Effect of Minimal Processing (HHP or Mild Heat Treatment) and the Conditions of Subsequent Storage on Biologically Active Components of Berry Purées István Dalmadi, Klára Pásztor-Huszár, Katalin Polyák-Fehér, Ildikó Zeke, Csaba Balla, József Farkas Corvinus University of Budapest Dept. Refr. & Livestock Prod. Tech., Hungary istvan.dalmadi@uni-corvinus.hu, klara.huszar@uni-corvinus.hu, katalin.feher@uni-corvinus.hu, ildiko.zeke@uni-corvinus.hu, csaba.balla@uni-corvinus.hu, jozsef.farkas@uni-corvinus.hu 1. Introduction Research results of the last few decades highlight more and more the relationship between proper nutrition and healthy organism. Several scientific facts support that we can fight with better chances serious diseases threatening our civilized society, like cancer and cardiovascular diseases, if we change our diet in a right way. Beside changing our rushing lifestyle, that includes more exercise and avoiding everyday stress situations, we can do much for our health by consuming less calories and more fruits and vegetables. With the increase of knowledge we can exceed empirical and traditional observations regarding beneficial effects of fruits and vegetables. Newer and newer fitonutrients become known and the mechanism of action of already known bioactive components becomes clear. Some examples: strong correlation was found between low vitamin C intake and cancer; Se was proved to strengthen the immune system. The phrases free radical or antioxidant are familiar ideas. Synthetic processing and marketing of health promoting components mean considerable business prospects to pharmaceutical industry and producers and distributors of food supplements. However, research results have drawn the attention on the fact that excessive intake of synthetic antioxidants above the physiological requirement is rather harmful than beneficial, since when becoming a pro-oxidant they can damage the biomolecules of human organism. Thus consumption of natural antioxidants is preferred to synthetic supplements. Fruits are food materials containing considerable amounts of bioactive components and among them some berries have substantial natural antioxidant content. Strawberry is the most widespread berry in the world. Its proportion of total berries reaches 6-65%. It contains high amounts of vitamin C, potassium, calcium, iron and phosphorus and the contents of anthocyanines, flavonoids and phenolic carbonic acids having significant antioxidant capacity are high in this berry. Raspberry has similarly favorable characteristics. It contains high quantities of vitamins C-, P- and B9. These berries are popular not only because of these facts, but because they are very palatable (sugar-acid ratio, aroma compounds). Unfortunately, there is a declining tendency in strawberry growing in Hungary since the 8s, which can be explained by the decrease in its profitability and the narrowing of domestic and export markets. The same applies to our raspberry growing, which was considered a successful branch up to the beginning of the 9s. This tendency might be stopped or even reversed, since the consumption of ready-to-eat, minimally processed and additive free fruits and vegetables has
rapidly increased in the developed countries in the last decade and a similar trend can be expected in Hungary as well. In the production of minimally processed foods one has to keep in mind that products have to undergo processes, where no additives are used, shelf life is safely increased, and the complex characteristics of foods, first of all organoleptic properties, nutrients and vitamins are only minimally affected. Results published in studies about high hydrostatic pressure treatment are very promising, thus this method became an important research area. In contradiction with traditional heat treatment, where undesirable changes occur during processing, high hydrostatic pressure can better retain color and aroma compounds and vitamins. Although some products are already available on the market, much research is needed to completely unveil the mechanism of action of this technology, to find its application areas and to determine the conditions of safe food production. Investigation of the effect of storage conditions after treatment is an important but in the international literature less studied issue. One has to keep in mind that investment costs of the technology are high, so it is expedient to use it only for high value added products. On the long term, high hydrostatic pressure, as a food preservation technology, is advisable to be used only when products of better quality can be produced this way than with heat treatment having equivalent pasteurization effect and much lower investment costs. Thus complex comparative investigations are necessary to compare the effects of the two methods. Microbiological, physical and chemical examinations and organoleptic analysis have to be performed to get a comprehensive view. At the same time it is not enough to obtain a product which is very similar to the original one directly after the given treatment, since storage conditions might drastically alter the characteristics of the product. Therefore the effect of posttreatment storage conditions has to be studied. Since the potential of long-term storage is limited for the sake of keeping freshness, thus I considered sufficient to examine a relatively short-term storage period. On the basis of the previously mentioned, the aim of this study was to see whether high hydrostatic technology less decreases biological activity (contents of vitamin C, total phenolics, total anthocyanins, antioxidant capacity) of fruit purées made of strawberry and raspberry, than heat treatment having the same pasteurization effect. 2. Material and methods Deep-frozen raspberry and strawberry were thawed then sieved and purées were prepared. Sugar content of the samples was adjusted to 2 ref % by the addition of granulated sugar and filled into plastic bottles. A part of the samples was heated in an Armfield FT4 processing vessel until 8 C - 5 min heat equivalent was reached. After heat treatment, samples were rapidly cooled in ice-water. The remaining part of the samples was pressurized in a Food Lab9 high hydrostatic pressure equipment at 6 MPa for 5 min. To preclude heating up of samples, 4 C water was circulated in the wall of the high pressure equipment. Berry purées were stored at three different temperatures (5, 1 and 2 C) for 4 weeks to study the effects of storage conditions (temperature and time). Samples were examined on the th, 14th and 28th days of storage.
