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Extraction and Preservation of Fruit Pulp and Juice

 

Extraction and Preservation of Fruit Pulp and Juice

Aim

To scientifically extract fruit juice and pulp using modern techniques and preserve them using thermal (pasteurization) and chemical methods for better shelf life and quality.

Objectives

  1. Understand juice extraction techniques (mechanical + enzymatic)
  2. Evaluate yield, quality, and physicochemical properties
  3. Learn preservation methods used in food industry
  4. Analyze important parameters like TSS (°Brix), acidity, and yield efficiency.

Principle

1. Juice Extraction Principle

  • Juice exists either:
    • In parenchymatous cells (apple, grape)
    • In specialized juice sacs (citrus)

Extraction depends on:

  • Cell rupture (mechanical/enzymatic)
  • Diffusion of intracellular liquid

Scientific concept:

  • Cell wall breakdown → increased juice yield
  • Use of pectinolytic enzymes improves yield of juice and pulp

2. Oxidation Control

Original mentioned aeration — but here is scientific explanation:

  • Oxygen exposure → enzymatic browning
  • Enzyme involved: Polyphenol oxidase (PPO)

Effects:

  • Vitamin C degradation
  • Colour loss
  • Off-flavour

Solution:

  • Minimal exposure to air
  • Use of antioxidants (ascorbic acid / citric acid)

The extraction of fruit juice and pulp depends on the structural characteristics of the fruit tissues and the location of juice within the cells. In fruits like apple, grape, and aonla, juice is distributed within parenchymatous cells and can be extracted by crushing and pressing. In contrast, citrus fruits contain juice in specialized sacs, requiring mechanical reaming for extraction. The process involves rupture of cell walls, allowing intracellular fluid to diffuse out. Scientific evidence suggests that enzymatic treatments such as pectinase application can enhance juice yield by breaking down pectin substances.

During extraction, exposure to oxygen should be minimized, as it leads to enzymatic browning caused by polyphenol oxidase, resulting in degradation of vitamin C and deterioration of color and flavor. This can be controlled by reducing aeration and using antioxidants like citric acid. Preservation of juices and pulp is achieved through pasteurization and chemical methods. Pasteurization involves heating the juice to around 85–90°C for a short duration to destroy microorganisms and inactivate enzymes without significantly affecting quality. Chemical preservatives such as sodium benzoate and potassium metabisulfite (KMS) are used to inhibit microbial growth, especially in acidic conditions.

 3. Preservation Principle

Pasteurization

  • Low acid foods: 90–100°C
  • High acid juices (pH < 4.5): 80–95°C for 15–30 sec (HTST method)

Purpose:

  • Destroy spoilage microorganisms
  • Inactivate enzymes

4. Chemical Preservation

Sodium benzoate:

  • Works best at pH < 4.5
  • Active form: Benzoic acid

Potassium metabisulfite (KMS):

  • Releases SO₂ (antimicrobial + antioxidant)
  • KMS also prevents enzymatic browning
  • Should not be added to the colourful products

Materials

A. Extraction

  • Fresh fruits (graded, washed)
  • Stainless steel knife (avoid Fe contamination)
  • Pulper / crusher / juice extractor
  • Hydraulic press (for high yield)
  • Muslin cloth
  • pH meter (NEW – scientific addition)
  • Refractometer (for TSS)

B. Preservation

  • Sodium benzoate (food grade)
  • Potassium metabisulfite
  • Citric acid
  • Glass bottles (sterilized at 121°C or boiling water)
  • Thermometer

Procedure

Step 1: Pre-treatment

Wash fruits with chlorinated water (50–100 ppm)

  • Peel and cut
  • Optional:
    • Add 0.1% citric acid solution to prevents browning

Step 2: Extraction

Citrus Fruits

  • Mechanical extraction using a reamer
  • Avoid crushing peel to prevents bitterness (limonin release)

Apple / Grape / Aonla

  • Crush and press using hydraulic press
  • Optional advanced step:
    • Add pectinase enzyme (0.05%)
    • Incubate 30–60 min to increase juice yield significantly

Mango / Tomato

  • Use pulper
  • Heatent (optional):
    • Blanching at 85–90°C for 2–3 min improves pulp recovery

 Step 3: Heat Processing

 Standard method:

1.      Heat juice to 85–90°C (not always 100°C high temp destroys flavour + vitamins

  1. Hold for 15–20 seconds (HTST)
  2. Fill in sterilized bottles
  3. Seal immediately

 Step 4: Chemical Preservation

 Sodium benzoate:

  • 600–1000 ppm (0.06–0.1%)

 KMS:

  • 1000–2000 ppm (0.1–0.2%)

 Added after cooling

 Observations

Add scientific measurements:

  • Juice yield (%)
  • Pomace (%)
  • pH (New)
  • TSS (°Brix)
  • Titratable acidity (%)

Calculations

Juice Yield (%): (Weight of juice/weight of fruit) * 100

Pomace (%): (Weight of residue/weight of fruit) * 100

 

Result

Juice yield (%)

Pomace (%)

TSS (°Brix)

Acidity (%)

pH

Preservation method effectiveness

Precautions

Avoid metal contamination (Fe, Cu → oxidation)

Maintain hygienic conditions (microbial control)

Avoid excessive heating

Use preservatives within FSSAI permissible limits

Store in cool and dark conditions


Top Viva Questions

Basic Questions

  1. What is fruit juice extraction?
    👉 Process of separating liquid from fruit tissues.
  2. What is pulp?
    👉 Semi-solid product containing fiber and juice.

Concept-Based Questions

  1. What is the role of pectin in fruits?
    👉 Holds cells together; its breakdown increases juice yield.
  2. What enzyme causes browning?
    👉 Polyphenol oxidase (PPO)
  3. What is TSS?
    👉 Total soluble solids (mainly sugars), measured in °Brix.

Preservation Questions

  1. What is pasteurization?
    👉 Heating below 100°C to destroy microbes.
  2. Why is high temperature not always used?
    👉 Destroys nutrients and flavour.
  3. What is HTST method?
    👉 High Temperature Short Time (85–90°C for few seconds).

Chemical Preservation

  1. Why is sodium benzoate used?
    👉 Antimicrobial, effective in acidic conditions.
  2. What is the function of KMS?
    👉 Releases SO₂ → antimicrobial + antioxidant.
  3. Why KMS is not used in coloured products?
    👉 Causes bleaching effect.

 Practical-Oriented Questions

  1. Why stainless steel equipment is used?
    👉 Prevents iron contamination and oxidation.
  2. What is pomace?
    👉 Residue left after juice extraction.
  3. Why filtration is required?
    👉 Removes suspended particles.

Advanced / High-Level Questions

  1. How can juice yield be increased?
    👉 By using pectinase enzyme.
  2. What is enzymatic browning?
    👉 Oxidation of phenols → brown colour.
  3. Why citric acid is added?
    👉 Prevents oxidation and improves shelf life.

 


Hello friends, I'am Dr. Subhrajyoti , from Odisha, India. I have completed my UG & PG from OUAT and Ph.D. from JAU. During my early year of teaching, I loved to provide important information to the young agriculturists and farmers. With the suggestions from my best friend Mr. S. R. Biswal, (Ph.D. Research Scholar; website designer & content editor of agriculture2u.com (blog &YouTube), I got interested to create such an amazing platform, where I can share my knowledge to a greater range of audience and also get enriched with new ideas and knowledge. I feel privileged to be in contact with you all. I would like to thank you all for your valuable support and encouragement through viewing my articles. I will always try my best to provide the quality and latest information on this website. Thank you….