‘Minimal processing’ describes non thermal technologies to process food in a manner to guarantee the food safety and preservation as well as to maintain as much as possible the fresh-like characteristics of fruits and vegetables.
Among others, visual properties of fresh-cut fruit and vegetable commodities are one of the most important parameter to evaluate the total quality of the product by consumers. Looking at the package, it will be possible to evaluate absence or presence of discoloration (enzymatic browning of cut surfaces, yellowing of green vegetables and pale color of bright vegetables), mechanical damage (foiled lettuce leaves, absence of cutting damage), as well as decay
Minimally processing can provide fresh and quality products through a hurdle approach.Minimally processing renders produce highly perishable, requiring chilled storage to ensure reasonable shelf life. No heat is applied to maintain fresh like characters.
During processing many cells are broken and intracellular products, such as oxidizing enzymes, are released accelerating the decay of the product. Additionally, the cut surfaces of any processed vegetable support better microbial growth. In fact, each step in the processing affects quality and microflora of fresh-cut fruit and vegetables. For these reasons, the cutting and shredding must be performed with knives or blades as sharp as possible made from stainless steel. However, many different solutions have been tested to avoid the acceleration of decay due to peeling, cutting or slicing. The newest tendency is called the immersion therapy.. Cutting a fruit while it is submerged in water will control turgor pressure, due to the formation of a water barrier that prevents movement of fruit fluids while the product is being cut. Additionally, the watery environment also helps to flush potentially damaging enzymes away from plant tissues.
On the other hand, UV-C light has been also used while cutting fruit to cause a hypersensitive defense response to take place within its tissues, reducing browning and injury of in fresh-cut products . Another alternative could be the use of water-jet cutting, a non-contact cutting method which utilizes a concentrated stream of high-pressure water to cut through a wide range of foodstuffs (Ingersoll Rand Ltd).
However, the main steps throughout the processing chain of minimal processing fruits and vegetables are washing and disinfection. For this reason, guidelines for packing fresh or minimally processed fruits and vegetables generally specify a washing or sanitizing step to remove dirt, pesticide residues, and microorganisms responsible for quality loss and decay.
The current published data suggests that any of the available washing and sanitizing methods, including some of the newest sanitizing agents such as chlorine dioxide, ozone, and peroxyacetic acid, were not capable of reducing microbial population by more than 90 or 99%. Additionally, different washing and disinfection treatments may negatively affect the nutritional and sensory quality of the product. However, little is known about nutritive value content of minimally processed produce. Therefore, washing and disinfection of the produce before preparation or consumption is recommended but does not guarantee that fresh produce is pathogen free .
On the other hand, the potential of MAP to extend shelf-life for many foods is well documented. It is known that beneficial modified atmospheres within fresh-cut produce packages are attained by correctly choosing packaging materials that will provide the appropriate levels of oxygen and carbon dioxide within a fresh-cut produce package. In fact, there are a wide variety of polymers and gas mixtures available for packaging fresh-cut produce that should be optimize for each commodity. However, there is still a major concern about the product safety associated with the use of MAP mainly due to the desired suppression of spoilage microorganisms which extends the shelf-life if compared to food products stored in a normal air environment, and this may create opportunities for slower growing pathogenic bacteria.
It would be expected that combinations of sanitizers and/or other intervention methods, would have additive, synergistic or antagonistic interactions. According to this, the hurdle technology looks after the combination of different preservation techniques as preservation strategy. The intelligent selection of hurdles in terms of the number required, the intensity of each and the sequence of applications to achieve a specified outcome are expected to have significant potential for the future of minimally processed fruit and vegetables.
Use of combined preservation methods
Recently, many studies have demonstrated the effectiveness of surface decontamination techniques to reduce the microbial risk involved with the consumption of fresh fruits and vegetables.
Nonionizing, artificial ultraviolet-C (UV-C) radiation is extensively used in a broad range of antimicrobial applications including disinfection of water, air, food preparation surfaces, food containers and surface disinfection of vegetable commodities. The ultraviolet light acts as an antimicrobial agent directly due to DNA damage and indirectly due to the induction of resistance mechanisms in different fruit and vegetables against pathogens. Exposure to UV-C also induces the synthesis of health-promoting compounds such as anthocyanins and stilbenoids. However, high UV doses, can cause damage to the treated tissue.Therefore, the possibility of decreasing the treatment intensity by combining two or more treatments to preserve the fruit and vegetable quality without decreasing the inactivation properties appears very promising . Additionally, UV-C light has already been recommended as best used in combination with other preservation techniques, since the accumulative damage due to microbial DNA appears effective in decreasing the overall number of bacteria cells, but does not result in complete sterilization. Further, these postharvest treatments can be easily added to other techniques such as chilling, disinfection and MAP to preserve quality of minimally processed fruits and vegetables.
