Title: Comparing the impact of high pressure high temperature and thermal sterilization on the volatile fraction of vegetable purees: a fingerprinting and kinetics approach
Other Titles: Een 'fingerprinting and kinetics' strategie voor de vergelijking van de vluchtige componenten van hogedruk-hogetemperatuur en thermisch gesterilizeerde groentepurees
Authors: Kebede, Biniam
Issue Date: 16-Dec-2014
Abstract: Since 2000, high pressure high temperature (HPHT) has been cited as an interesting processing technology to produce shelf-stable low-acid foods (although without industrial implementation so far). However, the knowledge on the effect of HPHT processing on food quality-related chemical reactions is far from being fully documented. Therefore, there is a need for a thorough approach to investigate the impact of HPHT processing on chemical reactions, in different food matrices, in comparison to thermal processing during processing and storage. This work aimed at comparing the impact of thermal and HPHT processing on chemical reactions during processing and storage. For the latter, since conducting a shelf-life study at ambient storage temperature is quite time and resource consuming, the potential of accelerated shelf-life testing (ASLT) was investigated. Since volatiles are often involved in known process-induced reactions (e.g., Maillard reaction), a high chance of finding differences in the process impact can be expected in the evaporative fraction of the processed foods. Therefore, in this study, the volatilizable food fraction was selected to start the investigation. In this PhD work, an integrated fingerprinting and kinetics methodological approach is developed and used as a central research strategy to identify and study quality changes induced by preservation and storage. To achieve the objective, the experimental part was divided into two: (i) quality impact comparison immediately after processing and (ii) quality evaluation during storage. For the first experimental part, to obtain a broader understanding on a wide range of reaction pathways, the comparison of process impact was performed on vegetables selected from a different botanical family, plant parts and color groups. Furthermore, to have a fair comparison, the vegetable purees were sterilized with thermal and HPHT processing that resulted in equivalent microbial safety (F0 = 5 min). Afterwards, chemical fingerprinting was used as an untargeted multivariate screening tool to identify potential differences in the volatile fraction of differently sterilized vegetables. Over all vegetables, chemical fingerprinting enabled selection of two dominant discriminative quality-related reactions: Strecker degradation and oxidative-degradation. Regarding the first reaction, HPHT sterilization appeared to suppress the formation of Strecker aldehydes. Regarding the latter reaction, oxidative degradation products of terpenes, free fatty acids and carotenoid were detected at higher levels after HPHT sterilization. However, as the integrated impact of the processing variables was investigated, it was not possible to link the observed process-induced changes to the process parameters pressure, temperature and time separately. Hence, a kinetic study was the next logical step to quantify the effects of single process parameters individually on the changes of these discriminative chemical reactions. In this PhD work, akinetic study was set-up only on one of the discriminant chemical groups (i.e., the Strecker aldehydes). As a case study, carrot puree was chosen. The formation rate of the Strecker aldehydes was clearly reduced by high pressure (600 MPa). For the second experimental part, it was investigated whether the observed effects of HPHT sterilization immediately after processing were still detectable during ambient storage. As a case study, a carrot puree was selected. In both thermal and HPHT sterilized carrot purees, Strecker aldehydes, terpenes, fatty acid derivatives and carotenoid degradation products were significantly changing during storage. The concentrations of terpenes decreased during storage, whereas the other compounds increased. During storage, the Strecker aldehydes increased at a comparable rate in thermal and HPHT processed samples. Even though terpenes were better preserved in HPHT treated samples immediately after processing, by the end of storage, the concentration of all terpenes decreased to almost the same level in both thermal and HPHT sterilized samples (with a higher degradation rate in HPHT sterilized samples). Finally, the potential of the integrated fingerprinting and kinetics approach to select quality indicators (markers) for ASLT of sterilized carrot puree was investigated. Terpenes, such as myristicin, alfa-terpinolene and L-ß-pinene, seem to be interesting quality indicators for ASLT. In general, this PhD work shows the potential of the fingerprinting and kinetics approach to identify and study complex food reactions induced by preservation and storage. Strecker degradation and oxidation-related degradation reactions were differently affected by HPHT sterilization in comparison to conventional thermal processing. Terpenes seem to be interesting markers for ASLT of sterilized carrot puree.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre for Food and Microbial Technology

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