Elsevier

Food Chemistry

Volume 162, 1 November 2014, Pages 176-185
Food Chemistry

Thermal degradation of cloudy apple juice phenolic constituents

https://doi.org/10.1016/j.foodchem.2014.04.005Get rights and content

Highlights

  • Degradation susceptibility of cloudy apple juice phenolic constituents.

  • Untargeted metabolomics approach conducted for process optimisation.

  • Procyanidin were the most heat labile phenolic compounds.

  • Low impact of the high-temperature short-time pasteurisation.

Abstract

Although conventional thermal processing is still the most commonly used preservation technique in cloudy apple juice production, detailed knowledge on phenolic compound degradation during thermal treatment is still limited. To evaluate the extent of thermal degradation as a function of time and temperature, apple juice samples were isothermally treated during 7200 s over a temperature range of 80–145 °C. An untargeted metabolomics approach based on liquid chromatography–high resolution mass spectrometry was developed and applied with the aim to find out the most heat labile phenolic constituents in cloudy apple juice. By the use of a high resolution mass spectrometer, the high degree of in-source fragmentation, the quality of deconvolution and the employed custom-made database, it was possible to achieve a high degree of structural elucidation for the thermolabile phenolic constituents. Procyanidin subclass representatives were discovered as the most heat labile phenolic compounds of cloudy apple juice.

Introduction

Despite the emerging of novel non-thermal preservation techniques, conventional thermal processing is still the most commonly used preservation technique in cloudy apple juice production (Rupasinghe & Yu, 2012). This practice is a result of its efficient inactivation of microorganisms and enzymes responsible for deterioration (Awuah, Ramaswamy, & Economides, 2007). Batch heating at 63–65 °C for 30 min. is the most traditional method (D’Amico et al., 2006). However, through the years, process optimisation was conducted by reducing processing times at high(er) temperatures in order to avoid undesirable quality changes during this process (Awuah et al., 2007). Currently, high temperature – short time (HTST) pasteurisation at 77–88 °C for 25–30 s is the most commonly used method for heat treatment of cloudy apple juice (Aguilar-Rosas, Ballinas-Casarrubias, Nevarez-Moorillon, Martin-Belloso, & Ortega-Rivas, 2007).

However, thermal processing can promote reactions that could affect colour, odour, flavour, texture and health-effect, which all could be linked to the change in phenolic profile (Niu et al., 2010). To predict the change in phenolic profile of cloudy apple juice during heat treatment, the knowledge of the phenolic composition as well as the kinetics of phenolic compound degradation, including the reaction rate as a function of temperature, are required (Vikram, Ramesh, & Prapulla, 2005).

In the past, kinetic studies regarding phenolic constituents of apple juice were mostly carried out in aqueous model solutions. For such solutions, it was already demonstrated that the heat sensitivity of phenolic compounds depends on their structure, in other words, to the phenolic subclass to which they belong (Buchner, Krumbein, Rohn, & Kroh, 2006). This tendency was confirmed in enriched apple juice during accelerated storage experiments (van der Sluis, Dekker, & van Boekel, 2005). However, it is difficult to use such intrinsic kinetic data for process optimisation given the fact that the matrix can protect against heat or promote the degradation (Ioannou, Hafsa, Hamdi, Charbonnel, & Ghoul, 2012).

Furthermore, in all available studies, only a limited set of well-known and often most abundant phenolic compounds are studied as a consequence of the employed ‘targeted approach’. Following such an approach, it is very time consuming to find out the identity of ‘the most heat labile phenolic constituents’, while these molecules could be just the ones that are best suited to be used as ‘quality targets’ during process optimisation.

A non-targeted approach imposes itself. Due to recent technological advances in the field of High-Resolution Mass Spectrometry (HRMS), untargeted metabolomics approaches have become a feasible approach to analyse simultaneous behaviour a large amount of molecular entities in complex matrices. Therefore, the objective of the present study was to find out the most heat labile phenolic constituents in cloudy apple juice by the application of a targeted metabolomics approach. Attention will be given to the pitfalls inherent to the large-scale liquid chromatography and mass spectrometry based untargeted screening method for gathering kinetic information.

Section snippets

Pilot scale cloudy apple juice production

Storage apples cv. ‘Jonagored’ (ULO storage for 10 months, caliber 65–70 mm), were purchased from a Belgian fruit auction and stored at normal atmosphere in a cold room (0 °C) until use. A combined washer/elevator/rasp mill combination (KWEM 1000, Kreuzmayr, Wallem, Germany) was used for washing and shredding the apples into mash. Subsequently, the apple mash was pressed by means of a spiral-filter pressed (VacuLIQ 1000, VacuLIQ, Hamminkeln, Germany) whereof optimised conditions were used (De

Data pretreatment

For the extraction of relevant information from the obtained chromatograms by means of an untargeted metabolomics approach, in our case, the variation in concentration of cloudy apple juice (13.8 °Brix, pH = 3.54) phenolic constituents of as a function of time and temperature (‘thermally induced variation’), several pitfalls inherent to large-scale LC–MS metabolomics should be circumvented.

First, the presence and variation (drift) of the chromatograms baseline offset hampers a meaningful signal

Conclusion

The research described in this paper demonstrates the high applicability of untargeted metabolomics approach in process optimisation with the aim to retain bioactive phenolic constituents in cloudy apple juice. The developed workflow consisting of baseline correction, alignment, filtering and deconvolution, made it possible to gather kinetic information from all detected putative phenolic constituents. Furthermore, by the use of a high resolution mass spectrometer, the high degree of in-source

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