Total phenolic and antioxidant capacity of berry purées were determined by spectrophotometric methods. Vitamin C content and determination of the individual anthocyanin compounds were performed by high performance liquid chromatography. 3. Results Figure 1. shows the changes in color compounds as a function of treatment method and storage conditions determined by HPLC. Three characteristic anthocyanin compounds in strawberry and four in raspberry could be identified. Comparing the control sample to the treated samples on -day it was apparent that none of the treatments caused significant changes. Both in heat treated and in pressurized samples approximately the same amounts of anthocyanins could be detected as in the control sample. Similar tendency could be observed in Figure 2. where changes in total phenol content, vitamin C content and antioxidant capacity are shown. This proves that the chosen treatment levels didn t cause drastic changes thus both treatments can be considered as a minimal processing method. Greater differencies could be observed in Figures 1. and 2. when samples stored for 28 days at different temperatures are compared to the -day samples or to each other. Graphs demonstrate well that storage temperature had a strong effect on the retention of bioactive components of berries. Components of samples stored at ambient temperature decreased the most in each case, followed by the samples stored at 1 C and the slightest decrese occurred in samples stored at 5 C. Picking out an example to quantify the rate of changes, 7-8% of anthocyanins were retained in the HHP-treated strawberry samples stored at 5 C compared to the initial state, while in samples stored at 2 C this value was only 11-15%. In heat-treated strawbery samples 64-68% of anthocyanins were preserved when stored at 5 C and 13-16% at 2 C. Storage temperature had more significant effect than the treatment method. This applied for almost all cases. Antioxidant capacity was an exception when heat treated samples of both berries stored at even 2 C had higher antioxidant capacity than the pressurized samples stored at 5 C. To see the direction of changes principle component analysis (PCA) was performed after leaving out the redundancies. By this multivariate data-reduction technique differencies between samples become more visible in a smaller dimension space. Results of PCA are shown in Figure 3. Zero-day samples of both fruits, but especially of strawberry, formed a relatively compact group, from which stored samples separated to a lesser or higher degree according to the temperature of storage. Among the stored samples, those stored at 5 or 1 C are relatively close to each other while samples stored at ambient temperature definitely separated from all the other samples. Considering, that separation according to storage time and temperature occurred along the first principal component, those were the most effective factors. Samples according to the treatments separated along the second principal component, that is, the treatments themselves had smaller effect than storage conditions.
35 3 25 2 15 1 5 12 1 8 6 4 2 Strawberry Cyanidin-3-glucoside Pelargonidin-3-glucoside 2 18 16 14 12 1 8 6 4 2 4 35 3 25 2 15 1 5 Raspberry Cyanidin-3-sophoroside Cyanidin-3-(2G-glucosylrutinoside) 16 Pelargonidin-3-arabinoside 7 Cyanidin-3-glucoside 14 12 1 8 6 4 2 6 5 4 3 2 1 Figure 1. Effect of treatments (HHP: 6 MPa, 5 min; Heat: 8 C, 5 min) and storage conditions (time and temperature) on anthocyanins of berry products 1 9 8 7 6 5 4 3 2 1 Cyanidin-3-rutinoside
Figure 2. Effect of treatments (HHP: 6 MPa, 5 min; Heat: 8 C, 5 min) and storage conditions (time and temperature) on total phenol-, Vitamin C content and antioxidant capacity of berry products Total phenol content (g/l) Vitamin C (mg/1g) 1.8 1.6 1.4 1.2 1..8.6.4.2. 2. 18. 16. 14. 12. 1. 8. 6. 4. 2.. Strawberry Raspberry Total phenol Total phenol content (g/l) Vitamin C Vitamin C (mg/1g) 1.2 1..8.6.4.2. 12. 1. 8. 6. 4. 2.. Antioxidant activity (µmol/l) 5. 45. 4. 35. 3. 25. 2. 15. 1. 5.. Antioxidant activity Antioxidant activity (µmol/l) 6 5 4 3 2 1
Figure 3. PCA score plots of the effect of treatments (HHP: 6 MPa, 5 min; Heat: 8 C, 5 min) and storage conditions (time and temperature) on bioactive components of berry products, based on the normalized data of Figure 1. and Figure 2. Strawberry.1.8.6.4 PC2.2 -.2 -.15 -.1 -.5.5.1 -.2.1 -.4 -.6 PC1 Raspberry Control day Heat day Heat 28 day 5 C Heat 28 day 1 C Heat 28 day 2 C HHP day HHP 28 day 5 C HHP 28 day 1 C HHP 28 day 2 C.5 PC2 -.4 -.3 -.2 -.1.1.2 -.5 -.1 -.15 PC1
4. Conclusions Regarding changes in bioactive components (anthocyanin content, total phenolics, vitamin C content) of berry purées we found that storage temperature was determinant. Extremely rapid decrease took place in samples stored at ambient temperature compared to the cold stored ones. This affirms that these products are not shelf-stable, cold chain has to be maintained. Differences were found between the cold stored samples as well, but not in such extent as in the samples stored at 2 C. Among flavonoid compounds determined by HPLC method, anthocyanins decreased as a result of treatment, storage temperature and storage time. Antioxidant capacity of all samples decreased during storage, but treatment methods had stronger influence than storage temperature. Antioxidant capacity decreased in a higher extent and rate in HHP treated samples than in the heat treated ones. This phenomenon can be attributed to the incorporated air during processing. Acknowledgement This research has been supported by National Development Agency of Hungary (TÁMOP 4.2.1/B-9/1/KMR/-21-5).