Profiling the impact of thermal processing on black raspberry phytochemicals using untargeted metabolomics

Abstract

Clinical and laboratory studies have implicated black raspberries (BRBs) and their associated phytochemicals in the modulation of several chronic diseases. Most research on the health benefits of BRBs is conducted using freeze-dried or otherwise minimally processed products, yet BRBs are typically consumed as thermally processed goods like jams and syrups. The objective of this work was to profile the chemical changes that result from thermal processing of BRB powder into a nectar beverage. Using an untargeted UHPLC-QTOF-MS metabolomics approach, key degradation products of anthocyanins were identified along with several other proposed phenolic degradants. The effects of processing on other key BRB compound groups, including ellagitannins, are also discussed. This work demonstrates the utility of an untargeted metabolomics approach in describing the chemistry of complex food systems and provides a foundation for future research on the impact of processing on BRB product bioactivity.

Keywords: Anthocyanins; Black raspberries; Chemical Fingerprinting; Ellagitannins; Flavonoids; Metabolomics; Phytochemicals; Rubus occidentalis; Thermal processing.

Figure 1.

Total monomeric anthocyanins (expressed as mg cyanidin-3-glucoside equivalents) in BRB powder and lyophilized nectar. A numeric correction was applied to the nectar values to account for other solids present. (*)Decrease in anthocyanin content was statistically significant (P<0.01).

Figure 2.

Hierarchical clustering analysis on features that differ ≥2 fold between lyophilized BRB powder and nectar made from that powder (P < 0.05). Features were clustered using Euclidian distance metrics and Ward’s linkage rule.

Figure 3.

Fragmentation pattern of proposed degradation product, 2-oxo-2-(2,4,6-trihydroxyphenyl) acetaldehyde.