Food processing - Class notes PDF

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Food processing Unit 6 Learning outcome • Define food processing and food preservation. • Recognize the reasons to process food. • Explain the principles of food preservation. • Recognize the underlying principles of food preservation in a variety of food processing technologies and operations. • Defend and/or critique a variety of processing operations used by the industry to minimize these biological hazards in the processed foods. Reasons to process food Food processing: Any operation carried out on raw food is called a process, which results in a processed food product. Reasons for food processing:  Preservation: Food preservation is extending the shelf life of the food.  To make the food edible.  To enhance nutritional quality of foods.  To make food more convenient to consume.  Price reduction is another reason to process food, by reduction in wastage Principles of food preservation  Asepsis: Asepsis means keeping out the microorganisms.  Slowing the growth of microbes: Microbes need certain level of water activity, pH, temperature, substrate, oxygen levels etc. to multiply at their optimal growth rate. If one or more of these conditions are changed such that the microbial growth rate declines, this would extend the shelf-life of the food.  Inhibit the growth of microbes: Microorganisms require certain conditions for their growth. The conditions can be modified to inhibit certain microbes.  Killing the microorganisms  Controlling chemical reactions in foods: Food color, texture or flavor can change over time due to chemical reactions taking place in the food. These reactions can be controlled by removing one of the reactants. Examples:  unsaturated fatty acids react easily with the oxygen leading to oxidative rancidity of the oil. If the oxygen can be kept away from the oil, the oxidation of the oil would not take place.  Fresh foods such as fruits and vegetables contain enzymes. Food can be preserved by inactivating such enzymes Thermal methods: Involve heat treatment.  Pasteurization: According to Encyclopedia Brittanica, “Pasteurization is the application of heat to a food product in order to destroy pathogenic (disease-producing) microorganisms, to inactivate spoilage-causing enzymes, and to reduce or destroy spoilage microorganisms.”

 The higher the temperature used, the shorter is the time needed for thermal destruction of microbes or inactivation of enzymes. Depending upon the population of microbes or the presence of enzymes in the food, specific temperature/time are determined to pasteurize the product. The goal is to destroy most of the pathogenic microbes and reduce the population of spoilage microbes while causing minimal changes to the sensory and nutritional properties of the food.  For example, milk pasteurization can be achieved by Low temperature long time (LTLT) treatment at 63C for 30 minutes or by High temperature short time (HTST) treatment at 73C for 15 sec or even higher temperature treatment at 94C for 0.1 sec. All these treatments result in similar destruction of microbes but the higher the temperatures used and thus less time, the less is the destruction on heat sensitive vitamins. Watch the video Milk from farm to our homes  Sterilization: Killing all the microorganisms in the food is termed as sterilization.  Commercial sterilization aims to reduce microbial population to 10-6 cells/spores per ml.  An example of commercial sterilization is Ultra high temperature (UHT) milk.  UHT treatment at temperatures higher than 138C for a few seconds can destroy most of the bacterial population without having significantly higher adverse impact on the sensory and nutritional properties of the milk.  UHT milk is often packaged in aseptically which are hermetically sealed. Aseptic package is a sterile package. Hermetic sealing doesn’t allow the microbes to enter the package.  Canning: The goal of canning is to destroy almost all the microbes (vegetative cells and spores) such that only 1 in a million cans have a microbial cell/spore.  The correct time/temperature for a specific product is determined experimentally is dependent on several factors including the type of food (for example starchy vs nonstarchy), the pH of food, size of the can, material from which the can is made, the viscosity of the food in the can etc.  Commercial canning has the following basic steps: cleaning the food for canning, filling the food in the can, exhausting (removal of air from the can), sealing the can (airtight seal), cooking (thermal treatment) of the food in the sealed can, and finally allowing the cans to cool to room temperature.  no microbes can enter the can, aerobic microbes cannot grow, most of the microbes are destroyed by intense heat treatment, thus the sealed can is stored at room temperature and has a shelf life of several years.  Since the discovery of Clostridium botulinum, canning procedures are developed to ensure that these microbes cannot multiply in the can and produce the neurotoxin botulinum. High acid foods (pH< 4.6) can be canned at 100C as at this temperature all the vegetative cells would be destroyed and the low pH will inhibit the germination of the spores. Low acid foods (pH>4.6) are canned at temperatures above 116C. High temperature is achieved in the industry by retort canning (pressure canning).  For Safe home canning, reliable methods must be used without any modifications. Home canning  Commercial canning process of baked beans  Blanching: Blanching it briefly dipping the food, typically vegetables and fruits, in boiling water followed by cooling under cold water to stop cooking. The purpose of this heat

