Behaviour of nutrients during processing lycopene

Data and information supplied in the scientific literature on lycopene degradation during common tomato processing, such as heat sterilisation, concentration by evaporation and dehydration, and also informationanddataon storageofprocessed tomato products, though sometimes inconsistentornotcompletelyclear,allowfor some general conclusions and comments.Sincetheoperatingconditionsapplied to the tests are either not well defined or donotcorrespondto thoseusedforindus-trial treatments, the results should be considered as being often unreliable.

The data seem to suggest that lycopeneisstabletoheattreatmentfortomato concentration and cooking and also duringprocessedtomatostorage.The stability is lower for products submitted to treatments which have damaged the cell walls and which have consequently reducedtheprotectiveeffect withrespectto lycopene coagula (Fig. 4.1).29 Exposure to oxygen, high temperature and low water activity may cause lycopene degradation. Researchers substantially agree that this compound is stable in commercial production processes, in terms of both degradation and isomerisation rate. Even air drying, which is a really severe treatment in terms of oxidative stress, does not cause serious lycopene losses.3^32 Some of these studies witnessed a relatively high lycopene loss and isomerisation in heat-treated tomato products; a possible reason for these results, which are in contrast to other data, could be the differing analytical methods and procedures that were applied. Various authors have demonstrated that lycopene is much less stable towards isomerisation and oxidation when it is solubilised in organic solvent.

FAIR Concerted Action 97-3233 made an assessment of the available literature which seems to indicate that lycopene is relatively stable during heat treatment, that it possesses a fair stability during storage, with only slight reduction under severe oxidative conditions such as hot-air drying and a light discoloration during deep freezing.29 However, much research does lead to contradictory conclusions about the supposed marked degradation effect of storage, probably owing to the fact that lycopene was frequently measured in second-stage tomato products, with high oil/fat percentages (sauces) which facilitated partial solubilisation of lycopene and its subsequent higher reactivity and degradation.

There are no data about how the lycopene content is affected by non-traditional heating processes such as microwaves, ohmic treatments and non-thermal pasteurisation processes using high pressure technology.

It therefore seemed interesting to report the results of the effects of storage conditions on the lycopene content of tomato purees obtained by different processing techniques, by summarising the trials conducted by Tamburini et al.33 using a pilot plant. Samples of tomato puree were prepared first by extracting the juice according to a conventional technique, varying the extraction temperature (at ambient temperature, series marked F, at 60°C or cold break, series marked C and at 90°C or hot break, series marked H) and pulper hole size (0 8/10mm, series marked 8 and 13/10mm, series marked 13), then by vacuum-concentrating the juice to 8°Brix and finally by hot filling it into lacquered tinplate cans. The samples obtained were subjected to different storage conditions and the changes in lycopene content were monitored over a 12-month period. In this way, six kinds of tomato puree with different physical characteristics (consistency, colour and granulometry) were obtained.

Fig. 4.1 Microscope photographs of a freshtomatosample(a)andtomato juice sample (b). Reproduced courtesy Volker Böhm - Institute of Nutrition Friedrich Schiller

University Jena.

Fig. 4.1 Microscope photographs of a freshtomatosample(a)andtomato juice sample (b). Reproduced courtesy Volker Böhm - Institute of Nutrition Friedrich Schiller

University Jena.

Tables 4.3 and 4.4 summarise all theresults;lycopenecontent valuesrepre-sent the mean of the different storage conditions (temperature) and the different effects of the various juice extraction treatmentsarehighlighted. Allinall,the better preservation of lycopene in the hot break-treated product is clearly shown graphically, whereas no granulometry induced protective effect seems to occur, at least under the conditions tested. As the data show, no difference occurs with the different processing techniques applied.

Table 4.3 Physicochemical characteristics of the purees obtained under different extraction conditions

Analyses Samples

F8 C8 H8 F13 C13 H13

Lycopene, mgkg-1

25.67 25.75

31.90 31.94

14.39 14.76

201 192

26.40 24.73

31.48 30.04

192 196

24.72 25.37

31.37 31.40

188 204

210 200 190 180 170

Lycopene 160 (ppm) 150 140 130 120 110 100

Time (months)

Fig. 4.2 Behaviour of the lycopene during 12 months' storage, as a function of the juice extraction conditions.

Hot break Cold break Room temperature

Extraction conditions

Time (months)

Fig. 4.2 Behaviour of the lycopene during 12 months' storage, as a function of the juice extraction conditions.

During storage, as shown in Fig. 4.2, a slight decrease in lycopene content occurs which seems to be linked to the type of heat treatment applied for juice extraction. An examination of the data obtained seems to reveal that lycopene is substantially stable to heat treatments, which reports the mean values of the variation over time in the lycopene content for all the samples. However, a detailed analysis of the changes occurring over time in samples prepared under different temperature conditions (ambient temperature, cold-break, hot-break) reveals that a hot-break process, although typically involving blanching at high temperature (more than 90°C) for some dozens of seconds, and which could cause a considerable decrease in lycopene content, actually lessens lycopene levels only to a limited extent. It seems to preserve the pigment over time better than either the cold-break process or extraction at room temperature. Lycopene content in the

Table 4.4 Variation over time in lycopene contents (total samples)

Storage time (months)

Lycopene ± s.d. (mgkg 1)

0

195.5 ± 1.1

2

188.0 ± 1.1

4

180.7 ± 1.1

6

177.4 ± 1.1

10

176.6 ± 1.1

12

176.9 ± 1.1

samples which have undergone the enzyme-inactivating hot-break process (90°C, samples H8 and H13) remain almost unchanged even after 12 months of storage, whereas the small variations in lycopene content of the cold-break-treated samples (C8 and C13) are similar to those occurring in samples which have received no heat treatment (F8 and F3).

The hot-break juice extraction technique lessens the initial lycopene content because of the severe heat effect, but in allowing the tomato cell structure to remain almost unchanged, preserves lycopene more efficiently over time against reactions that cause its destruction. This is different from what happens with other juice extraction techniques (at room temperature, cold break), where because the protective effect caused by the triggering of pectolytic reactions is absent, a decrease in lycopene content of 8-15% has already occurred after 4-6 months' storage.

The other effects that were analysed (diameter of the pulper holes and storage temperature) cause no significant technologically interesting variations in lycopene content. The results reported so far lead us to the conclusion that while lycopene remains within the original hydrophilic matrix and most of all, within a whole cell, it is quite stable. However, because of the subsequent low reactivity, it probably exhibits lower bioavailability and therefore could in practice be ineffective in exerting its potential antioxidant activity.

The study of the effect of manufacturing processes in the preparation of tomato powders on lycopene content and on colour carried out by Cabassi et al.32 highlighted a moderate loss (5%) of total lycopene content which can be traced back to isomerisation and oxidation phenomena. A comparison of the lycopene content found when different flexible packaging materials were used showed that the greatest preservation of lycopene was obtained by vacuum packaging in Al/poly-thene pouches. A very good result was also obtained using nitrogen packaging in polymer (polyethylene and polyvinylacetate) trays sealed with a polyethylene terephthalate film. In the packages containing air (and therefore oxygen) lycopene loss was decidedly higher (22-25%). The storage time showed a significant effect which was reflected in an average 13% decrease in total lycopene in the samples during the first month of storage. However, it must be noted that this average value reflects moderate decreases in vacuum and nitrogen packaging (2%) compared with packaging in the presence of air (24%). The more marked effect found during the first month of storage of the powders suggests that some lycopene, probably that present on the air-exposed surface, is more sensitive to the action of oxidants compared with the lycopene inside the granules themselves.

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