By: Amal Kumar, * Manoj Kumar Mahawar ** and Kirti Jalgaonkar **
Post-harvest loss of fruits and vegetables are estimated to be approx 5 to 30 percent in the supply chain from harvest to consumption due to lack of infrastructure for postharvest management, processing and value-added techniques. Modern lifestyles and diets have prompted the human to adequately store a variety of fruits and vegetables, influenced on the development and implementation of many methods and procedures for preservation. Valorisation by adopting recent and improved processing technologies provides a great opportunity for the growth and development of the food sector. Value addition refers to the process of changing or transforming a product from its original state to a more valuable state and it provides more variety to consumers with the improvement in the organoleptic properties. Traditional methods of value addition through preservation include: canning; drying/dehydration; preserves; freezing; preparation of intermediate moisture foods; beverages (fermented, carbonated); and juice powder using established standard techniques. There is a recent trend of valorisation through packaging and also using novel thermal (ohmic heating, microwave heating, radio frequency heating) and non-thermal (pulsed electric fields, high-pressure processing, ultrasound, and gamma radiation) processing technologies for preservation. Technological procedures of processing of fruit and vegetables can be classified into a few processing methods:
Traditional Processing Methods: Drying, concentrating, heating (cooking, baking, frying) cooling, use of additives – preservatives, acidification, fermentation;
Improved Traditional Methods of Processing: The application of increased temperatures (sterilization, pasteurization), the application of low temperature (cooling, freezing), aseptic packaging, controlled atmosphere, freeze-drying, microfiltration and membrane processes, modified atmosphere packaging
New Methods: High voltage pulse techniques, photodynamic inactivation, microwave processing – heating, high-pressure treatment, ionizing radiation, heating of electrical resistance effect and induction.
This article includes the overview and applications of important techniques viz. high-pressure processing, pulsed electric field, ohmic heating, irradiation technology, radio frequency identification, intelligence packaging for fruits and vegetables. Proper adoption of these novel techniques will help in increasing the shelf life in a way that the availability can also be assured during the offseason.
Cold Plasma Technology: Cold plasma is an emerging technology and it could be an alternative to commonly used agents, in order to decontaminate fruits and vegetables. Plasma processing is capable of reducing microbial populations on produce surfaces. This technique is very useful for microbial decontamination of food products, packaging material processing (to remove all unwanted organic contaminants, surface treatment, adding desired new qualities, etc.), and functionality modification of food materials. As of now, there was no mild surface decontamination technology available for products like cut fruits and vegetables and fresh meat, and this cold plasma can be safely used for these applications. All in all, cold plasma technology has potential in food decontamination by removing food-borne microbes.
High Pressure Processing: It is a non-thermal food preservation method used to inactivate pathogenic microorganism with minimal heat treatment, resulting in almost complete retention of nutritional and sensory characteristics of fresh food without sacrificing the shelf life. In this process, foods are treated under high pressure (100 to 800 MPa) by placing them in a medium, usually water in a thick-walled vessel and compressing the medium leading in the extension of the shelf life of processed food with retention of nutritional attributes. This method is mainly applicable for fruits and vegetables, jam, jellies, preserves, uncooked seafood, wet salads, purees, sauces, smoothies, chunks, slices, etc.
Pulse Electric Field: The pulsed electric field is a novel technique capable to permeabilise cells of fruit and vegetable tissues without increasing the product temperature and avoiding an excessive deterioration of the tissue. It mainly depends on electric field strength and treatment time. It holds potential as a low-temperature alternative pasteurisation process for sterilising food products. In PEF processing, a substance is placed between two electrodes and the pulsed electric field is applied. The applied electric field helps to enlarge the pores of the cell membranes which kills the cells and releases their contents. PEF has been demonstrated to be effective against various pathogenic and spoilage microorganisms and enzymes without considerable loss of flavour, colour and bioactive compounds.
Ohmic Heating: Ohmic heating is a thermal processing technique where heat is internally generated in a sample due to electrical resistance when the electric current is passed through it using a variety of voltage and current combinations. The particulate is heated by the dissipation of electric energy provides fast and uniform, leading to less thermal harm to the food. Beyond heating of fruits and vegetables, the applied field force underneath [the] resistance unit heating causes varied changes in quality and biological process parameters that embody inactivation of enzymes and microorganisms, degradation of heat sensitive compounds, challenges in the cell membrane, viscosity, pH, colour, and rheology. The food-related applications e.g. cooking, blanching, starch gelatinisation, sterilisation and pasteurisation.
Irradiation Technology: Irradiation is food safety and preservation technology that employs ionizing radiation to inactivate/kill microorganisms by damaging their DNA. The process involves exposing food, either in bulk or packaged, to ionizing or non-ionizing radiation for a specified amount of time. While treating the fruits or vegetables, a radiation source is held a few centimetres away from the product and dosage of 2.5 to 5 million rad is used to kill all microorganisms including bacteria. It destroys insects in all life cycle stages; inhibits sprouting on vegetables; and prevents some chemical deterioration. Currently, irradiation treatments have been approved for onions and potatoes to prevent their sprouting. The best advantage of this technology is that the food can be stored without refrigeration.
Radio Frequency Identification Technology (RFID): RFID uses radio waves to identify individual items. RFID tags help to find the perishing part on the basis of temperature, time, pressure, chemical sensing, etc. This technology is very useful in the agriculture sector as it helps to improve the management of information flow within the supply chain. The latest advancements in the RFID sensors tags have improved monitoring of the cold chain of perishable food products, environmental monitoring, irrigation, etc. RFID technology can also be used with time-temperature integrators to monitor the status or condition of an item, such as pressure, humidity, gas leakage and tampering. The tag continuously monitors and stores time-temperature data of fruits and vegetables throughout the supply chain. The data is checked at various predetermined points. If the goods are found spoiled/deteriorated, the information on the tag will help to determine the possible cause of spoilage by analysing the time-temperature data.
Intelligent packaging is the integration of sensor/indicator into the food packaging system that has intelligent functions for monitoring of food quality and safety, e.g. freshness, leakage, carbon dioxide, oxygen, pH, time or temperature, and pathogens. The technology ensures real-time quality control and safety monitoring in terms of consumers, authorities, and food producers. Also, it has been observed that this technology has potential in the development of new sensing systems integrated with the food packaging like control of weight, volume, colour, and appearance. The application of intelligent packaging in fruits (ripeness detection) and vegetables (freshness monitoring) have been found very useful. For ripeness detection, the sensor was developed to detect volatile compounds (e.g., ethylene, volatile acid, etc., these are produced during ripening). While for freshness monitoring, the sensor works based on pH change or volatile compounds produced gradually during degradation of vegetable. Furthermore, the sensor responses were found to correlate with pH, sensory evaluation, and bacterial growth patterns in food samples.
Among the above-mentioned technologies, only a few food and vegetable processing technologies have been tested in a real-time production environment or are used nowadays at the industrial level. In most scenarios, further research and development activities are still required to completely understand, optimise, and scale up these complex processes to unleash their full potential.
* Kerala Agricultural University, Kerala
** Horticultural Crop Processing Division, ICAR-CIPHET Abohar (Punjab)