treatment is to inactivate enzymes in the food, which otherwise would deteriorate the food quality. Dehydration: Removal of water prevents microbial growth.  Sun drying the least controlled method because the sun light temperature or humidity in the air cannot be controlled, this method takes the longest time of all the methods. Care must also be taken to ensure that the food is kept free from insects, dusts etc. Sun dried tomatoes  Plate drying, the food is placed on trays/plates and is heated in a hot chamber/cabinet. The chamber has an exhaust to let the moist air out. Some dehydrators also have a vacuum pump. This may be termed as vacuum drying. Another variation of the plate/cabinet drying is conveyor belt drying.  Drum drying is a method used for dehydrating viscous fluids to for powder. To make tomato soup powder, the soup is first prepared, then thickened by prolonged heating or by reverse osmosis, and then this viscous soup is put in troughs which are installed under a large hot drum which rolls into the viscous soup. The soup gets coated as a thin film on the drum and gets dried into a thin sheet due to the heat coming from the drum. This sheet is then scraped off and ground to form a powder. Drum dried potato flakes  Spray drying is done by atomizing the milk into droplets using an atomizer/spray in a hot chamber. As the fine droplets enter the chamber they almost instantaneously get dried before they fall at the bottom of the chamber. In addition to an atomizer, a vacuum pump is also equipped on the chamber to constantly remove the moist air from the chamber. Spray drying  Freeze drying, also know as lyophilization is based on the principle of sublimation. The food doesn’t need to be heated thus causing little damage to the nutrients and sensory properties of the food. Due to the absence of the water phase, there’s little leaching out of the nutrients and flavour compounds and minimal loss of the texture. More than 99% of the water can be removed by this method, leading to a better quality dehydrated product. Freeze dried instant coffee  Refrigeration: is cooling the food to above 0 C to 4C to slow down the microbial growth.  Apart from food safety, we refrigerate food to prevent their spoilage. Spoilage occurs either due to growth of spoilage causing microbes and/or due to the activity of the indigenous enzymes in the food.  According to Food and Agriculture Organization of United Nations, 45% of all vegetables and fruits grown are wasted. Are we a part of the problem?  Refrigeration has revolutionized our food supply by reducing food wastage  The consumers in the developed world waste more food than the consumers in the developing countries. In the underdeveloped countries, more food is wasted at production level due to the lack of infrastructure and advanced technology.  Freezing: Cooling the food to temperatures below 0 C to freeze the water in the food. The frozen water in the food is not available for the microbial growth. Thus, freezing halts microbial growth. This is why a safe food frozen properly will always remain safe.  How to thaw food safely?  With respect to the quality of food, the faster the food freezes, smaller are the ice crystals formed in the food, the better the food texture, color and flavor retention.  Individually Quick Frozen (IQF) technology: This has several variations but the basic principle is that the food is immersed in a cryogenic fluid such that the food freezes very quickly, and the individual pieces do not stick together. Commonly used cryogenic fluids are

liquid nitrogen (boiling point -196C) and liquid carbon dioxide (boiling point -79C). Below is shown the processing line of IQF edamame.  Edamame  USDA's guide to safe home freezing

 Changing the pH of the food (directly or indirectly)  Direct Addition of acids such as acetic acid, vinegar, citric acid, tartaric acid: examples pickle  Indirectly lowering the pH by fermenting by bacteria that produce acid in the food: Example, yogurt is made by adding Lactobacillus bulgaricus and Streptococcus thermophilus. The bacteria would multiply in milk using up the lactose and producing lactic acid. The lactic acid lowers the milk pH (fresh milk pH 6.5-6.7) to 4.3-4.4. Why does yogurt sometimes have mold growth?  Probiotic yogurt and other probiotic foods such as sauerkraut, kimchi, kefir.  Preservation by reducing water activity of the food  Sugar’s hygroscopic property is used in jam/jelly making  Table Salt (NaCl) as a cheap and effective preservative: Salt’s hygroscopic and osmotic properties are used to reduce water activity: Ex. Dehydrated fish by salting, or smoked fish  Special topic Table salt and hypertension  Table salt contains 40% sodium by weight.  Sodium recommendation: 1500 mg/day  Tolerable Upper Intake level: 2300 mg/day  Average intake in Canada: 2760 mg/day (2017), was 3400mg/day in 2004. Goal of below 2300mg/day by 2016 was established by Canadian Government.  It was reported that “… 58% of Canadians aged 1 year and older, and 72% of children between the ages of 4 and 13 years still exceed recommended limits of sodium intake.”.  77% of the sodium in our diet comes from processed food.  Why is too much salt bad for you?

Special Topic Table Salt and Hypertension

Table salt contains 40% sodium by weight. Sodium recommendation: 1500 mg/day Tolerable Upper Intake level: 2300 mg/day Average intake in Canada: 2760 mg/day (2017), was 3400mg/day in 2004. Goal of below 2300mg/day by 2016 was established by Canadian Government.  It was reported that “… 58% of Canadians aged 1 year and older, and 72% of children between the ages of 4 and 13 years still exceed recommended limits of sodium intake.”.  77% of the sodium in our diet comes from processed food. Why is too much salt bad for you?    

