Consumer awareness and increased availability of food assortment make natural and healthy food a permanent element of our diet. The trend of pro-health food is becoming popular, which results in the emergence of more high quality products. Unprocessed valuable fruit and vegetable products are becoming more and more popular.
Fresh, natural and minimally processed food is the idea of a rich in vegetables and fruits diet. The products with a high nutrient content, free of preservatives and artificial ingredients appear more and more frequently on store shelves. The products having highly bioavailability of compounds such as vitamins, antioxidants or essential fatty acids are called the functional food.
Food Science in Europe defined the functional food. "Food can be considered as functional if it has been proven beneficial for one or more functions of the organism over the nutritional effect, and its pro-health effect should be documented by scientific research" . The range of products for vegans is also growing. Store shelves are full of products for demanding consumers preferring this style of nutrition.
Absence of the preservatives obliges the producers to use another form of food preserving. The shelf- life of fresh fruits and vegetables is usually a few days. After this time, the symptoms of processes causing the spoilage are noticeable. The food quality deteriorates. So, how shelf-life a fresh strawberry mousse or chickpea paste have if raw fruit and vegetables are not suitable for consumption even after several dozen hours?
The manufactuters most often decide on pasteurization. The products stand on store shelves for several months, but high temperature treatment exposes them to losses of important nutrients and natural taste. The food properties are lost, as the pasteurization can negatively affect the nutrients and the aromatic substances present in the fruit and vegetable products.
Vegan Food Trend
A lot of brands in food industry are intensively working on new products development in this category. Vegan nutrition style is equally attractive for vegans and consumers consuming animal products on a daily basis. The vegan products, whose composition is dominated by legume plants and oilseeds, are an attractive source of protein with a suitable amino acid profile and essential fatty acids. There is a increasing interest in the assortment of fruit and vegetable products due to their high health value. An excellent example of this phenomenon are vegetable spreads. Hummus, the chickpea paste and sesame enjoys several times more popular than a few years ago, when hardly anyone had an idea of its existence. The dynamic development of vege products resulted in the formation of meatless meat and vegetable protein pastes. Soups, as well as vegetarian and vegan ready-to-eat meals are also more popular. The juices and cocktails in bottles as well as fruit mousses served as meal replacements have gained huge popularity. All these products are sold in convenient packaging.
Negative Impact of Heating
The main problem in the fruit and vegetable industry is short shelf-life of the raw materials and the sensitivie nutrients. This fact makes distribution more difficult. Non-preserved products after only a few hours are not suitable for consumption. This situation exposes the producers to losses. As a result, the manufacturers use thermal processes, such as high pasteurization to extend the shelf life. Unfortunately, this process often causes a change of quality of the food. The nutrients lost must be replenished, often not from natural sources. The high temperature has a negative impact on the nutritional value, but also for flavor compounds. The producer often declares that product consists only of natural and fresh fruit, no added sugar but the taste of the pasteurized product is characterized as bland and often have cooking aroma. The properties of these products often differs from fresh fruit and vegetables.
High Pressure for High Quality
High Pressure Processing known as HPP or cold pasteurization allows producers to take full advantage of the valuable qualities of fresh fruit and vegetables. The specificity of the high pressure treatment makes HPP products retain the same or even higher content of nutrient components, unlike thermal treated products. This provides better assimilation of vitamins, minerals and antioxidants. The product is characterized by full flavor, as HPP does not change the chemical compounds responsible for creating aroma in fruits and vegetables.
HPP technology makes creating a completely new food with an increased pro-health value and taste comparable to fresh raw materials possible. The effect of the high pressure processing of fruit and vegetable produts is a right amount of nutrients and natural taste qualities.
HPP fruit and vegetable products
- Mousses, fruit and vegetable purees
- Vegan products
- Vegetable pastes
- Hummus, pesto
- Cutted fruits and vegetables
- Sauces and dips
The high water content and the appropriate pH level make the high pressure processing a particularly beneficial way of preserving this fruit and vegetable product.
High Pressure Processing
Fruit and vegetable products subjected of the HPP process using the parameters relevant to a given assortment are characterized by extension of the shelf-life even up to 3 months in refrigeration conditions. The pressure range used in practice in the fruit and vegetable industry is usually 400- 600 MPa. Suitable adjustment of parameters allows to perform the process in the highest efficiency.
