at their best.

Process of ripening:

Cell division & expansion: formation of fruits from flower

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Maturation: attainment of complete growth & maturity

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Ripening: undergoes physiological and biochemical changes

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Senescence- condition or stage of deterioration

Changes occurring during ripening

Understanding the changes that occur during ripening is essential for determining the optimal harvesting time, post-harvest handling, and storage conditions.

1. Colour Change: One of the most apparent changes during ripening is the colour transformation of fruits. Many fruits change from green to various colours like red, orange, yellow, or purple as they ripen. This colour change is primarily due to the breakdown of chlorophyll and the synthesis of pigments such as carotenoids and anthocyanins.
2. Softening: As fruits ripen, their texture changes from firm and crisp to soft and tender. This softening is caused by the breakdown of cell walls, which leads to a reduction in cell-to-cell adhesion and an increase in the fruit's juiciness.
3. Flavour Development: Ripening is crucial for the development of desirable flavours in fruits. It involves the breakdown of complex compounds into simpler sugars and aromatic compounds, leading to a sweeter and more flavorful taste.
4. Aroma Production: Ripening is associated with the synthesis of volatile compounds responsible for the characteristic aroma of fruits. These aromatic compounds contribute to the fruit's distinct smell and play a significant role in the overall eating experience.
5. Starch to Sugar Conversion: During ripening, starches stored in the fruit are converted into sugars like glucose and fructose. This process increases the sweetness of the fruit and enhances its palatability.
6. Acid Reduction: Many fruits undergo a decrease in acidity during ripening. This reduction in acidity balances the sweetness, making the fruit more enjoyable to eat.
7. Respiration Rate: Ripening is associated with an increase in the rate of respiration in fruits. This increased respiration leads to the breakdown of stored nutrients, the production of energy, and the release of carbon dioxide and heat.
8. Change in Ethylene Production: Ethylene, a natural plant hormone, plays a key role in ripening. As fruits mature, they may produce more ethylene, which further accelerates the ripening process. Ethylene also promotes the synthesis of enzymes that contribute to various ripening changes.
9. Cellulose Breakdown: The breakdown of cellulose in the fruit cell walls occurs during ripening, contributing to the softening of the fruit.
10. Seed Development: In many fruits, the seeds mature and develop fully during ripening. This process ensures that the seeds are viable for reproduction when the fruit is consumed and later dispersed.
11. Loss of Green Pigment (Chlorophyll): Green fruits lose their green colour due to the degradation of chlorophyll during ripening, revealing the underlying pigments responsible for the final fruit colour.
12. Release of Volatile Compounds: Ripening fruits release volatile compounds, which not only contribute to their aroma but also attract animals for seed dispersal.

During ripening, fruits undergo a series of biochemical and physiological changes that are essential for their maturation, flavour development, and readiness for consumption. Understanding these changes is crucial for post-harvest management and delivering high-quality, ripe fruits to consumers. Let's explore the key changes that occur during ripening:

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