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 Irradiation: Food irradiation, also referred to as cold pasteurization, is exposing food to ionizing radiation such as gamma rays, electron beams, X-rays etc.  These are either high speed and/or high energy waves that destroy any biomolecules that come in their way.  At proper dose they are effective in destroying the biomolecules of microbes in and on the food thus sterilizing or reducing the microbial population.  Gamma rays can penetrate the food deeper than the electron beams.  These rays are produced by radioactive material but the radioactive material doesn’t touch the food that is being irradiated. The food is exposed only to the rays emanating from the radioactive material.  Please read the following document to understand food irradiation as a method of food preservation. Food irradiation  Some, not all foods are allowed to be irradiated in Canada. Please read the following to find out which foods are allowed to be irradiated and why, and how these foods must be labelled.  Irradiated foods in Canada, Canadian health Inspection Agency Packaging  Most processed food is packaged one way or the other. There are several reasons for packaging, including branding, putting mandatory and optional labeling information, preventing physical damage to the food, enabling shipping, preventing chemical deterioration, biological spoilage and pathogenic contamination, etc.  Glass: One of the oldest packaging material is made from silica (sand) and thus is biodegradable. It is odorless and chemically inert with virtually all food products, is immpermeable to gases and vapors, can ability to withstand high processing temperatures. Glass is rigid, provides good insulation, and can be produced in numerous different shapes. It is transparent and can be tinted to protect light-sensitive contents. Glass is heavier than most other packaging materials, and has poor durability.  Metals like tin, aluminum are often used especially in “canned” foods. Metals are highly malleable and very durable even when sheeting thin thus metallic containers can be much lighter than glass containers. The metals are impermeable to water, air/gases, microbes but some may react with the food contents. Many metallic containers are coated inside.  Paper is light weight, cheap and biodegradable, but is permeable to gases, moisture and fat, and has poor strength. Have you ever used paper packages for any food? Cardboards are a stronger form of paper but they are still very permeable. Tetra packaging  Plastic: Several types of plastics have been synthetically produced by polymerization and condensation of monomers. There are several advantages to using plastics for food packaging. Fluid and moldable, plastics can be made into sheets, shapes, and structures, offering considerable design flexibility. They are chemically resistant, inexpensive and lightweight with a wide range of physical and optical properties. The major disadvantage of plastics is their variable permeability to light, gases, vapors, and low molecular weight molecules. They are not biodegradable but many are recycled.

Packaging continued  City of Winnipeg says, “In Manitoba, plastic bags are not accepted in your recycling bin. Fortunately, many retailers in Manitoba accept your used plastic bags. Remember, reduce your use of plastic bags, reuse “single use” bags for hold household garbage, pet waste and other items and finally, recycle the ones already in your home.”  Another concern regarding the use of plastic for packaging food, is the leaching out of the chemical components the plastic. One component, Bisphenol A (BPA) has been banned to be used in infant products, in Canada. It may still be present in other products sold in the Canadian market. Canada has ALARA (As low as reasonably achievable) principle for BPA. BPA provides strength and clarity to the plastic.  Controlled or modified atmospheric packaging (CAP or MAP): The concentration of gases in the package are controlled or modified.  Oxygen absorbent patches can be used to minimize the availability of oxygen in the package to minimize the fruit ripening during its transport.  Bananas ripen very fast mainly because they continue to produce high levels of ethylene gas even after their harvest. Such fruits that continue to ripen after harvest are called climacteric fruits.  The bananas are picked green and are stored and transported in chambers that are kept cool at about 13C to slowdown their post-harvest respiration. Thus the ethylene production also stops. Their tissue gets damaged below 10C and they turn brown and fail to ripen at such low temperatures. They ripen quickly and unevenly at temperatures above 17C. Once the bananas reach the retail stores a modified atmosphere chamber is used to evenly ripen the bananas. The chamber is flushed with ethylene gas which speeds up the ripening of bananas.  Another example of MAP is in nitrogen packaging of chips. Potato chips fried in oil are packaged in bags filled with nitrogen gas to prevent rancidity.  Gas flushed meat packaging: A combination of oxygen and carbon dioxide prevents growth of both aerobic and anaerobic microbes  Chemical methods Canadian Food Inspection agency allows the use of certain chemicals that can act as preservatives. These are classified as below: Class 1 - curing preservatives; Class 2 - antibacterial; Class 3 - antifungal and antimycotic; Class 4 – antioxidants  Special topic: Nitrates and nitrites  Are very effective in killing pathogenic microbes, maintaining the red color of meat, and preventing the rancidity.  Research shows that nitrates and nitrites in acidic environment can form nitrosamines when they react with amino acids. Nitrosamines are carcinogenic  WHO, in 2014, declared that high processed meat consumption is linked with certain types of cancers (colorectal and stomach cancer mainly). (Note that it is about the processed meats, not just nitrates and nitrites) https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(15)00444-1/fulltext

 Synthetic preservatives: Certain chemicals like sodium benzoates, sulphates are antibacterial (class 2), while others like propionates and sorbates are antifungal (Class 3), and Ascrobic acid, Butylated hydroxytoulene (BHT) and Butylated hydroxyanisole (BHA) are antioxidants (class 4). Food Additives allowed in Canada: This list is a positive list. https://www.canada.ca/en/healthcanada/services/food-nutrition/food-safety/food-additives/lists-permitted/11-preservatives.html  Food processing: a boon or a bane?  Discuss When used as nouns, bane means a cause of misery or death, whereas boon means a prayer. Bane is also verb with the meaning: to kill, especially by poison. Boon is also adjective with the meaning: good....