HPP allows the preservation of healthy properties of jams, mousses or another fruit and vegetable products. The specificity of HPP is due to the fact that the high pressure only causes changes in high molecular compounds. Smaller substances, such as vitamins, natural colors or flavors remain intact. The technology consists in limiting the use of high temperature during the process, which is its biggest advantage. The nutritional value and natural taste of the products are comparable with fresh raw materials.
HPP is packaged food processing technology. The high water content in the processed fruit and vegetables makes the hydrostatic pressure in the product spreads out evenly in all directions and does not generate the cutting forces. The water protects the product against crushing. Pressure, unlike the heat treatment is immediate in the whole volume of the food product, regardless of its size and geometry.
The packaging is an important factor in HPP. It should have appropriate flexibility and barrier properties. The packaged product is placed in a pressure chamber, which is then vented and filled with water. The hydrostatic pressure generated by the pump is transferred to the product, where it is evenly distributed in its entire volume. The water content protects it from destruction. After the process, the product leaves the chamber in a completely unchanged state.A popular and effective form of packaging in fruit and vegetable HPP products are plastic packaging sealed with foil. It is a great solution for vegetable pastes and all kinds of dips. Mousses and purees are often packaged in a doypack type sachets. Liquid products, such as juices and soups are processed in plastic bottles. An example of a well-sold HPP product is the cold soup, Gazpacho.
High-pressure curing is also used to treat food products packaged in the MAP modified atmosphere system . The packaging has a high barrier properties, suitable to HPP technology. HPP is considered as natural process, because it does not influence on product, like traditional thermal treatment. The combination of HPP and modified atmosphere packaging enhances the effect of high pressure processing. The low oxygen content and high pressure inhibit the growth of microorganisms and the oxidation process, which causes the negative change of sensory attributes of fruit and vegetable products.
HPP combined with vacuum packaging technoloogy is equally effective. The popular in many market segments vacuum method is characterized by tight and durable packaging, which is particularly important in high pressure processing.
Natural Products Technology
Natural nad low-processed products conquer the food market. The only challenge for producers in the fruit and vegetable industry is the susceptibility of the raw material to quick spoilage. The main hazard of fruit and vegetable products are yeast and molds as well as lactic and acetic acid fermentation bacteria. The products are also exposed to the development of soil-borne pathogens, the microorobes particularly dangerous to human health.
Microbiological safety is a very important issue for a food producers. The report by the Association of Packaging Technology and Processing on global trends in food and beverage processing (PMMI) from 2018 informs that "despite the fact that pasteurization is still the basic technology of processing in the food industry, it does not fully satisfy the needs of modern society for natural food. The thermal processes can negatively affect the nutritional value and sensory properties of products ".
The manufacturers are looking for a method of preservation, which will allow effective elimination of microflora and will not cause undesirable changes in the product. The answer is innovative HPP technology, the technology of natural products. High pressure processing effectively destroys spoilage microbes extending the shelf-life of treated product. Pathogens appearing in foods, such as Pseudomonas, Listeria or E.Coli are successfully eliminated by high pressure. HPP is non-thermal process, so it protects the product against changes in physicochemical parameters. It results in natural properties of products without the loss of the quality. The producer gains a guaranteed market effect and a ready solution to the problems faced by the modern fruit and vegetable industry.
Fresh vegetable pastes are products with a few-day shelf-life. Kirse et al.  were investigated the influence of high pressure processing on the pea spreads. The raw pea paste after exceeding 7 days of storage exceeded the recommended limits of the number of determined microorganisms. The untreated paste was unfit for consumption after 15 days. In the case of the HPP paste during the entire storage period, the samples was characterized by the low and stable level of microorganisms, making it still a fresh product. The product was suitable for further storage .
Figure 1. The influence of HPP treatment on total viable count in maple pea spread during 15 days of storage at 4.0 °C 
Equally satisfying results were obtained by Guerrero-Beltrán et al. . The use of high-pressure treatment in the preservation of fruit mousse from mango resulted in the reduction of microbial cells below the limit of detection at all pressure levels. It was observed that growth of microbes in the raw samples was intensive. This means that there have been processes in the product that lead to spoilage and deterioration of the product's quality. There were no growth of the total number of microorganisms or yeast and molds In HPP purées at 27 days after processing. Thanks to the high-pressure treatment, the manufacturer can extend the product shelf-life. The process does not cause the nutritional value of fresh fruit and vegetables. The combination of HPP with refrigeration conditions is the way to provide high-quality products dedicated for customers.
