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Blanched vegetable manufacturing app
Blanched vegetable manufacturing
Blanching is an extremely simple technique wherein vegetables are briefly submerged in boiling water then, once they have reached the desired level of done-ness, plunged into an ice bath to stop the cooking process. Blanching sets the color and texture of the vegetable, keeping it from sagging out or turning dull.
Blanching (scalding vegetables in boiling water or steam for a short time) is a must for almost all vegetables to be frozen. It stops enzyme actions which can cause loss of flavor, color and texture. ... It also wilts or softens vegetables and makes them easier to pack. Blanching is defined as the enzyme (heat resistant) deactivation phenomena, which helps in retaining color, reduction in initial microbial growth, cleansing the product, product preheating prior to processing, and gas exhausting from plant tissue, and helps to release carotenoids, thus enhancing their bioavailability and extractability.
Blanching is a cooking process in which a food, usually a vegetable or fruit, is scalded in boiling water, removed after a brief, timed interval, and finally plunged into iced water or placed under cold running water (shocking or refreshing) to halt the cooking process. Blanching foods helps reduce quality loss over time. People often use blanching as a treatment prior to freezing, drying, or canning—heating vegetables or fruits to inactivate enzymes, modify texture, remove the peel, and wilt tissue. Blanching is also utilized to preserve color, flavor, and nutritional value. The process has three stages: preheating, blanching, and cooling. The most common blanching methods for vegetables/fruits are hot water and steam, while cooling is either done using cold water or cool air. Other benefits of blanching include removing pesticide residues and decreasing microbial load. Drawbacks to the blanching process can include leaching of water-soluble and heat sensitive nutrients and the production of effluent.
Blanching is a process used in the home kitchen as well as used as a pre-treatment in the food industry. In both cases, its main purpose is to inactivate enzymes that cause browning as well as textural changes and off-flavors. Enzymes that cause deterioration in fruits and vegetables include lipoxygenase, polyphenoloxidase, polygalacturonase, and chlorophyllase. Catalase and peroxidase are commonly used to determine blanching success, since they are the most thermal-resistant enzymes of concern. These enzymes are responsible for the loss of flavor, color, texture and nutritional qualities during product storage.
Blanching preserves the flavors found in fruits and vegetables by inactivating enzymes responsible for off-flavor development. The most common enzyme responsible for off-flavors is lipoxygenase (LOX), found in several vegetables.
The blanching process expels air trapped inside plant tissues, which is a vital step before canning. Blanching prevents the expansion of air during processing, which reduces strain on the containers and the risk of cans having faulty seams. Moreover, removing gas from foods like pears results in better texture and reduces oxidation of the product. Also, the intercellular gases removed results in better color retention.
Fruits, vegetable, and nut peeling are also important in food processing. When almonds or pistachios are blanched, the skin of the nut (botanically the seed coat surrounding the embryo) softens and can be easily removed later. Steam peeling produces less environmental pollution and peeling losses, as compared to chemical or manual peeling processes.
Other uses of blanching are enhancing drying rate and product quality, decreasing microbial load, removing pesticide and toxic residues, increasing extraction of bioactive compounds, surface cleaning, removing damaged seeds or foreign materials, killing parasites and their eggs, and reducing oil uptake.
Traditionally, blanching is done using either a water bath or saturated steam. In both methods, the food is heated for a short period of time and then introduced into either cold water or cold air to quickly stop the heating process. At the industrial level, foods move on a continuous conveyor belt through preheating, holding, and cooling. For hot water blanching, vegetables are immersed under pre-warmed water (70 to 100 °C) for varying amounts of time, depending on type and quantity. When the product is heated by water, greater uniformity of heating is achieved, especially when compared to hot air. This advantage allows hot water blanching at lower temperatures, but requires longer blanching times. Water is heated and cooled using heat exchangers and recirculated for continuous use, reducing costs.
Steam blanching systems inject hot air (~100 °C) onto food as it passes through the blanching system on a conveyor belt. This method greatly reduces the leaching of water-soluble compounds from the product and is the preferred technique for smaller foods and those with cut surfaces. Steam blanching is more energy-efficient, and the ability for quick heating allows for shorter processing times. This reduced heat exposure preserves color, flavor, and overall quality of the food; however, evaporation may occur leading to lower masses and product yields.
Directly following the heat treatment, vegetables/fruits are quickly chilled by cold water. A common alternative to cooling with cold water is cooling with cold air. This method of cooling prevents the leaching of water-soluble nutrients; however, the air causes evaporation and lowers the mass of the vegetable—a monetary disadvantage for industry.
Emerging technologies include ohmic, infrared, microwave, and radio frequency blanching.
