Valorization and Processing of Vegetable Fresh-Processing Residues

Introduction to Food Loss and Waste (FLW) and Sustainable Systems

• General Concerns Regarding Food Waste: Food waste is a global priority due to its constant threat to the environment and its role as a serious operational challenge for production plants and the food industry.
• Environmental and Economic Impact:
  • Food production is a resource-intensive activity.
  • By $2050$, the demand for agricultural products is expected to increase by $50\%$\, if dietary habits and waste levels remain unchanged.
  • In the European Union, food waste (FW) in $2016$ was estimated at $88 \text{ million tons}$. This amount represents an associated cost of $143 \text{ billion euros}$.
  • Approximately one-third of the edible parts of food produced for human consumption are lost or wasted globally.
  • Reducing FW in the upcoming decade is considered a priority that impacts four key pillars: nutrition, climate, circularity, and communities.
• Conceptual Definitions:
  • Food Loss and Waste (FLW): The Food and Agriculture Organization (FAO) works toward harmonizing this concept.
  • Food Waste (FW): EU legislation defines this as covering all stages from "farm to fork," excluding crops plowed in or not harvested.
• Supply Chain Distributions:
  • Primary production accounts for $25\%$\ of total losses.
  • Processing accounts for $24\%$\ of total losses.
  • Fruits and vegetables are the products that participate most in these percentages.
  • Losses in early processing are often due to high commercial standards resulting in discards, or the removal of edible parts (outer leaves, stems, or damaged parts) in fresh-processing lines.

Sustainable Food Systems and the Circular Economy

• The Circular Approach: Reintroducing waste into the production chain serves as raw material for new products, fitting the concepts of "circular economy," "industrial ecology," and "zero waste economy."
• European Green Deal: The European Commission has adopted a Circular Economy Action Plan promoting sustainable initiatives throughout the life cycle of products.
• Definition of Sustainable Food Systems (FAO, 2019): Systems must ensure sustainable consumption and production patterns while delivering safe, healthy, and nutritious diets.
• Sustainable Healthy Diets (FAO and WHO, 2019): Consumption should be adequate in energy and nutrients for growth and development, promoting all dimensions of well-being while maintaining low environmental impact and reducing food loss.
• Reformulation Strategy: Modifying the nutritional characteristics of commonly consumed processed foods via reformulation provides an opportunity to improve public health, aligning with the goal to "Ensure healthy lives and promote well-being for all at all ages."

Valorization of Vegetable Residues as Functional Powdered Ingredients

• Transformation Process: Dehydration and milling can be combined to convert perishable vegetable wastes into plant-based powders.
• Value of Fruit and Vegetable By-products: Often considered low-value material, these residues are actually rich sources of bioactive compounds including fiber, antioxidants, and various phytochemicals.
• Applications of Vegetable Powders:
  • Ingredients in confectionery, bakery, and distilling industries.
  • Used in dressings, soups, and ready-to-eat products.
  • Fortification of foods to improve nutritional value or technological properties (e.g., water retention, thickening, texturizing).
• Project-Specific Focus: A collaborative effort with an agricultural cooperative is currently developing functional ingredients from cabbage, carrot, celery, and leek residues.
• Annual Residue Estimates for the Cooperative:
  • Leeks: Approximately $180 \text{ tons}$ (including white parts and green leaves).
  • Cabbage: Approximately $250 \text{ tons}$ (outer leaves).
  • Carrots: Between $2,000$ and $3,000 \text{ tons}$.
  • Celery: Between $2,000$ and $3,000 \text{ tons}$.
• Methodological Goal: Integral use of by-products through dehydration rather than solvent extraction, avoiding the generation of further residues.\n

Scientific Context and Research Methodology

• Research Databases Used: Science Direct, Scopus, Emerald Insight, Springer Link, Taylor \& Francis Group, and Wiley Online Library.
• Total Publications Examined: Titles and abstracts of more than $120 \text{ publications}$ were examined, with $98 \text{ documents}$ serving as the basis for the review.
• Timeline of Research:
  • $80\%$\ of investigations were published between $2011$ and $2020$.
  • $45\%$\ were published between $2016$ and $2020$.
• Keyword Analysis (Figure 1): Research interest in "Functional Food" and "Waste/By-products" has increased dramatically, with total publications doubling roughly every $5 \text{ years}$.