Figure 2. The effect of HPP treatment on total viable count in mango purée stored 27 days at refrigerated conditions 
Figure 3. The effect of HPP treatment on yeasts and moulds in mango purée stored 27 days at refrigerated conditions 
Reduction of the pH level of a product is a technique often used by manufacturers to extend the shelf life of food. Low pH level inhibit the growth of spoilage microbes. However, there are microorgobes with increased tolerance to acidic environment, e.g. pathogens, bacteria particularly dangerous to health. Oyarzabal et al.  proved that Listeria monocytogenes, Salmonella and E. coli serotype O157: H7 can survive even during freezing at -23 ° C in such acidic fruits as apple or orange, as well as fruit juices and concentrates for a period of 12 weeks. This is a high degree of risk to the consumer .
The pH level of products is an important parameter affecting the efficiency of the HPP process. Combining of HPP with the low pH of food allows the manufacturer has the possibility to increase the safety of fruit and vegetable products. Huang et al  compared the number levels of E.coli O157: H7 and Salmonella in raw and high-pressure treated strawberry purée (pH 3.6). The samples were inoculated with pathogens at low and high number levels. It was observed that the pathogen degradation increased as pressure increased. The zero level was obtained at the higher parameters of the treatment. In addition, HPP completely reduced the yeast and molds in the product. There was no effect on the color and other properties of the strawberry puree. It was confirm the effectiveness of using HPP in combination with the low pH level of fruit products .
Table 1. Pressure inactivation of E.Coli O157:H7 and Salmonella spp. in strawberry purée treated at 200-500 MPa for 2 minutes. Product inoculated with high and low level of the pathogens 
High-pressure treatment is a particularly advantageous method for preserving the acidic food products. High pressure causes the degradation of pathogenic and spoilage microorganisms and the high water content in fruit and vegetable products strengthens the treatment. The treatment itself causes the degradation of microorgores cells, in addition the acidic environment prevents their regeneration by enhancing the germicidal effect of HPP. Additionally, the lower pH level can also inhibit germination of the pathogen spores and makes microorganisms more susceptible to subsequent injuries  .
Figure 4. Log reduction of total aerobic bacteria and yeasts and moulds in high acid banana purée (pH 4.03) treated by HPP immediately after treatment and after 1 day and 1 month of storage at 4°C 
Xu et al.  were investigated the high pressure treated fruit purées. The analyzes showed that acidic enviroment of the banana purée allowing almost complete reduction of microorganisms after high pressure processing. After 30 days of storage, the raw banana mousse was unfit for consumption, whereas in the HPP mousse level of microbes was remained stable. The process extended the shelf-life of the product. After the use of high pressure, the number of yeast and mold in the product was below the level recommended by Stannard et al.  (103 CFU/ml). The fruit and vegetable products are that mostly have the pH level below 4.6. This environment favors the high pressure treatment making the process even more effective. High pressure extending the shelf life of the product without affecting its high quality throughout the storage period .
High Nutritional Value
Fruit and vegetable products are a source of natural vitamins, antioxidants, minerals and dietary fiber. The World Health Organization (WHO) recommends to consume 400 grams fruit and vegetables per day.
Consuming of fresh and unprocessed fruits and vegetables is the most appropriate form of nutrition. However, there are products whose production technology limits the use of processes adversely affecting the content of nutrients.The properties of the products are comparable with fresh fruits and vegetables. These are HPP food products, products with the higher content of bioactive ingredients and substances having the positive effect on the health. A heating sensitive vitamins or antioxidants are higher resistant to high pressure. Reduction of the high temperature during processing eliminates losses of these thermally non-resistant compounds. High pressure makes their bioavailability higher due to the increased extraction these substances in the treated product.
Vitamin C, which beneficial properties has been proved is one of the well-known antioxidant compounds, It is water-soluble and high temperature sensitive vitamin, also is easily oxidized. During technological processes, fruits and vegetables, and then the final product are often subjected to thermal treatments. The consequence of this processes is the degradation of the ascorbic acid. An additional disadvantage of thermal processing of fruit and vegetable products is the loss of the natural taste and other other vitamins and antioxidants.
The procect solution of the vitamin C is HPP technology. High pressure, unlike temperature, does not causes the degradation of ascorbic acid, as it does not affect the chemical bonds in its structure.
