PHYSIOLOGICAL CHANGES IN VEGETABLES AFTER HARVESTING.pptx
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Post harvest physiological changes in vegetables Respiration, Transpiration, Ethylene Production, Growth and Development, Physical Damage. Horticulture.
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Lecture 7: Loss Assessment and Quality Evaluation
- Perishable fruits and vegetables are alive after harvest and require proper postharvest handling to maintain quality during storage, transport, and distribution to consumers. Improper practices can lead to major postharvest losses.
- Key goals are to harvest produce at optimal maturity and maintain internal and external quality until it reaches consumers in a desired form. Historical methods often killed the product to allow longer storage and transport.
- Major causes of postharvest loss include internal factors like respiration and senescence as well as environmental factors like temperature, pathogens, and physical damage. Proper temperature management is especially important as it influences the chemical reactions of respiration that determine shelf life.
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Postharvest losses are a major issue worldwide, with estimates of 5-25% in developed countries and 20-50% in developing countries. The main goals of postharvest handling are to harvest produce at optimal maturity, maintain quality during storage and distribution, and deliver produce to consumers in a form they will purchase. Key causes of postharvest loss include environmental factors like temperature, pathogens, and physical damage as well as internal factors like respiration and compositional changes. Proper postharvest practices and technologies can help reduce losses and maintain quality from field to fork.
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The document summarizes food preservation techniques and food spoilage mechanisms. It classifies foods based on shelf life, functions, processing, and categorizes spoilage as physical, microbial, chemical or enzymatic. Physical spoilage includes moisture changes and crystallization. Microbial spoilage is caused by molds, yeasts and bacteria. Chemical spoilage involves oxidation, proteolysis and Maillard reaction. Enzymatic reactions like pectin hydrolysis and lipolysis also cause food degradation. Various intrinsic and extrinsic factors influence the spoilage process.
Recommended
Lecture 7: Loss Assessment and Quality Evaluation
- Perishable fruits and vegetables are alive after harvest and require proper postharvest handling to maintain quality during storage, transport, and distribution to consumers. Improper practices can lead to major postharvest losses.
- Key goals are to harvest produce at optimal maturity and maintain internal and external quality until it reaches consumers in a desired form. Historical methods often killed the product to allow longer storage and transport.
- Major causes of postharvest loss include internal factors like respiration and senescence as well as environmental factors like temperature, pathogens, and physical damage. Proper temperature management is especially important as it influences the chemical reactions of respiration that determine shelf life.
Loss of nutrients
This document discusses the effects of various food processing methods on nutrients. It explains that while processing helps preserve foods, it can also negatively impact nutrients. Pasteurization, frying, fermentation, baking and other methods are outlined. For each, specific nutrients that may be reduced are identified, such as iodine with pasteurization or vitamin A with frying. The document provides a high-level overview of how common food processing techniques can impact the nutritional content of foods.
6258629.ppt
Postharvest losses are a major issue worldwide, with estimates of 5-25% in developed countries and 20-50% in developing countries. The main goals of postharvest handling are to harvest produce at optimal maturity, maintain quality during storage and distribution, and deliver produce to consumers in a form they will purchase. Key causes of postharvest loss include environmental factors like temperature, pathogens, and physical damage as well as internal factors like respiration and compositional changes. Proper postharvest practices and technologies can help reduce losses and maintain quality from field to fork.
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The document discusses the effects of food processing on nutrient content and food spoilage. It states that food processing aims to make food safe, of high quality, and convenient. Various processing methods like heating, milling, and freezing can affect nutrients. Heat processing may improve digestibility but also cause nutrient loss through reactions like Maillard browning. Freezing preserves nutrients if food is stored at proper temperatures. Food spoilage is caused by natural decay through enzymes or microbial growth of fungi like molds and yeasts or bacteria. Proper processing, storage, and preparation can help minimize nutrient loss and spoilage.
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Thawing fish involves increasing its temperature so that ice crystals melt back into water at around -10C. There are various methods of thawing fish, including refrigeration, cold water, and microwaves. Thawing has merits like increased yield, shorter cooking times, and tenderized texture from ice crystal formation disrupting muscle fibers. However, thawing also has demerits such as weight loss from water leeching out, reduced water holding capacity, and possible color and texture changes from oxidation and rigor mortis. Care must be taken to thaw fish slowly at low temperatures to minimize quality impacts.