Many researchers have already tested the synergistic effects of combining UV-C light with chemical disinfection and/or MAP on vegetable produce. The beneficial effects of combining chlorinated water to disinfect freshcut fruit and vegetables with UV-C light treatments and storage in MAP has already been tested. Most of the studies showed the effectiveness of microbial reductions in fresh-cut fruits and vegetables by using chemical disinfection, low UV-C light doses (from 1 to 4 kJ mK2) and storage under conventional MAP, without any detrimental effect on the organoleptical quality of the product.
UV-C light has also been combined with other postharvest treatments such as mild thermal treatments.Light pulses have been used successfully as a new technique for the inactivation of bacteria and fungi on the surface of food products when the major composition of the emitted spectrum is UV light. Additionally, combination of pulsed light with mild heat treatments in strawberries and cherries has also been reported.
Low-dose gamma irradiation is very effective reducing bacterial, parasitic, and protozoan pathogens in raw foods. Irradiation was approved by the FDA for use on fruits and vegetables at a maximum level of 1.0 kGy (IFT, 1983). It has already been tested in minimally processed fruit and vegetables observing that dose of 2.0 kGy strongly inhibited the growth of aerobic mesophilic and lactic microflora in shredded carrots .Additionally, it has been combined with Conventional disinfection methods such as chlorinated water or preservation technologies by using MAP . Treating fresh-cut lettuce with low-dose irradiation of about 0.20–0.35 kGy combined with a chlorine (80–100 ppm NaOCl) wash and MAP, increases the microbiological shelf-life without adversely affecting the visual quality or flavor of the product. Additionally, when inoculated cilantro was treated with a combination of irradiation (1.05 kGy) and chlorination (200 ppm), Escherichia coli O157:H7 was reduced more than 7 log cycles without adversely affecting the sensory quality of the product. This combined treatment was more efficient than irradiation or chlorination alone.
Non photochemical processes
Many combinations of physical and chemical treatments have been tested in recent years to enhance the antimicrobial action of different disinfectant agents. Among them, the use of acidic electrolyzed water (AcEW) produced by the electrolysis of an aqueous sodium chlorite solution as a disinfectant for minimally processed vegetable products has been successfully applied.
Chlorine dioxide (ClO2) has been recognized as a strong oxidizing agent with a broad biocidal effectiveness due to the high oxidation capacity of about 2.5 times greater than chlorine. Many studies have demonstrated its antimicrobial activity (Han, Guentert, Smith, Linton, & Nelson, 1999; Han, Sherman, Linton, Nielson, & Nelson, 2000) since its use was allowed in washing fruits and vegetables by the FDA (1998).
Power ultrasound, as used for cleaning in the electronics industry, has a potential application to fresh produce decontamination. Ultrasonic fields consist of waves at high amplitude, which form cavitation bubbles, which generate the mechanical energy which has a ‘cleaning action on surfaces.
A newer tendency has been reported by combining the efficacy of chemical disinfectant with the antimicrobial effect of bacteriocins produced by lactic acid bacteria. They investigated the efficacy of nisin and pediocin treatments in combination with EDTA, citric acid, sodium lactate, potassium sorbate and phytic acid in reducing Listeria monocytogenes on fresh-cut produce. Pediocin and nisin applications in combination with organic acids caused a significant reduction of native microflora and inoculated populations on fresh produce.
Finally, the combined use of several disinfectant agents has been widely report in the last few years. Combinations of lactic acid, chlorinated water, thyme essential oil solution, sodium lactate, citric acid, hydrogen peroxide, ozone and peroxyacetic acid were already tested. In general, combinations of chemical disinfectants maintain better both, sensory and microbial quality of the product.
Factors Affecting Quality
Main factors affecting quality of minimally processed produce are
Fruits and Vegetables for Minimal Processing
peeled and sliced potatoes; shredded lettuce and cabbage; washed and trimmed spinach;
chilled peach, mango,
and other fruit slices;
such as carrot and celery sticks
and cauliflower and broccoli florets;
packaged mixed salads; cleaned and diced onions;
peeled and cored pineapple; fresh sauces; peeled citrus fruits; and microwaveable fresh vegetable trays