Introduction
In many food processing operations, food products are converted from their natural state to a state where the original food is transformed so significantly that they are unrecognizable compared to the original form. For example, tomato is transformed into ketchup, and wheat is transformed into donuts. Because of this huge change, a processor may take the quality of the raw material for granted. A manufacturer may say, “I am making ketchup so there’s no problem in using tomatoes with some insect damage, or rotten spots here or there, or a bit of pesticide residue just over the limit. After all, who’s going to know after everything gets squashed together?” He may have been able to get away with a lax in quality raw material in the past. However, today it’s less likely he will be. Proper raw material preparation is essential to meet the high consumer demands of today.
Relationship Between Raw Material Quality and Finished Product Quality
Advances in technology have made it easier to detect poor quality raw materials such as the ability to rapidly and accurately detect and quantify microorganisms, harmful chemicals, and toxins. Food safety standards such as the Food Safety Modernization Act in the US have called for greater scrutiny of food processing operations to ensure that they are following high food safety standards.
The quality of your raw material will directly impact the quality of your end product. It’s the idea of “garbage in garbage out” used in computer technology. What you put in is indeed what you get out. However, since quality impacts cost and the amount consumers are willing to pay, then appropriate compromise in quality may have to be found, as long as safety is not compromised. For example, you may choose to process tomatoes that are too small, too big, or a bit soft for the fresh market, but you must never channel tomatoes into processing because they are infested or contaminated with harmful chemicals. So, how do we prepare raw materials for processing to make sure we produce quality food? Three unit operations to pay close attention to are cooling, cleaning, and sorting.
Unit Operations for Controlling Raw Material Quality
Cooling
After harvest, fruits and vegetables are not “dead”. Hundreds of chemical reactions are taking place within the food leading to a state of senescence (aging), including respiration. You remember respiration, right? It’s the opposite of photosynthesis where green plants use glucose already in the plant and oxygen in the atmosphere to produce carbon dioxide, water, and energy. This energy produces heat. Therefore if you pack apples in a box, eventually they will get warm. This warmth will increase other biological activity including the growth of microorganisms, leading to faster spoilage. That’s why fruits and vegetables must be cooled as soon as possible after harvest to ensure their freshness. Carcass after animal slaughter must also be chilled for the same reason. Methods of cooking may include putting the product in a refrigerator, floating them in water, immersing in cold water or crushed ice, air-cooling it with dry air, or washing it in a continuous stream of cool water.
Processors who also grow their own raw materials limit the time that it takes to get produce to processing by cooling directly on the farm, investing in refrigerated trucks, and/or building their processing facility in close proximity to the farm.
Cleaning
Food, whether it be from animals or plants is produced in the physical environment and is therefore exposed to the elements. Contaminants may fall in either physical, chemical, or biological hazards. Physical hazards may include leaves, slicks, stones, metal, plastic, dust, sand, insect parts, and rat droppings. Chemical hazards may include natural toxins such as mycotoxins and pesticides. Biological hazards may be bacteria, yeast, mold, parasites, and viruses. Much of these contaminants are removed at the cleaning stage. Cleaning may be by the dry or wet method.
Dry cleaning is common in grains and pulse processing. Cleaning may involve a variety of mechanisms. For example, passing the grain e.g. wheat through a stream of air to lift off light unwanted particles such as leaves and dust. Size separation devices such as sieves are used to separate contaminants that are larger or smaller than wheat. Gravity tables are employed to separate materials by density such as stones. Imaging machines are used to identify and separate contaminants by color, and magnets are used to trap and remove metals.
Wet cleaning methods are more suitable for food that will not absorb water such as fruits and fresh vegetables. It is a more effective method than dry cleaning for removing dust and pesticides. However, if water is not removed from the surface properly, this may lead to spoilage. The need for clean water and treatment of effluent at the end of the process may increase operational costs. Common methods of wet cleaning include soaking, spraying, and flotation of produce in troughs (called fluming).
Sorting
Sorting during the material preparation process involves placing produce into categories based on specifications or standards to be met. For example, foods may be processed based on differences in physical properties such as color, texture, size, shape, and weight. For example, pumpkins for the fresh market should preferably be of uniform shape, weight and size for packing. Those that have an irregular shape or are too big or too small can be diverted for cooking and pulping for use in value-added products such as pies and or dehydrated and added to soups. Separation may also be done based on chemical composition such as brix (sugar content). Juice processors for example will want fruits that have high sweetness with an acceptable balance of acidity. In flour milling, flour is sorted into different streams and packaged based on bran and protein content.