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Because of the low temperature used in processing, the quality of the rehydrated product is excellent. When solid objects like strawberries are freeze dried the original shape of the product is maintained. If the product to be dried is a liquid, as often seen in pharmaceutical applications, the properties of the final product are optimized by the combination of excipients (i.e., inactive ingredients). Primary applications of freeze drying include biological (e.g., bacteria and yeasts), biomedical (e.g., surgical transplants), food processing (e.g., coffee) and preservation.
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This document discusses the effects of food processing on nutrient content and food spoilage. It outlines various food processing methods like heating, freezing, canning, and dehydration and how they impact nutrients. While processing aims to make food safe, high quality, and convenient, it can reduce nutrient availability through chemical changes and nutrient losses. The document also examines the natural and microbial causes of food spoilage, like enzyme action, moisture loss, and fungi/bacterial growth. Proper processing and storage are necessary to minimize nutrient degradation and prevent spoilage.
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Because of the low temperature used in processing, the quality of the rehydrated product is excellent. When solid objects like strawberries are freeze dried the original shape of the product is maintained. If the product to be dried is a liquid, as often seen in pharmaceutical applications, the properties of the final product are optimized by the combination of excipients (i.e., inactive ingredients). Primary applications of freeze drying include biological (e.g., bacteria and yeasts), biomedical (e.g., surgical transplants), food processing (e.g., coffee) and preservation.
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Food Microbiology, food poisoning and food born diseases notes
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Unit 1 Food Processing and Preservation by Low temperature.pptx
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PHYSIOLOGICAL CHANGES IN VEGETABLES AFTER HARVESTING.pptx
- 1. PHYSIOLOGICAL CHANGES IN VEGETABLES AFTER HARVESTING
- 2. POSTHARVEST PHYSIOLOGY • The life of fruits and vegetables can be divided into three major physiological stages • The physiological changes after harvest till senescence is called postharvest physiology.
- 3. MAJOR POSTHARVEST PHYSIOLOGICAL CHANGES • Respiration • Ethylene production • Growth and development • Transpiration • Physiological breakdown • Physical damage
- 4. RESPIRATION • Stored organic materials (carbohydrates, protein, and fat) are broken down into simple products • Food reserves, especially sugars, get degraded in order to produce energy (in the form of ATP and NADH) to maintain cellular metabolic activity. • Energy is released • O2 is used and CO2 is produced C6H 12 O6 + 6O2 6CO2 + 6H2O + Energy (686 kcal)
- 5. EFFECTS OF RESPIRATION • Reduced food value (energy value) • Reduced flavor due to loss of volatiles • Reduce weight The rate of deterioration of vegetables is directly proportion to the respiration rate
- 6. ETHYLENE PRODUCTION • Naturally produced by vegetables as they ripen • Can lead to premature ripening if produced in excess • The presence of high CO2, reduced O2 and low temperature can inhibit ethylene production
- 7. GROWTH AND DEVELOPMENT • In some vegetables growth and development continue even after harvest Example • Sprouting of potato, onion and garlic • Rooting of onions
- 8. TRANSPIRATION • A physical process in which high amount of water is lost • Occurs through the cuticle, epidermis, stomata and hairs • Produce stored at high temperature will have high transpiration rate • It causes loss in quality i.e., undesirable changes in colour, taste and nutritive value
- 9. EFFECTS OF TRANSPIRATION • Loss in weight • Loss in appearance (Shrinking) • Loss in texture (softening, loss of crispiness and juiciness)
- 10. PHYSIOLOGICAL BREAKDOWN • Occurs when produce is exposed to an undesirable temperature • Chilling injury - when commodity is stored below their desired storage temperature • Heat injury - when commodity is exposed to direct sunlight or excessively high temperature • Freezing injury - when commodity is stored below their freezing temperature
- 11. PHYSICAL DAMAGE • Mechanical injury during harvesting, handling, storage and transportation • Bruising due to vibration, impact and compression