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Nieuwe versus conventionele thermische procestechnieken voor voedselconservering: Een nieuwe benadering van impactvergelijking / Novel versus traditional thermal processing technologies for food preservation: A new light on impact comparison.

  • Vervoort, Liesbeth; 56640;
Publication Date
Aug 31, 2012
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Ever since the invention of thermal processing as a method for food preservation in the 19th century, there has been a relentless search to reduce the degree of thermal damage to the quality of food products. Despite improvements in traditional thermal processing, the application of even minimal heat treatments still often causes quality losses, including nutritional as well as organoleptic degradation, particularly in foods with heat-sensitive components and/or characteristics. This knowledge has prompted the food industry and research community to explore alternative novel processing technologies, that would provide the same level of safety as conventional thermal processing, but which would be less harmful to food quality attributes. Among these, high pressure (HP) and pulsed electric field (PEF) processing have proven important potential to replace or complement conventional preservation methods, as they offer an opportunity to improve the balance between safety and quality characteristics of current thermally processed food products. The large amount of scientific studies published over the past decades suggest a superior quality of HP- and PEF-processed products over their thermally treated counterparts. However, in this doctoral thesis, the prevalent lack of fairly selected processing conditions in these studies, which may create a biased (positive) perception of novel processing, was denounced. In contrast to most previous comparative studies on novel and traditional thermal processing, in the current work a fair comparison was aimed at, by selecting processing conditions that assure an equivalent microbial safety. Moreover, pilot- and industrial-scale equipment were opted for, supporting conditions close to industrial application. To make this comparison, two approaches were applied. In the first experimental part of this research, the comparison was, as is customary, addressed by a targeted approach, in the sense that the impact on a selection of food quality attributes, that are considered of importance, was analysed. Notwithstanding the fact that the results from these analyses are undoubtedly of great value, focusing on known quality aspects unfortunately implies that possible unexpected or unintended effects of (novel) processing can be overlooked. Therefore, in the second experimental part, a new, non-targeted strategy was explored, to overcome the limitations of customary targeted analyses. Two relevant fruit- and vegetable-based model food products were selected as case-studies for this comparison: liquid, high-acid orange juice and solid, low-acid carrots. In the first part of this research, an extensive characterisation of the processing impact was pursued by analysing a wide range of targeted quality attributes. The first case study on mild pasteurisation of orange juice resulted only in significant differences in residual enzyme activities between thermal, HP and PEF processing. All other quality parameters investigated (°Brix, sugar profile, pH, organic acid profile, bitter compounds, colour, vitamin C, carotenoid profile, furfural and hydroxymethylfurfural) experienced no significantly different impact from the three pasteurisation techniques. These results proved that, although contradictory to what is often claimed, HP and PEF pasteurisation did not result in orange juice of superior quality compared to their thermally treated counterpart, when this comparison is based on microbially equivalent processing conditions.The second case study on carrot processing demonstrated that, for this product type, the potential benefit of HP over thermal processing was largely dependent on the processing intensity applied. For some properties (enzyme activities and texture), HP processing only had a significantly smaller impact than thermal processing at pasteurisation intensities, while others (colour, carotenoids and hydroxymethylfurfural) were only less affected by HP at sterilisation intensities. Thermal sterilisation had the largest impact on carrot quality, while all other treatments (mild and severe thermal pasteurisation, mild and severe HP pasteurisation and HP sterilisation) resulted in a comparable overall quality. This quality impact of thermal sterilisation was mostly determined by browning reactions and carotenoid degradation and isomerisation. In the second part of this thesis, the use of headspace fingerprinting was put forward as a non-targeted approach. This technique proved to be an attractive tool to compare the impact of novel and thermal processing, as it allows the evaluation of a more overall picture of the food, by monitoring a wide range of compounds, rather than focusing on a particular (group of) component(s).In the case study on mild pasteurisation of orange juice, no major differences in process impact were detected between thermal, HP and PEF processing, immediately after treatment. Only indirect impact differences were revealed during storage, which were attributed to microbial growth in untreated juice and differences in enzyme inactivation between thermally and HP-treated juices on the one hand, and PEF-treated juice on the other hand. On the contrary, important impact differences between thermal and HP processing of carrots were revealed, which became more pronounced upon increasing processing intensity. The majority could be related to Maillard reactions (furans), unsaturated fatty acid oxidation (aliphatic aldehydes) and carotenoid degradation. These reactions occurred significantly more during thermal processing and were determined by the thermal load, applied during processing. Only a few volatiles were exposed with higher concentration after HP treatment at some processing intensity levels, which could be attributed to enzymatic activities and terpinolene oxidation. The results from both targeted and non-targeted approaches of this doctoral research provide evidence that, for the processing conditions and food products applied, HP and PEF processing do not cause any significant differences in the major components regarding publichealth, in comparison to the corresponding products currently available on the market, ranging from fresh to thermally sterilised products. Therefore, no objections were encountered that would compromise the human metabolism or health after consumption of HP- or PEF-pasteurised orange juice and HP-pasteurised or sterilised carrots (in the context of the European Novel Foods Regulation). / status: published

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