Figure 5. Influence of high pressure processing on retention of vitamin C [%] in kiwifruit purée 
Soloman and Silva  were studied the effect of HPP on the properties of kiwi puree. HPP treatment did not cause a reduction level of the vitamin C in the product. Regardless of the pressure level, it was observed that the vitamin was stable at 200-600 MPa, in contrast to heat treatment. Operation at 85 ° C, 95 ° C and 105 ° C caused a partial degradation of the vitamin C, which makes thermal processes less effective than high pressure treatment .
Polyphenol compounds have strong antioxidant effects and have proven pro-health properties. It is a group of of several thousand biologically active substances present in fruits and vegetables. Their high content is characterized, for example, by berries or grapes. A wide spectrum of their activities includes anticancer activity. The polyphenols counteract atherosclerosis and have the positive effect on the eyesight. The phenolic compounds have antioxidant potential even 30 times stronger than ascorbic acid. However, their resistance to high temperature conditions is similar to the vitamin C. Thermal processes degradate the polyphenols as effectively as they remove bacteria from the product. The nutritional value of the products decreases, along with the valuable properties of the polyphenolic compounds.
Figure 6. Influence of HPP on polyphenols content in strwaberry and wild strawberry mousses during refrigerated storage. 
Ferrari et al.  proved that high pressure treatment is a process that allows to preserve nutrients in the product. Strawberry and wild strawberries mouuses were characterized by the stable content of polyphenols for 72 days of storage at refrigeration conditions. They were also microbiological stable, which prevented the symptoms of spoilage throughout this period. Slight fluctuations in the level of the polyphenols resulted from the residual enzymatic activity and the presence of oxygen, which could cause oxidation of compounds. In the measured pressure levels, researchers also observed an increasing of the polyphenolic compounds extractability.
Table 2. Effects of high hydrostatic pressure and thermall treatment on content of pholyphenols, anthocyanin and vitamine C in strawberry and blackberry purées. 
Table 2 presents the results of Patras et al. work on the effect of HPP on bioactive compounds content in the strawberry and the blackberry purée. The thermall treatement caused a significant change in the content at 70 ° C / 2min, the degradation of the vitamin C was noted at 21%. The use of high pressure processing influenced of the increasing of the polyphenolic compounds in products. In this case, the pasteurization was also less suitable, because in the thermally processed purees was noted the reduction of polyphenols and anthocyanins .
- Nutritional value losses
- Unnatural taste
- Cooked fruit aroma
- Reducing health properties
Pasteurization have impact on the flavor characteristics of the product, noticeably. The substances responsible for taste and aroma are degraded, content is decreasing, which directly affects the quality of the product.
The Innovative HPP technology enables the creation of new products with the characteristics of ripe fruits and vegetables. Despite the use of huge pressure levels HPP has a minimal effect on treated product. Due to the specific mechanism of high-pressure treatment, the color and taste properties of the product can be preserved, which is not guaranteed by traditional thermal processing. There is no imact on aromatic compounds and natural colors. The taste of high pressure treated products is similar to fresh fruit and vegetables. This makes the product attractive throughout its extended shelf life.
Figure 7. Sensory evaluation of control and pressure-treated grape juice during refrigerated storage (1 or 60 days at 4°C) 
Raw and high pressure treated grape juices were subjected to sensory analysis under suitably prepared conditions. There were no significant differences between the control and the HPP samples. There were no sensory changes in 1 day of storage. The both samples were characterized by freshness, a similar aroma and a sweet feeling. After 60 days, the changes were felt in the control sample of the juice. The level of perceptible sweetness was much lower. It was found the fermentation process in control samples, which was caused by microbiological growth. The HPP samples had stable acidity level, demonstrating the absence of fermentation processes. The HPP juice was not characterized by the taste of cooked fruits. The grass aroma was less noticeable in the HPP sample than in the raw juice. There were no changes significant in sweetness in HPP juice, in contrast to the raw juice. After 30 days the sweetness in control sample decreased.
The HPP grape juice was general acceptaced among the evaluators. High pressure processing combined with refrigerated storage is an effective way to extend the shelf life of fruit and vegetable products, while minimizing nutrient losses and sensory characteristics .
The HPP Advantages:
- Extending the shelf life without negative affecting the product
- Increased safety and elimination of microbiological hazards
- Preservation of natural flavors
- Clean label
- High nutritional value, without preservatives and artificial additives
- Innovative products with high quality
- Facilitated distribution and guaranteed market effect
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