Sensors & their Application in Food Processing Industries
Dawn C.P. Ambrose
In a food processing plant, food has to be carefully monitored for its safety and quality during the entire production process. As for the applications of monitoring technologies, they range across the food industry. These monitoring technologies comprises of process control (the moisture content of the food; viscosity and texture); pH and conductivity (acidity and salt content); sugar content (glucose and sucrose are the main sugars monitored); food freshness including the detection of microbes (Escherichia coli, Salmonella, etc.) and the detection of microbial toxins (liquid and gas); ingredient freshness (milk, meat, etc.); frying oil (viscosity and chemical make-up) and food quality including taste (electronic nose).
The conventional analytical methods for assessing quality and safety are very tedious, time consuming and require skill. Therefore there is a need to develop quick, sensitive and reliable techniques for quick monitoring of food quality and safety. This can be overcome by the application of sensor automation technique in the food processing industries. Sensors are components that are used to measure, monitor and control parameters such as temperature, pressure, liquid levels etc. for proper functioning of a food processing plant. They transform real magnitude into an electric signal transmitted to human readable display system. Sensors are of two types i.e., at line sensors and on line sensors. Common applications of sensor in the food processing include process monitoring, shelf-life investigation, freshness evaluation, quality control etc.
Sensors used in food processing industries
Due to their high level of functionality or application different sensors are used in the food processing industries which are explained below:
Thermo-sensors
Thermo-sensors are used for temperature measurement through an electrical signal. This electrical signal will be in the form of electrical voltage and is proportional to the temperature measurement. These thermo sensors have wide range of application in Process control, Food inspection, Freezers, Fermenting units, Baking ovens and smoking units. Four different types of temperature sensors are there namely: resistance temperature detector, infrared sensor, thermistor and thermocouple.
Pressure measuring sensors
Pressure measuring sensors also known as piezometers, pressure transmitters, pressure transducers, pressure indicators, are used for measuring the pressure and transform into an electrical signal. This electrical signal may wary depend on pressure imposed. There are different types of pressure measuring device such as Absolute pressure sensor, Gauge pressure sensor, Vacuum pressure sensor, differential pressure sensor, and sealed pressure sensor. Pressure and level measurement in the food, dairy, beverage and processing industries is required in piping, filters and tanks.
Electronic Nose
Commonly called as E-nose, they identify the smell more effective than the human nose. They are more accurate and precise, used to detect smell based on mechanism for chemical action. Also they can detect poisonous and harmful odour which human nose cannot detect. An e-nose is generally composed of a chemical sensing system (e.g., sensor array or spectrometer) and a pattern recognition system (e.g., artificial neural network). The recognition pattern in e-nose is used to determine one sample from another is based on headspace volatiles. These sensors are very commonly used in the field of agriculture, food processing, cosmetics etc. One of the major applications of the electronic nose in the food industry is to assess the freshness/spoilage of fruits and vegetables during the processing and packaging process. It is also to inspect quality of food and beverage based on it’s odour.
Electronic Tongue
The taste of a product manufactured in the food industry can be of vital importance to the commercial success of the product. Electronic tongue mimics the gustatory system of human beings. It artificially reproduces the taste sensation and can sense different tastes viz., sourness, astringency, bitterness, saltiness etc. E-tongue can be used for both qualitative and quantitative purpose. This instrument contains sensor array, electrochemical cells and appropriate pattern recognition system. Electronic Tongue finds its application in food processing industry like beer, wine, coffee, tea, fish, synthetic beverage, meat, grains, fruits and vegetable industry.
Bio Sensor
Microbial management during the food processing operations is strategic for preventing contamination and for improving the product safety, quality and production hygiene. Microbiological testing has been based on traditional “growth” based methods. These methods relied on nutrient media and have provided the basis for quantitative microbial assay for microbial safety and quality product release. The time required to get results using these techniques is long and forward processing decisions and confirming manufacturing processes are static, results that may take days are now deemed to be inadequate. In such case, biosensor plays a major role. A biosensor is a device which is used to measure the concentration of an analyte. In biosensors, a biological material (enzymes, antibody, whole cell and nucleic acid) is used to interact with the analyte. This interaction produces a physical and a chemical change which is detected by the transducer and converts in to an electric signal.
The electric signal is directly proportional to the concentration of the analyte. This signal is interpreted and converted to analyte concentration present in the sample. The biosensor market is highly competitive and is driven mainly by the medical and pharmaceutical sector. Blood glucose measurement still comprises about 85% of the world market for biosensors. The field of biosensors comprises two broad categories (1) sophisticated, high throughput laboratory machines capable of rapid accurate measurement of complex biological interactions and components and (2) easy to use portable devices for use by non-specialists for in situ monitoring. Biosensors may be used to measure carbohydrates, alcohols, and acids in fermented foods. The devices are mainly used for quality control processes in food production. They are also used in the assessment and analysis of produce such as wine, beer and yoghurt. They may also be used to detect any pathogenic organisms present in meat, poultry, eggs, and fish.
Photoelectric sensors
Photoelectric sensors are widely used in the food and beverage industry. By using light beams to detect a specific object, a photoelectric sensor can determine the presence or absence of the target material. This is critical to maintaining reliable systems and production in a food and beverage facility, as a photoelectric sensor can help monitor the process of proper packaging.
Food freshness sensor
The food freshness sensor is used to detect food spoilage, being highly sensitive to gaseous decay products of fruit, vegetables, milk and milk products, fish and meat.
Fruit and vegetable sugars ferment to form ethanol, to which the sensor is highly sensitive. The sensor is of the two electrode type, compact, fast responding, and consumes no power. It ideally lends itself to a traffic light classification whereby green would be all clear, yellow a warning of incipient spoilage, and red a confirmation that spoilage had occurred.
pH sensor
Variability of pH in food and beverage production can lead to critical differences in taste, freshness and shelf-life of a final product. Hence pH value is one of the parameters most frequently measured during inspection. pH sensor measures the acidity or alkalinity of a food. Measuring pH in food and beverage production provides essential insights into its quality, safety and shelf life. Enzymatic activity is strongly pH-dependent; during cheese-making, monitoring this parameter both improves yields and enhances the characteristic flavour of cheese. Controlling pH also regulates the growth of desired and undesirable microorganisms alike. Meat, dairy products, pasta, wine and fruit juice fall within the broad range of foods and beverages for which control of pH is important. There are several types of pH sensors available, including glass electrodes, ISFET (ion-selective field-effect transistor) sensors, and optical sensors. Glass Electrodes pH Sensors are made out of a glass bulb with a reference electrode and a sensitive electrode. When the glass electrode is submerged in the sample, the pH difference between the sample and the reference electrode produces a voltage that the sensor measures. ISFET sensors employ a field-effect transistor to assess the pH of a sample.
Author’s Bio
Central Institute of Agricultural Engineering, Regional Station, Coimbatore