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Title: Effect of thermal and high pressure processing on beta-carotene conversions and bioaccessibility: a study on carrot-based products
Other Titles: Effect van thermische en hogedrukprocesvoering op beta-caroteen conversies en biotoegankelijkheid: een studie op wortelgebaseerde producten
Authors: Knockaert, Griet
Issue Date: 30-Nov-2012
Abstract: ß-Carotene is an important micronutrient, because of its health-related properties. Carrots (Daucus carota) are a good source of ß-carotene in the human diet and are consumed fresh or as processed products (e.g. soups, juices, purees,…). Thermal processing, which is a conventional preservation technique for high moisture foods, is however known to negatively affect some quality aspects of carrots. In this context, high pressure processing with or without heat has been developed as an alternative preservation technique to thermal processing. The objective of this work was to compare the effect of thermal and high pressure processing, with or without heat, on ß-carotene. In the first part, the effect on ß-carotene conversions (isomerization and degradation) was investigated. In the second part, the effect of thermal and equivalent high pressure pasteurization and sterilization processes on ß-carotene concentration and bioaccessibility, measured by an in vitro digestion process, was studied in two different carrot-based products (carrot discs and carrot puree). Moreover, the impact of high pressure homogenization and addition of oil during the preparation of the carrot puree was investigated. During thermal processing, ß-carotene isomerization occurred and was clearly accelerated by the presence of oil. This is the result of solubilization of ß-carotene crystals in the oil droplets which makes them more susceptible to high temperatures. In an oil/carrot emulsion, as well as in an oil phase enriched with carrot ß-carotene, ß-carotene isomerization during thermal processing (85 °C – 130 °C) could be modeled by a fractional conversion model and did not significantly differ between the two matrices. 13-Cis-ß-carotene was the most important cis-isomer formed, followed by 15-cis-ß-carotene. The formation of 9-cis-ß-carotene only became pronounced after long treatments (> 30 to 60 min) at process temperatures above 115 °C. During combined thermal/high pressure processing on the other hand, ß-carotene isomerization occurred quite differently in both matrices and was dependent on the presence or absence of carrot cells. In an oil/carrot emulsion, ß-carotene isomerization was limited. Strengthening of the cell walls and formation of a pectin network in the cell wall of carrot cells during combined thermal/high pressure processing was hypothesized to hinder the transfer of ß-carotene to the oil phase, thereby protecting ß-carotene to isomerization. In the enriched oil phase on the other hand, in which no carrot cells are present, ß-carotene isomerization was not limited and was found to be pressure independent at 100 °C and to be almost temperature independent at 700 MPa. In contrast to thermal isomerization, thermal ß-carotene degradation was less pronounced in the enriched oil phase compared to the oil/carrot emulsion, possibly as a result of competition between fatty acids and ß-carotene foroxidation in the enriched oil phase. High pressure furthermore did not clearly affect ß-carotene degradation. High pressure homogenization of carrot puree at 50 MPa or higher could significantly increase the ß-carotene bioaccessibility. Thermal pasteurization as well as sterilization could always improve the ß-carotene bioaccessibility in carrot discs or in carrot puree and the effect was more pronounced when oil was present. For high pressure processing of carrot products on the other hand, the effect on ß-carotene bioaccessibility was dependent on the degree of intactness of the matrix and on the intensity level of the process. In most cases however, high pressure processing did not improve the ß-carotene bioaccessibility, not even when oil was present. In conclusion, the present work indicates that high pressure processing does not have a clear advantage over thermal processing concerning the selected nutritional quality parameters of carrot puree or carrot discs. In contrast to thermal processing, high pressure processing does not always result in an improved ß-carotene bioaccessibility compared to untreated carrot products. For thermal processing on the other hand, even in cases where processing resulted in ß-carotene loss by isomerization and/or degradation, the increase in ß-carotene bioaccessibility was probably high enough to transcend the negative effect caused by possible isomerization and/or degradation.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre for Food and Microbial Technology

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