Technology for Food Preservation

Food : Any material (solid or liquid) consumed for the purpose of fulfilling nutritional requirements of the body to sustain life. It usually come from plant (fruits, vegetables, oil seeds) and animal (meat, fish, poultry and eggs) sources.

Constituents are water (~90%), carbohydrates, fats, proteins, vitamins and minerals and trace elements.

Digestion is the biomechanical breaking down of food into smaller  components that can be absorbed into the blood stream.

v  Food Safety: Handling, preparation, and storage of food in ways that prevent food born illnesses. Unsafe food causes many acute and life-long diseases, ranging from diarrhea to various forms of cancer. WHO estimates that food and water borne diarrhoeal diseases taken together kill about 2.2m people annually, 1.9m of them children

v  Hazard Analysis Critical Control Point or HACCP is a systematic preventive approach to food safety that addresses physical, chemical, and biological hazards as a means of prevention rather than inspection of the finished product.

v  Food Security: Ensuring that all people at all times have both physical and economic access to the basic food that they need.

Types of Losses in Fruits and Vegetables

•          Estimated at 30 to 40% from farm to consumer due to

–        Physical/Mechanical damage during harvesting, handling and transportation

–        Quality degradation during storage of fresh produce due to continued respiration, enzymatic activity  and loss of water

–        Microbial spoilage of processed/fresh products by mould, yeast and bacteria

•          Food Preservation

    Keep the food safe i.e. Prevent microbial spoilage and thus extend shelf life of the food while  retaining its nutritional value

Ø  Value Addition Improve the economic/nutritional value of the food through formulation, processing or both. Degree of value addition depends on level of processing

Factors affecting shelf life

v  Product Characteristics

Ø  Moisture Content/ Water Activity (Aw)

Ø  pH

Ø  Composition

v  Storage Condition

Ø  Temperature

Ø  Air (Oxygen)

Ø  Relative Humidity

Methods of Food Preservation

o        Refrigeration/Controlled/Modified Atmosphere Storage

o        Freezing

o        Chemical Treatment (Potassium Metabisulphite, Sodium Benzoate etc)

o        Removal of Water (Drying, Freeze Drying, (20 to 25%)

o        Radiation (Gamma, Ultra Violet)

o        Thermal processing, Canning, Aseptic packaging

Controlled/Modified Atmosphere Storage

•          Composition of air (21% O₂, 78% N₂ and 1% the rest)

•          In controlled atmosphere (CA) storage concentrations of oxygen, carbon dioxide and nitrogen as well as temperature and humidity are regulated to extend the shelf life of fresh fruits and vegetables. Apples are largely stored by this method.

•          In dry commodities (grains, legumes and oilseeds) the primary aim of the CA is usually to control insect pests. Most insects cannot exist indefinitely without oxygen or in conditions of raised (>30%) carbon dioxide.

Storage Conditions for Vegetables and Fruits

Commodity	Temperature F	% Relative humidity	Storage Life Days	Ethylene sensitive
Apples	30—40	90-95	90-240	Y
Apricots	32	90-95	7-14	Y
Bananas	56-58	90-95	7-28	Y
Cauliflower	32	90-98	20-30
Mushrooms	32	95	12-17
Okra	45-50	90-95	7-14
Onions, bulb	32	65-70	30-180
Peaches	31-32	90-95	14-28	Y
Potatoes	40-50	90	56-140	Y
Spinach	32	95-100	10-14	Y
Strawberries	32	90-95	5-10
Tomatoes	62-68	90-95	7-28	Y

Thermal Processing

Thermal processing implies the controlled use of heat to increase, or decrease rates of reactions in foods.

Objective of sterilization is to destroy all microorganisms, that is, bacteria, yeasts and moulds, in the food material to prevent decomposition of the food, which makes it unattractive or inedible.

Sterilization prevents any pathogenic (disease-producing) organisms from surviving and being eaten with the food. Pathogenic toxins may be produced during storage of the food if certain organisms are still viable. Microorganisms are destroyed by heat, but the amount of heating required for the killing of different organisms varies.

•          Water Activity Aw = ERH/100

•          Water activity means energy.  If there isn’t high enough energy around micro organisms, they can’t transport water across their cell walls and they can’t grow.  Water activity gives food processors an absolute measure of whether mold, bacteria, and yeast will grow in their products. 

•          If your product is above 0.87 water activity units, it’s a “potentially hazardous food”, meaning you have to use temperature or pH to prove your product is safe.

Measuring heat killing efficiency

•          The thermal death time (TDT) is the shortest time necessary to kill all microorganisms in a suspension at a specific temperature and under defined conditions

•          The decimal reduction time (D, or D value) is the time required to kill 90% of the microorganisms or spores in a sample at a specific temperature

•          The Z value is the increase in temperature required to reduce D to 1/10 of its previous value

The F value is the time in minutes at a specific temperature (usually 250ºF or 121.1ºC) necessary to kill a population of cells or spore

Classification of foods based on pH

v  Low Acid Foods pH > 4.6

–        Anaerobes of the genus clostridium are main spoilage source in low acid canned foods.

–        Lethal dose of C-Botulinum toxin is 0.0084 mg for a 70 Kg human being

–        Optimum pH for C-Botulinum is 4.87 to 8.2. FDA has set minimum limit of 4.6 for this microbe.

v  Acid Foods (3.7<pH<4.6)

–        Spoilage may be caused by moulds, yeasts and acid resistant bacteria. Al these have low heat resistance

v   High Acid Foods (pH<3.7)

–        Spoilage by spore forming bacteria does not occur. Spoilage by moulds and yeasts may occur. Low heat resistance

Acidity of fruits and vegetables

•          Low Acid Foods (PH > 4.6)

                Mushroom, Peas, Corn, Pumpkin, Carrot, Okra, Garlic, Olives, Meat, Poultry, Milk,

•          Acid Foods (PH<4.6)

                Apples, Oranges, Cucumbers, Plums, Apricots, Pears, Peaches, Tomatoes

Canning

Thermal sterilization of canned foods has been one of the most widely used methods for food preservation during the twentieth century and has contributed significantly to the nutritional well-being of much of the world’s population (Teixeira and Tucker, 1997).

The goal of canning process is to thermally sterilize the food and pack in sealed containers under anaerobic conditions. The temperature and time required for achieving sterilization is product specific and depends on pH and physical properties of the food.

Head Space

v  Head Space

–        Jams, Jellies: 1/4 in.

–        Acid foods: 1/2 in.

–        Low Acid Foods: 1 in.

Spoilage Indicators

Ö Can Swelling

Ö Odor

Ö Color

Ö Internal Can Corrosion

Ö Low acid cans suspected of spoilage should be dumped in land fill. Unsealed cans should be detoxified, Never Taste

Aseptic Packaging

Ø  Food is sterilized at high temperature (149^oC) outside cans for 1 or 2 Seconds (UHT)

Ø  Heat Exchangers are employed

Ø  Immediate cooling is must

Ø  Foods can be packed in large containers with better quality retention.