Nutritional Background of Selected Vegetables

• Cabbage: Rich in glucosinolates and sulforaphane ($C_6H_{11}NOS_2$). Sulforaphane is a hydrolysis product of glucosinolates (catalyzed by the enzyme myrosinase) and is a potent anticancer substance.
• Carrots: A primary source of $\alpha$- and $\beta$-carotene, which are essential precursors to Vitamin A. They are also high in dietary fiber (DF).
• Celery: Notable for its high apigenin content, a flavone associated with significant health benefits. Additions of celery powder have been shown to increase total phenol content and antioxidant properties in breads.
• Leek: An important source of sulfides and phenolic compounds. Drying leek may reduce its antioxidant capacity by more than $50\%$\ due to the loss of ascorbic acid.

Comparison of Dehydration Techniques

• Hot Air Drying (HAD/AD):
  • Advantages: Inexpensive, easy to operate, allows for integral recovery of waste.
  • Disadvantages: Long drying times, potential for surface overheating, color darkening (browning), loss of flavor, and decreased rehydration capacity.
  • Impact: Can decrease thermolabile substances but is the most widely used industrial technique.
• Vacuum-Drying (VD):
  • Advantages: Lower drying temperatures and oxygen-deficient environments prevent oxidation. Higher effective moisture diffusivity compared to HAD.
  • Disadvantages: Batch process, small throughput, very high residence times ($20$ to $100 \text{ hours}$).
• Freeze-Drying (FD):
  • Advantages: Negligible nutrient loss, original color retention, high quality, and high porosity.
  • Disadvantages: Very high cost ($4$ to $8 \text{ times}$ higher than AD), long drying times ($24$ to $72 \text{ hours}$).
• Spray-Drying (SD):
  • Mechanism: Rapid evaporation for liquids/emulsions. Thermal energy evaporates water while the sample remains at a moderate temperature.
  • Limitation: Not suitable for integral valorization of solids as it requires solid-liquid extraction beforehand.
• Assisted and Combination Techniques:
  • Osmotic Dehydration (OD): Can reduce HAD processing time (e.g., from $8$ to $2 \text{ hours}$ in strawberry cubes).
  • Microwave-Assisted (MW): Uses electromagnetic fields for volumetric heating, reducing energy consumption and time.
  • Ultrasound-Assisted (US): Uses mechanical and cavitation effects to reduce internal and external mass transfer resistance.

Impact of Processing on Bioactive Compounds

• General Principle: Processing determines physicochemical and functional properties, as well as the bioaccessibility of compounds.
• Myrosinase and Sulforaphane in Cabbage:
  • Myrosinase Stability: Thermal stability typically ranges between $40$ and $60 \, ^{\circ}C$.
  • Sulforaphane Formation: Occurs when the vegetable temperature is between $25$ and $53.5 \, ^{\circ}C$. Degradation occurs above these temperatures.
  • Optimized Multi-stage Drying: High heating rates are initially used to reach $40 \, ^{\circ}C$. Afterward, the material temperature must be strictly controlled to not exceed $50 \, ^{\circ}C$.
  • Functional Threshold: For functional efficacy, powder should contain a minimum sulforaphane content of approximately $2.7 \text{ mg/L}$.
• Dietary Fiber (DF): There is a growing market for fiber-rich ingredients due to physiological health benefits. Fruit and vegetable by-products are considered major sources of DF, with wine grape pomace reported to contain as much as $61\%$\ DF.
• Antioxidant Stability: In experiments with wine grape pomace, antioxidant and fiber levels remained stable after $16 \text{ weeks}$ of storage.

Case Studies in Food Ingredient Valorization

• Apple and Citrus residues: Used to create fiber concentrates with high water retention and fat adsorption.
• Lulo fruit bagasse: High in phenols, flavonoids, and fiber.
• Blueberry and Persimmon: Blueberry residues provide anthocyanins; persimmon residues provide carotenoids.
• Mango peels: Applied to macaroni to improve antioxidant properties.
• Fruit and Vegetable Combinations: Ferreira et al. (2015) successfully used residues from orange, passion fruit, watermelon, and various greens to formulate biscuits and cereal bars rich in fiber and minerals.