Blanching time and temperature
It is important to consider the recommended times and temperatures for a food product when blanching. Times and temperatures are based on the type of food, size, shape, and other factors. Over-blanching can lead to an excessive loss of nutrients and aromatic compounds, as well as softening of the food. Blanching at temperatures or times lower than those recommended may not effectively inactivate all enzymes. In addition, this may also cause the release of more enzymes from the plant tissue, causing greater overall enzymatic activity and faster spoiling of the product.
Although blanching is a thermal process, the times and temperatures are not sufficient to effectively destroy all microorganisms. Blanching is often seen as a pre-process to later preservation steps. For example, blanching in the home is often done in combination with freezing; blanching in industry is also utilized before canning, dehydration, or heat sterilization.
A limitation to hot water blanching is the leaching of water-soluble nutrients and the degradation of thermal sensitive compounds. Vitamins, minerals, and other water-soluble compounds, such as proteins, sugars, and flavor compounds, diffuse out of the food and into the water, lowering the overall quality of the food. The degree to which compounds diffuse out of food depends on the food's composition and characteristics, the water to food ratio, the blanching temperature, and other variables. Ascorbic acid, thiamin, and many aromatic compounds are heat-sensitive.
A complication in the food industry is the production of effluent from water blanching systems. Blanching with reused water can lead to a buildup of water-soluble compounds that are considered pollutants, and therefore must be properly treated before being discharged. This can increase capital costs at the industrial level and has been a main reason for the development of newer blanching technologies.
Blanching Effect on microorganisms
Blanching reduces the numbers of contaminating microorganisms on the surface of foods and hence assists in subsequent preservation operations. This is particularly important in heat sterilisation (see Section 12.1), as the time and temperature of processing are designed to achieve a specified reduction in cell numbers. If blanching is inadequate, a larger number of microorganisms are present initially and this may result in a larger number of spoiled containers after processing. The effect of blanching on microorganisms has been described by a number of authors including, e.g., Breidt et al. (2000) who found that blanching whole cucumbers for 15 s at 80°C reduced bacteria by 2–3 log cycles. Blanching causes cell death and physical and metabolic changes within food cells. Heat damages cytoplasmic and other membranes, which become permeable and result in loss of cell turgor (Fig. 11.4). Water and solutes pass into and out of cells, resulting in nutrient losses. Heat also disrupts subcellular organelles, and their constituents become free to interact within the cell. Over-blanching can cause excessive softening and loss of flavour in the food, but the heat treatment is less severe than for example in heat sterilisation, and the resulting changes in food quality are less pronounced.
Food blanching: History
There are a number of techniques used by food manufacturers to reduce the risk of food-borne illness, one of which is blanching. While it’s used mostly for frozen vegetables, blanching is a safe and effective method to kill potentially-dangerous microbes and bacteria. Practically all frozen vegetables sold in the grocery store go through a blanching process before they end up on the shelves. If you’re interested in learning more about this technique and why it’s so effective, keep reading and we’ll give you the breakdown on blanching.
The word blanching actually means to whiten, but this can be somewhat confusing since it doesn’t always affect the colour of the food. There are times when this happens, but the colour of a blanched food typically doesn’t change. In the rare event that it does change the color of a food to white, the manufacturer will likely add a colour agent to give it a more desirable colour.
So what exactly is blanching? In short, it’s the process of cooking a food in boiling water for a short period of time before plunging it into freezing water. Once the food is placed in boiling water, it naturally kills off 99.9% of bacteria and microbes; thereby greatly reducing the chance of food-borne illness. It’s the same principle as boiling pasta or foods at home in your kitchen, except you aren’t freezing them afterwards. The purpose of freezing blanched foods is to preserve them and halt the cooking process.
The most commonly blanched foods include frozen vegetables, frozen fruit, nuts and bacon. These foods seem to hold up well under the stress of boiling water, which is why they are frequently blanched. While the main purpose of this technique is to kill microbes and germs, it oftentimes serves a different purpose – to make the food easier to eat. For instance, boiled peanuts are frequently enjoyed because of their soft texture that’s easy to break into it.
Some food manufacturers also use blanching techniques to remove unpleasant flavors. Certain exotic beans and other vegetables may contain tart or otherwise unwanted flavors that consumers don’t like. Thankfully, however, blanching can help to remove some of these flavors in fast, efficient and safe manner that’s not going to affect the integrity of the food.
French fries are another type of food that’s oftentimes blanched by manufacturers. There’s a key difference, however, in the method used to blanched them. Instead of boiling French fries with water, it’s done with oil. This allows for a hotter temperature, which in turn leads to crispier fries that aren’t soggy. After they are taken out of the oil, they are immediately frozen to better preserve them.
Blanching is a common practice that involves boiling a food for a short period of time before freezing it. Even though its main purpose is to kill germs, it can also make the food easier to consume. Hopefully this will give you a better understanding on how this all-too-common technique is used in the manufacturing business.