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Week 1: Introduction to Food Processing & Preservation (Overview of…
Week 1: Introduction to Food Processing & Preservation
Overview of food processing and preservation
Objectives of food processing & preservation
Food processing is the transformation of raw food materials into high quality, nutritious and safe foods through physical or chemical means.
Food Preservation is the employment of food processing operations to extend the shelf life by slowing or preventing spoilage of food, loss of quality and prolonging the edibility of foods.
Purposes of food processing & preservation
SENSORY
Improve product texture, flavor or colour
E.g. cooked vs raw meat
SHELF LIFE EXTENSION
Destroy/prevent microbial growth
Retard deteriorative effects such as oxidation
E.g. fresh vs pasteurized vs UHT milk
CONVENIENCE
Multi-seasonal availability
Easy to prepare/use by consumers or ready to eat
SAFETY Eliminate spoilage and pathogenic microbes
Remove anti-nutritional factors
VARIETY More choices and products from a raw material
E.g. fresh whole apple, into sliced/diced apple, apple juice, dried apple & apple filling
Functional, fortified Foods
Add functional ingredients or nutrients into foods to improve nutritional qualities
PROFITS Less wastage, increase distribution channels
Classification of food processing operations
Novel Techniques
Ohmic Heating or Joule Heating: alternating electric current is passed through foods or other materials resulting in internal generation of heat
Pulsed Electric Field Liquid foods place between two electrodes and subject to high electric field strengths in short pulses that result in rapid reduction of vegetative microbial cells in food.
High Pressure Processing: Either liquid or solid foods (with or without packaging) are subjected to pressure between 100 – 1000 MPa from few seconds to minutes at temperature from <O℃ to >100℃
High Temperature Processing
Pasteurization
Baking/Frying
Blanching: Inactivating of microbes
Dehydration
Evaporation
Sterilization
Low Temperature Processing
Freezing
Freeze Drying
Chilling
Ambient Temperature Processing
Separation
(E.g. Centrifugation, Filtration, Expression, Solvent Extraction)
Mixing and Forming/moulding
Fermentation
Size Reduction
(E.g. Homogenisation, Milling, Slicing)
Irradiation
Raw Material Preparation
(E.g. Cleaning, Sorting, Grading, Peeling)
Causes and control of food spoilage
Major cause of food spoilage
Reaction with oxygen
Change in colour
Enzymatic browning in fruits/vegetables by oxidizing enzymes
Change in flavour
Oxidative rancidity of unsaturated fatty acids, resulting off flavours
Loss of nutrients
Oxidation of antioxidants in foods e.g. vitamin A and C
Excessive gain/loss of moisture
Excessive Gain of Moisture
Condensation of food surface resulting in mould growth, Caking of powders, Losing of crispiness of nuts
Excessive Loss of Moisture
crumbling of bread and pastry, surfacing hardening of ham
Inappropriate temperature control
Uncontrolled cold
Uncontrolled freezing of milk may cause denaturation of protein resulting in curdling and breaking down of emulsion, causing fat separation.
Tropical fruits (mango, banana) suffer from “chill injury” when stored at 4ºC.
Uncontrolled heat
In meat, denaturation of protein causing toughing of muscle tissues, losing the water holding capacity or non enzymatic browning
In vegetable, losing of integrity causing soft texture, development of undesired colour and destruction of heat liable vitamin
Reaction with light
Destruction of Nutrients
E.g. photo-oxidation when milk is exposed to sunlight resulting in loss of riboflavin (vitamin B2)
Development of Off Flavours
E.g. Unsaturated fats react with light resulting photo oxidation giving rancid profile due to oxidation
Growth & activities of microorganisms
Water activity: Microorganisms have minimum water activity (Aw) that supports growth.
E.g. Bacteria dominates in high Aw (e.g. min. 0.9 aw) while yeast & mould in lower Aw (e.g. min. 0.7)
Oxygen Availability: Microorganisms have different oxygen requirement/tolerance.
E,g, Aerobes grow in presence of oxygen (e.g. mould), Anaerobes cannot tolerate oxygen (E.g. Clostridium botulinum) while Facultative anaerobes can grow in presence/absence of oxygen (E.g. E. coli)
pH: Different microorganisms have pH for maximal growth.
E.g. yeast more acidic than bacteria while mould can grow over wide range of pH
Temperature: Different microorganisms have different temperature requirement for optimal growth
E.g. mesophile, psychrophile and thermophile
Principles of controlling food spoilage
Keeping foods alive.
E.g. slaughter before usage
Keep foods clean & cool.
E.g. delay deterioration as microbes/enzymes are not completely destroyed/inactivated
Inactivate/control microbial & enzymatic activities and reduce/eliminate chemical reaction
E.g. Usage of solutes, acids, smoke, high/low temperature, usage of chemicals and radiation
Methods of food preservation that control food spoilage
Reduced Oxygen
Vacuum packaging, nitrogen flushing, oxygen scavengers
Reduced Water Activity
Reduced pH
E.g. Addition of acid or production of acetic/lactic acid during fermentation
Use of Chemical Preservatives
E.g. Sulphites, Nitrites, Sorbates, Benzoate
Use of Ionizing Radiation (Irradiation)
Use of Low Temperature
. Use of High Temperature (Thermal Processing)